[Federal Register Volume 89, Number 75 (Wednesday, April 17, 2024)]
[Proposed Rules]
[Pages 27502-27561]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2024-07116]



[[Page 27501]]

Vol. 89

Wednesday,

No. 75

April 17, 2024

Part II





Department of Transportation





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National Highway Traffic Safety Administration





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49 CFR Part 571





Federal Motor Vehicle Safety Standards; Fuel System Integrity of 
Hydrogen Vehicles; Compressed Hydrogen Storage System Integrity; 
Incorporation by Reference; Proposed Rule

  Federal Register / Vol. 89, No. 75 / Wednesday, April 17, 2024 / 
Proposed Rules  

[[Page 27502]]


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DEPARTMENT OF TRANSPORTATION

National Highway Traffic Safety Administration

49 CFR Part 571

[Docket No. NHTSA-2024-0006]
RIN 2127-AM40


Federal Motor Vehicle Safety Standards; Fuel System Integrity of 
Hydrogen Vehicles; Compressed Hydrogen Storage System Integrity; 
Incorporation by Reference

AGENCY: National Highway Traffic Safety Administration (NHTSA), 
Department of Transportation (DOT).

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: This notice proposes to establish two new Federal Motor 
Vehicle Safety Standards (FMVSS) specifying performance requirements 
for all motor vehicles that use hydrogen as a fuel source. The proposed 
standards are based on Global Technical Regulation (GTR) No. 13. FMVSS 
No. 307, ``Fuel system integrity of hydrogen vehicles,'' which would 
specify requirements for the integrity of the fuel system in hydrogen 
vehicles during normal vehicle operations and after crashes. FMVSS No. 
308, ``Compressed hydrogen storage system integrity,'' would specify 
requirements for the compressed hydrogen storage system to ensure the 
safe storage of hydrogen onboard vehicles. The two proposed standards 
would reduce deaths and injuries that could occur as a result of fires 
due to hydrogen fuel leakages and/or explosion of the hydrogen storage 
system.

DATES: You should submit your comments early enough to be received not 
later than June 17, 2024. In compliance with the Paperwork Reduction 
Act, NHTSA is also seeking comment on a revision to an existing 
information collection. For additional information, see the Paperwork 
Reduction Act Section under the Regulatory Notices and Analyses section 
below. All comments relating to the information collection requirements 
should be submitted to NHTSA and to the Office of Management and Budget 
(OMB) at the address listed in the ADDRESSES section on or before June 
17, 2024.
    Proposed Effective Date: The date 180 days after the date of 
publication of the final rule in the Federal Register.
    Proposed Compliance Date: The September 1st that is two years 
subsequent to the publication of the final rule.

ADDRESSES: You may submit comments to the docket number identified in 
the heading of this document by any of the following methods:
     Federal eRulemaking Portal: Go to http://www.regulations.gov. Follow the online instructions for submitting 
comments.
     Mail: Docket Management Facility: U.S. Department of 
Transportation, 1200 New Jersey Avenue SE, West Building Ground Floor, 
Room W12-140, Washington, DC 20590-0001.
     Hand Delivery or Courier: 1200 New Jersey Avenue SE, West 
Building Ground Floor, Room W12-140, between 9 a.m. and 5 p.m. ET, 
Monday through Friday, except Federal holidays.
     Fax: 202-493-2251.
    Instructions: All submissions must include the agency name and 
docket number. Note that all comments received will be posted without 
change to http://www.regulations.gov, including any personal 
information provided. Please see the Privacy Act discussion below. We 
will consider all comments received before the close of business on the 
comment closing date indicated above. To the extent possible, we will 
also consider comments filed after the closing date.
    Docket: For access to the docket to read background documents or 
comments received, go to http://www.regulations.gov at any time or to 
1200 New Jersey Avenue SE, West Building Ground Floor, Room W12-140, 
Washington, DC 20590, between 9 a.m. and 5 p.m., Monday through Friday, 
except Federal Holidays. Telephone: 202-366-9826.
    Privacy Act: In accordance with 5 U.S.C. 553(c), DOT solicits 
comments from the public to better inform its decision-making process. 
DOT posts these comments, without edit, including any personal 
information the commenter provides, to www.regulations.gov, as 
described in the system of records notice (DOT/ALL-14 FDMS), which can 
be reviewed at www.transportation.gov/privacy. In order to facilitate 
comment tracking and response, we encourage commenters to provide their 
name, or the name of their organization; however, submission of names 
is completely optional. Whether or not commenters identify themselves, 
all timely comments will be fully considered.
    Confidential Business Information: If you wish to submit any 
information under a claim of confidentiality, you should submit three 
copies of your complete submission, including the information you claim 
to be confidential business information, to the Chief Counsel, NHTSA, 
at the address given under FOR FURTHER INFORMATION CONTACT. In 
addition, you should submit two copies, from which you have deleted the 
claimed confidential business information, to the Docket at the address 
given above. When you send a comment containing information claimed to 
be confidential business information, you should include a cover letter 
setting forth the information specified in our confidential business 
information regulation (49 CFR part 512).

FOR FURTHER INFORMATION CONTACT: For technical issues, Ian MacIntire, 
General Engineer Special Vehicles & Systems Division within the 
Division of Rulemaking, at (202) 493-0248 or [email protected]. For 
legal issues, Paul Connet, Attorney-Advisor, NHTSA Office of Chief 
Counsel, at (202) 366-5547 or [email protected].

SUPPLEMENTARY INFORMATION:

Table of Contents

I. Executive Summary
II. Background
    A. Hydrogen Fueled Vehicles
    1. Hydrogen as a Motor Fuel
    2. Hydrogen Vehicle Systems
    B. Global Technical Regulation (GTR) No. 13
    1. Overview of the GTR Process
    2. History of GTR No. 13
III. Why is NHTSA issuing this proposal?
IV. Overview of Proposed Rules
    A. FMVSS No. 308, ``Compressed Hydrogen Storage System 
Integrity''
    1. Compressed Hydrogen Storage System
    2. General Requirements for the CHSS
    3. Performance Requirements for the CHSS
    4. Tests for Baseline Metrics
    5. Test for Performance Durability
    6. Test for Expected On-Road Performance
    7. Test for Service Terminating Performance in Fire
    8. Tests for Performance Durability of Closure Devices
    9. Labeling Requirements
    B. FMVSS No. 307, ``Fuel System Integrity of Hydrogen Vehicles''
    1. Fuel System Integrity During Normal Vehicle Operations
    2. Post-Crash Fuel System Integrity
    C. Lead Time
V. Rulemaking Analysis and Notices
VI. Public Participation

I. Executive Summary

    Vehicle manufacturers have continued to seek out renewable and 
clean alternative fuel sources to gasoline and diesel. Compressed 
hydrogen has emerged as a promising potential alternative because 
hydrogen is an abundant element in the atmosphere and does not produce 
tailpipe greenhouse gas emissions when used as

[[Page 27503]]

a motor fuel. However, hydrogen must be compressed to high-pressures to 
be an efficient motor fuel, and is also highly flammable, similar to 
other motor fuels. NHTSA has already set regulations ensuring the safe 
containment of other motor vehicle fuels such as gasoline in FMVSS No. 
301 and compressed natural gas in FMVSS No. 304, and the fuel integrity 
systems of those systems in FMVSS No. 301 and FMVSS No. 303, 
respectively. No such standards currently exist in the United States 
covering vehicles that operate on hydrogen. Accordingly, this document 
proposes two new Federal Motor Vehicle Safety Standards (FMVSSs) to 
address safety concerns relating to storage and use of hydrogen in 
motor vehicles, and to align the safety regulations of hydrogen 
vehicles with vehicles that operate using other fuel sources. This 
proposed rule was developed in concert with efforts to harmonize 
hydrogen vehicle standards with international partners through the 
Global Technical Regulation (GTR) process, and if adopted, would 
harmonize the FMVSSs with GTR No. 13, Hydrogen and Fuel Cell Vehicles.
    This document proposes the creation of two new safety standards: 
FMVSS No. 307, ``Fuel system integrity of hydrogen vehicles,'' and 
FMVSS No. 308, ``Compressed hydrogen storage system integrity.'' FMVSS 
No. 307 would regulate the integrity of the fuel system in hydrogen 
vehicles during normal vehicle operations and after crashes. To this 
end, it includes performance requirements for the hydrogen fuel system 
to mitigate hazards associated with hydrogen leakage and discharge from 
the fuel system, as well as post-crash restrictions on hydrogen 
leakage, concentration in enclosed spaces, container displacement, and 
fire. FMVSS No. 308 would regulate the compressed hydrogen storage 
system (CHSS) itself, and would primarily include performance 
requirements that would ensure the CHSS is unlikely to leak or burst 
during use, as well as requirements intended to ensure that hydrogen is 
safely expelled from the container when it is exposed to a fire. FMVSS 
No. 308 also specifies performance requirements for different closure 
devices in the CHSS.
    NHTSA is proposing that FMVSS Nos. 307 and 308 apply to all motor 
vehicle that use compressed hydrogen gas as a fuel source to propel the 
vehicle, regardless of the vehicle's gross vehicle weight rating 
(GVWR). However, while FMVSS No. 307 fuel system integrity requirements 
during normal vehicle operations would apply to both light vehicles 
(vehicles with a GVWR of 4,536 kg or less) and to heavy vehicles 
(vehicles with a GVWR greater than 4,536 kg), FMVSS No. 307 post-crash 
fuel system integrity requirements would only apply to compressed 
hydrogen fueled light vehicles and to all compressed hydrogen fueled 
school buses regardless of GVWR.
    While the proposed safety standards are drafted in accordance with 
GTR No. 13, there are differences between some proposed requirements 
and test procedures and GTR No. 13. This document highlights these 
differences and provides reasons for these differences in relevant 
sections of the preamble, and seeks public comment.

II. Background

A. Hydrogen Fueled Vehicles

1. Hydrogen as a Motor Fuel
    In the pursuit of sustainable, renewable, and clean transportation, 
vehicle manufacturers have continued to expand their pursuits of 
hydrogen as an alternative fuel source for automobiles. Unlike their 
gasoline or diesel counterparts, hydrogen-powered vehicles (hydrogen 
vehicles) do not produce carbon dioxide or other emissions. 
Furthermore, in contrast with battery electric vehicles, hydrogen 
vehicles do not require extended recharging from an external electrical 
source. These advantages, coupled with the relative abundance of 
hydrogen, make hydrogen vehicles an intriguing alternative to vehicles 
already offered in the market.
    Hydrogen vehicles harness the chemical energy within hydrogen using 
one of two methodologies. The first technique is similar to 
conventional internal combustion engines (ICE) powered by petroleum 
products. Hydrogen can be burned in a combustion engine and the energy 
released from this process used to move pistons that provide mechanical 
power to the vehicle. The second method utilizes a component called a 
fuel cell that converts the chemical energy in hydrogen into 
electricity. In this energy conversion process, hydrogen stored in the 
vehicle reacts with oxygen in the air to produce water and energy, in 
the form of electricity, which is then used to power the vehicle's 
mechanical operations. Hydrogen fuel cell vehicles (HFCVs), which are 
sometimes also referred to as fuel cell electric vehicles (FCEVs), are 
capable of continuous electrical generation so long as they have a 
steady supply of hydrogen fuel and oxygen.
    One complicating factor of using hydrogen as a mobile fuel source 
is its relatively low energy density. Compared to gasoline, which has a 
mass density of 803 grams per liter at 15 [deg]C, uncompressed hydrogen 
is extremely light, with a mass density of just 0.09 grams per liter at 
15 [deg]C, which means a vehicle operating on uncompressed hydrogen 
will have a significantly shorter range than a comparable gasoline-
powered vehicle. To overcome this, hydrogen is compressed to a very 
high pressure of up to 70 megaPascals (MPa) while stored on a hydrogen 
vehicle.\1\ Hydrogen compressed to 70 MPa at 15 [deg]C has a volumetric 
energy density of 4.8 mega Joules per liter (MJ/L), which is similar in 
order of magnitude to gasoline's volumetric energy density of 32 MJ/
L.2 3
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    \1\ At atmospheric pressure and ambient temperature, hydrogen is 
in a gaseous state. The physical state of hydrogen can be changed 
from gas to liquid through compression and cryogenic cooling, so 
hydrogen can be stored in both compressed gaseous and liquid forms. 
However, hydrogen typically exists in gaseous form at essentially 
all normal usage and storage temperatures.
    \2\ See Patrick Molloy, ``Run on Less with Hydrogen Fuel 
Cells.'' RMI, Oct. 2, 2019, https://rmi.org/run-on-less-with-hydrogen-fuel-cells/.
    \3\ See Department of Energy Hydrogen and Fuel Cell Technologies 
Office, ``Hydrogen Storage,'' https://www.energy.gov/eere/fuelcells/hydrogen-storage.
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    While compressed hydrogen is an excellent fuel source due to its 
high energy density, its high storage pressure and wide limits of 
flammability (i.e., concentrations at which a mixture of fuel and air 
is flammable) raise safety concerns. Specifically, hydrogen is 
flammable at concentrations ranging from 4 to 75 percent, by volume.\4\ 
By contrast, gasoline limits of flammability when mixed with air are 
from 1.0 to 7.6 percent, by volume.\5\ The velocity at which a hydrogen 
flame spreads at room temperature and atmospheric pressure is 
approximately 200 to 300 cm/s, whereas the velocity with which gasoline 
flames spread under the same conditions is approximately 40 cm/
s.6 7 These characteristics make hydrogen fuel sources more 
volatile than gasoline, and while NHTSA has existing FMVSS for gasoline 
vehicle fuel system integrity, no FMVSS yet apply to hydrogen storage 
and fuel systems. In particular, the safe use of hydrogen vehicles lies 
in preventing explosion of

[[Page 27504]]

the hydrogen container(s) and preventing leaks from the container(s) 
and fuel system which could lead to fire. Given the greater 
flammability of compressed hydrogen, safety standards applicable to 
their fuel system integrity are not only reasonable, but necessary.
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    \4\ See Hydrogen Compared with Other Fuels, https://h2tools.org/bestpractices/hydrogen-compared-other-fuels.
    \5\ Id.
    \6\ See 6 Things to Remember about Hydrogen vs Natural Gas, 
https://www.powereng.com/library/6-things-to-remember-about-hydrogen-vs-natural-gas.
    \7\ See Combustion fuels: density, ignition temperature and 
flame speed, https://thundersaidenergy.com/downloads/combustion-fuels-density-ignition-temperature-and-flame-speed/.
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    Despite the promise offered by hydrogen vehicles, they are still a 
diminutive fraction of the fleet. For model year 2022, there were two 
light hydrogen vehicle models offered for sale in the United States, 
whose sales by volume represented approximately 0.03% of the overall 
light vehicle fleet. There were no medium-or heavy-duty \8\ hydrogen 
vehicles offered for sale in the U.S. during the 2022 model year; \9\ 
however, manufacturers continue to state their intentions to explore 
hydrogen across all fleets.
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    \8\ Medium-duty vehicles have a gross vehicle weight rating 
(GVWR) greater than 4,536 kg and less than or equal to 11,793 kg. 
Heavy-duty vehicles have a GVWR greater than 11,793 kg.
    \9\ Toyota has a commercial bus called the Sora that is 
currently sold in Japan and Europe.
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2. Hydrogen Vehicle Systems
    Hydrogen vehicles--both fuel cell and ICE--share the same basic 
structure. Hydrogen enters the vehicle through the fueling receptacle, 
is stored in the CHSS, and is released from the CHSS as needed to power 
either the combustion engine or fuel cell where the energy stored in 
hydrogen is converted into mechanical.\10\ Figure-1 below shows an 
example of a hydrogen fuel cell vehicle (HFCV).\11\ A diagram of the 
main elements of a vehicle fuel system is shown in Figure-2.\12\
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    \10\ The chemical energy stored in the hydrogen fuel is 
converted into electric energy by the fuel cell, and the resulting 
electric energy is then be converted into mechanical energy by 
electric drive motor(s), thereby propelling the vehicle.
    \11\ Note that the vehicle depicted is a fuel cell vehicle. For 
a hydrogen ICE vehicle, the fuel cell would be replaced with a 
combustion engine.
    \12\ Figure-2 shows the main elements of a HFCV fuel system. In 
the case of a hydrogen ICE vehicle, the fuel cell system would be 
replaced by the ICE, and the electric propulsion management system 
would be replaced by the vehicle powertrain.
[GRAPHIC] [TIFF OMITTED] TP17AP24.000

Figure-1: Example of a HFCV Design 13
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    \13\ For further information on HFCV design, see https://afdc.energy.gov/vehicles/fuel_cell.html, and https://afdc.energy.gov/vehicles/how-do-fuel-cell-electric-cars-work.
[GRAPHIC] [TIFF OMITTED] TP17AP24.001


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Figure-2: A Schematic of a HFCV and Its Major Systems

a. CHSS
    During fueling, hydrogen is supplied from the fueling station to 
the vehicle through the vehicle's fueling receptacle. The hydrogen then 
flows to the CHSS for storage in the hydrogen container(s). The key 
functions of the CHSS are to receive compressed hydrogen through a 
check valve during fueling, contain the hydrogen until needed, and 
release hydrogen through an electrically activated shut-off valve to 
the hydrogen delivery system for use in powering the vehicle. The check 
valve prevents reverse flow in the vehicle fueling line. The shut-off 
valve between the storage container and the vehicle fuel delivery 
system controls the fuel flow out of the CHSS and automatically 
defaults to the closed fail-safe position when unpowered. In the event 
of a fire impinging on the CHSS, the TPRD provides a controlled release 
of hydrogen from the CHSS before the high temperature causes a 
hazardous burst of the container.
b. Hydrogen Delivery
    The hydrogen delivery system transfers hydrogen from the CHSS to 
the fuel cell system at the proper pressure and temperature for fuel 
cells to operate. This transfer process is accomplished through a 
series of flow control valves, pressure regulators, filters, piping, 
and heat exchangers.
c. Fuel Cell System
    The fuel cell system provides high-voltage electric power to the 
drive-train and vehicle batteries and capacitors. The fuel cell stack 
is the electricity-generating component of the fuel cell system. 
Individual fuel cells are electrically connected in series such that 
their combined voltage is between 300 and 600 Volts in direct current 
(VDC). Fuel cell stacks operate at high-voltage, which means a voltage 
greater than 60 VDC. The high voltage aspect of fuel cells are covered 
by FMVSS No. 305, ``Electric-powered vehicles: electrolyte spillage and 
electrical shock protection,'' and are not considered in this proposal.
    A typical fuel cell system includes a blower to feed air to the 
fuel cell system. Most of the hydrogen that is supplied to the fuel 
cell system is consumed within the fuel cells, but a tiny excess of 
hydrogen is required to ensure that there is no damage to the fuel cell 
from a lack of hydrogen, which can cause undesired chemical reactions 
that damage and degrade the fuel cell.\14\ The excess hydrogen is 
either catalytically removed or vented to the atmosphere in accordance 
with the requirements discussed below. A fuel cell system also includes 
auxiliary components to remove heat. Most fuel cell systems are cooled 
by a mixture of glycol and water. Pumps circulate the coolant between 
the fuel cells and a radiator.
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    \14\ A lack of hydrogen in a fuel cell, also known as hydrogen 
starvation, occurs when hydrogen fuel is exhausted at the fuel cell 
anode. This condition can lead to undesired chemical reactions 
occurring inside the fuel cell which can quickly degrade the fuel 
cell's catalyst and other components.
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d. Electric Propulsion and Power Management System
    The electric power generated by the fuel cell system is supplied to 
the electric propulsion power management system where it is used to 
power the electric drive-train that propels the vehicle. The throttle 
position is used by the drive-train controllers to determine the amount 
of power to be sent to the drive wheels. Many HFCVs use batteries or 
ultra-capacitors to supplement the output of the fuel cells. These 
vehicles may also recapture energy during braking through regenerative 
braking, which recharges the batteries or ultra-capacitors and thereby 
maximizes efficiency.\15\
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    \15\ The electric propulsion and power management system is 
covered by FMVSS No. 305, ``Electric-powered vehicles: electrolyte 
spillage and electrical shock protection,'' and is not considered in 
this proposal.
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e. Hydrogen ICE Vehicles
    Hydrogen ICE vehicles have an ICE instead of a fuel cell system. 
The ICE engine burns hydrogen to generate mechanical energy to propel 
the vehicle. These vehicles use a mechanical propulsion system instead 
of an electric propulsion system.

B. Global Technical Regulation (GTR) No. 13

    The proposed rule initiates the process of adopting Global 
Technical Regulation (GTR) No. 13 into the FMVSS. Based on GTR No. 13, 
this NPRM proposes requirements for the safe onboard storage and 
utilization of hydrogen in vehicles.
1. Overview of the GTR Process
    The United States became the first signatory to the 1998 United 
Nations/Economic Commission for Europe (UNECE) agreement (1998 
Agreement). The 1998 Agreement entered into force in 2000 and is 
administered by the World Forum for Harmonization of Vehicle 
Regulations working party (WP.29).\16\ The 1998 Agreement established 
the development of global technical regulations (GTRs) regarding the 
safety, emissions, energy efficiency and theft prevention of wheeled 
vehicles, equipment and parts.
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    \16\ The World Forum was initially named the Working Party on 
the Construction of Vehicles, a subsidiary of the Inland Transport 
Committee. It was renamed to the World Forum in 2000.
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    The 1998 Agreement contains procedures for establishing GTRs either 
through harmonizing existing regulations or developing new regulations. 
The GTR process provides NHTSA unique opportunities to enhance vehicle 
safety and improve government efficiency. It assists in developing the 
best safety practices from around the world, identifying and reducing 
unwarranted regulatory requirements, and leveraging scarce government 
resources for research and regulation. The process facilitates our 
effort to continuously improve and seek high levels of safety, 
particularly by helping us develop regulations that reflect a global 
consideration of current and anticipated technology and safety 
problems.
    Contracting Parties who vote in favor of a GTR are obligated by the 
1998 Agreement to ``submit the technical Regulation to the process'' 
used in the country to adopt the requirement into the agency's law or 
regulation.\17\ In the U.S., that process usually commences with an 
NPRM or Advance NPRM (ANPRM). The 1998 Agreement does not obligate 
Contracting Parties to adopt the GTR after initiating this process.\18\ 
The 1998 Agreement recognizes that governments have the right to 
determine whether the global technical regulations established under 
the Agreement are suitable for their own particular safety needs. Those 
needs vary from country to country due to differences in laws and in 
factors such as the traffic environment, vehicle fleet composition, 
driver characteristics and seat belt usage rates.
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    \17\ Article 7, 1998 Agreement, available at https://unece.org/text-1998-agreement.
    \18\ Id.
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2. History of GTR No. 13
    NHTSA began collaborating with the international community to 
develop a global technical regulation for hydrogen vehicles in the 
early 2000s. In 2005, WP.29 agreed to a proposal from Germany, Japan 
and the United States of America regarding how best to manage the 
development process for a hydrogen vehicle GTR. Pursuant to the 
proposal, the United States and Japan were designated co-chairs of an 
informal

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working group (IWG) to explore the safety aspects of hydrogen vehicles.
    In June 2007, WP.29 adopted an action plan prepared by the co-
sponsors to develop a GTR for compressed gaseous and liquefied hydrogen 
fuel vehicles. At the time, no hydrogen vehicles were commercially 
available. To allow for the advancement of hydrogen technologies, the 
co-sponsors' action plan split the GTR into two phases. Phase 1 would 
focus on developing a GTR for hydrogen vehicles based on current best 
practices. Phase 2 would commence subsequent to Phase 1, and supplement 
it by assessing any technological advancements and explore ways to 
harmonize vehicle crash tests to evaluate fuel system integrity.
    The IWG evaluated existing research and design standards for the 
development of a hydrogen vehicle GTR. To the extent possible, the 
group avoided design specific requirements and considered requirements 
and specification that were supported by research and technically 
justified. The main areas of focus in Phase 1 were: performance 
requirements for hydrogen storage systems, high-pressure closures, 
pressure relief devices, and fuel lines; specifications on limits on 
hydrogen releases during normal vehicle operations and post-crash; and 
requirements for electrical isolation and protection against electric 
shock during normal vehicle operations and post-crash.
    The draft GTR was recommended by the IWG at the December 2012 
session, and GTR No. 13 for Hydrogen and Fuel Cell Vehicles was 
codified by WP.29 on June 27, 2013, after a 6-year effort, with the 
United States voting in favor of the GTR. It specified safety-related 
performance requirements and test procedures with the purpose of 
minimizing human harm that may occur as a result of fire, burst, or 
explosion related to the hydrogen fuel system of vehicles, and/or from 
electric shock caused by a fuel cell vehicle's high voltage power train 
system.\19\ The regulation consists of system performance requirements 
for compressed hydrogen storage systems (CHSS), CHSS closure devices, 
and the vehicle fuel delivery system. In Phase 1, the IWG purposefully 
did not harmonize crash tests and instead elected to have Contracting 
Parties use their own methodologies.
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    \19\ The electrical safety requirements in GTR No. 13 Phase 1 
were incorporated into FMVSS No. 305. See 82 FR 44945.
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    Phase 2 was adopted at the 190th Session of WP.29 on June 21, 
2023.\20\ Phase 2 accomplished several goals, including: broadening of 
the scope and application of GTR No. 13 to cover heavy-duty/commercial 
vehicles; harmonizing, clarifying, and expanding the requirements for 
thermal-pressure relief devices' direction in case of controlled 
release of hydrogen; strengthening test procedures for containers with 
pressures below 70 MPa, including comprehensive fire exposure tests; 
and extending the requirements to 25 years to more accurately capture 
the expected useful life of vehicles. The U.S. voted in favor of 
adopting Phase 2 and is proposing to adopt the changes made to GTR No. 
13 by Phase 2 with this proposal.
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    \20\ A copy of GTR No. 13 as updated by the Phase 2 amendments 
is available at: https://unece.org/sites/default/files/2023-07/ECE-TRANS-180-Add.13-Amend1e.pdf.
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III. Why is NHTSA issuing this proposal?

    As a Contracting Party who voted in favor of GTR No. 13, the United 
States is obligated under the 1998 Agreement to ``submit the technical 
Regulation to the process'' used to adopt the requirement into the 
agency's law or regulation as a domestic standard. Today's proposal 
satisfies that obligation. In deciding whether to adopt a GTR as an 
FMVSS, we follow the procedural and substantive requirements for any 
other agency rulemaking, including the Administrative Procedure Act, 
the National Traffic and Motor Vehicle Safety Act (Safety Act) (49 
U.S.C. Chapter 301), Presidential executive orders, and DOT and NHTSA 
policies, procedures, and regulations.\21\ Under 49 U.S.C. 30111(a), 
FMVSSs must be practicable, meet the need for motor vehicle safety, and 
be stated in objective terms.\22\ Section 30111(b) states that, when 
prescribing such standards, NHTSA must, among other things, consider 
all relevant, available motor vehicle safety information; consider 
whether a standard is reasonable, practicable, and appropriate for the 
types of motor vehicles or motor vehicle equipment for which it is 
prescribed; and consider the extent to which the standard will further 
the statutory purpose of reducing traffic crashes and associated deaths 
and injuries.
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    \21\ NHTSA's policies in implementing the 1998 Agreement are 
published in 49 CFR part 553, appendix C, ``Statement of Policy: 
Implementation of the United Nations/Economic Commission for Europe 
(UNECE) 1998 Agreement on Global Technical Regulations--Agency 
Policy Goals and Public Participation.'' NHTSA's paramount policy 
goal under the 1998 Agreement is to ``[c]ontinuously improve safety 
and seek high levels of safety, particularly by developing and 
adopting new global technical regulations reflecting consideration 
of current and anticipated technology and safety problems.''
    \22\ ``Motor vehicle safety'' is defined in the Safety Act as 
``the performance of a motor vehicle or motor vehicle equipment in a 
way that protects the public against unreasonable risk of accidents 
occurring because of the design, construction, or performance of a 
motor vehicle, and against unreasonable risk of death or injury in 
an accident, and includes nonoperational safety of a motor 
vehicle.'' 49 U.S.C. 30102(a)(8).
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    This proposal marks a substantial step in meeting those procedural 
and substantive requirements. The proposal serves as notice of our 
intention to adopt the requirements of GTR No. 13 as FMVSS Nos. 307 and 
308 and provides an opportunity for the public to comment on the 
proposed requirements. In accordance with the APA, we seek comment on 
this proposal to help inform our decision-making, and will take all 
timely public comments into consideration when deciding whether (and if 
so, how) to proceed with a final rule, and the appropriateness of any 
potential modifications to the proposed performance standards that are 
appropriately within scope of the NPRM.
    NHTSA tentatively finds that the proposed standards fulfill a 
clear, if not immediately present, need for motor vehicle safety. The 
purpose of FMVSS No. 307, ``Fuel system integrity of hydrogen 
vehicles,'' and FMVSS No. 308, ``Compressed hydrogen storage system 
integrity,'' is to reduce deaths and injuries in hydrogen-powered 
vehicles occurring from fires that result from leakage after motor 
vehicle crashes. Hydrogen is highly flammable, with an exceptionally 
wide limit of flammability in the air and a high burning velocity. If 
hydrogen leaks from the fuel system, the risk of fire in or near the 
vehicle is substantial and gravely impairs the safety of vehicle 
occupants and others within the vicinity of the vehicle.
    Although the potential safety risk from hydrogen vehicles has not 
necessarily materialized, due to their current scarcity in the on-road 
fleet, NHTSA made the same determination about the safety need for fuel 
system and container integrity systems when it adopted FMVSS No. 301, 
Fuel system integrity, with the initial FMVSSs adopted in 1968,\23\ and 
in 1994 when NHTSA adopted FMVSS No. 303, Fuel system integrity of 
compressed natural gas vehicles,\24\ and FMVSS No. 304, Compressed 
natural gas fuel container

[[Page 27507]]

integrity.\25\ NHTSA faced a similar crossroads when developing FMVSS 
Nos. 303 and 304. Compressed Natural Gas (CNG) vehicles represented a 
very small portion of the total fleet size when NHTSA finalized the 
standards. The agency decided that the safety risk posed by CNG 
necessitated immediate action.\26\ Members of the public shared a 
similar sentiment with the agency and urged quick action at that time 
to coalesce safety practices.\27\ Today's proposal is the logical 
extension of NHTSA's existing standards that cover vehicles powered by 
other combustible fuel sources, except, for this NPRM, the agency has 
been able to draw on and benefit from the work of the international GTR 
No. 13 community in developing the proposed standards.
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    \23\ See 32 FR 2414 (February 3, 1967).
    \24\ See 59 FR 19648 (April 25, 1994).
    \25\ See 59 FR 49010 (September 26, 1994).
    \26\ 58 FR 5323 (January 23, 1993)
    \27\ See 59 FR 19648, 19657.
---------------------------------------------------------------------------

    We tentatively find the proposed requirements in this NPRM to be 
practicable. Both automobile and hydrogen container manufacturers 
provided technical expertise to the IWG on test procedures and 
determining the boundaries of practicability of requirements during the 
development of GTR No. 13. Furthermore, GTR No. 13 incorporates a 
number of voluntary industry standards, which are discussed throughout 
this preamble, that have been demonstrated as practicable. Given the 
industry input informing the GTR and that the GTR incorporates current 
technical standards now used in hydrogen vehicle safety designs, NHTSA 
believes that the proposed standards are practicable.
    The 1998 Agreement provides flexibilities to propose alternative 
technical regulations as necessary to ensure compliance with a 
jurisdiction's specific legal and safety need requirements. As noted in 
the forthcoming sections, NHTSA is proposing several modifications to 
the requirements in GTR No. 13 to conform with the Safety Act 
requirements for FMVSS, clarify the wording of the regulation, and 
improve objectivity.
    The agency believes that this proposed rule is timely. While 
hydrogen vehicles currently represent less than half a percent of the 
total sales of light vehicles and are still in the prototypical stage 
for heavier vehicles, there are several trends that may point to 
increased growth in the coming years. The slow adoption of hydrogen 
vehicles can be attributed to both the expense associated with 
developing a new powertrain and the lack of existing fueling 
infrastructure.\28\ Recent Federal legislation and spending has renewed 
the country's focus on incentivizing clean vehicles. The Inflation 
Reduction Act (IRA) allotted billions towards the development of clean 
vehicles and the infrastructure to support them. Manufacturers can 
claim credits for building or retooling facilities to build hydrogen-
powered vehicles under Qualifying Advanced energy project credit or can 
claim credits for each hydrogen vehicle produced pursuant to the 
Advanced manufacturing production credit.\29\ Consumers who purchase 
hydrogen vehicles can qualify for a $7,500 tax credit, and commercial 
enterprises can claim up to $40,000 for hydrogen fuel cell 
vehicles.\30\ Additionally, producers of clean hydrogen are also 
eligible for tax credits on a per-gallon basis.\31\ This list of 
incentives is not exhaustive, and NHTSA recognizes that the collective 
efforts at both the Federal and State level to incentive clean energy 
in the transportation industry are extensive and underline the 
importance of establishing safety standards presently, so that they are 
in place as the vehicles arrive in the marketplace.
---------------------------------------------------------------------------

    \28\ See, e.g. S. Hardman, E. Shiu, R. Steinberger-Wilckens, and 
T. Turrentine., Barriers to the adoption of fuel cell vehicles: A 
qualitative investigation into early adopters attitudes, 95 
Transportation Research Part A: Policy and Practice 166-82 (2017). 
https://www.sciencedirect.com/science/article/abs/pii/
S0965856415302408#:~:text=FCVs%20have%20some%20specific%20challenges,
and%20balance%20of%20plant%20components.
    \29\ See 26 U.S.C. 48C and 26 U.S.C. 45X, respectively.
    \30\ See 26 U.S.C. 30D and 26 U.S.C. 45W, respectively.
    \31\ 26 U.S.C. 45Z.
---------------------------------------------------------------------------

    Manufacturers continue to announce new forays into hydrogen 
vehicles, with some manufacturers citing the IRA as a catalyst for 
further development of hydrogen-powered vehicles.\32\ Hyundai and 
Toyota, the only two manufacturers with hydrogen vehicles for sale 
currently in the United States, have announced plans to introduce more 
consumer hydrogen vehicle lines covering additional body styles and 
expand their hydrogen vehicle offerings.\33\ Other manufacturers have 
announced plans to introduce their own hydrogen vehicle models,\34\ and 
new entrants to the automotive market are testing prototypes and 
concept vehicles.\35\ Manufacturers have also stated that they are 
exploring the viability of hydrogen heavy-duty vehicles.\36\
---------------------------------------------------------------------------

    \32\ See, e.g. Elizabeth Sturcken, ``Leading companies are using 
IRA tax credits for clean manufacturing and technology. Are you?'' 
Environmental Defense Fund, June 7, 2023, https://business.edf.org/insights/leading-companies-are-using-ira-tax-credits-for-clean-manufacturing-and-technology-are-you/.
    \33\ See Remeredzai J. Kuhadzai, ``Toyota Hilux Hydrogen Fuel 
Cell Pickup Prototype Unveiled'' https://cleantechnica.com/2023/01/11/toyota-starts-work-on-the-development-of-prototype-hydrogen-fuel-cell-toyota-hilux-pickup/ (Toyota plans to release the Helix only in 
Japan for the upcoming model year) and Toyota, ``PACCAR and Toyota 
Expand Hydrogen Fuel Cell Truck Collaboration to Include 
Commercialization.'' May 2, 2023, https://pressroom.toyota.com/paccar-and-toyota-expand-hydrogen-fuel-cell-truck-collaboration-to-include-commercialization/; see also Michelle Thompson, ``Hyundai 
hires new exec to help lead hydrogen initiatives.'' Repairer Driven 
News, June 29, 2023. https://www.repairerdrivennews.com/2023/06/29/hyundai-hires-new-exec-to-help-lead-hydrogen-initiatives/.
    \34\ For example, see Ken Silverstein, ``Electric Vehicles or 
Hydrogen Fuel Cell Cars? The Inflation Reduction Act Will Fuel 
Both.'' Forbes, Aug. 10, 2022, https://www.forbes.com/sites/kensilverstein/2022/08/10/electric-vehicles-or-hydrogen-fuel-cell-cars-the-inflation-reduction-act-will-fuel-both/?sh=2841d7634d01; 
see also Joey Capparella, ``Hydrogen-Powered Honda CR-V to Be Built 
in the U.S. Starting in 2024.'' Car and Driver, Nov. 30, 2022.
    \35\ See, Ezra Dyer, ``Pininfarina Reveals Pura Vision SUV 
Concept.'' Car and Driver, Aug. 1, 2023, https://www.caranddriver.com/news/a44690183/pininfarina-pura-vision-suv-concept-revealed/.
    \36\ See Rebecca Martineau, ``Fast Flow Future for Heavy-Duty 
Hydrogen Trucks: Expanded Capabilities at NREL Demonstrate High-
Flow-Rate Hydrogen Fueling for Heavy-Duty Applications.'' National 
Renewable Energy Laboratory, June 8, 2022, https://www.nrel.gov/news/program/2022/fast-flow-future-heavy-duty-hydrogen-trucks.html.
---------------------------------------------------------------------------

    NHTSA faced a similar crossroads when developing FMVSS Nos. 303 and 
304. Compressed Natural Gas (CNG) vehicles represented a very small 
portion of the total fleet size when NHTSA finalized the standards. The 
agency decided that the safety risk posed by keeping CNG at a high 
pressure necessitated an immediate action.\37\ Members of the public 
have shared a similar sentiment with the agency and urged quick action 
to coalesce safety practices for hydrogen powered vehicles.\38\
---------------------------------------------------------------------------

    \37\ 58 FR 5323.
    \38\ See 59 FR 19648, 19657.
---------------------------------------------------------------------------

    We believe that the proposed standards would provide regulatory 
certainty for manufacturers. Given manufacturers' purported interest in 
expanding their hydrogen offerings and the IRA incentives reducing the 
comparative costs of hydrogen vehicles, adopting safety regulations now 
would provide manufacturers clarity on how to design new vehicle lines. 
Further, having hydrogen safety standards in place should assist in 
alleviating the trepidation consumers have of newer technologies, 
whereas a failure to adequately address safety concerns in the earliest 
stages of development could have a negative impact on the deployment of 
this new technology. Manufacturers have also informed

[[Page 27508]]

NHTSA that they would like to see the agency coordinate and harmonize 
hydrogen standards with other nations.\39\ This proposal would 
accomplish all of these tasks.
---------------------------------------------------------------------------

    \39\ See, e.g. NHTSA-2004-18039-0020 at 17.
---------------------------------------------------------------------------

IV. Overview of Proposed Safety Standards

    The safe use of compressed hydrogen in vehicles lies primarily in 
preventing explosion of the hydrogen container(s) and preventing fuel 
leaks which could lead to fire or explosion. The leakage of hydrogen 
from the fuel system during normal vehicle operations and post-crash 
can pose safety hazards (fire or explosion) to vehicle occupants and 
the surroundings. In order to address the fire and explosion hazards 
associated with hydrogen vehicles, NHTSA is proposing to set 
performance requirements for the CHSS and the overall fuel system that 
are generally consistent with GTR No. 13.
    GTR No. 13, Section 5.1, ``Compressed hydrogen storage system,'' 
specifies performance-based CHSS requirements which address documented 
on-road stress factors. These stress factors include those identified 
in CNG vehicle containers as well as those that are unique to 
containment of high-pressure hydrogen. These requirements were 
developed to demonstrate the CHSS's capability to perform critical 
functions throughout service, including fueling/defueling events, 
parking under extreme vehicle and environmental conditions, 
environmental exposures, and performance in fire without explosion.
    GTR No. 13, Section 5.2, ``Vehicle fuel system,'' includes 
performance requirements to prevent and mitigate hydrogen leak from the 
fuel system and to warn vehicle occupants in the event of hydrogen 
concentration in the vehicle above flammable limits during normal 
vehicle operations and post-crash.
    Similar to how NHTSA originally established CNG standards, we are 
proposing to implement GTR No. 13 by establishing two new FMVSSs that 
would specify minimum performance standards for vehicles that use 
compressed hydrogen gas as a motor fuel.\40\ FMVSS No. 308, 
``Compressed hydrogen storage system integrity,'' would set out 
requirements for CHSS integrity. FMVSS No. 307, ``Fuel system integrity 
of hydrogen vehicles,'' would set out in-use and post-crash 
requirements for the overall fuel system, including the CHSS, hydrogen 
delivery system, and fuel cell.
---------------------------------------------------------------------------

    \40\ The standards proposed in this document would not apply to 
vehicles that use liquified hydrogen as a motor fuel.
---------------------------------------------------------------------------

    NHTSA is proposing that FMVSS Nos. 307 and 308 apply to all 
hydrogen-powered vehicles. This is a departure from Phase 1 of GTR No. 
13 which only applies to hydrogen powered light vehicles. As discussed 
below, the IWG of GTR No. 13 Phase 2 has expanded the applicability of 
the standard to hydrogen powered heavy vehicles. With the exception of 
crash tests for heavy vehicles, NHTSA finds that the technical 
standards in GTR No. 13 are practicable for heavy vehicles and address 
the same safety need found in light vehicles.
    Note that, consistent with GTR No. 13, NHTSA is proposing that 
FMVSS No. 308 be a vehicle-level standard, rather than an equipment 
standard.\41\ Some performance requirements and test procedures for the 
CHSS in FMVSS No. 308 are specific to the vehicle design and to its 
gross vehicle weight rating. NHTSA is aware this is a departure from 
FMVSS No. 304 that is an equipment standard which applies to CNG 
containers sold as replacement parts for CNG vehicles. At this time, 
hydrogen vehicle manufacturers are strictly controlling the CHSS 
installed in their vehicles and replacement parts are obtained from the 
vehicle manufacturer (similar to electric vehicle batteries). NHTSA 
will monitor the deployment of hydrogen vehicles and how consumers are 
replacing parts of the fuel system. Since such data is lacking at this 
time, NHTSA is proposing FMVSS No. 308 as a vehicle standard, 
consistent with GTR No. 13. NHTSA will re-evaluate this decision based 
on comments received and on field data on hydrogen vehicle deployment, 
repair, and replacement parts. NHTSA seeks comment on whether FMVSS No. 
308 should remain a vehicle standard, as well as whether FMVSS Nos. 307 
and 308 should be combined into a single standard in the final rule.
---------------------------------------------------------------------------

    \41\ This is in contrast to FMVSS No. 304, Compressed natural 
gas fuel container integrity, which is an equipment standard.
---------------------------------------------------------------------------

A. FMVSS No. 308, ``Compressed Hydrogen Storage System Integrity''

    FMVSS No. 308 would set out requirements for the performance of the 
CHSS and its subcomponents during normal use, with a particular focus 
on how the CHSS performs in a variety of incidents that a vehicle could 
experience during its lifetime operations and how well the component 
withstands usage.
    NHTSA is proposing that FMVSS No. 308 only be a vehicle standard. 
As explained in more detail below, some of the proposed requirements 
are conditional on the vehicle type and characteristics. Without the 
knowledge of the relevant vehicle, some of the proposed CHSS standards 
cannot be tested. For these reasons, NHTSA does not intend that the 
proposed standard should extend to cover replacement parts, even though 
they would be considered motor vehicle equipment and still subject to 
NHTSA's safety defect authority, and replacement parts when installed 
may not take the vehicle out of compliance with the proposed new FMVSS 
No. 308, per 49 U.S.C. 30122. NHTSA seeks comment on this approach.
1. Compressed Hydrogen Storage System
    The CHSS is defined to include all closure surfaces that provide 
primary containment of high-pressure hydrogen storage. The CHSS is 
defined to include the hydrogen container, check valve, shut-off valve 
and thermally-activated pressure relief device (TPRD), which are 
discussed in the sections below. Figure-3 illustrates a typical CHSS.
[GRAPHIC] [TIFF OMITTED] TP17AP24.002

Figure-3: Typical CHSS

a. Hydrogen Container
    The hydrogen container is the main component of a CHSS. The 
hydrogen container stores hydrogen at extremely high pressure. On 
current hydrogen vehicles, hydrogen has typically been stored at a 
nominal working pressure (NWP) of 35 MPa or 70 MPa, at 15 [deg]C. NWP 
means the gauge pressure that characterizes the normal operation of the 
system. Typically, the container is designed for a maximum allowable 
gas temperature of 85 [deg]C. If the temperature of hydrogen stored at 
NWP is increased from 15 [deg]C to 85 [deg]C, then the pressure inside 
the container will rise to the maximum allowable pressure of 25

[[Page 27509]]

percent above NWP.\42\ A container may consist of a single chamber or 
multiple permanently interconnected chambers. This allows designers 
flexibility in the overall shape of the CHSS.
---------------------------------------------------------------------------

    \42\ This is based on data published in the NIST Chemistry 
WebBook, Standard Reference Database Number 69, Thermophysical 
Properties of Fluid Systems (isochoric properties for hydrogen), 
available at https://webbook.nist.gov/chemistry/fluid/.
---------------------------------------------------------------------------

    Most containers used in hydrogen vehicles consist of two layers. 
The inner liner prevents gas leakage/permeation and is usually made of 
metal or thermoplastic polymer. The outer layer provides structural 
integrity and is usually made of metal or thermoset resin-impregnated 
fiber-reinforced composite. For instance, Type 3 containers consist of 
a metal liner reinforced with resin impregnated continuous filament, 
and Type 4 containers consists of a non-metallic liner with resin-
impregnated continuous filament.\43\
---------------------------------------------------------------------------

    \43\ The American National Standard for Compressed Natural Gas 
Fuel Vehicle Containers (2007) classifies containers into Types 1 
through 4 as follows:
    Type 1--Metal.
    Type 2--Resin impregnated continuous filament with metal liner 
with a minimum burst pressure of 125 percent of service pressure. 
This container is hoop-wrapped.
    Type 3--Resin impregnated continuous filament with metal liner. 
This container is full-wrapped.
    Type 4--Resin impregnated continuous filament with a non-
metallic liner.
---------------------------------------------------------------------------

    GTR No. 13 defines a container as ``the pressure-bearing component 
on the vehicle that stores the primary volume of hydrogen fuel in a 
single chamber or in multiple permanently interconnected chambers.'' 
NHTSA is proposing a similar definition with the following 
modifications:
     Replace ``the vehicle'' with ``a compressed hydrogen 
storage system'' to clarify that the container is a subcomponent of the 
CHSS, and therefore a container cannot exist on its own without the 
other components of the CHSS.
     Remove the word ``primary'' because this introduces 
ambiguity regarding secondary or tertiary volumes of hydrogen.
     Add the word ``continuous'' to clarify that a container 
does not have any valves or other obstructions that may separate its 
different chambers.
    Thus, NHTSA's proposed definition for ``container'' would be 
``pressure-bearing component of a compressed hydrogen storage system 
that stores a continuous volume of hydrogen fuel in a single chamber or 
in multiple permanently interconnected chambers.'' These changes are 
intended to clarify the definition and provide greater regulatory 
certainty as to what is considered part of the container. The changes 
do not alter the substantive requirements. NHTSA seeks comment on the 
proposed definition for the container.
b. Closure Devices
    GTR No. 13 refers to closure devices as ``primary'' closure 
devices. This creates ambiguity about potential secondary or tertiary 
closure devices. As a result, NHTSA will refer simply to ``closure 
devices.'' NHTSA therefore proposes to define the term ``closure 
devices'' as ``the check valve(s), shut-off valve(s) and thermally 
activated pressure relief device(s) that control the flow of hydrogen 
into and/or out of a CHSS,'' so it will be clear what components are 
covered under the standard. NHTSA seeks comment on removal of the word 
``primary'' and on the proposed definition for ``closure devices.''
(1) TPRD
    In the event of a fire, the TPRD provides a controlled release of 
hydrogen from the container before the high temperature from the fire 
weakens the container and causes a hazardous burst. TPRDs are designed 
to vent the entire hydrogen content of the container rapidly. These 
devices are designed to not be reset or reused once they have been 
activated.
(2) Check Valve
    During fueling, hydrogen enters the CHSS through a check valve. The 
check valve prevents back-flow of hydrogen into the fueling line or out 
of the fueling receptacle.
(3) Shut-Off Valve
    A shut-off valve prevents the outflow of stored hydrogen from the 
container when the vehicle is not operating or when a fault is detected 
that requires isolation of the CHSS. In GTR No. 13, the shut-off valve 
is defined as ``a valve between the container and the vehicle fuel 
system that must default to the `closed' position when not connected to 
a power source.'' NHTSA proposes adding the words ``electrically 
activated'' to the definition, so that a shut-off valve would be ``an 
electrically activated valve between the container and the vehicle fuel 
system that must default to the `closed' position when not connected to 
a power source.'' NHTSA seeks comment on the proposed definition of 
shut-off valve.
(4) Container Attachments
    The CHSS may include container attachments, which are non-pressure 
bearing parts attached to the container that provide additional support 
and/or protection to the container. Container attachments may only be 
removed with the use of tools for the purpose of maintenance and/or 
inspection. Container attachments include devices such as bump stops to 
mitigate impacts or shielding to mitigate surface damage to the 
container.
    In the GTR No. 13 test procedures, container attachments are 
included in some tests. Importantly, in some cases, the container 
attachments provide protection to the container that improves test 
performance. Including container attachments for testing is discussed 
in the sections below where applicable and where the container 
attachments may affect test performance.
    NHTSA proposes defining container attachments as ``non-pressure 
bearing parts attached to the container that provide additional support 
and/or protection to the container and that may be removed only with 
the use of tools for the specific purpose of maintenance and/or 
inspection.'' NHTSA seeks comment on the proposed definition of 
container attachments. In this definition, the word ``temporarily'' has 
been removed from the GTR definition because anything that can be 
removed temporarily can also be removed permanently. For clarity, NHTSA 
has also shifted the order of some words relative to the definition in 
GTR No. 13.
2. General Requirements for the CHSS
    NHTSA is proposing that the CHSS be required to include the 
functionality of a TPRD, shut-off valve, and check valve. These 
functions are required for the reasons stated above. However, NHTSA is 
aware of CNG vehicles that do not include check valves as part of their 
CNG storage system. In such CNG vehicles, the check valves are 
installed upstream between the fueling port and the CNG container, with 
additional valves to contain high pressure gas. NHTSA seeks comment on 
whether the check valves should be required as part of the CHSS.
    The CHSS would be required to have an NWP of 70 MPa or less. This 
is because working pressures above 70 MPa are currently considered 
impractical and may pose a safety risk given current known 
technologies. The energy density of hydrogen does not increase 
significantly when pressurized above 70 MPa, so there is no significant 
improvement in hydrogen storage efficiency at pressures above 70 MPa. 
Pressures above 70 MPa, however, may present a greater safety hazard. 
As a result, NHTSA proposes that all CHSS

[[Page 27510]]

must have an NWP less than or equal to 70 MPa. NHTSA seeks comment on 
this requirement, and specifically asks commenters to identify any 
technologies that can safely store hydrogen at pressures above 70 MPa.
    GTR No. 13 provided contracting parties with the discretion to 
require that the closure devices be mounted directly on or within each 
container. The relevant safety concern is that the high-pressure lines 
required to connect remotely-located closure devices with the container 
could be susceptible to damage or leak. However, the definition of a 
container is sufficiently broad that it includes such lines as part of 
the container. These lines will be considered part of the permanently 
interconnected chambers storing the continuous volume of hydrogen. 
Thus, any lines connecting to closure devices are themselves part of 
the container and will be included in the extensive container 
performance testing discussed below. If a container (which includes any 
lines connecting to closure devices) can successfully complete the 
performance testing in FMVSS No. 308, then the risk of failure of the 
lines has been addressed. Therefore, NHTSA tentatively concludes that 
it is not necessary to specify that closure devices be mounted directly 
on or within each container. NHTSA is also concerned that such a 
specification would be design restrictive. NHTSA is aware of CNG fuel 
systems where the closure devices are neither on nor within each 
container, and there have been no reported safety issues with such 
systems. Therefore, NHTSA is not proposing to include a requirement for 
closure devices to be on or within each container, and would instead 
leave the location of closure devices to manufacturer discretion. NHTSA 
seeks comment on requiring closure devices to be mounted directly on or 
within each container.
3. Performance Requirements for the CHSS
    The CHSS would be required to meet specific performance 
requirements when subjected to the performance tests listed below. The 
performance tests and the respective performance requirements are 
discussed in detail in subsequent sections:

 Tests for baseline metrics
 Test for performance durability
 Test for expected on-road performance
 Test for service terminating performance in fire
 Tests for performance durability of closure devices

    Several of these tests utilize a manufacturer-supplied value known 
as BPO. A container's BPO is a design parameter 
specified by the manufacturer to establish the expected initial burst 
pressure of the container. It is NHTSA's understanding that 
BPO, associated with median or midpoint burst pressure for a 
batch of containers, can vary between batches of containers. Therefore, 
in order to facilitate compliance testing, NHTSA is proposing that 
manufacturers specify the BPO associated with each container 
on the required container label (discussed below). NHTSA seeks comment 
on this labeling requirement, noting that it is not required by GTR No. 
13.
4. Tests for Baseline Metrics
    The container must be able to withstand high pressurization, as 
well as pressure cycling, which is a repeated pressurization and 
depressurization. Both of these stress factors occur during the service 
life of the vehicle as its fuel system is repeatedly depleted and 
refilled. Consistent with GTR No. 13, the proposed tests for baseline 
metrics would include two tests for the container: the baseline initial 
burst pressure test to evaluate resistance to burst at high pressure, 
and the baseline initial pressure cycle test to ensure the container is 
designed to leak before burst \44\ and to evaluate its ability to 
withstand pressure cycling without burst and without leakage within its 
service life.
---------------------------------------------------------------------------

    \44\ Leak before burst design of high pressure containers is a 
common safety feature to ensure a leak will develop before a 
catastrophic burst will occur. A leak is a less severe failure mode 
compared to a catastrophic burst of the high pressure container.
---------------------------------------------------------------------------

    During the initial burst pressure test, the container must 
demonstrate that as the pressure is increased inside the container, the 
point of failure is above a minimum pressure level, discussed below. In 
other words, the container must demonstrate a minimum burst pressure. 
Burst pressure is defined as the highest pressure reached inside a 
container during a burst test which results in structural failure of 
the container and resultant fluid loss through the container, not 
including gaskets or seals. Burst pressure is determined by the 
baseline initial burst pressure test discussed below.
    During the baseline initial pressure cycle test, the container must 
withstand pressure cycling that simulates repeated fueling and 
defueling by increasing the pressure inside the container to a high 
pressure level, then depressurizing it to low pressure, and repeating 
that process for a set number of cycles. The container must neither 
leak nor burst during an initial set of pressure cycles, and must not 
burst during a set number of pressure cycles beyond the initial set. 
These requirements are evaluated by the baseline pressure cycle life 
test discussed below.
    The physical forces on the load-bearing components of a container 
are the same regardless of whether the pressure is being applied with 
hydraulic fluid, hydrogen gas, or any other medium. Therefore, for 
practicability and safety purposes both tests would be conducted using 
hydraulic fluid to exert pressure inside the container.\45\ Hydraulic 
fluids, such as water or water with additives, are advantageous for 
these tests because they reduce the explosion risk associated with 
pneumatic pressurization. The explosion risk from pneumatic 
pressurization is high because compression of gas stores pressure-
volume energy (PV energy), whereas during hydraulic pressurization with 
an incompressible fluid, PV energy is negligible. In addition, the 
incompressible nature of hydraulic fluids means that pressure cycles 
can be accomplished much faster than pneumatic pressurization cycles. 
This is important given the high number of cycles required for the 
baseline pressure cycle test. The use of hydrogen gas pneumatic 
pressure cycling does introduce stress factors beyond basic 
pressurization/depressurization, as discussed later, and these are 
addressed separately in the test for expected on-road performance. 
Given that hydraulic pressure cycling provides these benefits without 
compromising the safety or stringency of the proposed standards, 
hydraulic pressure cycling is used for these tests.
---------------------------------------------------------------------------

    \45\ This is consistent with GTR No. 13.
---------------------------------------------------------------------------

a. Baseline Initial Burst Pressure
    The baseline initial burst pressure test verifies that the initial 
burst pressure of a container is both above a minimum specified 
pressure level and is within 10 percent of the manufacturer specified 
BPO. The requirement that the container tested must have a 
burst pressure within 10 percent of BPO is based 
on the need to control variability in container production. If a 
manufacturing process produces containers with highly variable initial 
burst pressures, there is a possibility of a container with a 
dangerously low burst pressure. NHTSA seeks comment on the safety need 
for specifying a limit on burst pressure variability in a batch and 
whether the 10 percent limit is appropriate; if commenters believe 
another limit is

[[Page 27511]]

appropriate, they are asked to provide supporting data.
    The minimum burst pressure, BPmin, in GTR No. 13 Phase 1 
was set at 225 percent of NWP for carbon fiber composite containers, 
and 350 percent NWP for glass fiber composite containers. The value for 
carbon fiber composite containers was chosen to be a conservative 
starting point based on experience from CNG vehicles. GTR No. 13 Phase 
1 made clear that the burst pressure requirement would be reviewed in 
Phase 2. The IWG of GTR No. 13 Phase 2 did review data on variability 
in initial burst pressure and end-of-life burst pressure (i.e., burst 
pressure after the test for performance durability, discussed in a 
later section), and determined that variation in burst pressure is 
actually low and that a minimum initial burst pressure of 200 percent 
NWP was appropriate for carbon fiber composite containers.\46\ The GTR 
No. 13 Phase 2 IWG assessment also noted that manufacturers generally 
design containers to have burst pressures well above the required 
minimum burst pressure, to ensure that a container can meet the 
performance requirements of the test for performance durability. These 
findings suggest it is possible to lower the minimum burst pressure 
requirement to 200 percent of NWP without reducing safety, because 
manufacturers will generally be outperforming this requirement anyway.
---------------------------------------------------------------------------

    \46\ A study was conducted by the Japanese Automobile Research 
Institute which evaluated the variability of containers' initial 
burst pressure, as well as the variability in end-of-life burst 
pressure. The study concluded that variability among the containers 
was low, and therefore a minimum initial burst pressure of 200 
percent NWP was acceptable and most consistent with the end-of-life 
burst pressure requirement.
    See GTR No. 13 Phase 2 file GTR13-3-03: https://wiki.unece.org/download/attachments/58525915/GTR13-3-03%20Initial%20burst%20pressure%20requirement%20_3rd%20GTR13%20IWG_June2018.pdf?api=v2.
---------------------------------------------------------------------------

    Furthermore, a 200 percent minimum initial burst pressure can be 
supported when coupled with the following requirements from the 
proposed test for performance durability (which are discussed in the 
following section): \47\
---------------------------------------------------------------------------

    \47\ The tests conducted by the Japanese Automobile Research 
Institute showed that containers with burst pressure which met the 
BPO 10 percent requirement and subjected to 
the durability sequential tests, were able to withstand the end-of-
life 180 percent NWP for four minutes and have an end-of-life burst 
pressure within -20 percent of BPO, even if the minimum 
initial burst pressure is reduced to 200 percent NWP.
---------------------------------------------------------------------------

     The container must withstand 180 percent NWP for 4 minutes 
at the end of the test for performance durability.
     The minimum burst pressure after the completion of the 
test for performance durability cannot be lower than 80 percent of 
BPO.
    In light of the variability in the minimum burst pressure and the 
need to meet the above two requirements at the end of the test for 
performance durability, NHTSA expects that manufacturers will 
ultimately design the container with an initial burst pressure well 
above 200 percent NWP.
    Accordingly, NHTSA believes that proposing BPmin to 200 
percent NWP, as set forth in GTR No. 13 Phase 2, meets the need for 
safety. Proposing the BPmin to 200 percent NWP facilitates 
hydrogen vehicle development without unnecessary overdesign of 
components. NHTSA seeks comment on the proposed BPmin of 200 
percent NWP instead of the 225 percent NWP specified in GTR No. 13 
Phase 1.
    In the case of containers having glass-fiber as a primary 
constituent, consistent with GTR No. 13 Phase 2, NHTSA is proposing a 
higher BPmin of 350 percent of NWP because these containers 
are highly susceptible to stress rupture as compared to carbon fiber 
containers. Stress rupture is a failure mode that relates to the 
intrinsic failure probability of the individual fibers that overwrap 
the container for support. This failure mode can occur when the fibers 
are held under stress for long periods of time (such as in a 
continuously pressurized container).\48\ The higher BPmin of 
350 percent of NWP provides protection from the risk of stress rupture 
in containers having glass-fiber composite as a primary constituent. 
NHTSA seeks comment on this proposed requirement and how NHTSA can 
determine if a container has glass-fiber as a primary constituent. 
NHTSA seeks comment on appropriate criteria to determine the primary 
constituent in this context.
---------------------------------------------------------------------------

    \48\ SAE Paper 2009-01-0012. Rationale for Performance-based 
Validation Testing of Compressed Hydrogen Storage by Christine S. 
Sloane, available at https://www.sae.org/publications/technical-papers/content/2009-01-0012/.
---------------------------------------------------------------------------

    In the case of containers constructed of both glass and carbon 
fibers, NHTSA proposes to apply the requirements according to the 
primary constituent of the container as specified by the manufacturer. 
NHTSA proposes that the manufacturer shall specify upon request, in 
writing, and within five business days, the primary constituent of the 
container. NHTSA proposes that the burst pressure of the container, for 
which the manufacturer fails to specify upon request, in writing, and 
within five business days, the primary constituent of the container, 
must not be less than 350 percent of NWP. NHTSA seeks comment on this 
proposed requirement.
    The test for performance durability, described below, includes a 
1000 hour high-temperature (85 [deg]C) static pressure test, which is 
designed to evaluate the container's resistance to stress rupture, in 
combination with other lifetime stress factors. Given that the high-
temperature static pressure test is focused directly on evaluating 
stress rupture risk, and the test for performance durability represents 
an overall worst-case lifetime of stress factors, regardless of fiber 
type, NHTSA seeks comment on whether the baseline initial burst 
pressure test even needs to be included in the standard's requirements.
    GTR No. 13 specifies that the baseline initial burst pressure test 
(as well as the initial pressure cycle test described below) be 
conducted at ambient temperatures between 5 [deg]C and 35 [deg]C. The 
IWG of GTR No. 13 determined that container burst strength is not 
affected by using this range of ambient temperature between 5 [deg]C 
and 35 [deg]C.\49\ This temperature range reduces test costs (thus 
improving the practicability of the proposed requirements) by enabling 
outdoor testing without special temperature controls. Extreme 
temperatures are addressed in later tests.
---------------------------------------------------------------------------

    \49\ See GTR No. 13, Part I, paragraph 81(d)(v).
---------------------------------------------------------------------------

    GTR No. 13 requires that the rate of pressurization be less than or 
equal to 1.4 MPa/s for pressures higher than 150 percent of the nominal 
working pressure. If the pressurization rate exceeds 0.35 MPa/s at 
pressures higher than 150 percent NWP, GTR No. 13 also requires that 
either the container is placed in series between the pressure source 
and the pressure measurement device, or that the time at the pressure 
above a target burst pressure exceeds 5 seconds. These requirements are 
designed to ensure that a pressure sensor will measure the pressure 
inside the container accurately. The pressurization rate limit ensures 
the pressure sensor will have enough time to read the pressure level as 
it rises. Placing the container in series between the pressure source 
and the pressure sensor ensures that the container will experience the 
pressure before the sensor, so there is no chance that the pressure 
sensor could read a pressure level that is not being experienced by the 
container. However, NHTSA is concerned that the second option that the 
time at the pressure above the target burst pressure exceeds 5 seconds 
is unclear and difficult to enforce. For example, it is not clear what 
pressure

[[Page 27512]]

the ``target burst pressure'' is referring to since the pressure may be 
increasing continuously. Therefore, this option is not being proposed 
as an alternative and the container will simply be placed in series 
between the pressure source and the pressure measurement device. NHTSA 
seeks comment on this decision.
b. Service Life and Number of Cycles for the Baseline Initial Pressure 
Cycle Test for Containers on Light and Heavy Vehicles
    As discussed above, hydrogen is highly flammable, and therefore, 
hydrogen containers must not leak during their service life. While 
hydrogen leakage is a serious safety concern, leaking hydrogen will 
likely dissipate quickly into the atmosphere given its density, and may 
or may not ignite/explode, whereas, a hydrogen container burst involves 
an explosion by definition and is therefore a far worse, catastrophic 
failure mode that must be prevented under all circumstances regardless 
of service life. As a result, hydrogen containers are designed to leak 
before bursting beyond their service lives. This ``leak before burst'' 
safety feature is also followed for other high-pressure vehicle fuel 
containers such as vehicle CNG fuel containers. Systems are typically 
designed such that the occurrence of leakage should result in vehicle 
shut down and subsequent repair or removal of the container from 
service, thereby preventing a burst of the container from occurring.
    The baseline pressure cycle test requirement is designed to provide 
an initial check for resistance to leak or burst due to pressure 
cycling during service, and a check that the container does in fact 
leak before burst after the container service life has been exceeded. 
Accordingly, the baseline initial pressure cycle test requires the 
container to (i) not leak or burst for a specified number of pressure 
cycles that are meant to represent maximum container service life, and 
(ii) leak before burst for a specified number of pressure cycles beyond 
the maximum service life. In the case of (i), the IWG of GTR No. 13 
Phase 1 gave contracting parties the option of selecting either 5,500, 
7,500, or 11,000 cycles as the expected maximum service life 
containers. In the case of (ii), the GTR explains that a greater number 
of pressure cycles (22,000) that far exceeds service life of containers 
is used to ensure that a container should leak before bursting during 
the expected service life.
    GTR No. 13 provides several examples of the maximum number of 
empty-to-full fueling cycles for vehicles under extreme service. These 
examples are described below and summarized in Table-1.
     Sierra Research Report No. SR2004-09-04 for the California 
Air Resource Board (2004) reported on vehicle lifetime distance 
traveled by scrapped California vehicles, which all showed lifetime 
distances traveled below 350,000 miles. Based on these figures and 200-
300 miles driven per full fueling, the maximum number of lifetime 
empty-to-full fuelings can be estimated as 1,200-1,800.
     Transport Canada reported that required emissions testing 
in British Columbia, Canada, in 2009 showed the five most extreme usage 
vehicles had odometer readings in the 500,000-600,000 miles range. 
Using the reported model year for each of these vehicles, this 
corresponds to less than 300 full fuelings per year, or less than one 
full fueling per day. Based on these figures and 200-300 miles driven 
per full fueling, the maximum number of empty-to-full fuelings can be 
estimated as 1,650-3,100.
     The New York City (NYC) taxicab fact book reports extreme 
usage of 200 miles in a shift and a maximum service life of five 
years.\50\ Less than 10 percent of vehicles remain in service as long 
as five years. The average mileage per year is 72,000 for vehicles 
operating two shifts per day and seven days per week. There is no 
record of any vehicle remaining in high usage through-out the full 5-
year service life. However, if a vehicle were projected to have fueled 
as often as 1.5-2 times per day and to have remained in service for the 
maximum 5-year NYC taxi service life, the maximum number of fuelings 
during the taxi service life would be 2,750-3,600.
---------------------------------------------------------------------------

    \50\ New York City taxicab fact book, Schaller Consulting 
(2006), http://www.schallerconsult.com/taxi/taxifb.pdf.
---------------------------------------------------------------------------

     Transport Canada reported a survey of taxis operating in 
Toronto and Ottawa that showed common high usage of 20 hours per day, 
seven days per week with daily driving distances of 335-450 miles. 
Vehicle odometer readings were not reported. In the extreme worst-case, 
it might be projected that if a vehicle could remain at this high level 
of usage for seven years (the maximum reported taxi service life); then 
a maximum extreme driving distance of 870,000-1,200,000 miles is 
projected. Based on 200-300 miles driven per full fueling, the 
projected full-usage 15-year number of full fuelings could be 2,900-
6,000.

                                                      Table 1--Expected Vehicle Usage Data Summary
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                                                      Number of lifetime empty-to-full
            Data source               Lifetime traveling distance (miles)      Distance per full-fueling (mile)                   filling
--------------------------------------------------------------------------------------------------------------------------------------------------------
Sierra Research Report No. SR2004-   350,000..............................  200-300..............................  1,200-1,800.
 09-04: California vehicles.
Transport Canada: Vehicle fleet      500,000-600,000......................  200-300..............................  1,650-3,100.
 &Taxi.
The New York City (NYC) taxicab      360,000 (5 year life)................  N/A (Fueling frequency 1.5-2 times/    2750-3600 (5 year life).
 fact book: Taxi usage.                                                      day).
Transport Canada: Taxi usage.......  870,000-1,200,000....................  200-300..............................  2,900-6,000.
--------------------------------------------------------------------------------------------------------------------------------------------------------

    Based on these examples, the IWG of GTR No. 13 Phase 1 set the 
minimum number of pressure cycles before leak at 5,500. The maximum 
number of cycles before leak was set at 11,000 cycles, which 
corresponds to a vehicle that remains in service with two full fuelings 
per day for 15 years (expected lifetime vehicle mileage of 2.2-3.3 
million miles). The last example above shows it is possible for a high 
usage taxi to experience 6,000 fueling cycles during seven years of 
service. Taxi service is representative of the most demanding 
circumstances a light vehicle will experience, so this example is 
considered worst-case. Furthermore, such a vehicle could be 
subsequently resold and experience further fuelings beyond 6,000. As a 
result, the IWG of GTR No. 13 Phase 2 concluded that the

[[Page 27513]]

choice of 5,500 cycles is not sufficient for containers on light 
vehicles. However, NHTSA concludes that the maximum choice of 11,000 
cycles is too extreme for light vehicles. A vehicle traveling 2.2-3.3 
million miles is unrealistic even for the most extreme service life for 
light vehicles. Accordingly, NHTSA proposes 7,500 as the number of 
cycles in the baseline initial pressure cycle test for which the 
container does not leak or burst. NHTSA believes that 7,500 pressure 
cycles is a reasonable representation of the maximum service life of a 
container, and notes that is greater than that presented in Table 1 for 
the Transport Canada taxi usage data.
    As discussed above, the worst-case scenario is a container failure 
by burst. To ensure the container leaks before burst beyond the maximum 
service life, the container is pressure cycled beyond the 7,500 cycles 
(representing maximum service life) until leak occurs without burst or 
up to a maximum of 22,000 hydraulic pressure cycles. For vehicles with 
nominal on-road driving range of 300 miles per full-fueling, 22,000 
hydraulic pressure cycles correspond to over 6 million miles, which is 
beyond extreme on-road vehicle lifetime range.
    The analysis summarized above considered light vehicles with a 
service life of 15 years. When conducting their analysis, the IWG of 
GTR No. 13 Phase 1 had limited information available on lifetime 
vehicle mileage and fuelings. In addition, hydrogen vehicles were a new 
technology and there was very little field experience available to draw 
upon. As a result, the IWG of GTR No. 13 Phase 1 was conservative in 
setting the number of cycles for the baseline initial cycle test. In 
the analysis provided above, short periods of extreme service were 
extrapolated to a full 15-year service life. This is not a realistic 
assumption because vehicles generally cannot last in extreme service 
for a full 15 years.
    To address this issue, the IWG of GTR No. 13 Phase 2 reviewed new 
data on the number of vehicle miles traveled. The analysis was also 
expanded to include heavy vehicles in addition to light 
vehicles.51 52 The data shows that the number of cycles 
presented in GTR No. 13 for light vehicles correspond more 
appropriately to a 25-year service life.
---------------------------------------------------------------------------

    \51\ See GTR No. 13 Phase 2 file GTR13-11-12b: The number of 
cycles, https://wiki.unece.org/download/attachments/123666576/GTR13-9-07%20TF1%20OICA%20GTR13%20Baseline%20Initial%20Cycles.pdf?api=v2.
    \52\ See GTR No. 13 Phase 2 file GTR13-9-07: Extension of the 
service life of the container to 25 years, https://wiki.unece.org/download/attachments/140706658/GTR13-11-12b%20TF1%20%20210927%20Estimation%20of%20VMT%20TF1-JAMA.pdf?api=v2.
---------------------------------------------------------------------------

    For heavy vehicles, the new data on the number of vehicle miles 
traveled that was collected in Phase 2 indicates a higher number of 
cycles are required for a 25-year service life than that for light 
vehicles. This is consistent with the fact that heavy vehicles 
typically travel farther and remain in service longer than light 
vehicles. Consequently, for heavy vehicle containers, the IWG of GTR 
No. 13 Phase 2 set the number of pressure cycles representing maximum 
container service life at 11,000. In accordance with GTR No. 13 Phase 
2, NHTSA proposes to require heavy vehicle containers to neither leak 
nor burst for 11,000 hydraulic pressure cycles, and also to leak 
without burst (or neither leak nor burst) beyond the 11,000 hydraulic 
pressure cycles up to a maximum of 22,000 pressure cycles. The proposed 
service life, number of hydraulic pressure cycles representing the 
maximum service life for which the container is required not to leak 
nor burst, and the number of pressure cycles beyond that representing 
maximum service life of the container for which the container is 
required to leak without burst or not leak nor burst at all is 
summarized in Table-2 for light and heavy vehicles.

 Table 2--Proposed Service Life and Number of Cycles in the Baseline Hydraulic Pressure Cycle Test for Light and
                                                 Heavy Vehicles
----------------------------------------------------------------------------------------------------------------
                                                                    Number of cycles
                                                                  representing maximum     Number of cycles for
                 Vehicle type                    Service life    service life for which    which the container
                                                    (years)      the container does not  leaks without burst, or
                                                                     leak nor burst      does not leak nor burst
----------------------------------------------------------------------------------------------------------------
Light.........................................              25                    7,500             7,501-22,000
Heavy.........................................              25                   11,000            11,001-22,000
----------------------------------------------------------------------------------------------------------------

    NHTSA seeks comment on the proposed number of cycles in Table-2. 
NHTSA seeks any additional data available related to vehicle life, 
lifetime miles travelled, and number of lifetime fuel cycles.
c. Details of the Baseline Initial Cycle Test for Containers on Light 
and Heavy Vehicles
    The low pressure during each cycle has been set at between 1 MPa to 
2 MPa. This is selected to make the test easy to conduct. NHTSA seeks 
comment whether this low-pressure range is sufficiently wide for test 
lab efficiency. The high pressure of 125 percent NWP is selected 
because this is the peak pressure that typically occurs during fueling. 
Furthermore, this is the high pressure used in the ANSI NGV 2-2007, 
Compressed Natural Gas Vehicle Fuel Containers, ambient cycling 
test.\53\
---------------------------------------------------------------------------

    \53\ ANSI NGV 2-2007, Compressed Natural Gas Vehicle Fuel 
Containers, 16.3 Ambient Cycling Test. https://webstore.ansi.org/standards/csa/ansingv22007.
---------------------------------------------------------------------------

    GTR No. 13 requires three new containers to be tested during the 
baseline initial pressure cycle test. However, NHTSA does not believe 
three new containers need to be tested under the U.S. self-
certification system where NHTSA buys and tests vehicles and equipment 
at the point of sale. Therefore, NHTSA has instead decided to base the 
value on the results of testing any one container for the baseline 
initial pressure cycle test. NHTSA seeks comment on this decision.
---------------------------------------------------------------------------

    \54\ Id.
---------------------------------------------------------------------------

    GTR No. 13's maximum hydraulic pressure cycle rate of 10 cycles/
minute is based on the requirement in ANSI NGV 2-2007 for the ambient 
cycling test.\54\ This pressure cycling rate is selected to allow for 
efficient compliance testing. Actual fueling cycles for hydrogen 
vehicles occur more slowly. For these reasons, the container 
manufacturer may specify a hydraulic pressure cycle profile that will 
prevent premature failure of the container due to test conditions 
outside of the container design envelope. Changing the hydraulic 
cycling profile does not

[[Page 27514]]

change the stringency of the test or the safety of the container. 
However, the cycling profile can be important because testing NHTSA 
conducted resulted in a container failure attributed to a rapid 
defueling profile that was not representative of defueling rates during 
normal use.55 56 NHTSA seeks comment on cycling profiles and 
whether the pressure cycling profile will significantly affect the test 
result. NHTSA seeks comment on more specifics of what manufacturers 
should be allowed to specify regarding an appropriate pressure cycling 
profile for testing their system.
---------------------------------------------------------------------------

    \55\ DOT HS_812_988. Hydrogen Container Performance Testing, 
https://rosap.ntl.bts.gov/view/dot/62645.
    \56\ Details are provided in the technical document ``Quantum 
GTR Pressure Cycle Discussion.pdf'' submitted to the docket of this 
NPRM.
---------------------------------------------------------------------------

    A burst may be preceded by an instantaneous moment of leakage, 
especially if observed in slow motion. Therefore, NHTSA proposes a 
minimum time of 3 minutes to sustain a visible leak before the test can 
end successfully due to ``leak before burst.'' NHTSA seeks comment on 
this additional requirement.
5. Test for Performance Durability
    The container must withstand stress factors beyond basic 
pressurization and pressure cycling without leakage or burst. The 
container must demonstrate its durability by not leaking or bursting 
during a service life of pressure cycling that includes the application 
of external stress factors. The container must also withstand 180 
percent NWP for four minutes \57\ after the application of all the 
external stress factors and have a burst pressure that is at least 80 
percent of its BPO at the end of a service life that 
includes external stress factors. This requirement is evaluated by the 
test for performance durability. The test for performance durability 
uses the same service life described above for the tests for baseline 
metrics, along with external stress factors applied to the container.
---------------------------------------------------------------------------

    \57\ The 180 percent NWP hold for 4 minutes is a simulation of a 
fueling station pressure regulation failure that results in over 
pressurization of the container. This test is conducted after all 
other external stresses have been applied to the container to 
simulate over-pressurization near the end-of-life of the container.
---------------------------------------------------------------------------

    A container is expected to encounter six types of external stress 
factors:

1. Impact (drop during installation and/or road wear)
2. Static high pressure from long-term parking
3. Over-pressurization from fueling and fueling station malfunction
4. Environmental exposures (chemicals and temperature/humidity)
5. Vehicle fire
6. Vehicle crash

    The test for performance durability addresses the first four of 
these external stresses. Fire is addressed in a separate section for 
fire. Crash performance is addressed through crash testing in FMVSS No. 
307. The test for performance durability is closely consistent with the 
industry standard SAE J2579_201806, Standard for Fuel Systems in Fuel 
Cell and Other Hydrogen Vehicles.\58\
---------------------------------------------------------------------------

    \58\ SAE J2579_201806. Standard for Fuel Systems in Fuel Cell 
and Other Hydrogen Vehicles. https://www.sae.org/standards/content/j2579_201806/
---------------------------------------------------------------------------

    Other than fire and vehicle crash, testing of the stresses 
compounded in a series is required.\59\ This is because a container may 
experience all of these stresses during its service life, and the 
safety need for a hydrogen system remains an issue for the vehicle's 
entire service life. For example, a container that was dropped during 
installation could thereafter be exposed to road wear, long term 
parking, fueling stresses, and environmental exposures. Accordingly, 
the proposed test for performance durability arranges these external 
stresses in a sequential application representing a severe in-service 
permutation of the stresses. The test sequence is as follows:
---------------------------------------------------------------------------

    \59\ This is in contrast to industry standards, wherein 
performance is evaluated after the application of a single stress 
factor in order to identify which stress factors cause failure.

 Proof pressure test
 Drop test
 Surface damage test
 Chemical exposure test and ambient-temperature pressure 
cycling test
 High temperature static pressure test
 Extreme temperature pressure cycling test
 Residual pressure test
 Residual strength burst test

    The test for performance durability is illustrated in Figure-4.

[[Page 27515]]

[GRAPHIC] [TIFF OMITTED] TP17AP24.003

Figure-4: Illustration of the Test for Performance Durability

    For similar reasons as those explained above for the baseline 
tests, the cycling pressure force on containers is applied 
hydraulically with non-corrosive fluid such as water or a mixture of 
anti-freeze and water to prevent freezing. This allows for improved 
test lab safety and faster pressurization and depressurization rates 
which decreases the cost to conduct the tests.
a. Proof Pressure Test
    The proof pressure test is typically done by the manufacturer 
before sale of the container. The proof pressure test is performed to 
confirm that the container will not leak nor burst due to a simple 
over-pressurization event to 150 percent NWP. The test pressure of 150 
percent NWP is selected because fueling stations are expected to 
provide over-pressure protection of 150 percent NWP. A proof pressure 
test is a stress factor that can in some cases result in micro-cracks 
appearing in the container. Micro-cracks may weaken a tank's wall 
strength, causing the potential for leaks or a burst during the proof 
pressure test or the subsequent performance durability testing. 
Therefore, it is important that all containers experience proof 
pressure.
    GTR No. 13 states that a container that has undergone a proof 
pressure test in manufacture is exempt from this test. However, NHTSA 
may not know whether a container has undergone the proof pressure test. 
As a result, NHTSA proposes that all containers will be subjected to 
the proof pressure test as part of the test for performance durability. 
In the event that a proof pressure test is conducted during manufacture 
and as part of the tests for performance durability, the container 
would experience two proof pressure tests. However, it is not expected 
that a second application will result in significantly more stress to 
the container than a single proof pressure test. NHTSA seeks comment on 
conducting the proof pressure test on all containers.
b. Drop Test
    The drop test is conducted to simulate dropping the container 
during handling or installation. Consistent with GTR No. 13, the 
unpressurized container may be dropped in any one of several 
orientations such as horizontal, vertical, or at a 45[deg] angle. In 
the case of a non-cylindrical or asymmetric container, the horizontal 
and vertical axes may not be clear. In such cases, the container will 
be oriented using its center of gravity and the center of any of its 
shut-off valve interface locations. The two points will be aligned 
horizontally (i.e., perpendicular to gravity), vertically (i.e., 
parallel to gravity) or at a 45[deg] angle relative to vertical. The 
center of gravity of an asymmetric container may not be easily 
identifiable, so NHTSA seeks comment on the appropriateness of using 
the center of gravity as a reference point for this compliance test and 
how to properly determine the center of gravity for a highly asymmetric 
container.
    The surface onto which the container is dropped must be a smooth, 
horizontal, uniform, dry, concrete pad or other flooring type with 
equivalent hardness. The drop height of 1.8 meters is selected to 
represent a drop from a forklift during installation. The four possible 
drop orientations are illustrated in Figure-5 below.

[[Page 27516]]

[GRAPHIC] [TIFF OMITTED] TP17AP24.004

Figure-5: The Four Possible Drop Orientations

    GTR No. 13 specifies a potential energy of at least 488 J during 
the vertical drops, along with a maximum drop height of 1.8 m, and a 
minimum drop height of 0.1 m. It is possible that a drop involving a 
very lightweight container could not simultaneously satisfy both the 
488 J minimum energy and the 1.8 m maximum height. The IWG of GTR No. 
13 Phase 2 resolved this conflict by specifying the vertical drop test 
potential energy of at least 488 J, with an overriding limitation that 
the drop height not exceed 1.8 m in any case. In the case of a 
lightweight container that would require a drop height over 1.8 m to 
reach 488 J of drop energy, the container should be dropped from 1.8 m, 
regardless of the potential energy. Similarly, a very heavy container 
could reach a potential energy \60\ of 488 J while being less than 0.1 
m above the drop surface. In this case, the container should be dropped 
from the 0.1 m minimum drop height.
---------------------------------------------------------------------------

    \60\ Potential energy is calculated as the product of container 
mass, gravitational acceleration, and the height from the center of 
gravity of the container to the surface onto which the container is 
dropped.
---------------------------------------------------------------------------

    For the angled drop, the container is dropped from any angle 
between 40[deg] and 50[deg] from the vertical orientation with the 
center of any shut-off valve interface location downward. However, if 
the lowest point of the container is closer to the ground than 0.6 m, 
the drop angle is changed such that the lowest point of the container 
is 0.6 m above the ground and the center of gravity is 1.8 m above the 
surface onto which it is dropped. This may result in a drop angle 
greater than 50[deg] from the vertical orientation.
    The drop test is conducted with an unpressurized container because 
the risk of dropping is primarily aftermarket during vehicle repair 
where a new storage system, or an older system removed during vehicle 
service, is dropped from a forklift during handling. Additionally, drop 
testing conducted by NHTSA under various conditions indicated that an 
unpressurized container is more susceptible to damage in the drop test 
than a pressurized container.\61\
---------------------------------------------------------------------------

    \61\ DOT HS_812_988. Hydrogen Container Performance Testing, 
https://rosap.ntl.bts.gov/view/dot/62645.
---------------------------------------------------------------------------

    The drop test is a test in which container attachments may improve 
performance by protecting the container when it impacts the ground. 
Consistent with GTR No. 13, the drop test is conducted on the container 
with any associated container attachments. NHTSA seeks comment on 
including container attachments for the drop test.
    It is possible that the container could experience damage from the 
drop test that prevents continuing with the remainder of the tests for 
performance durability. To address this possibility, NHTSA proposes 
that if any damage to the container following the drop test prevents 
further testing of the container, the container is considered to have 
failed the tests for performance durability and no further testing is 
conducted.
c. Surface Damage Test
    The surface damage test applies cuts and impacts to the surface of 
the container. The cuts on the surface simulate abrasions that can 
occur due to container mounting hardware or straps. The impacts 
simulate on-road impacts, such as flying gravel. The surface damage 
test consists of two linear cuts and five pendulum impacts.
    The linear cuts are created with a saw. The first cut is 0.75 
millimeters to 1.25 millimeters deep and 200 to 205 millimeters long. 
The second cut is 1.25 millimeters to 1.75 millimeters deep and 25 
millimeters to 28 millimeters long. The second cut is only applied if 
the container is to be affixed to the vehicle by compressing its 
composite surface.
    GTR No. 13 allowed all-metal containers to be exempt from the 
linear cuts because (1) metal is scratch resistant compared to non-
metal, and (2) metal containers can be so thin that the cuts would 
fully penetrate the container. NHTSA's proposal includes this 
exemption, but NHTSA seeks comment on whether another objective and 
practicable procedure exists for evaluating surface abrasions that 
could apply to all containers, such as, for example, the application of 
a defined cutting force to the container surface.
    The impacts are created with a pendulum impactor consisting of a 
pyramid with equilateral faces and square base, and with the summit and 
edges being rounded to a radius of 3 mm. The impact of the pendulum 
occurs with a nominal impact energy of 30 J. Prior to the impacts, the 
container is preconditioned at -40 [deg]C to simulate a worst-case 
temperature environment. The temperature of -40 [deg]C was selected 
based on industry standards.\62\ We note that weather records show 
temperatures

[[Page 27517]]

of -40 [deg]C can occur in northern locations of the United States.\63\
---------------------------------------------------------------------------

    \62\ SAE J2579_201806. Standard for Fuel Systems in Fuel Cell 
and Other Hydrogen Vehicles.
    \63\ Canadian Climate Normals, https://climate.weather.gc.ca/climate_normals/index_e.html.
---------------------------------------------------------------------------

    The surface damage test is a test in which container attachments 
may improve performance by shielding the container from the impacts. 
For containers with container attachments, GTR No. 13 specifies that if 
the container surface is accessible, then the test is conducted on the 
container surface. However, NHTSA is concerned that determining whether 
the container surface is accessible is subjective, because 
``accessible'' is not defined in the GTR and could have many potential 
meanings. Therefore, NHTSA is not proposing a specification involving 
the accessibility of the container surface. Instead, NHTSA proposes 
that if the container attachments can be removed using a process 
specified by the manufacturer, they will be removed and not included 
for the surface damage test nor for the remaining portions of the test 
for performance durability. Testing the container without its container 
attachments is representative of a situation in which installation 
personnel remove the container attachments and fail to re-install them 
before the container enters service. Container attachments that cannot 
be removed are included for the test. NHTSA seeks comment on including 
container attachments for the surface damage test.
    In accordance with GTR No. 13, NHTSA proposes specifying the 
pendulum impacts ``on the side opposite from the saw cuts.'' For 
containers with multiple permanently interconnected chambers, GTR No. 
13 specifies applying the pendulum impacts to a different chamber to 
that where the saw cuts were made. However, the agency is not proposing 
this distinction for pendulum impact location for containers with 
multiple permanently interconnected chambers because NHTSA is concerned 
that it may be less stringent (and thus, potentially less protective of 
safety) than when impacts are to the same chamber where the cuts were 
applied. NHTSA seeks comment on whether applying the impacts to the 
opposite side of the same chamber that received the saw cuts may be 
more stringent than applying the impacts to a separate chamber, and 
whether including the specification as written in GTR No. 13 would 
reduce stringency for containers with multiple permanently 
interconnected chambers relative to containers with a single chamber.
d. Chemical Exposure and Ambient Pressure Cycling Test
    Consistent with GTR No. 13, the chemical exposure test exposes the 
container to a range of chemicals that might be encountered in on-road 
service:
     Sulfuric acid at 19 percent in water to simulate battery 
acid.
     Sodium hydroxide at 25 percent in water to simulate lye.
     Methanol at 5 percent in gasoline to simulate fueling 
station fluids.
     Ammonium nitrate at 28 percent in water to simulate 
fertilizer.
     Methanol at 50 percent in water to simulate windshield-
washer fluid.
    A pad of glass wool saturated with one of the chemicals listed 
above is applied to each of the pendulum impact locations from the 
surface damage test. This is done to simulate each chemical exposure in 
an area where on-road damage has degraded the container's protective 
coating. The chemicals are applied with glass wool fibers to keep them 
in place and reduce evaporation.
    After the chemical exposures are in place, pressure cycling 
commences. The test for performance durability uses the same number of 
cycles as required by the baseline initial cycle test before leakage. 
This is a total of 7,500 cycles for light vehicles or 11,000 cycles for 
heavy vehicles. Of the total cycles, 60 percent are conducted with the 
chemical exposures in place, and at ambient temperature (5 [deg]C to 35 
[deg]C). All but the final 10 of these chemical exposure cycles are 
conducted from low pressure of 2 MPa to high pressure of 125 percent 
NWP, as in the baseline initial pressure cycle test. These cycles 
simulate extended vehicle use after impact damage and exposure to 
chemicals.
    The final 10 chemical exposure cycles are conducted to a high 
pressure of 150 percent NWP to simulate fueling station over-
pressurization. After completing chemical exposure cycles, the chemical 
exposure pads are removed, and the exposed areas are washed with water 
to remove excess chemicals.
    The chemical exposure test is a test in which container attachments 
may improve performance by shielding the container from the chemical 
exposures. Container attachments will be included in the chemical 
exposure test unless they were removed prior to the surface damage 
test. NHTSA seeks comment on including container attachments for the 
chemical exposure test.
e. High Temperature Static Pressure Test
    Consistent with GTR No. 13, the high temperature static pressure 
test involves holding the container for 1000 hours at 85 [deg]C and 125 
percent NWP. This test simulates an extended exposure to high static 
pressure and temperature, which is a condition that could occur in the 
case of a vehicle parked for an extended period of time. The primary 
risk associated with prolonged parking at high pressure and temperature 
is stress rupture. However, the stress rupture condition cannot be 
directly replicated because the relevant time period is years to 
decades. Alternatively, experimental data on the tensile stress failure 
of strands representative of those used in container composite wrapping 
showed that: 64 65
---------------------------------------------------------------------------

    \64\ SAE Paper 2009-01-0012. Rationale for Performance-based 
Validation Testing of Compressed Hydrogen Storage by Christine S. 
Sloane.
    \65\ Christine S. Sloane, Hydrogen Storage technology--Materials 
and Applications, edited by Lennie Klebanoff, Section III-12 with 
Figure 12.6 Glass fiber composite strands.
---------------------------------------------------------------------------

     For the glass fiber composite strands, the probability of 
failure for 25 years under tensile stress of 100 percent NWP is 
equivalent to 1000 hours under a tensile stress of 125 percent NWP.
     The time to failure increased when the load was reduced.
     Carbon fiber composite strands showed greater resistance 
to stress rupture than glass fiber composite strands in that a small 
reduction in the applied load resulted in a greater increase in time to 
failure for the carbon fiber composite strands than for the glass fiber 
composite strands.
     For carbon fiber composite strands, the probability of 
failure for 25 years under tensile stress of 100 percent NWP is 
approximately equivalent to 500 hours under tensile stress of 125 
percent NWP.
    An elevated temperature of 85 [deg]C is applied to account for 
heat-accelerated deterioration. The temperature of 85 [deg]C represents 
an extreme under-hood temperature for a dark/black-colored vehicle 
parked outside on asphalt in direct sunlight in 50 [deg]C ambient 
conditions.\66\ Including the extreme temperature condition of 85 
[deg]C in the high temperature static pressure test ensures that the 
container can sustain exposure to 85 [deg]C for 1000 hours under 
tensile stress of 125 NWP without experiencing stress rupture.
---------------------------------------------------------------------------

    \66\ SAE J2579_201806. Standard for Fuel Systems in Fuel Cell 
and Other Hydrogen Vehicles.
---------------------------------------------------------------------------

f. Extreme Temperature Pressure Cycling Test
    Consistent with GTR No. 13, the extreme temperature pressure 
cycling test involves pressure cycling at extreme temperatures and 
simulates operation

[[Page 27518]]

(fueling and defueling) in extreme temperature conditions. As mentioned 
above, the test for performance durability uses the same number of 
cycles as required by the baseline initial cycle test before leakage. 
This is a total of 7,500 cycles for light vehicles or 11,000 cycles for 
heavy vehicles. The extreme temperature pressure cycling test consists 
of 40 percent of these total cycles, of which half (20 percent of the 
total) are conducted at -40 [deg]C and the other half are conducted at 
85 [deg]C. The cold temperature -40 [deg]C is selected to simulate a 
worst-case extreme cold environment as explained above for the surface 
damage test, and the hot temperature of 85 [deg]C is selected for the 
same reasons discussed above for the high temperature static pressure 
test. During the cold pressure cycling, the maximum cycling pressure is 
only 80 percent NWP. This is because fueling pressures do not reach 100 
percent NWP when fueling in extreme cold because as temperature 
decreases, pressure also decreases. During the hot pressure cycling, 
the maximum cycling pressure is 125 percent NWP for the reasons 
discussed above for the baseline initial pressure cycle test.
    During the extreme temperature pressure cycling test, the relative 
humidity is maintained above 80 percent to represent high humidity that 
may foreseeably be encountered in the U.S. Humidity is known to degrade 
some materials due to the presence of moisture in humid air. Therefore, 
it is important to include the stress factor of humidity in the test 
for performance durability.
g. Residual Pressure Test
    Consistent with GTR No. 3, the residual pressure test requires 
pressurizing the container to 180 percent NWP and holding this pressure 
for 4 minutes. The 180 percent NWP hold for 4 minutes is a simulation 
of a fueling station pressure regulation failure that results in over-
pressurization of the container. This test is conducted after all other 
external stresses have been applied to the container to simulate over-
pressurization near the end of life of the container.67 68
---------------------------------------------------------------------------

    \67\ SAE J2579_201806. Standard for Fuel Systems in Fuel Cell 
and Other Hydrogen Vehicles. Appendix H.
    \68\ Christine S. Sloane, Hydrogen Storage technology--Materials 
and Applications, edited by Lennie Klebanoff, Section III-12 with 
Figure 12.6 Glass fiber composite strands.
---------------------------------------------------------------------------

h. Residual Strength Burst Test
    Consistent with GTR No. 13, the residual strength burst test 
involves subjecting the end-of-life container to a burst test identical 
to the baseline initial burst pressure test. The burst pressure at the 
end of the durability test is required to be at least 80 percent of the 
BPO specified on the container label. This effectively 
controls the burst pressure degradation rate throughout an extreme 
service life. Controlling degradation rate is important because, for 
example, a container starting with a very high BPO, say 400 
percent NWP, but then declining to 180 percent NWP indicates a high 
degradation rate. NHTSA is concerned that if such a container were to 
be kept in service beyond its intended service life, the high 
degradation rate could continue and lead to a high risk of burst. 
Therefore, the residual burst strength must be at least 80 percent of 
BPO. This concept is similar to the requirements for seat 
belt webbing in FMVSS No. 209 where both minimum breaking strength 
after abrasion (S4.2d) as well as maximum degradation rate after 
exposure to light and micro-organisms (S4.2e and S4.2f) are controlled.
6. Test for Expected On-Road Performance
    For ensuring safe operations, the CHSS must contain hydrogen 
without leakage or burst. The expected on-road performance test ensures 
the CHSS is able to effectively contain hydrogen without leakage or 
burst. Consistent with GTR No. 13, the test for expected on-road 
performance uses on-road operating conditions including fueling and 
defueling the container at different ambient conditions with hydrogen 
gas at low and high temperatures. The test also includes a static high-
pressure hold during which the CHSS is evaluated for hydrogen leakage 
and/or permeation of hydrogen from the CHSS. The container of the CHSS 
must withstand 180% NWP hold for 4 minutes and have a burst pressure 
that is at least 80 percent of its BPO at the end of the 
test for expected on-road performance. The test for expected on-road 
performance is closely consistent with the industry standard SAE 
J2579_201806.\69\
---------------------------------------------------------------------------

    \69\ SAE J2579_201806. Standard for Fuel Systems in Fuel Cell 
and Other Hydrogen Vehicles.
---------------------------------------------------------------------------

    While the test for performance durability evaluates the durability 
of the container when exposed to external stress factors combined with 
hydraulic pressure cycling, the test for expected on-road performance 
does not evaluate durability and instead focuses on pneumatic hydrogen 
fueling exposure, along with extreme temperature conditions. When 
fueling, hydrogen gas increases its temperature due to the Joule 
Thomson effect.\70\ As a result, pneumatic testing with hydrogen gas 
creates rapid temperature swings within the CHSS that do not occur 
during hydraulic cycling. Pneumatic testing also can result in hydrogen 
diffusion into materials, which can have deleterious chemical effects 
such as hydrogen embrittlement.\71\ Due to these unique stress factors, 
a pneumatic test using hydrogen gas is an effective method for 
evaluating the susceptibility of the CHSS to hydrogen permeation and 
leakage.
---------------------------------------------------------------------------

    \70\ For more information, see https://www.britannica.com/science/Joule-Thomson-effect.
    \71\ For more information, see https://www.sciencedirect.com/
topics/engineering/hydrogen-
embrittlement#:~:text=3.7%20Hydrogen%20Embrittlement-
,Hydrogen%20embrittlement%20(HE)%20refers%20to%20mechanical%20damage%
20of%20a%20metal,when%20hydrogen%20atoms%20are%20generated.
---------------------------------------------------------------------------

    Again, consistent with GTR No. 13, the test for expected on-road 
performance starts with a proof pressure test pressurizing the 
container with hydrogen to 150 percent NWP. This is followed by a total 
of 500 pressure cycles at various environmental conditions. The 500 
cycles are broken up into stages for low temperature cycling, high 
temperature cycling, and ambient temperature cycling. Table-3 shows the 
number of cycles during each stage, along with other applicable 
conditions. After the first 250 cycles, the CHSS is held at high 
pressure and temperature for up to 500 hours while it is evaluated for 
leakage and/or permeation. After the completion of all 500 cycles, the 
CHSS is again held at high pressure and temperature for 500 hours and 
evaluated for leakage and/or permeation.
    Following this second leakage/permeation evaluation, the container 
is pressurized with hydraulic fluid to 180% NWP and held for 4 minutes. 
The container then undergoes a residual strength burst test in a 
similar manner as that described for the test for performance 
durability. Similar to the test for performance durability, the 
container's residual burst pressure must be at least 80 percent of 
BPO. A visual schematic of the test is shown in Figure-6 
below.

[[Page 27519]]



                                              Table 3--Summary of the Test for Expected On-Road Performance
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                          Number of
            Stage of test                  cycles         Ambient conditions           Fuel delivery temperature              Pressurization medium
--------------------------------------------------------------------------------------------------------------------------------------------------------
Pneumatic proof pressure test to 150%   not appliable  5.0 [deg]C to 35.0       -40.0 [deg]C to -33.0 [deg]C..........  Hydrogen gas.
 NWP.                                                   [deg]C.
Low temperature cycling..............               5  -30.0 [deg]C to -25.0    15.0 [deg]C to 25.0 [deg]C............  Hydrogen gas.
                                                        [deg]C.
Low temperature cycling..............              20  -30.0 [deg]C to -25.0    -40.0 [deg]C to -33.0 [deg]C..........  Hydrogen gas.
                                                        [deg]C.
High temperature cycling.............              25  50.0 [deg]C to 55.0      -40.0 [deg]C to -33.0 [deg]C..........  Hydrogen gas.
                                                        [deg]C.
                                                       80% to 100% relative
                                                        humidity.
Ambient temperature cycling..........             200  5.0 [deg]C to 35.0       -40.0 [deg]C to -33.0 [deg]C..........  Hydrogen gas.
                                                        [deg]C.
Static pressure for up to 500 hours     not appliable  55.0 [deg]C to 60.0      not appliable.........................  Hydrogen gas.
 with leak/permeation evaluation.                       [deg]C.
High temperature cycling.............              25  50.0 [deg]C to 55.0      -40.0 [deg]C to -33.0 [deg]C..........  Hydrogen gas.
                                                        [deg]C, 80% to 100%
                                                        relative humidity.
Low temperature cycling..............              25  -30.0 [deg]C to -25.0    -40.0 [deg]C to -33.0 [deg]C..........  Hydrogen gas.
                                                        [deg]C.
Ambient temperature cycling..........             200  5.0 [deg]C to 35.0       -40.0 [deg]C to -33.0 [deg]C..........  Hydrogen gas.
                                                        [deg]C.
Static pressure for up to 500 hours     not appliable  55.0 [deg]C to 60.0      not appliable.........................  Hydrogen gas.
 with leak/permeation evaluation.                       [deg]C.
Residual pressure test...............  not applicable  not applicable.........  not applicable........................  Hydraulic fluid.
Burst test...........................  not applicable  not applicable.........  not applicable........................  Hydraulic fluid.
--------------------------------------------------------------------------------------------------------------------------------------------------------

                                                                                                                        [GRAPHIC] [TIFF OMITTED] TP17AP24.005
                                                                                                                        
Figure-6: Illustration of the Test for Expected On-Road Performance

a. Proof Pressure Test
    The proof pressure test is conducted in the same manner and for the 
same reasons discussed above for the test for performance durability. 
However, in this test, the container is pressurized to 150 percent NWP 
using hydrogen gas which has been pre-cooled to -40.0 [deg]C to -33.0 
[deg]C. This is the temperature range to which hydrogen fueling 
stations typically pre-cool hydrogen to offset the hydrogen's 
temperature increase during fueling.

[[Page 27520]]

b. Ambient and Extreme Temperature Gas Pressure Cycling Test
    The expected lifetime fueling exposure consists of 500 fuel cycles 
from 2 MPa to 125 percent NWP (empty-to-full) under a variety of 
ambient fueling temperatures. The number 500 is obtained through a 
calculation of expected vehicle lifetime driving range divided by 
driving range per full-fueling. This calculation and the data source is 
summarized in Table-4.

        Table 4--Maximum Number of Full Fueling/Defueling Cycles
------------------------------------------------------------------------
                      Expected vehicle  Expected vehicle  Expected worst-
                      lifetime driving    driving range   case number of
                            range       per full-fueling   full-fueling
------------------------------------------------------------------------
Data source.........  Sierra Research   2006-2007 market  ..............
                       Report No. SR     data of high
                       2004-09-04,       volume
                       September 22,     passenger
                       2004.             vehicle
                                         manufacturers
                                         in Europe,
                                         Japan, North
                                         America.
Calculation.........  250,000 km        483 km (300                  500
                       (155,000 miles).  miles).
------------------------------------------------------------------------

    Some vehicles may exceed 500 fuel cycles if partial fueling occurs 
in the vehicle lifetime. However, the stress of full fueling exceeds 
the stress of partial fueling because of the higher pressure and 
temperature change during full-fueling. NHTSA believes that, as a 
result, 500 full-fueling cycles should provide robust demonstration of 
leak-free fueling capability.
    The industry standard SAE J2601_202005 Fueling protocols for light 
duty gaseous hydrogen surface vehicles establishes industry-wide 
fueling protocols for the fueling of hydrogen into passenger vehicles. 
The guidelines include: \72\
---------------------------------------------------------------------------

    \72\ SAE J2601_202005. Fueling Protocols for Light Duty Gaseous 
Hydrogen Surface Vehicles. https://www.sae.org/standards/content/j2601_202005/.

1. The maximum pressure within the vehicle fuel system is 125 percent 
NWP
2. Gas temperature within the vehicle fuel system is less than or equal 
to 85 [deg]C
3. Fuel flow rate at dispenser nozzle is less than or equal to 60 g/s
4. The dispenser is capable of dispensing fuel at temperatures between 
-40 [deg]C and -33 [deg]C

    These guidelines are applied at hydrogen fueling stations when 
fueling hydrogen vehicles. During the ambient and extreme temperature 
gas pressure cycling test, the rate of pressurization must be greater 
than or equal to the ramp rate specified by a table of ramp rates based 
on SAE J2601_202005, according to the CHSS volume, the ambient 
conditions, and the fuel delivery temperature. If the required ambient 
temperature is not available in the table, the closest ramp rate value 
or a linearly interpolated value is used. This ensures that the fueling 
cycles are similar to those that would occur during on-road service. 
Table-5 shows the ramp rates based on SAEJ2601_202005, for different 
CHSS volume, the ambient conditions, and the fuel delivery temperature. 
GTR No. 13 specifies that the pressure ramp rate shall be decreased if 
the measured internal temperature in the container exceeds 85 [deg]C.

                                       Table 5--Pressure Ramp Rates for the Test for Expected On-Road Performance
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                      CHSS pressurization rate (MPa/min)
                                                     ---------------------------------------------------------------------------------------------------
                                                        50.0 [deg]C to 55.0       5.0 [deg]C to 35.0     -30.0 [deg]C to -25.0    -30.0 [deg]C to -25.0
                   CHSS volume (L)                         [deg]C ambient           [deg]C ambient           [deg]C ambient           [deg]C ambient
                                                      conditions -33.0 [deg]C  conditions -33.0 [deg]C  conditions -33.0 [deg]C   conditions 15.0 [deg]C
                                                        to -40.0 [deg]C fuel     to -40.0 [deg]C fuel     to -40.0 [deg]C fuel     to 25.0 [deg]C fuel
                                                        delivery temperature     delivery temperature     delivery temperature     delivery temperature
--------------------------------------------------------------------------------------------------------------------------------------------------------
50..................................................                      7.6                     19.9                     28.5                     13.1
100.................................................                      7.6                     19.9                     28.5                      7.7
174.................................................                      7.6                     19.9                     19.9                      5.2
250.................................................                      7.6                     19.9                     19.9                      4.1
300.................................................                      7.6                     16.5                     16.5                      3.6
400.................................................                      7.6                     12.4                     12.4                      2.9
500.................................................                      7.6                      9.9                      9.9                      2.3
600.................................................                      7.6                      8.3                      8.3                      2.1
700.................................................                      7.1                      7.1                      7.1                      1.9
1000................................................                      5.0                      5.0                      5.0                      1.4
1500................................................                      3.3                      3.3                      3.3                      1.0
2000................................................                      2.5                      2.5                      2.5                      0.7
2500................................................                      2.0                      2.0                      2.0                      0.5
--------------------------------------------------------------------------------------------------------------------------------------------------------

    Extreme environmental temperatures around the world are summarized 
in Table-6. To ensure safety in extremely hot conditions, some fueling 
pressure cycles are conducted at 50 [deg]C. To ensure safety in 
extremely cold conditions, consistent with GTR No. 13 Phase 2 
amendments, some fueling pressure cycles are conducted at -25 [deg]C. 
The temperature -25 [deg]C is used instead of -40 [deg]C because 
testing at -40 [deg]C is impractical during the test for expected on-
road performance. Specifically, a test apparatus must operate at well 
below -40 [deg]C in order to maintain the temperature surrounding the 
CHSS at -40 [deg]C. In addition, at -40 [deg]C, test laboratories 
encounter difficulties such as freezing valves and failing o-ring 
seals. This can significantly increase test cost. Furthermore, testing 
conducted by

[[Page 27521]]

NHTSA found that, for the test for expected on-road performance, 
testing at -25 [deg]C yields the same results as testing at -40 
[deg]C.\73\ This change does not compromise the safety intent of the 
test because in-tank gas temperatures will reach -40 [deg]C due to gas 
expansion during depressurization. In addition, pressure cycling under 
the extreme cold condition of -40 [deg]C is tested separately during 
the test for performance durability. Therefore, -25 [deg]C is proposed 
as the extreme cold temperature for the test for expected on-road 
performance, which is consistent with the Phase 2 amendment to GTR No. 
13. In summary, NHTSA is proposing 50 [deg]C for the high temperature 
pressure cycles and -25 [deg]C for the cold temperature pressure 
cycles.
---------------------------------------------------------------------------

    \73\ DOT HS_811_832. Cumulative Fuel System Life Cycle and 
Durability Testing of Hydrogen Containers, https://www.nhtsa.gov/sites/nhtsa.gov/files/811832.pdf.

                          Table 6--Extreme Environmental Temperatures Around the World
----------------------------------------------------------------------------------------------------------------
                                                                                                  Extremes of
                                                                     Frequency of sustained         ambient
              Temperature                   Areas that occurs           exposure to this         environmental
                                                                       temperature (year)      temperature used
                                                                                                 for this test
----------------------------------------------------------------------------------------------------------------
Around 50 [deg]C......................  desert areas of lower      5 percent................           50 [deg]C
                                         latitude countries.
Less or equal to -40 [deg]C...........  countries north of the     5 percent................          -40 [deg]C
                                         45th parallel.
Less than -30 [deg]C..................  countries north of the     5 percent of vehicle life  ..................
                                         45th parallel.
----------------------------------------------------------------------------------------------------------------
Data source: Environment Canada 1971-2000.

    As described above, hydrogen fueling stations typically pre-cool 
hydrogen to between -40 [deg]C and -33 [deg]C. However, a fueling 
station failure could result in the fueling station delivering hydrogen 
at ambient temperature. This would lead to very high temperatures 
inside the CHSS after a full fueling. To account for this risk, the 
first 5 cycles in the ambient and extreme temperature gas pressure 
cycling test are conducted with hydrogen fuel at between 15 [deg]C and 
25 [deg]C, as opposed to the pre-cooled hydrogen between -40 [deg]C and 
-33 [deg]C which is used for the remaining 495 cycles.
    All pressure cycles are performed to 100 percent state-of-charge 
(SOC). SOC is defined by the ratio of hydrogen density at a given 
temperature and pressure to hydrogen density at NWP and 15 [deg]C.\74\ 
Specifying 100 percent SOC ensures an equivalent quantity of hydrogen 
in the CHSS regardless of the resulting temperature and pressure. For 
example, 100 percent NWP at 15 [deg]C corresponds to 80 percent NWP at 
-40 [deg]C. In either case, however, the CHSS is at 100 percent SOC 
(fully fueled).
---------------------------------------------------------------------------

    \74\ Since the hydrogen gas density varies nonlinearly with 
temperature and pressure, a table is provided in the regulatory text 
for hydrogen density at different pressures and temperatures.
---------------------------------------------------------------------------

    The first 10 cycles (cold cycles) are performed with the CHSS 
stabilized with the external air temperature surrounding the CHSS at -
25 [deg]C at the beginning of the cycle. This ensures there is no 
residual heat present from the previous fueling cycle and maximizes the 
severity of the cold external temperature. However, the process to 
equilibrate a storage system is time-consuming. As a result, the next 
15 cycles are performed with an external air temperature surrounding 
the CHSS of -25 [deg]C, but without CHSS equilibration to the external 
temperature.
    The next 25 cycles are performed with an external temperature of 50 
[deg]C. For the first 5 of these cycles, the CHSS is stabilized with 
the external air temperature surrounding the CHSS at the at the 
beginning of the cycle. At this point, the external temperature to the 
system is at its hottest, and the CHSS pressure is at its minimum. The 
fueling process will then progressively heat the contents of the CHSS 
until full (100 percent SOC). At this point, the CHSS reaches its 
hottest possible interior temperature. In addition, these 25 cycles are 
performed with the relative humidity over 80 percent surrounding the 
CHSS. This adds the stress of excessive humidity which is common in 
extreme hot climates. Specifically, the high humidity keeps a thin film 
of water on surfaces where dissimilar metals may be in contact, such as 
valve to tank interfaces or valve body to valve connection interfaces. 
This water film adds the necessary conduction path to effect galvanic 
corrosion. Galvanic corrosion can cause pitting and other forms of 
metal loss which can degrade the strength of materials and impact 
sealing surfaces. Therefore, it is important to include the stress 
factor of humidity in the test for expected on-road performance
    The next 200 cycles are performed with ambient external temperature 
of (5 [deg]C to 35 [deg]C). This represents a normal ambient 
temperature. After these 200 cycles (at a total cycle count of 250), 
the extreme temperature static gas pressure leak/permeation test is 
performed. This test is discussed in the next section. However, after 
the completion of the permeation test, pressure cycling continues for 
an additional 250 cycles.
    The first 25 of these additional cycles (cycle count 251-275) are 
performed with the extreme hot external temperature of 50 [deg]C. The 
next 25 cycles (cycle count 276-300) are performed with the extreme 
cold temperature -25 [deg]C. In this series, the order of extreme hot 
and cold cycles is switched. This accounts for compounding stress from 
transitioning from hot cycling to cold cycling, as opposed to the 
previous series, which transitioned from cold to hot. The final 200 
cycles (cycle count 301-500) are performed with ambient external 
temperature of 5 [deg]C to 35 [deg]C. After the completion of cycling, 
the extreme temperature static gas pressure leak/permeation test is 
performed for a second time.
    GTR No. 13 states that if system controls that are active in 
vehicle service prevent the pressure from dropping below a specified 
pressure, the test cycles during the ambient and extreme temperature 
gas pressure cycling test must not go below that specified pressure. In 
addition, GTR No. 13 states that if devices and/or controls are used in 
the intended vehicle application to prevent an extreme internal 
temperature, the test may be conducted with these devices and/or 
controls in place. However, NHTSA's approach to testing involves the 
agency independently purchasing (on the open market) and then testing 
vehicles. With this approach, NHTSA has no way of determining what 
system controls and/or devices are active in the vehicle,

[[Page 27522]]

because this information is typically proprietary and is not publicly 
available. As a result, all cycles would be performed with an initial 
pressure of between 1 MPa and 2 MPa and extreme internal temperatures 
will not be prevented during cycling. Furthermore, and importantly for 
safety, this is a condition that could occur in the event the system 
controls and/or devices fail in service.
c. Extreme Temperature Static Gas Pressure Leak/Permeation Test
    Leak and permeation are risk factors for fire hazards, particularly 
when parking in confined spaces such as garages. The extreme 
temperature static gas pressure leak/permeation test is designed to 
simulate extended parking in a confined space under an elevated 
temperature. In these conditions, hydrogen can leak or permeate from 
the CHSS and slowly accumulate in the surrounding air. During the 
extreme temperature static gas pressure leak/permeation test, the 
pressurized CHSS at 100% SOC is held at 55 [deg]C for a period of up to 
500 hours. Any hydrogen leakage and/or permeation from the CHSS cannot 
exceed the limit of 46 milliliter/hour (mL/h) per liter of CHSS water 
capacity. This limit is discussed below. The test may end before 500 
hours if three consecutive hydrogen permeation rates separated by at 
least 12 hours are within 10 percent of the prior rate because this 
indicates a permeation steady state has been reached. NHTSA seeks 
comment on how to accurately measure or otherwise determine the 
permeation rate from the CHSS.
    The leak/permeation limit is characterized by the many possible 
combinations of vehicles and garages, and the associated test 
conditions. The leak/permeation limit is defined to restrict the 
hydrogen concentration from reaching 25 percent lower flammability 
limit (LFL) by volume. The LFL of hydrogen is lowest concentration of 
hydrogen in which a hydrogen gas mixture is flammable. National and 
international standard bodies (such as National Fire Protection 
Association [NFPA] and IEC) recognize 4 percent hydrogen by volume in 
air as the LFL.\75\ The conservative 25 percent LFL limit accounts for 
concentration non-homogeneities and is equivalent to 1 percent hydrogen 
concentration in air.76 77
---------------------------------------------------------------------------

    \75\ See Gases--Explosion and Flammability Concentration Limits. 
https://www.engineeringtoolbox.com/explosive-concentration-limits-d_423.html.
    \76\ Data for hydrogen dispersion behavior, garage and vehicle 
scenarios, including garage sizes, air exchange rates and 
temperatures, and the calculation methodology are found in the 
following reference prepared as part of the European Network of 
Excellence HySafe: P. Adams, A. Bengaouer, B. Cariteau, V. Molkov, 
A.G. Venetsanos, ``Allowable hydrogen permeation rate from road 
vehicles,'' https://h2tools.org/sites/default/files/2019-08/paper_-_part_1.pdf.
    \77\ NFPA 30A-2015, Code for Motor Fuel Dispensing Facilities 
and Repair Garages, 7.4.7.1, https://www.nfpa.org/codes-and-standards/all-codes-and-standards/list-of-codes-and-standards/detail?code=30A.
---------------------------------------------------------------------------

    Worst case ventilation in structures where hydrogen vehicles can be 
parked is expected to be at or below 0.18 air changes per hour, but the 
exact design value is highly dependent on the type and location of 
structures in which the vehicles are parked. In the case of light 
passenger vehicles, an extremely low air exchange rate (of 0.03 
volumetric air changes per hour) has been measured in ``tight'' wood 
frame structures (with plastic vapor barriers, weather-stripping on the 
doors, and no vents) that are sheltered from wind and are very hot (55 
[deg]C) with little daily temperature swings that can cause density-
driven infiltration. The resulting discharge limit for a light vehicle 
that tightly fits into a garage of 30.4 cubic meters (m\3\) with 0.03 
volumetric air exchange per hour is 150 mL/minute (at 115 percent NWP 
for full fill at 55 [deg]C), corresponding to no more than 1 percent 
hydrogen concentration in air.
    In order to determine the leak/permeation limit for the expected 
on-road performance test, consistent with GTR No. 13, the vehicle-level 
150 mL/min leak/permeation limit is expressed in terms of allowable 
leak/permeation for each container in the storage system at 55 [deg]C 
and 115 percent NWP. This corresponds to 46 mL/hour(h)/Liter(L)-water-
capacity for each container in the storage system.\78\ The use of this 
limit is applicable to light vehicles that are smaller or larger than 
the base described above. If, for example, the total water capacity of 
the light vehicle storage system is 330 L (or less) and the garage size 
is 50 m\3\, then the 46 mL/h/L-water-capacity requirement results in a 
steady-state hydrogen concentration of no more than 1 percent. This can 
be shown by calculating the allowable discharge from the light vehicle 
based on the requirement of 46 mL/h/L per container volume capacity 
(that is, 46 mL/h/L x 330L/(60 min/h) = 253 mL/min) which is similar to 
the allowable discharge based on the garage size of 50 m\3\ with an air 
exchange rate of 0.03 volumetric air exchanges per hour (that is, 150 
mL/min x 50 m\3\/30.4 m\3\ = 247 mL/min). Since both results are 
essentially the same, the hydrogen concentration in the garage is not 
expected to exceed 1 percent for light vehicles with storage systems of 
330L (or less) in 50 m\3\ garages.
---------------------------------------------------------------------------

    \78\ Data for hydrogen dispersion behavior, garage and vehicle 
scenarios, including garage sizes, air exchange rates and 
temperatures, and the calculation methodology are found in the 
following reference prepared as part of the European Network of 
Excellence HySafe: P. Adams, A. Bengaouer, B. Cariteau, V. Molkov, 
A.G. Venetsanos, ``Allowable hydrogen permeation rate from road 
vehicles,'' https://h2tools.org/sites/default/files/2019-08/paper_-_part_1.pdf.
---------------------------------------------------------------------------

    Since the discharge limit has been found to be reasonably scalable 
depending on the vehicle size, the discharge limit for alternative 
vehicle sizes in tight-fitting garages with 0.03 volumetric air 
exchanges per hour can be determined from the 150 mL/minute discharge 
limit computed above using a scaling factor R computed as:

R = (Vwidth+1) (Vheight+0.5) 
(Vlength+1)/30.4

where:

Vlength, Vwidth, and Vheight are 
the dimensions of the vehicle in meters,

    Similarly, the use of 46 mL/h/L-water-capacity requirement for 
storage system containers is also scalable to larger medium-duty and 
heavy-duty vehicles. Figure-7 shows the required volumetric air 
exchange rate that would result in less than 25 percent LFL of hydrogen 
by volume in garages of various sized vehicles equipped with CHSS that 
have no more than a 46 mL/L/H permeation rate. Examples of current or 
currently-planned hydrogen vehicles shown in Figure-7 indicate that the 
required ventilation rate for garages of large vehicles (buses and 
tractor-trailers) is lower than that of small vehicles (passenger 
cars). Light hydrogen vehicles which can possibly be parked in tight 
garages (with as low as 0.03 volumetric air changes per hour) are 
required to have permeation/leak rate less than of 46 mL/hour(h)/
Liter(L)-water-capacity for each container in the vehicle's CHSS.\79\ 
Even though medium-duty and heavy-duty vehicles are not expected to be 
parked in such ``tight'' garages as is the case with light vehicles, in 
order to better meet the safety need, we conservatively assume an 
equivalent rate of 0.03 volumetric air exchanges for garages of these 
vehicles.
---------------------------------------------------------------------------

    \79\ This leak/permeation limit for each container ensures that 
the hydrogen concentration is lower than 25 percent of the lower 
flammability limit (LFL) by volume and the hydrogen concentration in 
air is less than 1 percent.

---------------------------------------------------------------------------

[[Page 27523]]

While it is foreseeable that medium-duty and heavy-duty vehicles may be 
parked in more open (naturally-ventilated) or mechanically-ventilated 
spaces, the 46 mL/h/L-water-capacity requirement for storage system 
containers provides a safety margin in the event of mechanical 
ventilation failures.
[GRAPHIC] [TIFF OMITTED] TP17AP24.006

Figure-7: Required Volumetric Air Exchange Rate (Ventilation Rate) of 
Enclosed Space Surrounding a Hydrogen Vehicle That Results in Less Than 
25 Percent Lower Flammability Limit of Hydrogen by Volume

    In addition to the required leak/permeation limit discussed above, 
GTR No. 13 also includes a localized leak requirement. This requirement 
is based on the SAE technical paper 2008-01-0726, Flame Quenching 
Limits of Hydrogen Leaks.\80\ This paper states that the lowest 
possible flammable flow for hydrogen is about 0.005 milligrams per 
second (mg/s) (3.6 normal millilitres per minute (NmL/min)).\81\ As a 
result, if a hydrogen permeation rate over 0.005 mg/s is detected, a 
localized leak test ensures that the hydrogen is not all emanating from 
the same localized area of the container. This leak test is conducted 
as a bubble test. In a bubble test, a surfactant solution is applied 
across the CHSS and the tester observes for the formation of bubbles in 
the solution resulting from any leaks. If bubbles are detected, the 
test lab estimates the leak rate based on the average size of the 
bubbles and the number of bubbles generated per unit of time.
---------------------------------------------------------------------------

    \80\ SAE Technical report 2008-01-0726. Flame Quenching Limits 
of Hydrogen Leaks. Figure 3 to Figure 9. https://www.sae.org/publications/technical-papers/content/2008-01-0726/.
    \81\ A normal milliliter, also known as a standard cubic 
centimeter, represents the volume a gas would occupy at standard 
temperature (0 [deg]C) and standard pressure (1 atmosphere).
---------------------------------------------------------------------------

    However, NHTSA is concerned that this requirement would not meet 
the Safety Act requirement for FMVSSs to be objective, due to the 
subjective estimation of bubble sizes. Therefore, the localized leak 
requirement has not been included in FMVSS No. 308. Furthermore, NHTSA 
believes that the primary safety risk of accumulating hydrogen is 
already addressed by the overall permeation limit of 46 mL/h/L-water-
capacity. NHTSA seeks comment on not including the localize leak 
requirement during the extreme temperature static gas pressure leak/
permeation test. If commenters believe it should be included, NHTSA 
requests that they explain (1) how they believe it could be made more 
objective and (2) how specifically it would add to the standard's 
ability to meet the safety need.
d. Residual Pressure Test & Residual Strength Burst Test
    The residual pressure test and residual strength burst test are 
conducted in the same manner and for the same reasons discussed above 
for the test for performance durability.
7. Test for Service Terminating Performance in Fire
    Vehicle fire presents a severe risk to the safe containment of 
hydrogen. Fire can rapidly degrade the container while simultaneously 
increasing the pressure inside the container. To avoid the possibility 
of burst, CHSS should be designed to vent their pressurized contents 
when exposed to fire. Under the proposed standard, the CHSS must vent 
its pressurized hydrogen during the test for service terminating 
performance in fire, discussed below, which simulates a vehicle fire. 
The CHSS must expel its contents (high pressure hydrogen gas) in a 
controlled manner through its TPRD(s) without the occurrence of burst.
    A comprehensive examination of CNG container in-service failures 
between 2000 and 2008 showed that the majority of fire incidents 
occurred on storage systems that did not utilize properly designed 
TPRDs.\82\ The in-service failures resulted when TPRDs did not respond 
to protect the container due to the lack of adequate heat exposure on 
the TPRDs, while a small ``localized'' fire degraded the container wall 
elsewhere, eventually causing the container to burst. Prior to GTR. No. 
13, localized fire exposure had not been addressed in regulations or 
industry standards. The test for service terminating performance in 
fire

[[Page 27524]]

addresses both localized and engulfing fires with two respective test 
stages.
---------------------------------------------------------------------------

    \82\ SAE Technical Paper 2011-01-0251. Establishing Localized 
Fire Test Methods and Progressing Safety Standards for FCVs and 
Hydrogen Vehicles. https://www.sae.org/publications/technical-papers/content/2011-01-0251/.
---------------------------------------------------------------------------

    The test for service terminating performance in fire evaluates the 
CHSS. It is possible that vehicle manufacturers may add additional fire 
protection features as part of overall vehicle design, and GTR No. 13 
includes the option of conducting CHSS fire testing with vehicle 
shields, panels, wraps, structural elements, and other features as 
specified by the manufacturer. However, adding vehicle-level protection 
features is not practical for testing. Furthermore, NHTSA believes that 
it is important for safety that the CHSS itself can withstand fire and 
safely vent in the event its shielding is compromised--for example, if 
a crash damages the shielding, and the shielding was an integral part 
of the CHSS's ability to withstand fire, then the CHSS should be able 
to vent properly before it explodes. As a result, vehicle-level 
protection measures are not evaluated by the test for service 
terminating performance in fire. However, if a CHSS includes container 
attachments, these attachments are included in the fire test. NHTSA 
seeks comment on excluding vehicle-specific shielding and on including 
container attachments as part of the fire test, particularly in the 
case of container attachments which can be removed using a process 
specified by the manufacturer.
    The fire test temperature targets set forth in GTR No. 13 are based 
on vehicle fire experiments conducted by the Japanese Automobile 
Research Institute (JARI).\83\ Some key findings from these vehicle-
level fire experiments are as follows:
---------------------------------------------------------------------------

    \83\ Id.
---------------------------------------------------------------------------

     About 30 to 50 percent of the JARI vehicle fires resulted 
in a ``localized'' fire. In these cases, the data indicated the 
container could have been locally degraded before TPRDs would have 
activated.
     Thermal gravimetric analysis (TGA) indicated that 
composite container materials begin to degrade rapidly at 300 [deg]C.
     While the vehicle fires often lasted 30-60 minutes, the 
period of localized fire container degradation lasted less than 10 
minutes.
     Peak temperatures on the test containers' surfaces reached 
700 [deg]C during the localized fire stages.
     The rise in peak temperature near the end of the localized 
fire period often indicated the transition to an engulfing fire.
     Peak temperatures on the test containers' surfaces reached 
1000 [deg]C during the engulfing fire stage.
    Based upon these experiments, temperature limits were defined in 
GTR No. 13 to characterize the thermal exposure during the localized 
and engulfing fire stages:
     The minimum container surface temperature during the 
localized fire stage for the side of the container facing the fire was 
set to 450 [deg]C to create a challenging but realistic thermal 
condition.
     The maximum container surface temperature during the 
localized fire stage for the side of the container facing the fire and 
for the sides of the container was set to 700 [deg]C.
     The minimum container surface temperature during the 
engulfing fire stage on the side of the container facing the fire was 
set to 600 [deg]C, because this was the lowest value observed for this 
side of the container during the engulfing fire stage.
     A maximum temperature limit on the bottom of the container 
during the engulfing stage was not necessary as the temperature is 
naturally limited.
    The updates to the fire test by the IWG of GTR No. 13 Phase 2 
focused on improving the repeatability and reproducibility across test 
laboratories. Two significant improvements to the fire test are (1) the 
use of a pre-test checkout procedure and (2) basic burner 
specifications. The pre-test checkout requires conducting a preliminary 
fire exposure on a standardized steel container to verify that 
specified fire temperatures can be achieved for the localized and 
engulfing fire segments of the test prior to conducting the fire test 
on a CHSS. During this pre-test checkout, the fuel flow is adjusted to 
achieve fire temperatures within the limits given in Table-7 as 
measured on the surface of the pre-test steel container. The use of a 
pre-test steel container instead of an actual CHSS improves the 
accuracy and repeatability of the test because it avoids possible 
container material degradation that could affect the temperature 
measurements.

                               Table 7--Pre-Test Checkout Temperature Requirements
----------------------------------------------------------------------------------------------------------------
                               Temperature range on
         Fire stage             bottom of pre-test     Temperature range on sides    Temperature range on top of
                                    container             of pre-test container          pre-test container
----------------------------------------------------------------------------------------------------------------
Localized..................  450 [deg]C to 700        less than 750 [deg]C........  less than 300 [deg]C.
                              [deg]C.
Engulfing..................  Average temperatures of  Not applicable..............  Average temperatures of the
                              the pre-test container                                 pre-test container surface
                              surface measured at                                    measured at the three top
                              the three bottom                                       locations must be at least
                              locations must be                                      100 [deg]C, and when
                              greater than 600                                       greater than 750 [deg]C,
                              [deg]C.                                                must also be less than the
                                                                                     average temperatures of the
                                                                                     pre-test container surface
                                                                                     measured at the three
                                                                                     bottom locations.
----------------------------------------------------------------------------------------------------------------

    In addition to temperature requirements, GTR No. 13 also specifies 
required heat release rates per unit area (HRR/A) during the localized 
and engulfing fire stages. The HRR/A is calculated using the lower 
heating value (LHV) of the fuel, which is measured in megajoules of 
energy released per kilogram of fuel consumed. To obtain HRR/A, the 
fuel flow rate is multiplied by LHV and then divided by the burner 
area. GTR No. 13 specifies a standardized calculation for burner area. 
NHTSA has considered the specification for HRR/A and determined that it 
could result in over-specification of the test parameters, potentially 
making it very difficult to conduct the test. In addition, NHTSA 
believes that the detailed temperature specifications for the pre-test 
container during the pre-test checkout are sufficient to ensure 
repeatability and reproducibility of the test.\84\ Therefore, NHTSA is 
not proposing specifications for HRR/A. NHTSA seeks comment on this 
decision.
---------------------------------------------------------------------------

    \84\ Testing conducted to support enhancement of the fire test 
specifications in GTR No. 13 Phase 2 indicated that the container 
surface temperature specifications in the pre-test container fire 
test along with the burner temperatures provided the needed 
repeatability and reproducibility of the test.

---------------------------------------------------------------------------

[[Page 27525]]

    The dimensions of the pre-test steel container for the pre-test 
checkout are similar to those of the containers from the JARI vehicle 
fire tests. The standard pre-test steel container is fabricated from 
12-inch Schedule 40 NPS pipe along with end caps. The diameter of this 
---------------------------------------------------------------------------
pipe is 12 inches (304 mm), while the length is:

 at least 800 mm
 not greater than 1.65 m
 greater than or equal to the length of the CHSS to be tested, 
unless the CHSS is greater than 1.65 m

    The pre-test steel container is instrumented with thermocouples in 
the same manner as the containers in the JARI vehicle fire tests and 
mounted above the burner in the same manner as the CHSS to be fire 
tested. Thermocouples are located along the cylindrical section of the 
pre-test container at the bottom surface exposed to the burner flame, 
mid-height along the left and right side of the cylindrical surface, 
and top surface opposite the direct exposure to the burner flame. 
Example thermocouple locations are shown below in Figure-8.
[GRAPHIC] [TIFF OMITTED] TP17AP24.007

Figure-8: Thermocouple Locations for the Pre-Test Checkout

    The positioning of the pre-test container relative to the localized 
and engulfing zones of the burner in the pre-test checkout must be 
consistent with the positioning of the CHSS over the burner that is to 
be tested.
    The three thermocouples along the bottom (labeled TBL25, TBC25, 
TBR25 in Figure-8) are considered burner monitor thermocouples. These 
thermocouples are positioned 25 mm below the pre-test container. Since 
these thermocouples are intended to monitor the burner, an alternative 
would be to position these thermocouples relative to the burner itself. 
NHTSA seeks comment on whether it is preferable to position the burner 
monitor thermocouples relative to the pre-test container or relative to 
the burner.
    The pre-test checkout is performed at least once before the 
commissioning of a new test site. Additionally, if the burner and test 
setup is modified to accommodate a test of different CHSS 
configurations than originally defined or serviced, then repeat of the 
pre-test checkout is needed prior to performing CHSS fire tests. NHTSA 
seeks comment on the frequency of conducting this pre-test checkout for 
ensuring repeatability of the fire test on CHSS.
    After the pre-test checkout is satisfactorily completed, the steel 
pre-test container is removed and the CHSS to be fire tested is mounted 
for testing. The CHSS fire test is then conducted with fuel flow 
settings identical to the pre-test checkout. The profile of the CHSS 
fire test is shown in Figure-9. During the CHSS fire test, the only 
thermocouples used are the burner monitor thermocouples, which are 
positioned 25 mm below the bottom of the CHSS. Temperatures on the 
surface of the CHSS will vary naturally based on interactions with the 
flames, and these temperatures are not controlled during the CHSS fire 
test. The burner monitor thermocouples are used only to ensure the 
burner is producing a fire closely matching the pre-test checkout.
    The localized fire continues for a total of 10 minutes and then the 
test transitions to the engulfing stage which continues until the test 
is complete (test completion is discussed below). The minimum value for 
the burner monitor temperature during the localized fire stage 
(TminLOC) is calculated by subtracting 50 [deg]C from the 
minimum of the 60-second rolling average of the burner monitor 
temperature in the localized fire zone of the pre-test checkout. The 
minimum value for the burner monitor temperature during the engulfing 
fire stage (TminENG) is calculated by subtracting 50 [deg]C 
from the minimum of the 60-second rolling average of the average burner 
monitor temperature in the engulfing fire zone of the pre-test 
checkout.

[[Page 27526]]

[GRAPHIC] [TIFF OMITTED] TP17AP24.008

Figure-9: Temperature Profile of the Fire Test

    NHTSA has conducted CHSS fire testing to verify the feasibility of 
the test for service termination performance in fire as currently 
proposed. Overall, the testing was completed successfully, 
demonstrating the feasibility of the proposed test for service 
terminating performance in fire. The results of this testing are 
summarized in the test report GTR No. 13 Fire and Closures Tests.\85\
---------------------------------------------------------------------------

    \85\ See the report titled ``GTR No. 13 Fire and Closures 
Tests'' submitted to the docket of this NPRM. This report will also 
be submitted to the National Transportation Library. https://rosap.ntl.bts.gov/.
---------------------------------------------------------------------------

    In some cases during testing, however, temperatures measured at the 
burner monitor thermocouples did not satisfy the required 
TminENG. NHTSA's testing indicated that the airflow during 
the pre-test may be different from that of the CHSS if the pre-test 
container length is substantially different from that of the CHSS to be 
tested. The difference in air flow between the two tests could cause 
differences in fire input to the CHSS compared to the pre-test 
container. Therefore, NHTSA recommends that for CHSS of length between 
600 mm and 1650 mm, the difference in the length of the pre-test 
container and the CHSS be no more than 200 mm. NHTSA seeks comment on 
whether this recommendation should be a specification for the pre-test 
container.
    In addition, NHTSA seeks comment on the requirement for 
TminENG. In particular, NHTSA seeks comment on allowing for 
a wider variation than 50 [deg]C below the pre-test temperatures. A 
variation of 50 [deg]C is small in the context of fire temperatures, 
and such a small variation limit may make the test more difficult for 
test labs to conduct. Furthermore, as currently specified, 
TminLOC and TminENG would be time-dependent 
variables because they are based on a time-dependent rolling average. 
Having TminLOC and TminENG being time-dependent 
is complex and would make the testing difficult to monitor. NHTSA seeks 
comment on a simpler calculation for TminLOC and 
TminENG that will result in constant values for 
TminLOC and TminENG. NHTSA proposes that 
TminLOC be calculated by subtracting 50 [deg]C from the 
minimum value of the 60-second rolling average of the burner monitor 
temperature in the localized fire zone of the pre-test checkout. 
Similarly, NHTSA proposes that TminENG be calculated by 
subtracting 50 [deg]C from minimum value of the 60-second rolling 
average of the average of the three burner monitor temperatures during 
the engulfing fire stage of the pre-test checkout. NHTSA seeks comment 
on whether these revised calculations for TminLOC and 
TminENG should be required.
    GTR No. 13 specifies additional pre-test checkout procedures 
intended for irregularly shaped CHSS which are expected to impede air 
flow through the burner. These procedures involve constructing a pre-
test plate having similar dimensions to the CHSS to be tested. A second 
pre-test checkout is conducted using the pre-test plate and using the 
burner monitor thermocouples. If the burner monitor thermocouple 
temperatures do not satisfy both TminLOC and 
TminENG, then the pre-test plate is raised by 50 mm, and a 
third pre-test checkout is conducted. GTR No. 13 specifies that this 
process is repeated until burner monitor thermocouple temperatures 
satisfy TminLOC and TminENG. NHTSA has considered 
this additional pre-test process and determined that it is unnecessary. 
The goal of the pre-test checkout is a repeatable and reproducible fire 
exposure among different testing facilities. NHTSA has determined there 
is no need for design-specific modification to the fire test procedure. 
Furthermore, the additional pre-test procedures add considerable 
complexity to the test procedure, and as a result could undermine the 
repeatability and reproducibility of the fire test. Therefore, NHTSA is 
not proposing these additional pre-test procedures. NHTSA seeks comment 
on this decision. If commenters believe that the additional pre-test 
procedures are necessary, NHTSA requests that they explain (1) how they 
would improve the safety outcome of the standard, and (2) how they 
would improve the

[[Page 27527]]

repeatability and reproducibility of the fire test.
    Liquefied petroleum gas, also known as liquified propane gas or 
simply LPG, is the selected fuel for the test burner because it is 
globally available and easily controllable to maintain the required 
thermal conditions. The use of LPG was deemed adequate by the IWG to 
reproduce the thermal conditions on the steel container that occurred 
during the JARI vehicle fire tests without concerns of carbon formation 
that can occur with other liquid fuels. The relatively low hydrogen to 
carbon (H/C) ratio of LPG at approximately 2.67 allows the flame to 
display flame radiation characteristics (from carbon combustion 
products) more similar to petroleum fires (with a H/C of roughly 2.1) 
than natural gas, for example, which has an H/C ratio of approximately 
4.0. Also, The LPG flame is more uniform and is easier to control than 
natural gas and gasoline flames. For this reason, LPG fuel is the 
choice for most testing purposes to improve the repeatability and 
reproducibility of the test.
    To further improve test reproducibility, a burner configuration is 
defined in S6.2.5.1 with localized and engulfing fire zones. The burner 
configuration specifications are listed in Table-8 below.

                     Table-8--Burner Specifications
------------------------------------------------------------------------
                  Item                             Description
------------------------------------------------------------------------
Nozzle Type............................  Liquefied petroleum gas fuel
                                          nozzle with air pre-mix.
     LPG Orifice in Nozzle.....  1 mm  0.1 mm inner
                                          diameter.
     Air Ports in Nozzle.......  Four holes, 6.4 mm 
                                          0.6 mm inner diameter.
     Fuel/Air Mixing Tube in     10 mm  1 mm inner
     Nozzle.                              diameter.
Number of Rails........................  Six.
Center-to-center Spacing of Rails......  105 mm  5 mm.
Center-to-center Nozzle Spacing Along    50 mm  5 mm.
 the Rails.
------------------------------------------------------------------------

    These specifications allow the fire test to be performed without a 
burner development program. NHTSA believes that use of a standardized 
burner configuration is a practical way of conducting fire testing and 
should reduce variability in test results through commonality in 
hardware. Flexibility is provided to adjust the length of the engulfing 
fire zone to match the CHSS length, up to a maximum of 1.65 m. This 
allows test laboratories to reduce burner fuel consumption when testing 
small containers. The width of the burner, however, is fixed at 500 mm 
for all fire tests, regardless of the width or diameter of the CHSS 
container to be tested, so that each CHSS is evaluated with the same 
fire condition regardless of size. The length of the localized fire 
zone is also fixed to 250 mm for all fire tests. An example of a 
typical burner is shown in Figure-10 and Figure-11 below. NHTSA seeks 
comment on a specification for the burner rail tubing shape and size, 
which can affect the spacing between the nozzle tips.
    GTR No. 13 specifies that the CHSS is rotated relative to the 
localized burner to minimize the ability for TPRDs to sense the fire 
and respond. GTR No. 13 specifies establishing a worst-case based on 
the specific CHSS design. However, NHTSA is concerned that establishing 
a worst-case based on a specific design may be subjective. NHTSA 
instead proposes that the CHSS is positioned for the localized fire by 
orienting the CHSS relative to the localized burner such that the 
distance from the center of the localized fire exposure to the TPRD(s) 
and TPRD sense point(s) is at or near maximum. This provides a 
challenging condition where the TPRD(s) may not sense the localized 
fire. The engulfing fire zone includes the localized fire zone and 
extends along the complete length of the container, in one direction, 
towards the nearest TPRD or TPRD sense point, up to a maximum burner 
length of 1.65 m. Some examples of possible burner orientations are 
shown in Figure-12 and Figure-13. NHTSA seeks comment on the proposed 
orientation of the CHSS relative to the localized burner.
BILLING CODE 4910-59-P
[GRAPHIC] [TIFF OMITTED] TP17AP24.009

Figure-10: Example Burner Top View

[[Page 27528]]

[GRAPHIC] [TIFF OMITTED] TP17AP24.010

Figure-11: Example Burner Side View
[GRAPHIC] [TIFF OMITTED] TP17AP24.011

Figure-12: Example Burner Orientations With Single TPRD

[[Page 27529]]

[GRAPHIC] [TIFF OMITTED] TP17AP24.012

Figure-13: Example Burner Orientations With Two TPRDs

BILLING CODE 4910-59-C
    When testing is conducted outdoors, wind shielding is required to 
prevent wind from interfering with the flame temperatures. In order to 
ensure that wind shields do not obstruct the drafting of air to burner, 
which could cause variations in test results, the wind shields need to 
be at least 0.5 m away from the CHSS being tested. Finally, for 
consistency, the wind shielding used for the pre-test checkout must be 
the same as that for the CHSS fire test. NHTSA seeks comment on whether 
specifications for wind shielding should be provided in the regulatory 
text of the standard, and if so, what the specifications should be. As 
an additional approach to addressing wind interference with flame 
temperatures, NHTSA is considering for the final rule to limit average 
wind velocity during testing to 2.24 meters/second, as in FMVSS No. 
304.\86\ NHTSA seeks comment on limiting wind speed during testing.
---------------------------------------------------------------------------

    \86\ FMVSS No. 304, ``Compressed natural gas fuel container 
integrity,'' https://www.ecfr.gov/current/title-49/subtitle-B/chapter-V/part-571/subpart-B/section-571.304.
---------------------------------------------------------------------------

    In order to minimize hazard, jet flames occurring anywhere other 
than a TPRD outlet, such as the container walls or joints, cannot 
exceed 0.5 meters in length. NHTSA seeks comment on how to accurately 
measure jet flames.
    Consistent with GTR No. 13, if venting occurs though the TPRD(s), 
the venting is required to be continuous so the vent lines do not 
experience periodic flow blockages which could interfere with proper 
venting. The fire test is completed successfully after the CHSS vents 
its contents and the CHSS pressure falls to less than 1 MPa. If the 
CHSS has not vented below 1 MPa within 60 minutes for vehicles with a 
GVWR of 4,536 kg (10,000 pounds) or less, or 120 minutes for vehicles 
with a GVWR over 4,536 kg (10,000 pounds), the CHSS is considered to 
have failed the test.
    The value of 1 MPa is selected such that the risk of stress rupture 
after venting is minimal. The time limits are selected to represent 
long-lasting fires such as battery fires or vehicle fires occurring 
inside of building structures. The time limit for heavy vehicles is 
longer because heavy vehicles are larger in size and often carry cargo 
or refuse. Both of these factors tend to prolong fire duration.
8. Tests for Performance Durability of Closure Devices
    Like the CHSS, closure devices (like the TPRD, check valve and 
shut-off valve) must be durable and maintain their expected operational 
capabilities during their lifetime of service. Closure devices must 
demonstrate their operability and durability in service by completing a 
series of performance tests as discussed below. Closure device 
operability and durability is essential for the integrity of the CHSS 
because these devices isolate the high-pressure hydrogen from the 
remainder of the fuel system and the environment. While the closure 
devices are challenged in the CHSS performance tests above, additional 
specific tests may further enhance safety. In addition, specific 
component testing enables equivalent components to be safely exchanged 
in a CHSS.
    The tests for performance durability of closure devices in GTR No. 
13 are closely consistent with the industry standards CSA/ANSI HPRD 1-
2021, Thermally activated pressure relief devices for compressed 
hydrogen vehicle fuel containers, and CSA/ANSI HGV 3.1-2022, Fuel 
System Components for Compressed Hydrogen Gas Powered 
Vehicles.87 88 The tests for performance durability of 
closure devices carry a significant test burden. To evaluate a single 
TPRD design, 13 TPRD units are required for a total of 29 individual 
tests (some units undergo multiple tests in a sequence). Similarly, to 
evaluate a single shut-off valve or check valve, 8 units are required 
for a total of 17 individual tests. While NHTSA is proposing these 
requirements to be consistent with GTR No. 13, NHTSA seeks comment on 
whether testing of this extent is necessary to meet the need for 
safety, or whether it is still possible to meet the need for safety 
with a less-burdensome test approach or with a subset of the test for 
performance durability of closure devices. If commenters believe 
another approach or subset of tests is appropriate and meets the need 
for safety, NHTSA requests that commenters provide specific detail on

[[Page 27530]]

(1) the alternate approach or subset of tests and (2) how it meets the 
need for safety adequately.''
---------------------------------------------------------------------------

    \87\ See. https://webstore.ansi.org/standards/csa/csaansihprd2021.
    \88\ See. https://webstore.ansi.org/standards/csa/csaansihgv2015r2019.
---------------------------------------------------------------------------

    Furthermore, FMVSS represent minimum performance requirements for 
safety. FMVSS does not address issues such as component reliability or 
best practices. These considerations are left to industry standards. 
NHTSA seeks comment on whether a reduced subset of the tests for 
performance durability of closure devices could ensure safety with a 
lower overall test burden. In such a subset, only those tests directly 
linked to critical safety risks would be included.
    The tests for performance durability of closure devices are 
conducted on finished components representative of normal production. 
To enable outdoor testing without special temperature controls that 
would increase testing costs, NHTSA proposes that testing be conducted 
at an ambient temperature of 5 [deg]C to 35 [deg]C, unless otherwise 
specified. In addition, GTR No. 13 specifies that all tests be 
performed using either:
     Hydrogen gas compliant with SAE J2719_202003, Hydrogen 
Fuel Quality for Fuel Cell Vehicles, or
     Hydrogen gas with a hydrogen purity of at least 99.97 
percent, less than or equal to 5 parts per million of water, and less 
or equal to 1 part per million particulate, or
     A non-reactive gas instead of hydrogen.
    The standard J2719_202003 specifies maximum concentrations of 
individual contaminants such as methane and oxygen. Limiting these 
individual contaminants are critical for fuel cell operation, however, 
they are unlikely to affect the results of the tests for performance 
durability of closure devices.
    As a result, FMVSS No. 308 will only require hydrogen with a purity 
of at least 99.97 percent, less than or equal to 5 parts per million of 
water, and less or equal to 1 part per million particulate. NHTSA seeks 
comment on any other impurities that could affect the results of the 
tests for performance durability of closure devices.
    Using a non-reactive gas for testing would have the benefit of 
reducing the test lab safety risk related to handling pressurized 
hydrogen. However, it is not clear if replacing hydrogen with a non-
reactive gas reduces stringency and therefore may not adequately 
address the safety need. As a result, this option has not been proposed 
in FMVSS No. 308. NHTSA seeks comment on whether testing with a non-
reactive gas instead of hydrogen reduces test stringency. If commenters 
believe (and can explain) that it does not reduce test stringency, 
NHTSA requests that they identify a suitable non-reactive gas to 
replace hydrogen, such as helium or nitrogen, and explain why it is 
suitable.
a. TPRD
    Failure of a TPRD to properly vent in the event of a fire could 
lead to burst. Accordingly, TPRDs must demonstrate operability and 
durability in service by successfully completing the applicable tests 
for performance durability of closure devices. This is a series of TPRD 
performance tests with requirements discussed below.
    GTR No. 13 does not consider the possibility of the TPRD activating 
during the pressure cycling test, temperature cycling test, salt 
corrosion test, vehicle environment test, stress corrosion cracking 
test, drop and vibration test, or leak test. The temperatures applied 
during these tests are not characteristic of fire and therefore should 
not cause the TPRD to activate. TPRD activation in the absence of 
temperatures characteristic of a fire indicates that the TPRD is not 
functioning as intended and presents a safety risk due to the hazards 
associated with TPRD discharge. As a result, NHTSA is proposing that if 
the TPRD activates at any point during the pressure cycling test, 
temperature cycling test, salt corrosion test, vehicle environment 
test, stress corrosion cracking test, drop and vibration test, or leak 
test, that TPRD will be considered to have failed the test. NHTSA seeks 
comment on this proposed requirement.
(1) Pressure Cycling Test
    Similar to the CHSS test for expected on-road performance, the 
pressure cycling test would evaluate a TPRD's ability to withstand 
repeated pressurization and depressurization. One TPRD unit undergoes 
15,000 internal pressure cycles with hydrogen gas. While the proposed 
15,000 pressure cycles for the TPRD is consistent with GTR No. 13, 
NHTSA notes that this number of cycles is higher than the maximum 
11,000 pressure cycles applied to containers. NHTSA seeks comment on 
the need for 15,000 pressure cycles for TPRDs. The testing is performed 
under the conditions shown in Table-9 with a maximum cycling rate of 10 
cycles per minute.

                        Table 9--Test Conditions
------------------------------------------------------------------------
                                                            Temperature
             Pressure                 Number of cycles       ([deg]C)
------------------------------------------------------------------------
2 MPa to 150% NWP.................  First 10............              85
2 MPa to 125% NWP.................  Next 2,240..........              85
2 MPa to 125% NWP.................  Next 10,000.........              20
2 MPa to 80% NWP..................  Final 2,750.........             -40
------------------------------------------------------------------------

    The pressure cycling test is designed to replicate fueling events 
during service. This is important because over time, repeated fueling 
events can produce fatigue failures. NHTSA seeks comment on the number 
of TPRD pressure cycles. The first 10 cycles use 150 percent NWP to 
replicate over-pressurization events at fueling stations. The remaining 
cycles are conducted to 125 percent NWP for the reasons discussed above 
for the baseline pressure cycle test.
    The test temperature of 85 [deg]C for the first 2,250 cycles and 
the test temperature of -40 [deg]C for the final 2,750 cycles are 
selected to replicate the extreme hot and cold environments described 
above for the test for performance durability. After the completion of 
pressure cycling, the TPRD units are subjected to the Leak Test, 
Benchtop Activation Test, and Flow Rate Test. These three tests, 
discussed below, verify the essential functions of the TPRD.
(2) Accelerated Life Test
    A TPRD needs to activate at its intended activation temperature, 
but also must not activate prematurely due to a long-duration exposure 
to elevated temperature that is below its activation temperature. 
Holding the TPRD at an elevated temperature TL could lead to creep 
failure of the materials within the TPRD and result in a false 
activation. The purpose of the accelerated life test is to evaluate the 
TPRD's ability to activate at intended activation

[[Page 27531]]

temperature, while demonstrating resistance to creep failure at 
elevated temperatures that are below its activation temperature.
    During the test, the TPRD units are pressurized with hydrogen at 
125 percent NWP and placed in a temperature-controlled environment. One 
unit is tested at the manufacturer's specified activation temperature, 
Tf, and one unit is tested at the accelerated life temperature, TL, 
given by the expression: \89\
---------------------------------------------------------------------------

    \89\ Details are provided in the technical document ``New 
equation for calculating accelerated life test temperature.pdf'' 
submitted to the docket of this NPRM.
[GRAPHIC] [TIFF OMITTED] TP17AP24.013


where [beta] = 273.15 if T is in Celsius and [beta] = 459.67 if T is in 
Fahrenheit, T85 = 85 [deg]C (185 [deg]F), and Tf is the 
manufacturer's specified activation temperature. The unit tested at Tf 
must activate in less than 10 hours and the unit tested at TL must not 
activate in less than 500 hours. The required 500 hours without 
activation demonstrates the unit's resistance to creep.
(3) Temperature Cycling Test
    Similar to the container and CHSS, the TPRD must be able to 
withstand extreme temperatures while in service. A study found that 
pressure release devices at extreme cold temperature as low as -40 
[deg]C could cause a TPRD gas release failure.\90\ The temperature 
cycling test evaluates a TPRD's ability to withstand extreme 
temperature conditions that may lead to gas release failures when 
combined with pressure cycling. The TPRD is first exposed to 15 thermal 
cycles by alternating between hot (85 [deg]C) and cold (-40 [deg]C) 
temperature baths. This is to simulate rapid swings in environmental 
temperature, which can stress the TPRD through thermal expansion and 
contraction. The TPRD is then pressure cycled in the cold bath for 100 
cycles at 80 percent NWP to simulate fueling and defueling in an 
extreme cold environment. After these stresses have been applied, the 
TPRD is subjected to the low-temperature condition Leak Test, Benchtop 
Activation Test, and Flow Rate Test. These three tests, discussed 
below, verify the essential functions of the TPRD. Only the low-
temperature condition leak test is conducted after the temperature 
cycling test because leaks are most likely to occur at low 
temperatures.
---------------------------------------------------------------------------

    \90\ Livio Gambone et al., Performance testing of pressure 
relief devices for NGV cylinders, June 1997.
---------------------------------------------------------------------------

(4) Salt Corrosion Resistance Test
    The purpose of the salt corrosion resistance test is to verify that 
the TPRD can withstand an extreme external salt corrosion environment. 
The test occurs in a chamber designed to coat the TPRD with atomized 
droplets of salt solution. This creates a highly corrosive environment. 
The chamber cycles through wet and dry stages to maximise corrosion 
affects. The parameters for this test, such as the chamber design, the 
salts and water used, the salt concentrations, temperatures, humidity 
levels and cycle times are all based on HGV 3.1-2022 and HPRD 1-
2021.91 92 93 After the salt corrosion exposure, the TPRD 
units are subjected to the Leak Test, Benchtop Activation Test, and 
Flow Rate Test. These tests, discussed below, verify the essential 
functions of the TPRD. NHTSA seeks comment on the clarity and 
objectivity of the salt corrosion resistance test procedure. If 
commenters have suggestions on how to change the salt corrosion 
resistance test procedure, NHTSA asks that they please explain how 
their suggested changes improve the clarity and objectivity, and how 
they continue to meet the need for safety represented by this test.
---------------------------------------------------------------------------

    \91\ CSA/ANSI HGV 3.1-2022 Fuel System Components For Compressed 
Hydrogen Gas Powered Vehicles.
    \92\ CSA/ANSI HPRD 1-2021 Thermally activated pressure relief 
devices for compressed hydrogen vehicle fuel containers.
    \93\ HGV 3.1, HPRD 1, GTR No. 13, and the proposed FMVSS No. 308 
reference the standards ASTM D1193-06(2018), Standard Specification 
for Reagent Water and ISO 6270-2:2017 Determination of resistance to 
humidity. ASTM D1193-06(2018) provides specification for the water 
to be used during salt corrosion resistance testing. https://www.astm.org/d1193-06r18.html.
    ISO 6270-2:2017 provides specifications for the cyclic corrosion 
chamber to be used. https://www.iso.org/standard/64858.html.
    These two standards would be incorporated by reference into the 
proposed FMVSS No. 308. A summary of these two standards is provided 
in Section V. Regulatory Analyses and Notices of this notice.
---------------------------------------------------------------------------

(5) Vehicle Environment Test
    The purpose of the vehicle environment test is to demonstrate that 
the TPRD can withstand exposure to chemicals that might be encountered 
during on-road service. Prior to testing, the inlet and outlet ports 
are capped because the test is not intended to expose the interior of 
the TPRD. The TPRD is then exposed to the following fluids for 24 hours 
each at 20 [deg]C:
     Sulfuric acid at 19 percent in water to simulate battery 
acid.
     Ethanol at 10 percent in gasoline to simulate fueling 
station fluids.
     Methanol at 50 percent in water to simulate windshield-
washer fluid.
    The TPRD is exposed to all of fluids separately in a sequence. The 
fluids are replenished as needed for complete exposure throughout the 
duration of the test. After exposure to each chemical fluid, the unit 
is wiped off and rinsed with water to end any reactions that may be 
occurring.
    GTR No. 13 does not specify the method of exposure to these 
chemical solutions. The method described in HPRD 1-2021 is to immerse 
the test unit in each fluid.\94\ The duration of 24 hours is based on 
industry practices. NHTSA seeks comment on the exposure method.
---------------------------------------------------------------------------

    \94\ CSA/ANSI HPRD 1-2021, Thermally activated pressure relief 
devices for compressed hydrogen vehicle fuel containers.
---------------------------------------------------------------------------

    After the conclusion of the exposures, the TPRD unit is subjected 
to the Leak Test, Benchtop Activation Test, and Flow Rate Test. These 
tests, discussed below, verify the essential functions of the TPRD. In 
addition to these subsequent tests, the TPRD must not show signs of 
cracking, softening, or swelling. GTR No. 13 further specifies that 
``cosmetic changes such as pitting or staining are not considered 
failures.'' NHTSA seeks comment on including this specification, and 
notes that pitting can be an aggressive form of corrosion which can 
ultimately lead to component failure due to cracking at the pitting 
site.
(6) Stress Corrosion Cracking Test
    The purpose of the stress corrosion cracking test is to ensure that 
the TPRD can resist stress corrosion cracking. Stress corrosion 
cracking is the growth of crack formation in a corrosive environment. 
It can lead to unexpected and sudden failure of normally ductile metal 
alloys subjected to a tensile stress, especially at elevated 
temperature. In particular, TPRDs containing copper-based alloys can be 
susceptible to stress corrosion cracking in the presence of aqueous 
ammonia. This is a significant risk because ammonia can be found in the 
natural and vehicle environment.
    The TPRD test unit is degreased to remove any protective grease 
that may be present. The unit is then exposed for ten days to a moist 
ammonia-air mixture maintained in a glass chamber. Under GTR No. 13, 
the moist ammonia-air mixture is achieved using an ammonia-water 
mixture with specific gravity of 0.94. Specific gravity is affected by 
temperature and, therefore, is an inconvenient metric for concentration 
specification because concentrations will need to be adjusted for 
different temperatures. NHTSA seeks comment on a more direct metric for 
ammonia

[[Page 27532]]

concentration specification, such as 20 weight percent ammonium 
hydroxide in water.
    The chamber is maintained at atmospheric pressure and 35 [deg]C. 
This simulates a slightly elevated temperature. In GTR No. 13, the only 
requirement to pass the stress corrosion cracking test is that the 
components must not exhibit cracking or delaminating due to this test. 
NHTSA seeks comment on this performance requirement and whether there 
are alternative requirements for this test beyond basic visual 
inspection, such as subjecting the TPRD to the leak test.
(7) Drop and Vibration Test
    The purpose of the drop and vibration test is to evaluate the 
TPRD's ability to withstand drop and vibration. Dropping a TPRD could 
occur during installation, and vibration is likely to occur during on-
road service. A TPRD may be dropped in any one of six different 
orientations covering the opposing directions of three orthogonal axes: 
vertical, lateral and longitudinal. After the drop, the TPRD unit is 
examined for damage that would prevent its installation in a test 
fixture for vibration according to the manufacturer's instructions. If 
damage is present that would prevent installation, the TPRD is 
discarded, and it is not considered a test failure. Damage that would 
prevent its installation is acceptable because the TPRD could never 
enter service with this type of damage.
    A TPRD that is not discarded after the drop test proceeds to the 
vibration test. In addition, one new undamaged TPRD that was not 
dropped is also subjected to the vibration test. The units are vibrated 
for 30 minutes along each of the three orthogonal axes (vertical, 
lateral, and longitudinal). The units are vibrated at a resonant 
frequency which is determined by using an acceleration of 1.5 g and 
sweeping through a sinusoidal frequency range of 10 to 500 Hz with a 
sweep time of 10 minutes. According to GTR No. 13, the resonance 
frequency is identified by a ``pronounced'' increase in vibration 
amplitude. However, if the resonance frequency is not found, the test 
is conducted at 40 Hz. Specifying a pronounced increase in vibration 
amplitude could be partially subjective. NHTSA seeks comment on a more 
objective criteria for establishing resonance, such as a frequency 
where the amplitude of the response of the test article is at least 
twice the input energy as measured by response accelerometers. 
Furthermore, the acceleration level was not defined in GTR No. 13 for 
the resonant dwells. NHTSA seeks comment on an appropriate acceleration 
level for the resonant dwells.
    After vibration, the TPRD units are subjected to the Leak Test, 
Benchtop Activation Test, and Flow Rate Test. These tests, discussed 
below, verify the essential functions of the TPRD.
(8) Leak Test
    The leak test evaluates the TPRD's basic ability to contain 
hydrogen at ambient and extreme temperature conditions. In particular, 
the leak test is used after other tests to verify the TPRD's integrity 
after undergoing the stresses from previous tests. Each TPRD under test 
is conditioned for one hour by immersion in a temperature-controlled 
liquid at ambient temperature, high temperature, and low temperature. 
These test temperatures and corresponding test pressures are as 
follows:

 Ambient temperature: 5 [deg]C to 35 [deg]C, test at 2 MPa and 
125 percent NWP
 High temperature: 85 [deg]C, test at 2 MPa and 125 percent NWP
 Low temperature: -40 [deg]C, test at 2 MPa and 100 percent NWP

    The above temperatures are selected for the same reasons discussed 
above for the test for performance durability. At the ambient and high 
temperature tests, the TPRD is evaluated for leaks at 2 MPa and 125 
percent NWP. The test pressure of 125 percent NWP represents the peak 
pressure that typically occurs during fueling. For the low temperature 
test, however, the maximum pressure is reduced to 100 percent NWP 
because maximum fueling pressure is lower in extremely cold 
environments. NHTSA seeks comment on the need to perform the leak test 
at 2 MPa in addition to the higher pressures.
    After the required pre-conditioning period, the evaluation for leak 
involves observing the pressurized valve for hydrogen bubbles while 
immersed in the temperature-controlled fluid. If hydrogen bubbles are 
observed, the leak rate is measured by any method available to the test 
lab. The total leak rate must be less than 10 NmL/h, which represents 
an extremely low leak rate. NHTSA seeks comment on the leak rate 
requirement of 10 NmL/hour. This leak rate of 10 NmL/hour is much lower 
than the minimum hydrogen flow rate of 3.6 NmL/min necessary for 
initiating a flame.\95\ NHTSA seeks comment on objective methods for 
measuring the leak rate.
---------------------------------------------------------------------------

    \95\ SAE Technical report 2008-01-0726. Flame Quenching Limits 
of Hydrogen Leaks. The paper finds that the lowest possible 
flammable flow is about 0.005 mg/s (3.6 NmL/min).
---------------------------------------------------------------------------

(9) Benchtop Activation Test
    The purpose of the benchtop activation test is to demonstrate that 
the TPRD will activate as intended when exposed to high temperature. As 
with the leak test, the benchtop activation test is applied after other 
tests to ensure the TPRD retains its basic functions after other 
stresses have been applied.
    The test setup consists of either an oven or a chimney which is 
capable of controlling air temperature and flow to achieve 600 [deg]C 
in the air surrounding the test sample. This provides a sufficiently 
high air temperature to activate TPRDs. TPRD units are pressurized to 
25 percent NWP or 2 MPa, whichever is less. This provides sufficient 
pressure for activation.
    Three new TRPD units are tested to establish a baseline activation 
time, which is the average of the activation time of the three new 
TPRDs. TPRD units used in the pressure cycling test, accelerated life 
test, temperature cycling test, salt corrosion resistance test, vehicle 
environment test, and drop and vibration test are also tested in the 
benchtop activation test and these TPRDs must activate within 2 minutes 
of the average activation time established from the tests with the new 
units.
    GTR No. 13 does not provide any information on how to proceed in 
the event that a TPRD does not activate at all during the benchtop 
activation test. A TPRD that does not activate when inserted into the 
oven or chimney is not functioning as intended and therefore presents a 
safety risk. As a result, NHTSA is proposing that if a TPRD does not 
activate within 120 minutes from the time of insertion into the oven or 
chimney, the TPRD is considered to have failed the test. The time limit 
of 120 minutes is selected based on the maximum possible duration of 
the CHSS fire test. NHTSA seeks comment on this requirement.
(10) Flow Rate Test
    After benchtop activation, the flow rate test evaluates the TPRD 
for flow capacity to ensure that the flow rate of a TPRD exposed to the 
various environmental conditions during prior testing is similar to 
that of a new TPRD. This test can be performed with hydrogen, air, or 
any other inert gas because the test simply evaluates flow rate through 
the TPRD. Flow rate through the TPRD is measured with the inlet 
pressurized to 2 MPa and the outlet unpressurized. This pressure 
difference generates flow through the

[[Page 27533]]

TPRD. The lowest measured flow rate must be no less than 90 percent of 
a baseline flow rate established as the measured flow rate of a new 
TPRD. This ensures low variation in flow rates and that all TPRDs 
tested are free from blockages.
    The number of significant figures used in the measurement of flow 
rate can impact the test result. For example, a test flow rate of 1.7 
flow units compared against a baseline flow rate of 2.0 flow units does 
not meet the requirement. However, in this case, if flow rate were 
measured using only one significant figure, the two flow rates would be 
identical (2 flow units). As a result, NHTSA proposes requiring that 
the flow rate be measured in units of kilograms per minute with a 
precision of at least 2 significant digits. NHTSA seeks comment on this 
proposed requirement.
(11) Atmospheric Exposure Test
    GTR No. 13 includes an atmospheric exposure test to ensure that 
non-metallic components which are exposed to the atmosphere and provide 
a fuel-containing seal have sufficient resistance to oxygen. This is 
because oxygen can degrade non-metallic components. The oxygen exposure 
of 96 hours at 70 [deg]C at 2 MPa, is based on industry 
standards.96, 97 The requirement to pass this test is that 
the component not crack nor show visible evidence of deterioration.
---------------------------------------------------------------------------

    \96\ ASTM D572-04(2019) Standard Test Method for Rubber--
Deterioration by Heat and Oxygen. https://www.astm.org/d0572-04r19.html.
    \97\ ISO 188:2011 Rubber, vulcanized or thermoplastic--
Accelerated ageing and heat resistance tests. https://www.iso.org/standard/57738.html.
---------------------------------------------------------------------------

    However, NHTSA is concerned that this test is not objectively 
enforceable because the requirement involves a subjective determination 
of evidence of deterioration. Furthermore, the test would require NHTSA 
to determine which components are non-metallic, exposed to the 
atmosphere, and provide a fuel-containing seal. As a result, this test 
has not been included in FMVSS No. 308. NHTSA seeks comment on not 
including the atmospheric exposure test.
b. Check Valves and Shut-Off Valves
    Failure of a check valve or shut-off valve to properly contain 
pressure within the CHSS can lead to a severe hydrogen leak. 
Accordingly, check valves and shut-off valves must demonstrate their 
operability and durability in service by completing the applicable 
tests for performance durability of closure devices. This is a series 
of performance tests applicable to check valves and shut-off valves 
with requirements described below.
(1) Hydrostatic Strength Test
    Since the check valve and the shut-off valve ensure containment of 
high pressure hydrogen, the hydrostatic strength test is conducted to 
ensure the valves are able to withstand extreme pressure of up to 250 
percent NWP. Additionally, the test also ensures that the burst 
pressure of the valves exposed to various environmental conditions 
during prior testing is not degraded beyond 80 percent of a new 
unexposed valve's burst pressure.
    One new unit is tested to establish a baseline failure pressure, 
which must be at least 250 percent NWP, and other units are tested as 
specified in other sections, after being subjected to other tests. All 
outlet openings are plugged, and valve seats or internal blocks are 
placed in the open position. This allows the test pressure to be 
distributed throughout the valve. The strength test is performed at 20 
[deg]C with a hydrostatic pressure of 250 percent NWP applied at the 
inlet. This high pressure simulates an extreme over-pressurization and 
is held for three minutes.
    From 250 percent NWP, the hydrostatic pressure is increased at a 
rate of less than or equal to 1.4 MPa/second to avoid failure due to 
rapid pressurization. The pressure continues to increase until the 
component fails. The failure pressure of previously tested units should 
be no less than 80 percent of the failure pressure of the baseline unit 
unless the hydrostatic pressure exceeds 400 percent NWP.
    In the event of a leak, it may become impossible for the test 
laboratory to increase pressure on the valve. This occurs when any 
increase in applied pressure is offset by leakage flow, thereby 
negating the pressure increase. If this occurs, it is not possible to 
complete testing. To address this issue, NHTSA is proposing that valves 
shall not leak during the hydrostatic strength test, and that a leak 
would constitute a test failure. NHTSA seeks comment on the requirement 
that valves not leak during the hydrostatic strength test.
(2) Leak Test
    The leak test evaluates the valve's basic ability to contain 
hydrogen at ambient and extreme temperature conditions. In particular, 
the leak test is used after other tests to verify the valve's integrity 
after undergoing the stresses from previous tests. Each valve under 
test is conditioned for one hour by immersion in a temperature-
controlled liquid at ambient temperature, high temperature, and low 
temperature. These test temperatures and corresponding test pressures 
are as follows:

 Ambient temperature: 5 [deg]C to 35 [deg]C, test at 2 MPa and 
125 percent NWP
 High temperature: 85 [deg]C, test at 2 MPa and 125 percent NWP
 Low temperature: -40 [deg]C, test at 2 MPa and 100 percent NWP

    These temperatures and pressures are selected for the same reasons 
described above for the TPRD leak test. After the required pre-
conditioning period, the evaluation for leak involves observing the 
pressurized valve for hydrogen bubbles while immersed in the 
temperature-controlled fluid. If hydrogen bubbles are observed, the 
leak rate is measured by any method available to the test lab. Similar 
to the TPRD leak test, the total leak rate must be less than 10 NmL/h. 
For the same reasons discussed above for the TPRD leak test, NHTSA 
seeks comment on the leak rate requirement of 10 NmL/h and seeks 
comment on objective methods for measuring the leak rate.
(3) Extreme Temperature Pressure Cycling Test
    Similar to the extreme temperatures applied to containers and CHSS, 
the shut-off valve and the check valve must be able to withstand 
extreme temperatures while in service. The extreme temperature pressure 
cycling test simulates extreme temperature conditions that may lead to 
gas release failures when combined with pressure cycling.
    Check valves and shut-off valves may also be subject to ``chatter'' 
which is an excess of vibration that causes the valves to open and 
close quickly and repeatedly. This causes a clicking and rattling noise 
that is referred to as chatter. Valves can develop chatter when they 
are not able to handle the pressure applied or are improperly sized. 
Chatter of a valve can cause excessive wear of the valve mechanism that 
can cause failure of the valve over time. Therefore, this test 
evaluates the check valve and shut-off valve for chatter after the 
extreme temperature pressure cycling.
    The total number of operational cycles is 15,000 for the check 
valve, consistent with the 15,000 cycles used for the TPRD above. The 
total number of operational cycles is 50,000 for the shut-off valve. 
The higher 50,000 cycles for the shut-off valve reflects the multiple 
pressure pulses the shut-off valve experiences as it opens and closes 
repeatedly during service. In contrast, the check valve only 
experiences a

[[Page 27534]]

pressure pulse during fueling. NHTSA seeks comment on the number of 
pressure cycles for check valves and shut-off valves.
    Pressure cycling is conducted at different environmental 
temperatures and pressures:

 Ambient: Between 5.0 [deg]C and 35.0 [deg]C, 100 percent NWP
 High: 85 [deg]C, 125 percent NWP
 Low: -40 [deg]C, 80 percent NWP

    For a check valve, the pressure is applied in six incremental 
pulses to the valve inlet with the outlet closed. The pressure is then 
vented from the inlet, with outlet side pressure reduced to below 60 
percent NWP prior to the next cycle. This simulates the fueling 
process. The valve is held at the corresponding temperature for the 
duration of the cycling at each condition.
    For a shut-off valve, the pressure is applied through the inlet 
port. The shut-off valve is then energized to open the valve and the 
pressure is reduced to any pressure less than 50 percent of the 
specified pressure range. The shut-off valve is then de-energized to 
close the valve prior to the next cycle. This simulates operation of 
the shut-off valve during service. The valve is held at the 
corresponding temperature for the duration of the cycling at each 
condition.
    After cycling, each valve is subjected to 24 hours of ``chatter 
flow'' to simulate the chatter condition described above. Chatter flow 
means the application of a flow rate of gas through the valve that 
results in chatter as described above. NHTSA is concerned, however, 
that the application of chatter flow could be partially subjective. 
NHTSA seeks comment on the following aspects of the chatter flow test:
     Appropriate methodology or a procedure for inducing 
chatter flow.
     Appropriate instrumentation and criteria to measure and 
quantify chatter flow such as a decibel meter and minimum sound 
pressure level.
     How to proceed in cases where no chatter occurs.
     The specific safety risks that are addressed by the 
chatter flow test.
     The possibility of not including the chatter flow test.
    In the case of shut-off valves, GTR No. 13 specifies the chatter 
flow test is required only in the case of a shut-off valve which 
functions as a check valve during fueling and that the flow rate used 
to induce chatter should be within the normal operating conditions of 
the valve. However, NHTSA has no way of determining whether a shut-off 
valve is functioning as a check valve during fueling or the normal 
operating conditions of the valve. As a result, NHTSA is proposing that 
the chatter flow test will apply to all shut-off valves and will not 
specify flow rate limitations for the chatter flow test. NHTSA seeks 
comment on this decision.
    After the completion of the chatter flow test, the valve must 
comply with the leak test and the hydrostatic strength test to verify 
it retains its basic ability to contain hydrogen and resist burst due 
to over-pressurization.
(4) Salt Corrosion Resistance Test
    The salt corrosion resistance test is conducted in the same manner 
and for the same reasons discussed above for TPRDs. At the completion 
of the salt corrosion resistance test, the tested valve must comply 
with the ambient temperature leak test and the hydrostatic strength 
test to verify it retains its basic ability to contain hydrogen and 
resist burst due to over-pressurization.
(5) Vehicle Environment Test
    The vehicle environment test is conducted in the same manner and 
for the same reasons discussed above for TPRDs. At the completion of 
the vehicle environment test, the tested valve shall comply with the 
leak test and the hydrostatic strength test to verify it retains its 
basic ability to contain hydrogen and resist burst due to over-
pressurization. In addition to these subsequent tests, the valve shall 
not show signs of cracking, softening, or swelling.
(6) Atmospheric Exposure Test
    GTR No. 13 includes an atmospheric exposure test for check valves 
and shut-off valves identical to the atmospheric exposure test for 
TPRDs. However, this test has not been included for check valves and 
shut-off valves for the same reasons it was not included for TPRDs. 
NHTSA seeks comment on not including the atmospheric exposure test for 
check valves and shut-off valves.
(7) Electrical Tests
    The electrical tests apply to the shut-off valve only. The 
electrical tests evaluate the shut-off valve for:
     Leakage, unintentional valve opening, fire, and/or melting 
after exposure to an abnormal voltage.
     Failure of the electrical insulation between the power 
conductor and casing when the valve is exposed to a high voltage.
    The exposure to abnormal voltage is conducted by applying twice the 
valve's rated voltage or 60 V, whichever is less to the valve for at 
least one minute. After the test, the valve is subject to the leak test 
and leak requirements. The test for electrical insulation is conducted 
by applying 1000 V between the power conductor and the component casing 
for at least two seconds, consistent with the industry standards NGV 
3.1-2012 and HGV 3.1-2022.98 99 The isolation resistance 
between the valve and the casing must be 240 k[Omega] or more. This 
represents a high level of resistance to prevent the valve casing from 
being energized in the event the power conductor short circuits within 
the valve.\100\
---------------------------------------------------------------------------

    \98\ NGV 3.1-2012. Fuel system components for compressed natural 
gas powered vehicles. https://webstore.ansi.org/standards/csa/ansingv2012csa12.
    \99\ HGV 3.1-2022. Fuel system components for compressed 
hydrogen gas powered vehicles.
    \100\ Id.
---------------------------------------------------------------------------

    Some valves may have requirements specified by their manufacturers 
for peak and hold pulse width modulation duty cycle. NHTSA seeks 
comment on whether and how to adjust the proposed test procedure to 
account for a manufacturer's specified peak and hold pulse width 
modulation duty cycle requirements.
(8) Vibration Test
    The vibration test evaluates a valve's resistance to vibration. The 
valve is pressurized to 100 percent NWP and exposed to vibration for 30 
minutes along each of the three orthogonal axes (vertical, lateral, and 
longitudinal). After the test, the valve is inspected for visual 
exterior damage and required to comply with the ambient temperature 
leak test. Vibration is conducted along the three orthogonal axes to 
cover different possible mounting positions within a vehicle.\101\
---------------------------------------------------------------------------

    \101\ Id.
---------------------------------------------------------------------------

    The vibration frequencies used for the test are determined by 
frequency sweeps along each axis in the range of 10 Hz to 500 Hz. The 
most severe resonant frequency in each axis is selected for the test. 
Resonant frequencies are determined as those frequencies of the 
vibration table that result in considerably different acceleration 
measurements from an accelerometer mounted to the acceleration table 
and that mounted on the component under test. If a most severe resonant 
frequency is determined, the component undergoes vibration at that 
frequency for 30-minutes. If no resonant frequency is found, then 40 Hz 
is selected for that axis. The vibration acceleration is 1.5 g, which 
represents vibration acceleration within a typical vehicle.
    This test is conducted with the valve pressurized to 100 percent 
NWP to

[[Page 27535]]

simulate vibrations occurring while the valve is in service. After 
vibration, the valve shall comply with the leak test and the 
hydrostatic strength test to verify it retains its basic ability to 
contain hydrogen and resist burst due to over-pressurization.
    GTR No. 13 also contains a requirement that ``each sample shall not 
show visible exterior damage that indicates that the performance of the 
part is compromised.'' Showing signs of damage is a subjective measure 
and lacks the objectivity needed per the Motor Vehicle Safety Act. 
Therefore, this language has been removed.
(9) Stress Corrosion Cracking Test
    The stress corrosion cracking test is conducted in the same manner 
and for the same reasons discussed above for TPRDs.
9. Labeling Requirements
    Labels on a container are important for informing the consumer that 
the container is intended for hydrogen fuel, information on the nominal 
working pressure of the container, and information on when the 
container should be removed from service. The information on the 
container labels would also facilitate the agency's enforcement efforts 
by providing a ready means of identifying the container and its 
manufacturer, and by providing the information needed for conducting 
compliance tests. NHTSA tentatively concludes that the container 
label(s) include the following information:

 Manufacturer, serial number, date of manufacture
 The statement ``Compressed Hydrogen Only.''
 The container's NWP in MPa and pounds per square inch (psi).
 Date when the system should be removed from service
 BPO in MPa and psi.

B. FMVSS No. 307, ``Fuel System Integrity of Hydrogen Vehicles''

    FMVSS No. 307 would set requirements for the vehicle fuel system to 
mitigate hazards associated with hydrogen leakage and discharge from 
the fuel system, as well as requirements to ensure hydrogen leakage, 
hydrogen concentration in enclosed spaces of the vehicle, and hydrogen 
container displacement are within safe limits post-crash. A hydrogen 
fuel system includes the fueling receptacle, CHSS, fuel cell system or 
internal combustion engine, exhaust systems, and the fuel lines that 
connect these systems. Table-10 lists the requirements for the hydrogen 
fuel system to be incorporated in FMVSS No. 307, which includes 
separate sections for normal vehicle operations and post-crash 
requirements. The fuel system integrity requirements for normal vehicle 
operations would apply to all hydrogen-fueled vehicles, while the post-
crash fuel system integrity requirements only apply to light vehicles. 
NHTSA seeks comment on the application of FMVSS No. 307 to all 
vehicles, including heavy vehicles (vehicles with a GVWR greater than 
4,536 kg (10,000 pounds).\102\
---------------------------------------------------------------------------

    \102\ The proposed FMVSS No. 307 would apply, in general, to all 
hydrogen vehicles regardless of GVWR. However, not all vehicles 
would be subject to crash testing under FMVSS No. 307. As described 
below, passenger cars, multipurpose passenger vehicles, trucks and 
buses with a GVWR of less than or equal to 4,536 kg would be subject 
to barrier crash testing. School buses with a GVWR greater than 
4,536 kg would also be subject a barrier crash test. Heavy vehicles 
other than school buses with a GVWR greater than 4,536 kg would not 
be subject to crash testing under the proposed standard.

Table 10--Performance Test Requirements for Hydrogen Vehicle Fuel System
                                Integrity
------------------------------------------------------------------------
 
-------------------------------------------------------------------------
Performance test requirements for hydrogen vehicle fuel system
Fuel system integrity requirements for light and heavy vehicles during
 normal vehicle operations.
    Fueling receptacle requirements.
    Over-pressure protection for the low-pressure system.
    Hydrogen discharge systems.
    Protection against flammable conditions.
    Fuel system leakage requirements.
    Tell-tale warning to driver.
Post-crash fuel system integrity requirements for light vehicles.
    Fuel leakage limit.
    Concentration limit in enclosed spaces.
    Container displacement.
------------------------------------------------------------------------

1. Fuel System Integrity During Normal Vehicle Operations
    The first half of the proposed FMVSS No. 307 would adopt GTR No. 
13's protections during the normal operation of the vehicle. The 
proposed requirements in this section apply to all hydrogen fuel 
vehicles regardless of GVWR.
a. Fueling Receptacles
    This proposal includes five performance requirements for the 
hydrogen fueling receptacle. These requirements ensure safe use and 
proper function of the receptacle. If hydrogen is not properly 
contained by the fueling receptacle, hydrogen may escape into the 
surrounding environment where it may accumulate and become ignited, 
leading to an explosion or fire.
    The first requirement for the fueling receptacle is to prevent 
reverse flow to the atmosphere. This requirement is intended to prevent 
hydrogen leakage out of the fueling receptacle.
    The second requirement is for a label with the statement, 
``Compressed Hydrogen Only'' as well as the statement ``Service 
pressure __ MPa (__ psig).'' Including this information on a label near 
the fueling receptacle is intended to prevent incorrect fueling. 
Incorrect fueling with a fuel other than hydrogen or with a hydrogen 
pressure greater than the vehicle NWP could damage the fuel system. The 
label must also contain the statement, ``See instructions on fuel 
container(s) for inspection and service life.''
    The third requirement is for positive locking that prevents the 
disconnection of the fueling hose during fueling. This requirement is 
intended to prevent the fueling nozzle from being prematurely removed 
during fueling, which could result in hydrogen leakage.
    The fourth requirement is for protection against ingress of dirt 
and water to protect the fueling receptacle from contamination that 
could lead to degradation of the fuel system over time. A degraded fuel 
system is a safety risk because it could lead to a failure to contain 
hydrogen.
    The fifth requirement is to prevent the receptacle from being 
mounted in a location that would be highly

[[Page 27536]]

susceptible to crash deformations in order to prevent degradation in 
the event of a crash. The receptacle is also prevented from being 
mounted in the enclosed or semi-enclosed spaces of the vehicle because 
these areas can accumulate hydrogen.\103\
---------------------------------------------------------------------------

    \103\ Enclosed or semi-enclosed spaces means the volumes within 
the vehicle, external to the hydrogen fuel system (fueling 
receptacle, CHSS, fuel cell system or internal combustion engine, 
fuel lines, and exhaust systems) such as the passenger compartment, 
luggage compartment, and space under the hood.
---------------------------------------------------------------------------

    The assessment for all five receptacle requirements is by visual 
inspection. NHTSA seeks comment on these proposed requirements for the 
fueling receptacle and on the objectivity of assessment by visual 
inspection.
b. Over-Pressure Protection for Low-Pressure Systems
    Hydrogen is stored on hydrogen vehicles at high pressures. However, 
fuel cells and hydrogen combustion engines require lower pressures to 
operate, and higher pressures have the potential to damage their 
internal mechanisms. As a result, downstream fuel lines are designed 
for much lower pressures than the CHSS. Pressure regulators are used 
between the CHSS and the downstream lines to lower the pressure 
delivered downstream.
    NHTSA is proposing to adopt GTR No. 13's requirement of over-
pressure protection for low-pressure systems. Accordingly, the agency 
proposes requiring countermeasures to prevent failure of downstream 
components in the event a pressure regulator fails to properly reduce 
the fuel pressure from the much higher pressure in the CHSS. The 
activation pressure of the overpressure protection device would be 
lower than or equal to the maximum allowable working pressure for the 
appropriate section of the hydrogen system as determined by the 
manufacturer. NHTSA seeks comment on the requirement for an 
overpressure protection device in the fuel system and how to test the 
performance of such a device.
c. Hydrogen Discharge Systems
    TPRDs are designed to discharge the hydrogen stored in the CHSS to 
mitigate the risk of a rupture when the temperature surrounding the 
CHSS reaches a dangerous temperature. However, venting a flammable fuel 
source during an emergency can create its own potential hazard if 
handled improperly. For those reasons, we believe there is a safety 
need to propose standards for the hydrogen discharge system.
    The first proposed requirement is that the TPRD vent line be 
protected from ingress of dirt or water to prevent contamination that 
could degrade or compromise the TPRD or the TPRD discharge stream. This 
requirement protects the TPRD from degradation due to the ingress of 
dirt and water. A degraded TPRD that fails to activate during a fire 
could lead to a container burst. Alternatively, if the vent line itself 
became clogged by dirt and water, it could fail to properly vent the 
hydrogen in the event of a TPRD activation.
    Next, we are proposing several requirements from GTR No. 13 related 
to the TPRD vent discharge direction. The primary purpose of these 
requirements is to prevent additional safety hazards due to hydrogen 
discharge from the TPRD that could compromise other vehicle components 
and/or inhibit the ability of passengers to safely exit the vehicle. 
Accordingly, we propose that the TPRD discharge must not be directed 
towards nor impinge upon:
    1. Any enclosed or semi-enclosed spaces where hydrogen could 
unintentionally accumulate, such as the trunk, passenger compartment, 
or engine compartment.
    2. The vehicle wheel housing.
    3. Hydrogen gas containers--if the hydrogen being released from the 
TPRD becomes ignited, this would pose a burst risk.
    4. Rechargeable electrical energy storage system (REESS) because if 
the TPRD discharge became ignited, this could engulf the REESS and 
start a battery fire.
    5. Any emergency exit(s) or service door(s), because this would 
create a hazard to persons exiting the vehicle.
    In addition to these requirements from GTR No. 13, we believe an 
additional requirement is necessary to protect potential occupants 
attempting to exit the vehicle or first responders approaching the 
vehicle. We are proposing that hydrogen vented through the TPRD(s) be 
directed upwards within 20[deg] of vertical relative to the level 
surface or downwards within 45[deg] of vertical relative to the level 
surface. This requirement would prevent the TPRD discharge from being 
directed horizontally, which would create a hazard to persons exiting 
the vehicle and/or to first responders approaching the vehicle. NHTSA 
seeks comment on this additional requirement for TPRD discharge 
direction, and on the proposed discharge angles.
    NHTSA is proposing that the discharge direction from TPRDs and 
other pressure relief devices is evaluated through visual inspection. 
We seek comment on whether there is a more appropriate test.
d. Vehicle Exhaust System
    NHTSA is proposing to adopt GTR No. 13's vehicle exhaust system 
requirements. Similar to the previous requirements, elevated 
concentrations of hydrogen in the exhaust increases the risk of a fire. 
The GTR requires that the hydrogen concentration never exceed eight 
percent, and not exceed four percent for any three second moving 
average value of the hydrogen concentration.
    At an ambient temperature of 20 [deg]C, 4 percent by volume of 
hydrogen in air can ignite and propagate in the direction opposite 
gravity. However, the propagation is extremely weak and not sustained. 
At approximately eight percent hydrogen, ignition of hydrogen/air 
mixture can propagate in any direction regardless of ignition source 
location. Furthermore, tests demonstrated that as the hydrogen 
concentration approaches eight percent, exhaust becomes intermittently 
flammable, igniting in the presence of an ignition source, but 
extinguishing when the ignition source is removed.\104\ As a result, 
fire occurring at eight percent hydrogen concentration is small and 
fairly easy to extinguish. Therefore, limiting the hydrogen content of 
any instantaneous peak to eight percent limits the hazard to near the 
exhaust discharge point even if an ignition source is present.
---------------------------------------------------------------------------

    \104\ SAE Technical Report 2007-01-437. Development of Safety 
Criteria for Potentially Flammable Discharges from Hydrogen Fuel 
Cell Vehicles, Local Discharge Flammability--Flowing Exhaust. 
https://www.sae.org/publications/technical-papers/content/2007-01-0437/.
---------------------------------------------------------------------------

    NHTSA is proposing adopting the test requirement outlined in GTR 
No. 13. The test procedure would be conducted after the vehicle has 
been set to the ``on'' or ``run'' position for at least five minutes 
prior to testing. A hydrogen measuring device is placed in the center 
line of the exhaust within 100 mm from the external discharge point. 
The fuel system would undergo a shutdown, start-up, and idle operation 
to stimulate normal operating conditions. The measurement device used 
should have a response time of less than 0.3 seconds to ensure an 
accurate three second moving average calculation. Response times higher 
than 0.3 seconds could result in inaccurate data collection because the 
sensor may not have time to register the true concentration levels 
before recording each data point.
    The time period of three seconds for the rolling average ensures 
that the

[[Page 27537]]

space around the vehicle remains non-hazardous in the case of an idling 
vehicle in a closed garage. This is conservatively determined by 
assuming that a standard size vehicle purges the equivalent of a 250 kW 
(340 HP) fuel cell system. The power system output of a Toyota Mirai is 
182 HP. The time is then calculated for a nominal space occupied by a 
standard passenger vehicle (4.6 meters x 2.6 meters x 2.6 meters) to 
build up to 25 percent of the LFL, or one percent by volume in air. The 
time limit for this rolling-average situation is determined to be three 
seconds.\105\
---------------------------------------------------------------------------

    \105\ SAE 2578_201408. Recommended Practice for General Fuel 
Cell Vehicle Safety. Appendix C3. https://www.sae.org/standards/content/j2578_201408/.
---------------------------------------------------------------------------

e. Fuel System Leakage
    GTR No. 13 includes fuel system leakage requirements specifying no 
leakage from the fuel lines. A flammable or explosive condition can 
arise if hydrogen leaks from the fuel lines. However, the safety risk 
of a leak applies to the entire fuel system, not only to the fuel 
lines. As a result, NHTSA is proposing that the fuel system leakage 
requirement for no leakage apply to the entire hydrogen fuel system 
downstream of the shut-off valve, which includes the fuel lines and the 
fuel cell system. NHTSA is further proposing to define fuel lines to 
include all piping, tubing, joints, and any components such as flow 
controllers, valves, heat exchangers, and pressure regulators. From a 
safety standpoint, there is no difference between a leak coming from 
fuel line piping, and a leak coming from a valve, pressure regulator, 
or the fuel cell system itself. While NHTSA is proposing a strict no 
leakage standard, we are seeking comment on whether there is a safe 
level of hydrogen that may leak, and if so, what would be an objective 
leakage limit and how to accurately quantify hydrogen leakage from the 
fuel system.
    NHTSA is proposing to test this requirement using either a gas leak 
detector or leak detecting liquid (bubble test).\106\ NHTSA seeks 
comment if one of these tests is preferrable. NHTSA is also proposing 
that the test would be conducted with the fuel system at NWP after 
having been in the ``on'' or ``run'' position for at least five 
minutes. We believe these conditions produce an elevated likelihood of 
leakage. We seek comment on whether alternative conditions would better 
simulate realistic scenarios when downstream lines are more likely to 
leak.
---------------------------------------------------------------------------

    \106\ As discussed above, a bubble leak test is not an objective 
method for quantifying a leakage rate during the extreme temperature 
static gas pressure leak/permeation test. However, NHTSA is 
proposing a strict no leakage requirement for the test for fuel line 
leakage. This requirement does not require that the leak be 
quantified, and therefore, a bubble test may be used to evaluate 
this requirement. Any observed bubble would indicate leakage and 
constitute a failure of the test for fuel line leakage.
---------------------------------------------------------------------------

f. Protection Against Flammable Conditions
    The final component of GTR No. 13's safety measures for the fuel 
system during normal use is ensuring that the enclosed and semi-
enclosed spaces of the vehicle do not accumulate potentially dangerous 
concentrations of hydrogen.
    The agency proposes requiring a visual warning within 10 seconds in 
the event that the hydrogen concentration in an enclosed or semi-
enclosed space exceeds 3.0 percent (75 percent of the LFL). This 
concentration limit for the warning is selected because while 3.0 
percent hydrogen is below the LFL, and is therefore inflammable, 
accumulation of hydrogen to 3.0 percent indicates the presence of a 
leak and the potential for continued hydrogen accumulation beyond the 
LFL. Additionally, in accordance with GTR No. 13, we propose requiring 
the shut-off valve to close within 10 seconds if at any point the 
concentration in an enclosed or semi-enclosed space exceeds 4.0 percent 
(the LFL). Closure of the shut-off valve isolates the CHSS and ensures 
hydrogen cannot accumulate beyond the LFL. The details of the warning 
itself are discussed below in the following section.
    GTR No. 13 provides two options for evaluating this requirement. 
The first option is to use a remote-controlled release of hydrogen to 
simulate a leak, along with laboratory-installed hydrogen concentration 
detectors in the enclosed or semi-enclosed spaces. The laboratory-
installed hydrogen concentration detectors are used to verify that the 
required warning and shut-off valve closure occur at the appropriate 
hydrogen concentrations in the enclosed or semi-enclosed spaces. GTR 
No. 13 allows for the remote-controlled release of hydrogen to be drawn 
from the vehicle's own CHSS. Therefore, by using this option, it is 
possible for a vehicle to meet the requirements without a built-in 
hydrogen concentration detector. This is accomplished by the vehicle 
monitoring hydrogen outflow from its CHSS. The vehicle can then trigger 
the required warning and shut-off valve closure if significant hydrogen 
outflow from the CHSS is detected that is not accounted for by fuel 
cell hydrogen consumption.
    The second option for evaluating the requirement is to use an 
induction hose and a cover to apply hydrogen test gas directly to the 
vehicle's built-in hydrogen concentration detector(s) within the 
enclosed or semi-enclosed spaces. Test gas with a hydrogen 
concentration of 3.0 to 4.0 percent is used to verify the warning, and 
test gas with a hydrogen concentration of 4.0 to 6.0 percent is used to 
verify the closure of the shut-off valve. The warning and shut-off 
valve closure must occur within 10 seconds of applying the respective 
test gas to the detector. The warning is verified by visual inspection, 
and the shut-off valve closure can be verified by monitoring the 
electric power to the shut-off valve or by the sound of the shut-off 
valve activation.
    This second option indirectly requires the presence of at least one 
hydrogen concentration detector in the enclosed or semi-enclosed spaces 
that can detect the hydrogen test gas and trigger the warning and shut-
off valve closure at appropriate hydrogen concentration levels. NHTSA 
is proposing this second option as the only test method in FMVSS No. 
307, which would thereby require each vehicle to have at least one 
built-in hydrogen concentration detector. NHTSA seeks comment on 
requiring built-in hydrogen concentration detectors and seeks comment 
on the reliability of the required warning and shut-off valve closure 
for vehicles that do not have built-in hydrogen concentration 
detectors.
    In addition to the above requirement regarding a warning and shut-
off valve closure, GTR No. 13 includes a requirement that any failure 
downstream of the main hydrogen shut off valve shall not result in any 
level of hydrogen concentration in the passenger compartment. This 
requirement is evaluated by applying a remote-controlled release of 
hydrogen simulating a leak in the fuel system, along with laboratory-
installed hydrogen concertation detectors in the passenger compartment. 
After remote release of hydrogen, GTR No. 13 requires that the hydrogen 
concentration in the passenger compartment not exceed 1.0 percent. The 
number, location, and flow capacity of the release points for the 
remote-controlled release of hydrogen are defined by the vehicle 
manufacturer.
    A concentration of 1.0 percent hydrogen is inflammable at only 25 
percent of the LFL for hydrogen. NHTSA has determined there is no need 
to apply such a stringent concentration limit in the passenger 
compartment. NHTSA is instead proposing that the

[[Page 27538]]

remote-controlled release of hydrogen shall not result in a hydrogen 
concentration exceeding 3.0 percent in the enclosed or semi-enclosed 
spaces of the vehicle (including the passenger compartment). NHTSA 
believes that this is a more balanced requirement that ensures there is 
no accumulation of hydrogen too near the LFL in any enclosed or semi-
enclosed spaces of the vehicle. NHTSA seeks comment on this requirement 
and on specific test procedures for initiating a remote-controlled 
release of hydrogen in a vehicle.
    To evaluate this requirement, NHTSA proposes that a hydrogen 
concentration detector be installed in any enclosed or semi-enclosed 
space where hydrogen may accumulate from the simulated hydrogen 
release. After the remote-controlled release of hydrogen, the hydrogen 
concentration would be measured continuously using the laboratory-
installed hydrogen concertation detector. The test would be completed 
five minutes after initiating the simulated leak or when the hydrogen 
concentration does not change for three minutes, whichever is longer. 
Five minutes is selected as the minimum time for monitoring the 
hydrogen concentration because five minutes is generally considered a 
sufficient time frame for vehicle occupants to evacuate in the event of 
an emergency.
    The test procedures in this section are intended to work together 
to ensure safety. Primary protection is provided by ensuring that 
hydrogen cannot accumulate as a result of a leak beyond a 3.0 percent 
concentration in the enclosed or semi-enclosed spaces. This ensures 
that there is no potential for ignition to occur due to hydrogen 
leakage. The requirement for the visual warning and shut-off valve 
closure serves as a secondary measure in preventing a flammable 
condition from occurring in the event of a failure resulting in an 
accumulation of hydrogen.
    The proposed test procedures in this section would be conducted 
without the influence of any wind. NHTSA seeks comment on providing 
more specific wind protection requirements and seeks comment on 
limiting the maximum wind velocity during testing to 2.24 meters/second 
as in FMVSS No. 304.\107\
---------------------------------------------------------------------------

    \107\ FMVSS No. 304, ``Compressed natural gas fuel container 
integrity.'' https://www.ecfr.gov/current/title-49/subtitle-B/chapter-V/part-571/subpart-B/section-571.304.
---------------------------------------------------------------------------

g. Warning for Elevated Hydrogen Concentration
    While the aim of the GTR and this proposal is to set safety 
requirements that prevent hydrogen from leaking and causing hazardous 
conditions, if hydrogen manages to accumulate to the LFL of 4.0 
percent, there is a risk of a fire or explosion occurring. As discussed 
above, NHTSA is proposing requiring a telltale \108\ warning when 
hydrogen concentration exceeds 3.0 percent in the enclosed or semi-
enclosed spaces of the vehicle. Given the serious threat posed by 
elevated hydrogen levels in the passenger compartment, NHTSA is 
proposing the visual warning be red in color and remain illuminated 
while the vehicle is in operation with hydrogen concentration levels 
exceeding 3.0 percent in enclosed or semi-enclosed spaces of the 
vehicle. The visual warning must be in clear view of the driver. For a 
vehicle with automated driving systems and without manually-operated 
driving controls, the visual warning must be in clear view of all the 
front seat occupants. NHTSA seeks comment on whether the warning should 
be in clear view of all occupants, including occupants in rear seating 
positions, in vehicles with automated driving systems. NHTSA also seeks 
comment on whether an auditory warning be required when hydrogen 
concentration exceeds 3.0 percent in the enclosed or semi-enclosed 
spaces of the vehicle.
---------------------------------------------------------------------------

    \108\ A telltale is an optical signal that, when illuminated, 
indicates the actuation of a device, a correct or improper 
functioning or condition, or a failure to function.
---------------------------------------------------------------------------

    NHTSA is also proposing that a telltale be activated if the 
hydrogen warning system malfunctions, such as in the case of a circuit 
disconnection, short circuit, sensor fault, or other system failure. 
NHTSA proposes that when the telltale activates for these circumstances 
that it illuminates as yellow to distinguish a malfunction of the 
warning system from that of excess hydrogen concentration.
2. Post-Crash Fuel System Integrity
    The second half of proposed FMVSS No. 307 are post-crash 
requirements for the fuel system. After a vehicle crash, there is a 
high risk of hydrogen escaping from the CHSS and other parts of the 
vehicle fuel system due to structural damage. The primary safety 
strategy applied in GTR No. 13 is to ensure the proper containment of 
hydrogen in the container and the fuel system after a crash has 
occurred.
    In accordance with GTR No. 13, NHTSA is proposing that the post-
crash requirements only apply to passenger cars, multipurpose passenger 
vehicles, trucks and buses with a GVWR less than or equal to 4,536 kg 
(10,000 pounds) and to all school buses, that use hydrogen fuel for 
propulsion power. NHTSA is not proposing that these post-crash 
requirements apply to all heavy vehicles with a GVWR greater than 4,536 
kg (10,000 pounds). We are tentatively making this decision because 
there is not a comparable crash test for heavy vehicles to conduct the 
tests necessary for compliance assessment. NHTSA seeks comment on 
whether heavy vehicles should be subject to these proposed post-crash 
requirements and if so, what crash tests should NHTSA conduct on 
heavier vehicles.
    During Phase I of GTR No. 13, the IWG decided not to attempt 
creating a uniform crash test and instead provided the option to 
Contracting Parties to determine the appropriate test based on their 
existing standards. NHTSA is proposing to use the crash tests 
equivalent to those applied to conventionally fueled vehicles in 
accordance with FMVSS No. 301. For light vehicles with a GVWR under 
4,536 kg, these crash tests include an 80 kilometers per hour (km/h) 
(~50 miles per hour (mph)) impact of a rigid barrier into the rear of 
the vehicle, a 48 km/h (~30 mph) frontal crash test into a rigid 
barrier, and a 53 km/h (~33 mph) impact of a moving deformable barrier 
into the side of the vehicle. For school buses with a GVWR greater than 
or equal to 4,536 kg, the crash test is a moving contoured barrier 
impact at 48 km/h. NHTSA has determined that it is appropriate to apply 
equivalent crash tests to hydrogen vehicles as those for conventionally 
fueled vehicles. NHTSA seeks comment on whether there are alternative 
crash tests that should be used for the forthcoming proposed 
regulations.
    NHTSA is proposing that there be no fire during the test, and that 
vehicles meet three additional post-crash requirements described by GTR 
No. 13. These three requirements echo the same safety goals of the 
first half of FMVSS No. 307. They are designed to prevent CHSS bursts, 
the creation of additional hazards caused by hydrogen leakage, and to 
protect occupants.
    The first proposed requirement is based on FMVSS No. 301. FMVSS No. 
301 S5.5 and S5.6 specifies that the total amount of allowable energy 
loss for gasoline fuel from impact through the 60-minute interval after 
motion has ceased is 72,590 kiloJoules (KJ). This total amount of 
allowable energy loss

[[Page 27539]]

when applied to hydrogen and its energy density, equates to 606 grams 
of hydrogen loss. From the total allowable hydrogen mass leakage of 606 
g, the total allowable volumetric leakage, with a reference temperature 
of 15 [deg]C, during 60-minute interval after impact can be calculated 
as follows:
[GRAPHIC] [TIFF OMITTED] TP17AP24.014

where 2.0159 gram/mole is the molar weight of a hydrogen molecule and 
22.41 liter/mole is the molar volume of hydrogen at standard 
conditions, and the factor 288/273 adjusts the calculation for a 
temperature of 15 [deg]C. Therefore, the allowable volumetric flow rate 
of hydrogen after impact through the 60-minute interval after impact 
has ceased is: 7107 NL/60 minutes = 118 NL/minute.\109\
---------------------------------------------------------------------------

    \109\ For additional information, see the associated technical 
document ``Post-crash hydrogen leakage limit for FMVSS No. 307.pdf'' 
in the docket of this NPRM. Reference: SAE 2578_201408. Recommended 
Practice for General Fuel Cell Vehicle Safety. Appendix A.1.1.
---------------------------------------------------------------------------

    The volumetric flow of hydrogen gas leakage from the CHSS must not 
exceed an average of 118 normal liters per minute (NL/min) from the 
time of vehicle impact through a time interval [Delta]t of at least 60-
minutes after impact. This leakage limit of 118 NL/min is equivalent to 
a total allowable mass leakage of 606 grams of hydrogen gas in 60 
minutes.
    The volumetric leak rate of hydrogen post-crash is determined as a 
function of the pressure in the container before and after the crash 
test. The interval [Delta]t is at least 60 minutes after impact to 
provide time for any leaks to reduce the CHSS pressure by an accurately 
measurable amount. For a pressure drop to be measured accurately by a 
sensor, the drop should be at least 5 percent of the pressure sensor's 
full range. However, for a CHSS larger than about 400 liters, 60 
minutes may be insufficient for a leak exceeding the leakage limit to 
result in 5 percent of full range pressure drop. This is due to the 
non-linear relationship between the density and pressure of hydrogen 
and helium gas. Therefore, the variables of CHSS volume, sensor range, 
and CHSS NWP need to be considered when determining the time interval 
[Delta]t. GTR No. 13 provides an equation to increase [Delta]t as 
necessary to ensure an accurate pressure drop measurement as described 
in the following:
    The time interval after impact, [Delta]t, shall be the greater of:
    (1) 60 minutes; or
    (2) [Delta]t = VCHSS x NWP/1000 x ((-0.027 x NWP + 4) x 
Rs-0.21)-1.7 x Rs, where Rs = 
Ps/NWP, Ps is the pressure range of the pressure 
sensor (MPa), NWP is the Nominal Working Pressure (MPa), and 
VCHSS is the volume of the CHSS (L).
    Helium may be used in place of hydrogen during crash-testing, as a 
safer alternative to hydrogen, with the corresponding calculation 
modifications discussed below. Due to the differing physical properties 
of hydrogen and helium gas, the allowable leakage limit for helium is 
75 percent of the 118 NL/min allowed for hydrogen. This corresponds to 
a helium leakage limit of 88.5 NL/min.
    The second requirement ensures hydrogen does not accumulate in the 
enclosed or semi-enclosed spaces which could present a post-crash 
hazard. This hydrogen concentration limit is set to four percent by 
volume (for helium, this corresponds to a concentration of three 
percent by volume). This requirement is satisfied if the CHSS shut-off 
valve(s) are confirmed to be closed within five seconds of the crash 
and there is no hydrogen leakage from the CHSS. If the shut-off valve 
has closed and the leakage from the CHSS is no more than 118 NL/min, it 
is not likely for hydrogen to accumulate in enclosed or semi-enclosed 
spaces.
    For the purpose of measuring the hydrogen concentration, GTR No. 13 
specifies that data from the sensors shall be collected at least every 
five seconds and continue for a period of 60 minutes. GTR No. 13 also 
discusses filtering of the data to provide smoothing of the data, but 
is unclear about the exact data filtration method to be used. NHTSA 
proposes using a three data point rolling average for filtering the 
data steam. Since a data point will collected at least every five 
seconds, this rolling average will be, at most, a 15-second rolling 
average. NHTSA seeks comment on this proposed data filtration method.
    The third requirement in GTR No. 13 that NHTSA is proposing is 
requiring that the container(s) remains attached to the vehicle by at 
least one component anchorage, bracket, or any structure that transfers 
loads from the device to the vehicle structure. This ensures that a 
container is not separated from the vehicle during a crash. Most 
containers rely at least partially on the vehicle for protection and 
shielding. As a result, the container cannot be allowed to separate 
from the vehicle during a crash. This requirement is evaluated by 
visual inspection of the container attachment points.
    NHTSA will evaluate the presence of vehicle fire by visual 
inspection for the duration of the test, which includes the time needed 
to determine fuel leakage from the CHSS.
    GTR No. 13 specifies that each contracting party maintain its 
existing national crash tests (frontal, side, rear and rollover) for 
post-crash evaluation. However, the crash tests specified in FMVSS No. 
301 and post-crash requirements are only intended for light vehicles. 
In GTR No. 13 Phase 1, the scope of the regulation was confined to 
light vehicles under 4,536 kg (10,000 pounds). Since the scope of GTR 
No. 13 was expanded under Phase 2 to cover heavy vehicles, the IWG 
considered different alternative options to replace full vehicle crash 
tests for heavy vehicles. However, none of these alternative options 
for heavy vehicles were implemented into GTR No. 13 Phase 2.
    Under Phase 2, the European Union proposed sled tests to replace 
full-scale crash testing for light and heavy vehicles. The sled test 
proposal involved applying several acceleration pulses to CHSS mounted 
on a sled with attachment structures similar to those on a 
corresponding hydrogen vehicle. The acceleration pulses of three 
separate sled tests simulate a peak of 10 g acceleration in the forward 
and rearward direction of travel, and 8 g in the direction 
perpendicular to the direction of travel.
    NHTSA questioned the safety need for this sled test during the IWG 
discussions on the European Union proposal. The proposed sled test's 
only performance requirement is for the CHSS to remain attached to the 
vehicle by at least one anchorage point. In the U.S., there is no 
corresponding sled test for CNG heavy vehicles, and NHTSA is not aware 
of any safety issues related to anchorage failures in CNG heavy 
vehicles. Therefore, NHTSA questions the safety relevance of a sled 
test for hydrogen-fueled heavy vehicles. NHTSA seeks comment on the 
safety need for a heavy vehicle sled test.
    GTR No. 13 Phase 2 also considered the possibility of an impact 
test for heavy vehicles in place of a full-scale vehicle crash test. 
The potential impact

[[Page 27540]]

test would be conducted on the CHSS along with relevant vehicle-
specific shielding, panels and/or structural supports on the vehicle. 
It would thereby simulate a vehicle-level crash test without destroying 
an entire vehicle. Since the manufacturer is most familiar with the 
protective design features of their vehicle, the manufacturer would 
specify which shields, panels, and protective structures to include in 
the impact test. After the impact, the CHSS would be required to meet 
the same leakage limit described above for light vehicles. The 
concentration limit in enclosed spaces and the container displacement 
requirement would not apply because the impact test would not involve a 
full vehicle. NHTSA seeks input and comment with supporting data on 
implementing a possible alternative heavy vehicle impact test for the 
CHSS.
    NHTSA seeks comment on the possibility of including a moving 
contoured barrier impact test on heavy vehicles (other than school 
buses) in accordance with S6.5 of FMVSS No. 301. This test would allow 
for a moving contoured barrier to impact the CHSS along with shields, 
panels, and protective structures specified by the manufacturer at any 
angle. Such an impact test would evaluate the ability of side-saddle 
mounted CHSS to withstand light vehicle impacts and meet the allowable 
leakage limits.

C. Lead-Time

    NHTSA is proposing that the rule take effect the September 1st the 
year after the final rule is published. As discussed above, NHTSA 
believes that the requirements in the proposal are closely aligned to 
current industry practice and manufacturers will not require an 
extended lead-time. NHTSA seeks comment on whether any of the 
requirements necessitate additional lead-time.

V. Rulmaking Analyses and Notices

Executive Order 12866, Executive Order 13563, and DOT Regulatory 
Policies and Procedures

    We have considered the potential impact of this proposed rule under 
Executive Order 12866, Executive Order 13563, and DOT Order 2100.6A. 
This NPRM is nonsignificant under E.O. 12866 and was not reviewed by 
the Office of Management and Budget. It is also not considered ``of 
special note to the Department'' under DOT Order 2100.6A, Rulemaking 
and Guidance Procedures.
    Today, there are only two publicly available vehicle models that 
may be affected by the proposed rule, which collectively equal less 
than 5,000 vehicles sold per model year. Most manufacturers and vehicle 
lines currently in production would be unaffected by this proposal. Of 
those vehicles that would be covered by today's proposed standards, we 
expect the compliance cost to be minimal. As discussed earlier, the few 
manufacturers that already offer hydrogen vehicles in the marketplace 
already take safety precautions to attempt to emulate the safety of 
conventional and battery electric vehicles, and adhere to the industry 
guidelines that informed the creation of GTR No. 13. As today's 
proposed rule is intended to coalesce industry practice and future 
designs through harmonized regulations, we also do not expect that the 
proposal would pose a significant cost to those manufacturers, nor for 
those manufacturers that may be planning to enter the market.
    Given NHTSA is proposing these standards during the early 
development of hydrogen vehicles, there is no baseline to compare 
today's proposal against. While we anticipate the regulations, if 
adopted, would promote safer hydrogen vehicles, we cannot quantify this 
benefit with any degree of certainty, especially given we cannot 
forecast what the industry would look like in the absence of our 
proposed standard. Furthermore, most of the safety benefits that would 
accrue to this rule, would only be realized when hydrogen vehicles 
become more prevalent and the net present value of these costs and 
benefits would be minimal.
    We seek comment on all of these assumptions and ask commenters, if 
they do disagree with this assessment, to identify which portions of 
the proposal may accrue costs and identify a methodology for 
quantifying the potential costs and benefits of this proposal.

Regulatory Flexibility Act

    Pursuant to the Regulatory Flexibility Act (5 U.S.C. 601 et seq., 
as amended by the Small Business Regulatory Enforcement Fairness Act 
(SBREFA) of 1996), whenever an agency is required to publish a notice 
of proposed rulemaking or final rule, it must prepare and make 
available for public comment a regulatory flexibility analysis that 
describes the effect of the rule on small entities (i.e., small 
businesses, small organizations, and small governmental jurisdictions). 
The Small Business Administration's regulations at 13 CFR part 121 
define a small business, in part, as a business entity ``which operates 
primarily within the United States.'' (13 CFR 121.105(a)(1)). No 
regulatory flexibility analysis is required if the head of an agency 
certifies the proposed or final rule will not have a significant 
economic impact on a substantial number of small entities. SBREFA 
amended the Regulatory Flexibility Act to require Federal agencies to 
provide a statement of the factual basis for certifying that a proposed 
or final rule will not have a significant economic impact on a 
substantial number of small entities.
    I certify that the proposed standards would not have a significant 
impact on a substantial number of small entities. This proposed action 
would create FMVSS Nos. 307 and 308 to establish minimum safety 
requirements for the CHSS and fuel system integrity of hydrogen 
vehicles. FMVSS Nos. 307 and 308 are vehicle standards. We anticipate 
any burdens of the standard will fall onto manufacturers of hydrogen 
vehicles. NHTSA is unaware of any small entities that are planning to 
manufacture hydrogen vehicles. Furthermore, NHTSA is proposing to adopt 
standards similar to those already in place across industry. Thus, we 
anticipate the impacts of this NPRM on all manufacturers to be minimal 
regardless of manufacturer size.

Executive Order 13132

    NHTSA has examined this proposed rule pursuant to Executive Order 
13132 (64 FR 43255, August 10, 1999) and concluded that no additional 
consultation with States, local governments or their representatives is 
mandated beyond the rulemaking process. The Agency has concluded that 
this action would not have ``federalism implications'' because it would 
not have ``substantial direct effects on States, on the relationship 
between the national government and the States, or on the distribution 
of power and responsibilities among the various levels of government,'' 
as specified in section 1 of the Executive order. This proposed rule 
would apply to motor vehicle manufacturers. Further, no State has 
adopted requirements regulating the CHSS or fuel integrity of hydrogen 
powered vehicles. Thus, Executive Order 13132 is not implicated and 
consultation with State and local officials is not required.
    NHTSA rules can preempt in two ways. First, the National Traffic 
and Motor Vehicle Safety Act contains an express preemption provision: 
When a motor vehicle safety standard is in effect under this chapter, a 
State or a political subdivision of a State may prescribe or continue 
in effect a standard applicable

[[Page 27541]]

to the same aspect of performance of a motor vehicle or motor vehicle 
equipment only if the standard is identical to the standard prescribed 
under this chapter. 49 U.S.C. 30103(b)(1). It is this statutory command 
by Congress that preempts any non-identical State legislative and 
administrative law addressing the same aspect of performance.
    The express preemption provision described above is subject to a 
savings clause under which compliance with a motor vehicle safety 
standard prescribed under this chapter does not exempt a person from 
liability at common law. 49 U.S.C. 30103(e). Pursuant to this 
provision, State common law tort causes of action against motor vehicle 
manufacturers that might otherwise be preempted by the express 
preemption provision are generally preserved.
    However, the Supreme Court has recognized the possibility, in some 
instances, of implied preemption of such State common law tort causes 
of action by virtue of NHTSA's rules, even if not expressly preempted. 
This second way that NHTSA rules can preempt is dependent upon there 
being an actual conflict between an FMVSS and the higher standard that 
would effectively be imposed on motor vehicle manufacturers if someone 
obtained a State common law tort judgment against the manufacturer, 
notwithstanding the manufacturer's compliance with the NHTSA standard. 
Because most NHTSA standards established by an FMVSS are minimum 
standards, a State common law tort cause of action that seeks to impose 
a higher standard on motor vehicle manufacturers will generally not be 
preempted. However, if and when such a conflict does exist--for 
example, when the standard at issue is both a minimum and a maximum 
standard--the State common law tort cause of action is impliedly 
preempted. See Geier v. American Honda Motor Co., 529 U.S. 861 (2000).
    Pursuant to Executive Order 13132 and 12988, NHTSA has considered 
whether this proposed rule could or should preempt State common law 
causes of action. The agency's ability to announce its conclusion 
regarding the preemptive effect of one of its rules reduces the 
likelihood that preemption will be an issue in any subsequent tort 
litigation. To this end, the agency has examined the nature (i.e., the 
language and structure of the regulatory text) and objectives of this 
proposed rule and finds that this rule, like many NHTSA rules, would 
prescribe only a minimum safety standard. As such, NHTSA does not 
intend this NPRM to preempt State tort law that would effectively 
impose a higher standard on motor vehicle manufacturers rule. 
Establishment of a higher standard by means of State tort law will not 
conflict with the minimum standard adopted here. Without any conflict, 
there could not be any implied preemption of a State common law tort 
cause of action.

Executive Order 12988 (Civil Justice Reform)

    When promulgating a regulation, Executive Order 12988 specifically 
requires that the agency must make every reasonable effort to ensure 
that the regulation, as appropriate: (1) Specifies in clear language 
the preemptive effect; (2) specifies in clear language the effect on 
existing Federal law or regulation, including all provisions repealed, 
circumscribed, displaced, impaired, or modified; (3) provides a clear 
legal standard for affected conduct rather than a general standard, 
while promoting simplification and burden reduction; (4) specifies in 
clear language the retroactive effect; (5) specifies whether 
administrative proceedings are to be required before parties may file 
suit in court; (6) explicitly or implicitly defines key terms; and (7) 
addresses other important issues affecting clarity and general 
draftsmanship of regulations.
    Pursuant to this Order, NHTSA notes as follows. The preemptive 
effect of this proposed rule is discussed above in connection with E.O. 
13132. NHTSA notes further that there is no requirement that 
individuals submit a petition for reconsideration or pursue other 
administrative proceeding before they may file suit in court.

Executive Order 13609 (Promoting International Regulatory Cooperation)

    Executive Order 13609, ``Promoting International Regulatory 
Cooperation,'' promotes international regulatory cooperation to meet 
shared challenges involving health, safety, labor, security, 
environmental, and other issues and to reduce, eliminate, or prevent 
unnecessary differences in regulatory requirements.
    Today's proposed rule adopts the technical requirements of GTR 
No.13, a technical standard for hydrogen vehicles adopted by the United 
Nations Economic Commission for Europe (UNECE) World Forum for 
Harmonization of Vehicle Regulations (WP.29). As a Contracting Party 
who voted in favor of GTR No. 13, NHTSA is obligated to initiate 
rulemaking to incorporate safety requirements and options specified in 
GTR. While today's proposal does contain some differences from GTR No. 
13 to reflect U.S. law, they are consistent with the regulatory process 
envisioned and encourage from the outset of GTR No. 13. NHTSA will 
continue to participate with the international community on GTR No. 13, 
and evaluate further amendments on their merits as they are adopted by 
WP.29.
    NHTSA has analyzed this proposed rule under the policies and agency 
responsibilities of Executive Order 13609, and has determined this 
proposal would have no effect on international regulatory cooperation.

National Environmental Policy Act

    NHTSA has analyzed this NPRM for the purposes of the National 
Environmental Policy Act. The agency has determined that implementation 
of this action would not have an adverse impact on the quality of the 
human environment. As described earlier, the proposal would coalesce 
industry practice into uniformed regulations and harmonize with 
international standards. NHTSA expects the changes to existing vehicles 
would be minimal, and mitigating the hazards associated with hydrogen 
leakage and discharge from the fuel system, as well as instituting 
post-crash restrictions on hydrogen leakage, concentration in enclosed 
spaces, container displacement, and fire, would result in a public 
health and safety benefit.
    For these reasons, the agency has determined that implementation of 
this action would not have any adverse impact on the quality of the 
human environment.

Paperwork Reduction Act

    Under the procedures established by the Paperwork Reduction Act of 
1995 (PRA) (44 U.S.C. 3501, et seq.), Federal agencies must obtain 
approval from the OMB for each collection of information they conduct, 
sponsor, or require through regulations. A person is not required to 
respond to a collection of information by a Federal agency unless the 
collection displays a valid OMB control number. The Information 
Collection Request (ICR) for a revision of a previously approved 
collection described below will be forwarded to OMB for review and 
comment. In compliance with these requirements, NHTSA asks for public 
comments on the following proposed collection of information for which 
the agency is seeking approval from OMB. In this NPRM, we are proposing 
a revision to an existing OMB approved collection, OMB Clearance No. 
2127-0512, Consolidated Labeling Requirements for Motor Vehicles 
(except the VIN). We are soliciting public comment for the

[[Page 27542]]

proposed addition of labeling requirements for FMVSS Nos. 307 and 308.
    Title: Consolidated Labeling Requirements for Motor Vehicles 
(except the VIN).
    OMB Control Number: OMB Control No. 2127-0512.
    Type of Request: Revision of a previously approved collection.
    Type of Review Requested: Regular.
    Requested Expiration Date of Approval: 3 years from the date of 
approval.
    Summary of the Collection of Information: FMVSS No. 307 specifies 
requirements for the integrity of motor vehicle fuel systems using 
compressed hydrogen as a fuel source. Each hydrogen vehicle must have a 
permanent label which lists the fuel type, service pressure, and a 
statement directing vehicle users/operators to instructions for 
inspection and service life of the fuel container. FMVSS No. 308 
specifies requirements for the integrity of compressed hydrogen storage 
systems (CHSS). Each hydrogen container must have a permanent label 
containing manufacturer contact information, the container serial 
number, manufacturing date, date of removal from service, and 
applicable BPO burst pressure. If the proposed requirements 
are made final, we will submit a request for OMB clearance of the 
proposed collection of information and seek clearance prior to the 
effective date of the final rule.
    Description of the likely respondents: Vehicle manufacturers.
    Estimated Number of Respondents: 20.
    Estimated Total Annual Burden Hours: $8,468.
    It is estimated that vehicle manufacturers will provide labels on 
10 different hydrogen vehicle models. Since manufacturers have provided 
CNG vehicles with similar required labels for many years, it is 
estimated that manufacturers will have a generalized label template 
which only requires minor adjustments for hydrogen and then population 
with the required information. There is an annual 1.0 hour burden for 
manufacturers to have a Mechanical Drafter put the correct information 
into a label template to create a model specific label. The annual 
burden for this label creation is 10 hours (10 CNG vehicle model labels 
* 1 hour per model label) and $404 (10 CNG vehicle model labels * 1 
hour per model label * $28.37 labor rate per hour / 70.3% of labor rate 
as total wage compensation). Manufacturers will also bear a cost burden 
of $1,884 (2,850 hydrogen vehicles * $0.73 per label) for the required 
labels to be attached to the CNG vehicles. The combined total annual 
burden to vehicle manufacturers from the requirements to have the 
specified label text on hydrogen vehicles is 10 hours and $2,288. These 
hour and cost burdens represent a new addition to this information 
collection request.
    It is estimated that vehicle manufacturers will provide labels on 
10 different hydrogen container models. Since manufacturers have 
provided CNG containers with similar labels for many years, it is 
estimated that manufacturers will have a generalized label template 
which only requires only minor adjustments for hydrogen and then 
population with their current contact information, the container serial 
number, manufacturing date, date of removal from service, and 
applicable BPO burst pressure. There is an annual 1.0 hour 
burden for manufacturers to have a Mechanical Drafter put the correct 
information into a label template to create a model specific label. The 
annual burden for this label creation is 10 hours (10 hydrogen 
container model labels * 1.0 hours per model label) and $404 (10 
hydrogen container models labels * 1.0 hours per model label * $28.37 
labor rate per hour / 70.3% of labor rate as total wage compensation). 
Manufacturers will also bear a cost burden of $5,776 (7,910 hydrogen 
containers * $0.730 per label) for the required labels to be attached 
to the hydrogen containers. The combined total annual burden to vehicle 
manufacturers from the requirements to have the specified label text on 
hydrogen containers is 10 hours and $6,180. These hour and cost burdens 
represent a new addition to this information collection request.
    Public Comments Invited: You are asked to comment on any aspects of 
this information collection, including (a) whether the proposed 
collection of information is necessary for the proper performance of 
the functions of the Department, including whether the information will 
have practical utility; (b) the accuracy of the Department's estimate 
of the burden of the proposed information collection; (c) ways to 
enhance the quality, utility and clarity of the information to be 
collected; and (d) ways to minimize the burden of the collection of 
information on respondents, including the use of automated collection 
techniques or other forms of information technology.
    Please submit any comments, identified by the docket number in the 
heading of this document, by the methods described in the ADDRESSES 
section of this document to NHTSA and OMB. Although comments may be 
submitted during the entire comment period, comments received within 30 
days of publication are most useful.

National Technology Transfer and Advancement Act

    Under the National Technology Transfer and Advancement Act of 1995 
(NTTAA) (Pub. L. 104) Section 12(d) of the National Technology Transfer 
and Advancement Act (NTTAA) requires NHTSA to evaluate and use existing 
voluntary consensus standards in its regulatory activities unless doing 
so would be inconsistent with applicable law (e.g., the statutory 
provisions regarding NHTSA's vehicle safety authority) or otherwise 
impractical. Voluntary consensus standards are technical standards 
developed or adopted by voluntary consensus standards bodies. Technical 
standards are defined by the NTTAA as ``performance-based or design-
specific technical specification and related management systems 
practices.'' They pertain to ``products and processes, such as size, 
strength, or technical performance of a product, process or material.''
    Examples of organizations generally regarded as voluntary consensus 
standards bodies include ASTM International, the Society of Automotive 
Engineers (SAE), and the American National Standards Institute (ANSI). 
If NHTSA does not use available and potentially applicable voluntary 
consensus standards, we are required by the Act to provide Congress, 
through OMB, an explanation of the reasons for not using such 
standards.
    Today's proposed standards are consistent with voluntary standards 
cited above such as SAEJ2578_201408, SAEJ2579_201806, HPRD-1 2021, and 
HGV 3.1 2022.
    We are proposing to incorporate by reference ISO 6270-2:2017, 
Determination of resistance to humidity, Second Edition, November 2017 
into Sec.  571.308. ISO 6270-2:2017 specifies methods for assessing the 
resistance of materials to humidity by focusing on how materials behave 
when exposed to high humidity. The standard provides detailed 
procedures for conducting tests in controlled environments where 
humidity is the primary variable. These environments simulate 
conditions that materials might encounter during their lifecycle, 
thereby offering insights into potential degradation processes such as 
corrosion, mold growth, or other forms of moisture-induced damage. The 
standard sets out guidelines for preparing test specimens, the 
conditions

[[Page 27543]]

under which the tests should be conducted, and the criteria for 
evaluating the results, including specifying the temperature, humidity 
levels, and duration of exposure necessary to evaluate a material's 
resistance to humidity. ISO 6270-2:2017 is available on the ISO web 
page for purchase and a copy is available for review at NHTSA's 
headquarters in Washington, DC through the means identified in 
ADDRESSES.\110\
---------------------------------------------------------------------------

    \110\ See, https://www.iso.org/standard/64858.html.
---------------------------------------------------------------------------

    We are proposing to incorporate by reference ASTM D1193-06, 
Standard Specification for Reagent Water, approved March 22, 2018 into 
Sec.  571.308. ASTM D1193-06 is a standard that outlines specifications 
for reagent water quality across various scientific and analytical 
applications. This standard defines the requirements for the purity of 
water used in laboratories, ensuring that experiments and tests are not 
compromised by water impurities that could affect the results. It 
categorizes water into different types (I, II, III, and IV), each with 
specific purity levels suitable for particular applications, ranging 
from high-precision analytical work to general laboratory procedures. 
The standard details methods for testing and validating the quality of 
water, including the acceptable limits for contaminants like organic 
and inorganic compounds, as well as microbial content. It also provides 
guidelines for the storage and handling of reagent water to maintain 
its purity. ASTM D1193-06 is available on the ASTM's online reading 
room and a copy is available for review at NHTSA's headquarters in 
Washington, DC through the means identified in ADDRESSES.\111\
---------------------------------------------------------------------------

    \111\ See, https://www.astm.org/d1193-06r18.html.
---------------------------------------------------------------------------

    This proposal to adopt GTR No. 13 is consistent with the goals of 
the NTTAA. This NPRM proposes to adopt a global consensus standard. The 
GTR was developed by a global regulatory body and is designed to 
increase global harmonization of differing vehicle standards. The GTR 
leverages the expertise of governments in developing safety 
requirements for hydrogen fueled vehicles. NHTSA's consideration of GTR 
No. 13 accords with the principles of NTTAA as NHTSA's consideration of 
an established, proven regulation has reduced the need for NHTSA to 
expend significant agency resources on the same safety need addressed 
by GTR No. 13.

Unfunded Mandates Reform Act

    Section 202 of the Unfunded Mandates Reform Act of 1995 (UMRA) 
requires Federal agencies to prepare a written assessment of the costs, 
benefits, and other effects of proposed or final rules that include a 
Federal mandate likely to result in the expenditure by State, local, or 
Tribal governments, in the aggregate, or by the private sector, of more 
than $100 million annually (adjusted for inflation with base year of 
1995). Adjusting this amount by the implicit gross domestic product 
price deflator for the year 2020 results in $158 million (113.625/
71.868 = 1.581). Before promulgating a rule for which a written 
statement is needed, section 205 of the UMRA generally requires the 
agency to identify and consider a reasonable number of regulatory 
alternatives and adopt the least costly, most cost-effective, or least 
burdensome alternative that achieves the objectives of the rule. The 
provisions of section 205 do not apply when they are inconsistent with 
applicable law. Moreover, section 205 allows the agency to adopt an 
alternative other than the least costly, most cost-effective, or least 
burdensome alternative if the agency publishes with the final rule an 
explanation of why that alternative was not adopted.
    This NPRM would not result in expenditures by State, local, or 
Tribal governments, in the aggregate, or by the private sector in 
excess of $158 million (in 2020 dollars) annually. As a result, the 
requirements of Section 202 of the Act do not apply.

Executive Order 13045 (Protection of Children From Environmental Health 
and Safety Risks)

    Executive Order 13045, ``Protection of Children from Environmental 
Health and Safety Risks,'' (62 FR 19885, April 23, 1997) applies to any 
proposed or final rule that: (1) Is determined to be ``economically 
significant,'' as defined in E.O. 12866, and (2) concerns an 
environmental health or safety risk that NHTSA has reason to believe 
may have a disproportionate effect on children. If a rule meets both 
criteria, the agency must evaluate the environmental health or safety 
effects of the rule on children and explain why the rule is preferable 
to other potentially effective and reasonably feasible alternatives 
considered by the agency.
    This rulemaking is not subject to the Executive order because it is 
not economically significant as defined in E.O. 12866.

Executive Order 13211

    Executive Order 13211 (66 FR 28355, May 18, 2001) applies to any 
rulemaking that: (1) is determined to be economically significant as 
defined under E.O. 12866, and is likely to have a significantly adverse 
effect on the supply of, distribution of, or use of energy; or (2) that 
is designated by the Administrator of the Office of Information and 
Regulatory Affairs as a significant energy action. This rulemaking is 
not subject to E.O. 13211 as this rule is not economically significant 
and should not have an adverse effect on the supply of, distribution 
of, or use of energy as explained in our discussion of Executive Orders 
12866 and 13563.

Plain Language

    Executive Order 12866 requires each agency to write all rules in 
plain language. Application of the principles of plain language 
includes consideration of the following questions:
     Have we organized the material to suit the public's needs?
     Are the requirements in the rule clearly stated?
     Does the rule contain technical language or jargon that 
isn't clear?
     Would a different format (grouping and order of sections, 
use of headings, paragraphing) make the rule easier to understand?
     Would more (but shorter) sections be better?
     Could we improve clarity by adding tables, lists, or 
diagrams?
     What else could we do to make the rule easier to 
understand?
    If you have any responses to these questions, please include them 
in your comments on this proposal.

Regulation Identifier Number (RIN)

    The Department of Transportation assigns a regulation identifier 
number (RIN) to each regulatory action listed in the Unified Agenda of 
Federal Regulations. The Regulatory Information Service Center 
publishes the Unified Agenda in April and October of each year. You may 
use the RIN contained in the heading at the beginning of this document 
to find this action in the Unified Agenda.

VI. Public Participation

How do I prepare and submit comments?

    To ensure that your comments are correctly filed in the Docket, 
please include the Docket Number in your comments.
    Your comments must be written and in English. Your comments must 
not be more than 15 pages long. NHTSA established this limit to 
encourage you to write your primary comments in a concise fashion. 
However, you may attach necessary additional documents

[[Page 27544]]

to your comments, and there is no limit on the length of the 
attachments.
    If you are submitting comments electronically as a PDF (Adobe) 
file, NHTSA asks that the documents be submitted using the Optical 
Character Recognition (OCR) process, thus allowing NHTSA to search and 
copy certain portions of your submissions.
    Please note that pursuant to the Data Quality Act, in order for 
substantive data to be relied on and used by NHTSA, it must meet the 
information quality standards set forth in the OMB and DOT Data Quality 
Act guidelines. Accordingly, NHTSA encourages you to consult the 
guidelines in preparing your comments. DOT's guidelines may be accessed 
at https://www.transportation.gov/regulations/dot-information-dissemination-quality-guidelines.

Tips for Preparing Your Comments

    When submitting comments, please remember to:
    Identify the rulemaking by docket number and other identifying 
information (subject heading, Federal Register date and page number).
    Explain why you agree or disagree, suggest alternatives, and 
substitute language for your requested changes.
    Describe any assumptions you make and provide any technical 
information and/or data that you used.
    If you estimate potential costs or burdens, explain how you arrived 
at your estimate in sufficient detail to allow for it to be reproduced.
    Provide specific examples to illustrate your concerns and suggest 
alternatives.
    Explain your views as clearly as possible, avoiding the use of 
profanity or personal threats.
    To ensure that your comments are considered by the agency, make 
sure to submit them by the comment period deadline identified in the 
DATES section above.
    For additional guidance on submitting effective comments, see 
https://www.regulations.gov/docs/Tips_For_Submitting_Effective_Comments.pdf.

How can I be sure my comments were received?

    If you wish Docket Management to notify you upon its receipt of 
your comments, enclose a self-addressed, stamped postcard in the 
envelope containing your comments. Upon receiving your comments, Docket 
Management will return the postcard by mail.

How do I submit confidential business information?

    If you wish to submit any information under a claim of 
confidentiality, you should submit three copies of your complete 
submission, including the information you claim to be confidential 
business information, to the Chief Counsel, NHTSA, at the address given 
above under FOR FURTHER INFORMATION CONTACT. In addition, you should 
submit a copy from which you have deleted the claimed confidential 
business information to the docket. When you send a comment containing 
information claimed to be confidential business information, you should 
include a cover letter setting forth the information specified in our 
confidential business information regulation. (49 CFR part 512.)

Will the Agency consider late comments?

    NHTSA will consider all comments that the docket receives before 
the close of business on the comment closing date indicated above under 
DATES. To the extent possible, NHTSA will also consider comments that 
the docket receives after that date. If the docket receives a comment 
too late for the agency to consider it in developing a final rule, 
NHTSA will consider that comment as an informal suggestion for future 
rulemaking action.

How can I read the comments submitted by other people?

    You may read the comments received by the docket at the address 
given above under ADDRESSES. You may also see the comments on the 
internet (http://regulations.gov).
    Please note that even after the comment closing date, NHTSA will 
continue to file relevant information in the docket as it becomes 
available. Further, some people may submit late comments. Accordingly, 
the agency recommends that you periodically check the docket for new 
material.
    Anyone is able to search the electronic form of all comments 
received into any of our dockets by the name of the individual 
submitting the comment (or signing the comment, if submitted on behalf 
of an association, business, labor union, etc.). You may review DOT's 
complete Privacy Act Statement in the Federal Register published on 
April 11, 2000 (Volume 65, Number 70; Pages 19477-78).

List of Subjects in 49 CFR Part 571

    Imports, Incorporation by reference, Motor vehicle safety, 
Reporting and recordkeeping requirements, Tires.

    In consideration of the foregoing, NHTSA proposes to amend 49 CFR 
part 571 as set forth below.

PART 571--FEDERAL MOTOR VEHICLE SAFETY STANDARDS

0
1. The authority citation for part 571 continues to read as follows:

    Authority: 49 U.S.C. 322, 30111, 30115, 30117 and 30166; 
delegation of authority at 49 CFR 1.95.

0
2. Section 571.5 is amended by:
0
a. In paragraph (d), redesignating paragraphs (19) through (39) as 
paragraphs (20) through (40) and adding paragraph (19); and
0
b. In paragraph (i), redesignating paragraphs (1) through (4) as 
paragraphs (2) through (5) and adding paragraph (1).
    The additions read as follows:


Sec.  571.5   Matter incorporated by reference.

* * * * *
    (d) * * *
    (19) ASTM D1193-06 (Reapproved 2018), Standard Specification for 
Reagent Water, approved March 22, 2018; into Sec.  571.308.
* * * * *
    (i) * * *
    (1) ISO 6270-2:2017, Determination of resistance to humidity, 
Second Edition, November 2017; into Sec.  571.308.
* * * * *
0
3. Section 571.307 is added to read as follows:


Sec.  571.307   Standard No. 307; Fuel system integrity of hydrogen 
vehicles.

    S1. Scope. This standard specifies requirements for the integrity 
of motor vehicle hydrogen fuel systems.
    S2. Purpose. The purpose of this standard is to reduce deaths and 
injuries occurring from fires that result from hydrogen fuel leakage 
during vehicle operation and after motor vehicle crashes.
    S3. Application. This standard applies to each motor vehicle that 
uses compressed hydrogen gas as a fuel source to propel the vehicle.
    S4. Definitions.
    Check valve means a valve that prevents reverse flow.
    Closure devices mean the check valve(s), shut-off valve(s) and 
thermally activated pressure relief device(s) that control the flow of 
hydrogen into and/or out of a CHSS.
    Container means a pressure-bearing component of a compressed 
hydrogen storage system that stores a continuous volume of hydrogen 
fuel in a single chamber or in multiple permanently interconnected 
chambers.
    Container attachments means non-pressure bearing parts attached to 
the container that provide additional support or protection to the 
container

[[Page 27545]]

and that may be removed only with the use of tools for the specific 
purpose of maintenance or inspection.
    Compressed hydrogen storage system (CHSS) means a system that 
stores compressed hydrogen fuel for a hydrogen-fueled vehicle, composed 
of a container, container attachments (if any), and all closure devices 
required to isolate the stored hydrogen from the remainder of the fuel 
system and the environment.
    Enclosed or semi-enclosed spaces means the volumes external to the 
hydrogen fuel system such as the passenger compartment, luggage 
compartment, and space under the hood.
    Fuel cell system means a system containing the fuel cell stack(s), 
air processing system, fuel flow control system, exhaust system, 
thermal management system and water management system.
    Fueling receptacle means the equipment to which a fueling station 
nozzle attaches to the vehicle and through which fuel is transferred to 
the vehicle.
    Fuel lines means all piping, tubing, joints, and any components 
such as flow controllers, valves, heat exchangers, and pressure 
regulators.
    Hydrogen concentration means the percentage of the hydrogen 
molecules within the mixture of hydrogen and air (equivalent to the 
partial volume of hydrogen gas).
    Hydrogen fuel system mean the fueling receptacle, CHSS, fuel cell 
system or internal combustion engine, fuel lines, and exhaust systems.
    Luggage compartment means the space in the vehicle for luggage, 
cargo, and/or goods accommodation, bounded by a roof, hood, floor, side 
walls being separated from the passenger compartment by the front 
bulkhead or the rear bulkhead.
    Maximum allowable working pressure (MAWP) means the highest gauge 
pressure to which a component or system is permitted to operate under 
normal operating conditions.
    Nominal working pressure (NWP) means the settled pressure of 
compressed gas in a container or CHSS fully fueled to 100 percent state 
of charge and at a uniform temperature of 15 [deg]C.
    Normal milliliter means a quantity of gas that occupies one 
milliliter of volume when its temperature is 0 [deg]C and its pressure 
is 1 atmosphere.
    Passenger compartment means the space for occupant accommodation 
that is bounded by the roof, floor, side walls, doors, outside glazing, 
front bulkhead, and rear bulkhead or rear gate.
    Pressure relief device (PRD) means a device that, when activated 
under specified performance conditions, is used to release hydrogen 
from a pressurized system and thereby prevent failure of the system.
    Rechargeable electrical energy storage system (REESS) means the 
rechargeable energy storage system that provides electric energy for 
electrical propulsion.
    Service door means a door that allows for the entry and exit of 
vehicle occupants under normal operating conditions.
    Shut-off valve means an automatically activated valve between the 
container and the remainder of the hydrogen fuel system that must 
default to the ``closed'' position when not connected to a power 
source.
    State of charge (SOC) means the density ratio of hydrogen in the 
CHSS between the actual CHSS condition and that at NWP with the CHSS 
equilibrated to 15 [deg]C, as expressed as a percentage using the 
formula:
[GRAPHIC] [TIFF OMITTED] TP17AP24.015


where [rho] is the density of hydrogen (g/L) at pressure (P) in 
MegaPascals (MPa) and temperature (T) in Celsius ([deg]C) as listed 
in the table below or linearly interpolated therein.


                                                                Table 1 to Sec.   571.307
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                              Pressure (Mpa)
              Temperature ([deg]C)               -------------------------------------------------------------------------------------------------------
                                                     1      10      20      30      35      40      50      60      65      70      75      80     87.5
--------------------------------------------------------------------------------------------------------------------------------------------------------
-40.............................................     1.0     9.7    18.1    25.4    28.6    31.7    37.2    42.1    44.3    46.4    48.4    50.3    53.0
-30.............................................     1.0     9.4    17.5    24.5    27.7    30.6    36.0    40.8    43.0    45.1    47.1    49.0    51.7
-20.............................................     1.0     9.0    16.8    23.7    26.8    29.7    35.0    39.7    41.9    43.9    45.9    47.8    50.4
-10.............................................     0.9     8.7    16.2    22.9    25.9    28.7    33.9    38.6    40.7    42.8    44.7    46.6    49.2
0...............................................     0.9     8.4    15.7    22.2    25.1    27.9    33.0    37.6    39.7    41.7    43.6    45.5    48.1
10..............................................     0.9     8.1    15.2    21.5    24.4    27.1    32.1    36.6    38.7    40.7    42.6    44.4    47.0
15..............................................     0.8     7.9    14.9    21.2    24.0    26.7    31.7    36.1    38.2    40.2    42.1    43.9    46.5
20..............................................     0.8     7.8    14.7    20.8    23.7    26.3    31.2    35.7    37.7    39.7    41.6    43.4    46.0
30..............................................     0.8     7.6    14.3    20.3    23.0    25.6    30.4    34.8    36.8    38.8    40.6    42.4    45.0
40..............................................     0.8     7.3    13.9    19.7    22.4    24.9    29.7    34.0    36.0    37.9    39.7    41.5    44.0
50..............................................     0.7     7.1    13.5    19.2    21.8    24.3    28.9    33.2    35.2    37.1    38.9    40.6    43.1
60..............................................     0.7     6.9    13.1    18.7    21.2    23.7    28.3    32.4    34.4    36.3    38.1    39.8    42.3
70..............................................     0.7     6.7    12.7    18.2    20.7    23.1    27.6    31.7    33.6    35.5    37.3    39.0    41.4
80..............................................     0.7     6.5    12.4    17.7    20.2    22.6    27.0    31.0    32.9    34.7    36.5    38.2    40.6
85..............................................     0.7     6.4    12.2    17.5    20.0    22.3    26.7    30.7    32.6    34.4    36.1    37.8    40.2
--------------------------------------------------------------------------------------------------------------------------------------------------------

    Thermally-activated pressure relief device (TPRD) means a non-
reclosing PRD that is activated by temperature to open and release 
hydrogen gas.
    S5. Hydrogen fuel system.
    S5.1. Fuel system integrity during normal vehicle operations.
    S5.1.1. Fueling receptacle requirements.
    (a) A compressed hydrogen fueling receptacle shall prevent reverse 
flow to the atmosphere.
    (b) A label shall be affixed close to the fueling receptacle 
showing the following information:
    (1) The statement, ``Compressed hydrogen gas only.''
    (2) The statement, ``Service pressure __ MPa (__ psig).''
    (3) The statement, ``See instructions on fuel container(s) for 
inspection and service life.''
    (c) The fueling receptacle shall ensure positive locking of the 
fueling nozzle.
    (d) The fueling receptacle shall be protected from the ingress of 
dirt and water.
    (e) The fueling receptacle shall not be mounted to or within the 
impact energy-absorbing elements of the vehicle and shall not be 
installed in enclosed or semi-enclosed spaces.
    S5.1.2. Over-pressure protection for the low-pressure system. An 
overpressure protection device is required downstream of a pressure 
regulator to protect the low-pressure

[[Page 27546]]

portions of the hydrogen fuel system from overpressure. The activation 
pressure of the overpressure protection device shall be less than or 
equal to the MAWP for the respective downstream section of the hydrogen 
fuel system.
    S5.1.3. Hydrogen discharge systems.
    S5.1.3.1. Pressure relief systems.
    (a) If present, the outlet of the vent line for hydrogen gas 
discharge from the TPRD(s) of the CHSS shall be protected from ingress 
of dirt and water.
    (b) With the vehicle on a level surface, the hydrogen gas discharge 
from the TPRD(s) of the CHSS shall be directed upwards within 20[deg] 
of vertical relative to the level surface or downwards within 45[deg] 
of vertical relative to the level surface.
    (c) The hydrogen gas discharge from TPRD(s) of the CHSS shall not 
impinge upon:
    (1) Enclosed or semi-enclosed spaces;
    (2) Any vehicle wheel housing;
    (3) Container(s);
    (4) REESS(s);
    (5) Any emergency exit(s) as identified in FMVSS No. 217; nor
    (6) Any service door(s).
    S5.1.3.2. Vehicle exhaust system. When tested in accordance with 
S6.5, the hydrogen concentration at the vehicle exhaust system's point 
of discharge shall not:
    (a) Exceed an average of 4.0 percent by volume during any moving 
three-second time interval, and
    (b) Exceed 8.0 percent by volume at any time.
    S5.1.4 Protection against flammable conditions.
    (a) When tested in accordance with S6.4.1, a warning in accordance 
with S5.1.6 shall be provided within 10 seconds of the application of 
the first test gas. When tested in accordance with S6.4.1, the main 
shut-off valve shall close within 10 seconds of the application of the 
second test gas.
    (b) When tested in accordance with S6.4.2, the hydrogen 
concentration in the enclosed or semi-enclosed spaces shall be less 
than 3.0 percent.
    S5.1.5 Fuel system leakage. When tested in accordance with S6.6, 
the hydrogen fuel system downstream of the shut-off valve(s) shall not 
leak.
    S5.1.6 Tell-tale warning. The warning shall be given to the driver, 
or to all front seat occupants for vehicles without a driver's 
designated seating position, by a visual signal or display text with 
the following properties:
    (a) Visible to the driver while seated in the driver's designated 
seating position or visible to all front seat occupants of vehicles 
without a driver's designated seating position;
    (b) Yellow in color if the warning system malfunctions;
    (c) Red in color if hydrogen concentration in enclosed or semi-
enclosed spaces exceeds 3.0 percent by volume;
    (d) When illuminated, shall be visible to the driver (or to all 
front seat occupants in vehicles without a driver's designated seating 
position) under both daylight and night-time driving conditions; and
    (e) Remains illuminated when hydrogen concentration in any of the 
vehicle's enclosed or semi-enclosed spaces exceeds 3.0 percent by 
volume or when the warning system malfunctions, and the ignition 
locking system is in the ``On'' (``Run'') position or the propulsion 
system is activated.
    S5.2. Post-crash fuel system integrity. Each vehicle with a gross 
vehicle weight rating (GVWR) of 4,536 kg or less to which this standard 
applies must meet the requirements in S5.2.1 through S5.2.4 when tested 
according to S6 under the conditions of S7. Each school bus with a GVWR 
greater than 4,536 kg to which this standard applies must meet the 
requirements in S5.2.1 through S5.2.4 when tested according to S6 under 
the conditions of S7.
    S5.2.1. Fuel leakage limit. If hydrogen gas is used for testing, 
the volumetric flow of hydrogen gas leakage shall not exceed an average 
of 118 normal liters per minute for the time interval, [Delta]t, as 
determined in accordance with S6.2.1. If helium is used for testing, 
the volumetric flow of helium leakage shall not exceed an average of 
88.5 normal litres per minute for the time interval, [Delta]t, as 
determined in accordance with S6.2.2.
    S5.2.2. Concentration limit in enclosed spaces. One of the 
requirements in (a), (b) or (c).
    (a) Hydrogen gas leakage shall not result in a hydrogen 
concentration in the air greater than 4.0 percent by volume in enclosed 
or semi-enclosed spaces for 60 minutes after impact when tested in 
accordance with S6.3.
    (b) Helium gas leakage shall not result in a helium concentration 
in the air greater than 3.0 percent by volume in enclosed or semi-
enclosed spaces for 60 minutes after impact when tested in accordance 
with S6.3.
    (c) The shut-off valve of the CHSS shall close within 5 seconds of 
the crash.
    S5.2.3. Container displacement. The container(s) shall remain 
attached to the vehicle by at least one component anchorage, bracket, 
or any structure that transfers loads from the container to the vehicle 
structure.
    S5.2.4. Fire. There shall be no fire in or around the vehicle for 
the duration of the test.
    S6. Test Requirements.
    S6.1. Vehicle Crash Tests. A test vehicle with a GVWR less than or 
equal to 4,536 kg, under the conditions of S7, is subject to any one 
single barrier crash test of S6.1.1, S6.1.2, and S6.1.3. A school bus 
with a GVWR greater than 4,536 kg, under the conditions of S7, is 
subject to the contoured barrier crash test of S6.1.4. A vehicle 
subject to S6 need not undergo further testing.
    S6.1.1. Frontal barrier crash. The test vehicle, with test dummies 
in accordance with S6.1 of 571.301 of this chapter, traveling 
longitudinally forward at any speed up to and including 48.0 km/h, 
impacts a fixed collision barrier that is perpendicular to the line of 
travel of the vehicle, or at an angle up to 30 degrees in either 
direction from the perpendicular to the line of travel of the vehicle.
    S6.1.2. Rear moving barrier impact. The test vehicle, with test 
dummies in accordance with S6.1 of 571.301 of this chapter, is impacted 
from the rear by a barrier that conforms to S7.3(b) of 571.301 of this 
chapter and that is moving at any speed up to and including 80.0 km/h.
    S6.1.3. Side moving deformable barrier impact. The test vehicle, 
with the appropriate 49 CFR part 572 test dummies specified in 571.214 
at positions required for testing by S7.1.1, S7.2.1, or S7.2.2 of 
Standard 214, is impacted laterally on either side by a moving 
deformable barrier moving at any speed between 52.0 km/h and 54.0 km/h.
    S6.1.4. Moving contoured barrier crash. The test vehicle is 
impacted at any point and at any angle by the moving contoured barrier 
assembly, specified in S7.5 and S7.6 in 571.301 of this chapter, 
traveling longitudinally forward at any speed up to and including 48.0 
km/h.
    S6.2. Post-crash CHSS leak test.
    S6.2.1. Post-crash leak test for CHSS filled with compressed 
hydrogen.
    (a) The hydrogen gas pressure, P0 (MPa), and 
temperature, T0 ([deg]C), shall be measured immediately 
before the impact. The hydrogen gas pressure Pf (MPa) and 
temperature, Tf ([deg]C) shall also be measured immediately 
after a time interval [Delta]t (in minutes) after impact. The time 
interval, [Delta]t, starting from the time of impact, shall be the 
greater of:
    (1) 60 minutes; or
    (2) [Delta]t = VCHSS x NWP/1000 x ((-0.027 x NWP + 4) x 
Rs - 0.21) - 1.7 x Rs

where Rs = Ps/ NWP, Ps is the 
pressure range of the pressure sensor (MPa), NWP is the Nominal 
Working Pressure (MPa), and VCHSS is the volume of the 
CHSS (L).


[[Page 27547]]


    (b) The initial mass of hydrogen M0 (g) in the CHSS 
shall be calculated from the following equations:

P0' = P0 x 288 / (273 + T0)
[rho]0' = -0.0027 x (P0')\2\ + 0.75 x 
P0' + 1.07
M0 = [rho]0' x VCHSS

    (c) The final mass of hydrogen in the CHSS, Mf (in 
grams), at the end of the time interval, [Delta]t, shall be calculated 
from the following equations:

Pf' = Pf x 288/(273 + Tf)
[rho]f' = -0.0027 x (Pf')\2\ + 0.75 x 
Pf' + 1.07
Mf = [rho]f' x VCHSS

where Pf is the measured final pressure (MPa) at the end 
of the time interval, and Tf ([deg]C) is the measured 
final temperature.

    (d) The average hydrogen flow rate over the time interval shall be 
calculated from the following equation:

VH2 = (Mf - M0)/[Delta]t x 22.41/2.016 
x (Ptarget/P0)

where VH2 is the average volumetric flow rate (normal 
millilitres per min) over the time interval.

    S6.2.2 Post-crash leak test for CHSS filled with compressed helium.
    (a) The helium pressure, P0 (MPa), and temperature, 
T0 ([deg]C), shall be measured immediately before the impact 
and again immediately after a time interval starting from the time of 
impact. The time interval, [Delta]t (min), shall be the greater of:
    (1) 60 minutes; or
    (2) [Delta]t = VCHSS x NWP/1000 x ((-0.028 x NWP + 5.5) 
x Rs - 0.3) - 2.6 x Rs

where Rs = Ps/NWP, Ps is the 
pressure range of the pressure sensor (MPa), NWP is the Nominal 
Working Pressure (MPa), and VCHSS is the volume of the 
CHSS (L).

    (b) The initial mass of helium M0 (g) in the CHSS shall 
be calculated from the following equations:

P0' = P0 x 288 / (273 + T0)
[rho]0' = -0.0043 x (P0')\2\ + 1.53 x 
P0' + 1.49
M0 = [rho]0' x VCHSS

    (c) The final mass of helium Mf (g) in the CHSS at the 
end of the time interval, [Delta]t (min), shall be calculated from the 
following equations:

Pf' = Pf x 288/(273 + Tf)
[rho]f' = -0.0043 x (Pf')\2\ + 1.53 x 
Pf' + 1.49
Mf = [rho]f' x VCHSS

where Pf is the measured final pressure (MPa) at the end 
of the time interval, and Tf ([deg]C) is the measured 
final temperature.

    (d) The average helium flow rate over the time interval shall be 
calculated from the following equation:

VHe = (Mf - M0)/[Delta]t x 22.41/4.003 
x (Ptarget/P0)

where VHe is the average volumetric flow rate (normal 
millilitres per min) of helium over the time interval.

    S6.3. Post-crash concentration test for enclosed spaces.
    (a) Sensors shall measure either the accumulation of hydrogen or 
helium gas, as appropriate, or the reduction in oxygen.
    (b) Sensors shall have an accuracy of at least 5 percent at 4.0 
percent hydrogen or 3.0 percent helium by volume in air, and a full-
scale measurement capability of at least 25 percent above these 
criteria. The sensor shall be capable of a 90 percent response to a 
full-scale change in concentration within 10 seconds.
    (c) Prior to the crash impact, the sensors shall be located in the 
passenger and luggage compartments of the vehicle as follows:
    (1) At any interior point at any distance between 240 mm and 260 mm 
of the headliner above the driver's seat or near the top center of the 
passenger compartment.
    (2) At any interior point at any distance between 240 mm and 260 mm 
of the floor in front of the rear (or rear most) seat in the passenger 
compartment.
    (3) At any interior point at any distance between 90 mm and 110 mm 
below the top of luggage compartment(s).
    (d) The sensors shall be securely mounted on the vehicle structure 
or seats and protected from debris, air bag exhaust gas and 
projectiles.
    (e) The vehicle shall be located either indoors or in an area 
outdoors protected from direct and indirect wind.
    (f) Post-crash data collection in enclosed spaces shall commence 
from the time of impact. Data from the sensors shall be collected at 
least every 5 seconds and continue for a period of 60 minutes after the 
impact.
    (g) The data shall be compiled into a three-data-point rolling 
average prior to evaluating the applicable concentration limit in 
accordance with S5.2.2(a) or S5.2.2(b).
    S6.4. Test procedure for protection against flammable conditions.
    S6.4.1. Test for hydrogen gas leakage detectors.
    (a) The vehicle shall be set to the ``on'' or ``run'' position for 
at least 5 minutes prior to testing, and left operating for the test 
duration. If the vehicle is not a fuel cell vehicle, it shall be warmed 
up and kept idling. If the test vehicle has a system to stop idling 
automatically, measures shall be taken to prevent the engine from 
stopping.
    (b) Two mixtures of air and hydrogen gas shall be used in the test: 
The first test gas has any hydrogen concentration between 3.0 and 4.0 
percent by volume in air to verify function of the warning, and the 
second test gas has any hydrogen concentration between 4.0 and 6.0 
percent by volume in air to verify function of the shut-down.
    (c) The test shall be conducted without any influence of wind.
    (d) A vehicle hydrogen leakage detector located in the enclosed or 
semi-enclosed spaces is enclosed with a cover and a test gas induction 
hose is attached to the hydrogen gas leakage detector.
    (e) The hydrogen gas leakage detector is exposed to continuous flow 
of the first test gas specified in (b) until the warning turns on.
    (f) Then the hydrogen gas leakage detector is then exposed to 
continuous flow of the second test gas specified in (b) until the main 
shut-off valve closes to isolate the CHSS. The test is completed when 
the shut-off valve closes.
    S6.4.2. Test for integrity of enclosed spaces and detection 
systems.
    (a) The test shall be conducted without influence of wind.
    (b) Prior to the test, the vehicle is prepared to simulate remotely 
controllable hydrogen releases from the fuel system or from an external 
fuel supply. The number, location, and flow capacity of the release 
points downstream of the shut-off valve are defined by the vehicle 
manufacturer.
    (c) A hydrogen concentration detector shall be installed in any 
enclosed or semi-enclosed volume where hydrogen may accumulate from the 
simulated hydrogen release.
    (d) Vehicle doors, windows and other covers are closed.
    (e) The vehicle shall be set to the ``on'' or ``run'' position for 
at least 5 minutes prior to testing, and left operating for the test 
duration. If the vehicle is not a fuel cell vehicle, it shall be warmed 
up and kept idling. If the test vehicle has a system to stop idling 
automatically, measures shall be taken to prevent the engine from 
stopping.
    (f) A leak shall be simulated using the remote controllable 
function.
    (g) The hydrogen concentration is measured continuously until the 
end of the test.
    (h) The test is completed 5 minutes after initiating the simulated 
leak or when the hydrogen concentration does not change for 3 minutes, 
whichever is longer.
    S6.5. Test for the vehicle exhaust system.
    (a) The vehicle shall be set to the ``on'' or ``run'' position for 
at least 5 minutes prior to testing.
    (b) The measuring section of the measuring device shall be placed 
along the centerline of the exhaust gas flow within 100 mm of where the 
exhaust is released to the atmosphere.

[[Page 27548]]

    (c) The exhaust hydrogen concentration shall be continuously 
measured during the following steps:
    (1) The fuel cell system shall be shut down.
    (2) The fuel cell system shall be immediately restarted.
    (3) After one minute, the vehicle shall be set to the ``off'' 
position and measurement continues until the until the vehicle shut-
down is complete shut-down procedure is completed.
    (d) The measurement device shall have a resolution time of less 
than 300 milliseconds;
    (e) Have a measurement response time (t0 - 
t90) of less than 2 seconds, where t0 is the 
moment of hydrogen concentration switching, and t90 is the 
time when 90 percent of the final indication is reached and have a 
resolution time of less than 300 milliseconds (sampling rate of greater 
than 3.33 Hz).
    S6.6. Test for fuel system leakage. The vehicle CHSS shall be 
filled with hydrogen to any pressure between 90 percent NWP and 100 
percent NWP for the duration of the test for fuel system leakage.
    (a) The vehicle shall be set to the ``on'' or ``run'' position for 
at least 5 minutes prior to testing, and left operating for the test 
duration. If the vehicle is not a fuel cell vehicle, it shall be warmed 
up and kept idling. If the test vehicle has a system to stop idling 
automatically, measures shall be taken to prevent the engine from 
stopping.
    (b) Hydrogen leakage shall be evaluated at accessible sections of 
the hydrogen fuel system downstream of the shut-off valve(s), using a 
gas leak detector or a leak detecting liquid as follows:
    (1) When a gas leak detector is used, detection shall be performed 
by operating the leak detector for at least 10 seconds at locations as 
close to fuel lines as possible.
    (2) When a leak detecting liquid is used, hydrogen gas leak 
detection shall be performed immediately after applying the liquid.
    S7. Test Conditions. The requirements of S5.2 shall be met under 
the following conditions. Where a range of conditions is specified, the 
vehicle must be capable of meeting the requirements at all points 
within the range.
    (a) Prior to conducting the crash test, instrumentation is 
installed in the CHSS to perform the required pressure and temperature 
measurements if the vehicle does not already have instrumentation with 
the required accuracy.
    (b) The CHSS is then purged, if necessary, following manufacturer 
directions before filling the CHSS with compressed hydrogen or helium 
gas.
    (c) The target fill pressure Ptarget shall be calculated 
from the following equation:

Ptarget = NWP x (273 + To)/288

where NWP is in MPa, To is the ambient temperature in 
[deg]C to which the CHSS is expected to settle, and 
Ptarget is the target fill pressure in MPa after the 
temperature settles.

    (d) The container(s) shall be filled to any pressure between 95.0 
percent and 100.0 percent of the calculated target fill pressure.
    (e) After fueling, the vehicle shall be maintained at rest for any 
duration between 2.0 and 3.0 hours before conducting a crash test in 
accordance with S6.1.
    (f) The CHSS shut-off valve(s) and any other shut-off valves 
located in the fuel system downstream hydrogen gas piping shall be in 
normal driving condition immediately prior to the impact.
    (g) The parking brake is disengaged and the transmission is in 
neutral prior to the crash test.
    (h) Tires are inflated to manufacturer's specifications.
    (i) The vehicle, including test devices and instrumentation, is 
loaded as follows:
    (1) A passenger car, with its fuel system filled as specified in 
S7(d), is loaded to its unloaded vehicle weight plus its rated cargo 
and luggage capacity weight, secured in the luggage area, plus the 
necessary test dummies as specified in S6, restrained only by means 
that are installed in the vehicle for protection at its seating 
position.
    (2) A multipurpose passenger vehicle, truck, or bus with a GVWR of 
10,000 pounds or less, whose fuel system is filled as specified in 
S7(d), is loaded to its unloaded vehicle weight, plus the necessary 
test dummies as specified in S6, plus 136.1 kg, or its rated cargo and 
luggage capacity weight, whichever is less, secured to the vehicle and 
distributed so that the weight on each axle as measured at the tire-
ground interface is in proportion to its gross axle weight rating 
(GAWR). Each dummy shall be restrained only by means that are installed 
in the vehicle for protection at its seating position.
    (3) A school bus with a GVWR greater than 10,000 pounds, whose fuel 
system is filled as specified in S7(d), is loaded to its unloaded 
vehicle weight, plus 54.4 kg of unsecured weight at each designated 
seating position.
0
5. Section 571.308 is added to read as follows:


Sec.  571.308   Standard No. 308; Compressed hydrogen storage system 
integrity.

    S1. Scope. This standard specifies requirements for compressed 
hydrogen storage systems used in motor vehicles.
    S2. Purpose. The purpose of this standard is to reduce deaths and 
injuries occurring from fires that result from hydrogen leakage during 
vehicle operation and to reduce deaths and injuries occurring from 
explosions resulting from the burst of pressurized hydrogen containers.
    S3. Application. This standard applies to each motor vehicle that 
uses compressed hydrogen gas as a fuel source.
    S4. Definitions.
    BPO means the manufacturer-supplied median burst pressure for a 
batch of new containers.
    Burst means to break apart or to break open.
    Burst pressure means the highest pressure achieved for a container 
tested in accordance with S6.2.2.1.
    Check valve means a valve that prevents reverse flow.
    Closure devices mean the check valve(s), shut-off valve(s) and 
thermally activated pressure relief device(s) that control the flow of 
hydrogen into and/or out of a CHSS.
    Container means a pressure-bearing component of a compressed 
hydrogen storage system that stores a continuous volume of hydrogen 
fuel in a single chamber or in multiple permanently interconnected 
chambers.
    Container attachments means non-pressure bearing parts attached to 
the container that provide additional support and/or protection to the 
container and that may be removed only with the use of tools for the 
specific purpose of maintenance and/or inspection.
    Compressed hydrogen storage system (CHSS) means a system that 
stores compressed hydrogen fuel for a hydrogen-fueled vehicle, composed 
of a container, container attachments (if any), and all closure devices 
required to isolate the stored hydrogen from the remainder of the fuel 
system and the environment.
    Nominal working pressure (NWP) means the settled pressure of 
compressed gas in a container or CHSS fully fueled to 100 percent state 
of charge and at a uniform temperature of 15 [deg]C.
    Normal milliliter means a quantity of gas that occupies one 
milliliter of volume when its temperature is 0 [deg]C and its pressure 
is 1 atmosphere.
    Pressure relief device (PRD) means a device that, when activated 
under specified performance conditions, is

[[Page 27549]]

used to release hydrogen from a pressurized system and thereby prevent 
failure of the system.
    Service life (of a container) means the time frame during which 
service (usage) is authorized by the manufacturer.
    Shut-off valve means an electrically activated valve between the 
container and the remainder of the vehicle fuel system that must 
default to the ``closed'' position when unpowered.
    State of charge (SOC) means the density ratio of hydrogen in the 
CHSS between the actual CHSS condition and that at NWP with the CHSS 
equilibrated to 15 [deg]C, as expressed as a percentage using the 
formula:
[GRAPHIC] [TIFF OMITTED] TP17AP24.016

where [rho] is the density of hydrogen (g/L) at pressure (P) in 
MegaPascals (MPa) and temperature (T) in Celsius ([deg]C) as listed 
in the table below or linearly interpolated therein.

                                                                Table 2 to Sec.   571.307
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                        Pressure (MPa)
        Temperature ([deg]C)        --------------------------------------------------------------------------------------------------------------------
                                        1        10       20       30       35       40       50       60       65       70       75       80      87.5
--------------------------------------------------------------------------------------------------------------------------------------------------------
-40................................      1.0      9.7     18.1     25.4     28.6     31.7     37.2     42.1     44.3     46.4     48.4     50.3     53.0
-30................................      1.0      9.4     17.5     24.5     27.7     30.6     36.0     40.8     43.0     45.1     47.1     49.0     51.7
-20................................      1.0      9.0     16.8     23.7     26.8     29.7     35.0     39.7     41.9     43.9     45.9     47.8     50.4
-10................................      0.9      8.7     16.2     22.9     25.9     28.7     33.9     38.6     40.7     42.8     44.7     46.6     49.2
0..................................      0.9      8.4     15.7     22.2     25.1     27.9     33.0     37.6     39.7     41.7     43.6     45.5     48.1
10.................................      0.9      8.1     15.2     21.5     24.4     27.1     32.1     36.6     38.7     40.7     42.6     44.4     47.0
15.................................      0.8      7.9     14.9     21.2     24.0     26.7     31.7     36.1     38.2     40.2     42.1     43.9     46.5
20.................................      0.8      7.8     14.7     20.8     23.7     26.3     31.2     35.7     37.7     39.7     41.6     43.4     46.0
30.................................      0.8      7.6     14.3     20.3     23.0     25.6     30.4     34.8     36.8     38.8     40.6     42.4     45.0
40.................................      0.8      7.3     13.9     19.7     22.4     24.9     29.7     34.0     36.0     37.9     39.7     41.5     44.0
50.................................      0.7      7.1     13.5     19.2     21.8     24.3     28.9     33.2     35.2     37.1     38.9     40.6     43.1
60.................................      0.7      6.9     13.1     18.7     21.2     23.7     28.3     32.4     34.4     36.3     38.1     39.8     42.3
70.................................      0.7      6.7     12.7     18.2     20.7     23.1     27.6     31.7     33.6     35.5     37.3     39.0     41.4
80.................................      0.7      6.5     12.4     17.7     20.2     22.6     27.0     31.0     32.9     34.7     36.5     38.2     40.6
85.................................      0.7      6.4     12.2     17.5     20.0     22.3     26.7     30.7     32.6     34.4     36.1     37.8     40.2
--------------------------------------------------------------------------------------------------------------------------------------------------------

    Thermally-activated pressure relief device (TPRD) means a non-
reclosing PRD that is activated by temperature to open and release 
hydrogen gas.
    TPRD sense point means instrumentation that detects elevated 
temperature for the purpose of activating a TPRD.
    S5. Requirements.
    S5.1. Requirements for the CHSS. Each vehicle CHSS shall include 
the following functions: shut-off valve, check valve, and TPRD. Each 
vehicle CHSS shall have a NWP of 70 MPa or less. Each vehicle 
container, closure device, and CHSS, shall meet the applicable 
performance test requirements listed in the table below.

                             Table 3 to S5.1
------------------------------------------------------------------------
            Requirement section                      Test article
------------------------------------------------------------------------
S5.1.1. Tests for baseline metrics.........  Container.
S5.1.2. Test for performance durability....  Container.
S5.1.3. Test for expected on-road            CHSS.
 performance.
S5.1.4. Test for service terminating         CHSS.
 performance in fire.
S5.1.5. Tests for performance durability of  Closure devices.
 closure devices.
------------------------------------------------------------------------

    S5.1.1. Tests for baseline metrics.
    S5.1.1.1 Baseline initial burst pressure. The manufacturer shall 
immediately specify upon request, in writing, and within five business 
days: the primary constituent of the container. When a new container 
with its container attachments (if any) is tested in accordance with 
S6.2.2.1, all of the following requirements shall be met:
    (a) The burst pressure of the container shall not be less than 2 
times NWP.
    (b) The burst pressure of the container having glass-fiber 
composite as a primary constituent shall not be less than 3.5 times 
NWP.
    (c) The bust pressure of the container for which the manufacturer 
fails to specify upon request, in writing, and within five business 
days, the primary constituent of the container, shall not be less than 
3.5 times NWP.
    (d) The burst pressure of the container shall be within 10 percent 
of the BPO listed on the container label.
    S5.1.1.2. Baseline initial pressure cycle test. When a new 
container with its container attachments (if any) is hydraulically 
pressure cycled in accordance with S6.2.2.2 to any pressure between 
125.0 percent NWP and 130.0 percent NWP,
    (a) containers for vehicles with a GVWR of 10,000 pounds or less
    (1) shall not leak nor burst for at least 7,500 cycles, and
    (2) thereafter shall not burst for an additional 14,500 cycles. If 
the required pressure cannot be achieved due to leakage or if a visible 
leak occurs for more than 3 minutes while conducting the test as 
specified in S5.1.1.2(a)(2), the test is stopped and not considered a 
failure.
    (b) containers for vehicles with a GVWR of over 10,000 pounds
    (1) shall not leak nor burst for at least 11,000 cycles, and
    (2) thereafter shall not burst for an additional 11,000 cycles. If 
the required pressure cannot be achieved due to leakage or if a visible 
leak occurs for more than 3 minutes while conducting the test as 
specified in S5.1.1.2(b)(2), the test is stopped and not considered a 
failure.
    S5.1.2. Test for performance durability. A new container shall not 
leak nor burst when subjected to the sequence of tests in S5.1.2.1 to 
S5.1.2.7. Immediately following S5.1.2.7, and without depressurizing 
the container, the container is subjected to a burst test in accordance 
with S6.2.2.1(c) and S6.2.2.1(d). The burst pressure of the container 
at the end of the sequence of

[[Page 27550]]

tests in this section shall not be less than 0.8 times the 
BPO listed on the container label. The sequence of tests and 
the burst pressure test are illustrated in Figure 1.
    S5.1.2.1. Proof pressure test. The container with its container 
attachments (if any) is hydraulically pressurized in accordance with 
S6.2.3.1 to any pressure between 1.500 times NWP and 1.550 times NWP 
and held for any duration between 30.0 to 35.0 seconds.
    S5.1.2.2. Drop test. The container with its container attachments 
(if any) is dropped once in accordance with S6.2.3.2 in any one of the 
four orientations specified in that section. Any container with damage 
from the drop test that prevents further testing of the container in 
accordance with S6.2.3.4 shall be considered to have failed to meet the 
test for performance durability requirements.
    S5.1.2.3. Surface damage test. The container, except if an all-
metal container, is subjected to the surface damage test in accordance 
with the S6.2.3.3. Container attachments designed to be removed shall 
be removed and container attachments that are not designed to be 
removed shall remain in place. Container attachments that are removed, 
shall not be reinstalled for the remainder of S5.1.2; container 
attachments that are not removed, shall remain in place for the 
remainder of S5.1.2.
    S5.1.2.4. Chemical exposure and ambient-temperature pressure 
cycling test. The container is exposed to chemicals in accordance with 
S6.2.3.4 and then hydraulically pressure cycled in accordance with 
S6.2.3.4 for 60 percent of the number of cycles as specified in 
S5.1.1.2(a)(1) or S5.1.1.2(b)(1) as applicable. For all but the last 10 
of these cycles, the cycling pressure shall be any pressure between 
125.0 percent NWP and 130.0 percent NWP. For the last 10 cycles, the 
pressure shall be any pressure between 150.0 percent NWP and 155.0 
percent NWP.
    S5.1.2.5. High temperature static pressure test. The container is 
pressurized to any pressure between (or equal to) 125 percent NWP and 
130 percent NWP and held at that pressure no less than 1,000 and no 
more than 1,050 hours in accordance with S6.2.3.5 and with the 
temperature surrounding the container at any temperature between 85.0 
[deg]C and 90.0 [deg]C.
    S5.1.2.6. Extreme temperature pressure cycling test. The container 
is pressure cycled in accordance with S6.2.3.6 for 40 percent of the 
number of cycles specified in S5.1.1.2(a)(1) or S5.1.1.2(b)(1) as 
applicable. The pressure for the first half of these cycles equals any 
pressure between 80.0 percent NWP and 85.0 percent NWP with the 
temperature surrounding the container equal to any temperature between 
-45.0 [deg]C and -40.0 [deg]C. The pressure for the next half of these 
cycles equals any pressure between 125.0 percent NWP and 130.0 percent 
NWP and the temperature surrounding the container equal to any 
temperature between 85.0 [deg]C and 90.0 [deg]C and the relative 
humidity surrounding the container not less than 80 percent.
    S5.1.2.7. Residual pressure test. The container is hydraulically 
pressurized in accordance with S6.2.3.1 to a pressure between 180.0 
percent NWP and 185.0 percent NWP and held for any duration between 240 
to 245 seconds.
    S5.1.3. Test for expected on-road performance. When subjected to 
the sequence of tests in S5.1.3.1 to S5.1.3.2, the CHSS shall meet the 
permeation and leak requirements specified in S5.1.3.3 and shall not 
burst. Thereafter, the container of the CHSS shall not burst when 
subjected to a residual pressure test in accordance with S5.1.3.4. 
Immediately following S5.1.3.4, and without depressurizing the 
container, the container of the CHSS is subjected to a burst test in 
accordance with S6.2.2.1(c) and S6.2.2.1(d). The burst pressure of the 
container at the end of the sequence of tests in this section shall not 
be less than 0.8 times the BPO listed on the container 
label.
    S5.1.3.1. Proof pressure test. The container of the CHSS is 
pressurized with hydrogen gas to any pressure between 1.500 times NWP 
and 1.550 times NWP and held for any duration between 30 to 35 seconds 
in accordance with the S6.2.3.1 test procedure. The ambient temperature 
surrounding the container shall be at any temperature between 5.0 
[deg]C to 35.0 [deg]C. The fuel delivery temperature used for 
pressurizing the container with hydrogen shall be at any temperature 
between -40.0 [deg]C to -33.0 [deg]C.
    S5.1.3.2. Ambient and extreme temperature gas pressure cycling 
test. The CHSS is pressure cycled using hydrogen gas for 500 cycles 
under any temperature and pressure condition for the number of cycles 
as specified in the Table to S5.1.3.2, and in accordance with the 
S6.2.4.1 test procedure. A static gas pressure leak/permeation test 
performed in accordance with S5.1.3.3 is conducted after the first 250 
pressure cycles and after the remaining 250 pressure cycles.

                                                                   Table 4 to S5.1.3.2
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                 Initial system          Fuel delivery        Cycle initial and
          Number of cycles             Ambient conditions         equilibration           temperature           final pressure      Cycle peak pressure
--------------------------------------------------------------------------------------------------------------------------------------------------------
5..................................  -30.0 [deg]C to -25.0   -30.0 [deg]C to -25.0   15.0 [deg]C to 25.0    1.0 MPa to 2.0 MPa...  100.0% SOC to 105.0%
                                      [deg]C.                 [deg]C.                 [deg]C.                                       SOC.
5..................................  -30.0 [deg]C to -25.0   -30.0 [deg]C to -25.0   -40.0 [deg]C to -33.0  1.0 MPa to 2.0 MPa...  100.0% SOC to 105.0%
                                      [deg]C.                 [deg]C.                 [deg]C.                                       SOC.
15.................................  -30.0 [deg]C to -25.0   not appliable.........  -40.0 [deg]C to -33.0  1.0 MPa to 2.0 MPa...  100.0% SOC to 105.0%
                                      [deg]C.                                         [deg]C.                                       SOC.
5..................................  50.0 [deg]C to 55.0     50 [deg]C to 55 [deg]C  -40.0 [deg]C to -33.0  1.0 MPa to 2.0 MPa...  100.0% SOC to 105.0%
                                      [deg]C 80% to 100%      80% to 100% relative    [deg]C.                                       SOC.
                                      relative humidity.      humidity.
20.................................  50.0 [deg]C to 55.0     not appliable.........  -40.0 [deg]C to -33.0  1.0 MPa to 2.0 MPa...  100.0% SOC to 105.0%
                                      [deg]C, 80% to 100%                             [deg]C.                                       SOC.
                                      relative humidity.
200................................  5.0 [deg]C to 35.0      not appliable.........  -40.0 [deg]C to -33.0  1.0 MPa to 2.0 MPa...  100.0% SOC to 105.0%
                                      [deg]C.                                         [deg]C.                                       SOC.
Extreme temperature static gas       55.0 [deg]C to 60.0     55.0 [deg]C to 60.0     not appliable........  not appliable........  100.0% SOC to 105.0%
 pressure leak/permeation test        [deg]C.                 [deg]C.                                                               SOC.
 S5.1.3.3.

[[Page 27551]]

 
25.................................  50.0 [deg]C to 55.0     not appliable.........  -40.0 [deg]C to -33.0  1.0 MPa to 2.0 MPa...  100.0% SOC to 105.0%
                                      [deg]C,.                                        [deg]C.                                       SOC.
                                     80% to 100% relative
                                      humidity.
25.................................  -30.0 [deg]C to -25.0   not appliable.........  -40.0 [deg]C to -33.0  1.0 MPa to 2.0 MPa...  100.0% SOC to 105.0%
                                      [deg]C.                                         [deg]C.                                       SOC.
200................................  5.0 [deg]C to 35.0      not appliable.........  -40.0 [deg]C to -33.0  1.0 MPa to 2.0 MPa...  100.0% SOC to 105.0%
                                      [deg]C.                                         [deg]C.                                       SOC.
Extreme temperature static gas       55.0 [deg]C to 60.0     55.0 [deg]C to 60.0     not appliable........  not appliable........  100.0% SOC to 105.0%
 pressure leak/permeation test        [deg]C.                 [deg]C.                                                               SOC.
 S5.1.3.3.
--------------------------------------------------------------------------------------------------------------------------------------------------------

    S5.1.3.3. Extreme temperature static gas pressure leak/permeation 
test. When tested in accordance with S6.2.4.2 after each group of 250 
pneumatic pressure cycles in S5.1.3.2, the CHSS shall not discharge 
hydrogen more than 46 millilitres per hour (mL/h) for each litre of 
CHSS water capacity.
    S5.1.3.4. Residual pressure test. The container of the CHSS is 
hydraulically pressurized in accordance with S6.2.3.1 to any pressure 
between 1.800 times NWP and 1.850 times NWP and held at that pressure 
for any duration between 240 to 245 seconds.
    S5.1.4. Test for service terminating performance in fire. When the 
CHSS is exposed to the two-stage localized or engulfing fire test in 
accordance with S6.2.5, the container shall not burst. The pressure 
inside the CHSS shall fall to 1 MPa or less within the test time limit 
specified in S6.2.5.3(o). Any leakage or venting, other than that 
through TPRD outlet(s), shall not result in jet flames greater than 0.5 
m in length. If venting occurs though the TPRD, the venting shall be 
continuous.
    S5.1.5. Tests for performance durability of closure devices. All 
tests are performed at ambient temperature of 5 [deg]C to 35 [deg]C 
unless otherwise specified.
    S5.1.5.1. TPRD requirements. The TPRD shall not activate at any 
point during the test procedures specified in S6.2.6.1.1, S6.2.6.1.3, 
S6.2.6.1.4, S6.2.6.1.5, S6.2.6.1.6, S6.2.6.1.7, and S6.2.6.1.8.
    (a) A TPRD subjected to pressure cycling in accordance with 
S6.2.6.1.1, shall be sequentially tested in accordance with S6.2.6.1.8, 
S6.2.6.1.9, and S6.2.6.1.10;
    (1) When tested in accordance with S6.2.6.1.8, the TPRD shall not 
exhibit leakage greater than 10 normal milliliters per minute (NmL/
hour).
    (2) When tested in accordance with S6.2.6.1.9, the TPRD shall 
activate within no more than 2 minutes of the average activation time 
of three new TPRDs tested in accordance with S6.2.6.1.9;
    (3) When tested in accordance with S6.2.6.1.10, the TPRD shall have 
a flow rate of at least 90 percent of the highest baseline flow rate 
established in accordance with S6.2.6.1.10;
    (b)(1) A TPRD shall activate in less than ten hours when tested at 
the manufacturer's specified activation temperature in accordance with 
S6.2.6.1.2.
    (2) When tested at the accelerated life temperature in accordance 
with S6.2.6.1.2, a TPRD shall not activate in less than 500 hours and 
shall not exhibit leakage greater than 10 NmL/hour when tested in 
accordance with S6.2.6.1.8;
    (c) A TPRD subjected to temperature cycling testing in accordance 
with S6.2.6.1.3 shall be sequentially tested in accordance with 
S6.2.6.1.8(a)(3), S6.2.6.1.9, and S6.2.6.1.10;
    (1) When tested in accordance with S6.2.6.1.8(a)(3), the TPRD shall 
not exhibit leakage greater than 10 NmL/hour;
    (2) When tested in accordance with S6.2.6.1.9, the TPRD shall 
activate within no more than 2 minutes of the average activation time 
of three new TPRDs tested in accordance with S6.2.6.1.9;
    (3) When tested in accordance with S6.2.6.1.10, the TPRD shall have 
a flow rate of at least 90 percent of the highest baseline flow rate 
established in accordance with S6.2.6.1.10;
    (d) A TPRDs subjected to salt corrosion resistance testing in 
accordance with S6.2.6.1.4 shall be sequentially tested in accordance 
with S6.2.6.1.8, S6.2.6.1.9, and S6.2.6.1.10;
    (1) When tested in accordance with S6.2.6.1.8, the TPRD shall not 
exhibit leakage greater than 10 NmL/hour;
    (2) When tested in accordance with S6.2.6.1.9, the TPRD shall 
activate within no more than 2 minutes of the average activation time 
of three new TPRDs tested in accordance with S6.2.6.1.9;
    (3) When tested in accordance with S6.2.6.1.10, the TPRD shall have 
a flow rate of at least 90 percent of the highest baseline flow rate 
established in accordance with S6.2.6.1.10;
    (e) A TPRD subjected to vehicle environment testing in accordance 
with S6.2.6.1.5 shall not show signs of cracking, softening, or 
swelling, and thereafter shall be sequentially tested in accordance 
with S6.2.6.1.8, S6.2.6.1.9, and S6.2.6.1.10.
    (1) When tested in accordance with S6.2.6.1.8, the TPRD shall not 
exhibit leakage greater than 10 NmL/hour.
    (2) When tested in accordance with S6.2.6.1.9, the TPRD shall 
activate within no more than 2 minutes of the average activation time 
of three new TPRDs tested in accordance with S6.2.6.1.9,
    (3) When tested in accordance with S6.2.6.1.10, the TPRD shall have 
a flow rate of at least 90 percent of the highest baseline flow rate 
established in accordance with S6.2.6.1.10;
    (f) A TPRD subjected to stress corrosion cracking testing in 
accordance with S6.2.6.1.6 shall not exhibit visible cracking or 
delaminating;
    (g) A TPRD shall be subjected to drop and vibration testing in 
accordance with S6.2.6.1.7. If the TPRD progresses beyond S6.2.6.1.7(c) 
to complete testing under S6.2.6.1.7(d), it shall then be sequentially 
tested in accordance with S6.2.6.1.8, S6.2.6.1.9, and S6.2.6.1.10.
    (1) When tested in accordance with S6.2.6.1.8, the TPRD shall not 
exhibit leakage greater than 10 NmL/hour.
    (2) When tested in accordance with S6.2.6.1.9, the TPRD shall 
activate within no more than 2 minutes of the average activation time 
of three new TPRDs tested in accordance with S6.2.6.1.9,
    (3) When tested in accordance with S6.2.6.1.10, the TPRD shall have 
a flow rate of at least 90 percent of the highest baseline flow rate 
established in accordance with S6.2.6.1.10;

[[Page 27552]]

    (h) One new TPRD subjected to leak testing in accordance with 
S6.2.6.1.8 shall not exhibit leakage greater than 10 NmL/hour;
    (i) Three new TPRDs are subjected to a bench top activation test in 
accordance with S6.2.6.1.9. The maximum difference in the activation 
time between any two of the three TPRDs shall be 2 minutes or less.
    S5.1.5.2. Check valve and shut-off valve requirements. This section 
applies to both check valves and shut-off valves.
    (a) A valve subjected to hydrostatic strength testing in accordance 
with S6.2.6.2.1 shall not leak nor burst at less than 250 percent NWP;
    (b) A valve subjected to leak testing in accordance with S6.2.6.2.2 
shall not exhibit leakage greater than 10 NmL/hour;
    (c)(1) A check valve shall meet the requirements when tested 
sequentially as follows:
    (i) The check valve shall reseat and prevent reverse flow after 
each cycle when subjected to 13,500 pressure cycles in accordance with 
S6.2.6.2.3 to any pressure between 100.0 and 105.0 percent NWP and at 
any temperature between 5.0 [deg]C and 35.0 [deg]C;
    (ii) The same check valve shall reseat and prevent reverse flow 
after each cycle when subjected to 750 pressure cycles in accordance 
with S6.2.6.2.3 to any pressure between 125.0 and 130.0 percent NWP and 
at any temperature between 85.0 [deg]C and 90.0 [deg]C;
    (iii) The same check valve shall reseat and prevent reverse flow 
after each cycle when subjected to 750 pressure cycles in accordance 
with S6.2.6.2.3 to any pressure between 80.0 and 85.0 percent NWP and 
at any temperature between -45.0 [deg]C and -40.0 [deg]C;
    (iv) The same check valve shall be subjected to chatter flow 
testing in accordance with S6.2.6.2.4;
    (v) When tested in accordance with S6.2.6.2.2, the same check valve 
shall not exhibit leakage greater than 10 NmL/hour;
    (vi) When tested in accordance S6.2.6.2.1, the same check valve 
shall not leak nor burst at less than 250 percent NWP nor burst at less 
than 80 percent of the burst pressure of the new unit tested in 
accordance with S5.1.5.2(a) unless the burst pressure of the valve 
exceeds 400 percent NWP.
    (2) A shut-off valve shall meet the requirements when tested 
sequentially as follows:
    (i) The shut-off valve shall be subjected to 45,000 pressure cycles 
in accordance with S6.2.6.2.3 to any pressure between 100.0 and 105.0 
percent NWP and at any temperature between 5.0 [deg]C and 35.0 [deg]C;
    (ii) The same shut-off valve shall be subjected to 2,500 pressure 
cycles in accordance with S6.2.6.2.3 to any pressure between 125.0 and 
130.0 percent NWP and at any temperature between 85.0 [deg]C and 90.0 
[deg]C;
    (iii) The same shut-off valve subjected to 2,500 pressure cycles in 
accordance with S6.2.6.2.3 to any pressure between 80.0 and 85.0 
percent NWP and at any temperature between -45.0 [deg]C and -40.0 
[deg]C;
    (iv) The same shut-off valve shall be subjected to chatter flow 
testing in accordance with S6.2.6.2.4;
    (v) When tested in accordance with S6.2.6.2.2, the same shut-off 
valve shall not exhibit leakage greater than 10 NmL/hour;
    (vi) When tested in accordance S6.2.6.2.1, the same shut-off valve 
shall not leak nor burst at less than 250 percent NWP nor burst at less 
than 80 percent of the burst pressure of the new unit tested in 
accordance with S5.1.5.2(a) unless the burst pressure of the valve 
exceeds 400 percent NWP.
    (d) A valve subjected to salt corrosion resistance testing in 
accordance with S6.2.6.1.4 shall be tested sequentially in accordance 
with S6.2.6.2.2 followed by S6.2.6.2.1.
    (1) When tested in accordance with S6.2.6.2.2, the valve shall not 
exhibit leakage greater than 10 NmL/hour;
    (2) When tested in accordance S6.2.6.2.1, the valve shall not leak 
nor burst at less than 250 percent NWP nor burst at less than 80 
percent of the burst pressure of the new unit tested in accordance with 
S5.1.5.2(a) unless the burst pressure of the valve exceeds 400 percent 
NWP;
    (e) A valve subjected to vehicle environment testing in accordance 
with S6.2.6.1.5 shall not show signs of cracking, softening, or 
swelling and shall be tested sequentially in accordance with S6.2.6.2.2 
followed by S6.2.6.2.1. Cosmetic changes such as pitting or staining 
are not considered failures.
    (1) When tested in accordance with S6.2.6.2.2, the valve shall not 
exhibit leakage greater than 10 NmL/hour;
    (2) When tested in accordance S6.2.6.2.1, the valve shall not leak 
nor burst at less than 250 percent NWP nor burst at less than 80 
percent of the burst pressure of the new unit tested in accordance with 
S5.1.5.2(a) unless the burst pressure of the valve exceeds 400 percent 
NWP;
    (f) A shut-off valve shall have a minimum resistance of 240 
k[Omega] between the power conductor and the valve casing, and shall 
not exhibit open valve, smoke, fire, melting, or leakage greater than 
10 NmL/hour when subjected to electrical testing in accordance with 
S6.2.6.2.5 followed by leak testing in accordance with 6.2.6.2.2;
    (g) A valve subjected to vibration testing in accordance with 
S6.2.6.2.6 shall be tested sequentially in accordance with S6.2.6.2.2 
followed by S6.2.6.2.1.
    (1) When tested in accordance with S6.2.6.2.2, the valve shall not 
exhibit leakage greater than 10 NmL/hour;
    (2) When tested in accordance S6.2.6.2.1, the valve shall not leak 
nor burst at less than 250 percent NWP nor burst at less than 80 
percent of the burst pressure of the new unit tested in accordance with 
S5.1.5.2(a) unless the burst pressure of the valve exceeds 400 percent 
NWP;
    (h) A valve shall not exhibit visible cracking or delaminating when 
subjected to stress corrosion cracking testing in accordance with 
S6.2.6.1.6;
    S5.1.6. Labeling. Each vehicle container shall be permanently 
labeled with the information specified in paragraphs (a) through (f) of 
this section. Any label affixed to the container in compliance with 
this section shall remain in place and be legible for the 
manufacturer's recommended service life of the container. The 
information shall be in English and in letters and numbers that are at 
least 6.35 millimeters (\1/4 \inch) high.
    (a) The statement: ``If there is a question about the proper use, 
installation, or maintenance of this compressed hydrogen storage 
system, contact ___,'' inserting the vehicle manufacturer's name, 
address, and telephone number. The name provided shall be consistent 
with the manufacturer's filing in accordance with 49 CFR part 566.
    (b) The container serial number.
    (c) The statement: ``Manufactured in ___,'' inserting the month and 
year of manufacture of the container.
    (d) The statement ``Nominal Working Pressure ___ MPa (___psig)'' 
Inserting the nominal working pressure which shall be no greater than 
70 MPa.
    (e) The statement ``Compressed Hydrogen Gas Only.''
    (f) The statement: ``Do Not Use After ___'' inserting the month and 
year that mark the end of the manufacturer's recommended service life 
for the container.
    (g) The statement: ``This container should be visually inspected 
for damage and deterioration after a motor vehicle accident or fire, 
and either (i) at least every 12 months when installed on a vehicle 
with a GVWR greater than 4,536 kg, or (ii) at least every 36 months or 
36,000 miles, whichever comes first,

[[Page 27553]]

when installed on a vehicle with a GVWR less than or equal to 4,536 
kg.''
    (h) The statement: ``The burst pressure BPO applicable 
to this container is ___'' inserting the manufacturer's specified value 
of BPO in MPa.
    S6. Test procedures
    S6.1. [Reserved]
    S6.2. Test procedures for compressed hydrogen storage.
    S6.2.1. Unless otherwise specified, data sampling for pressure 
cycling under S6.2 shall be at least 1 Hz.
    S6.2.2. Test procedures for baseline performance metrics.
    S6.2.2.1. Burst test.
    (a) The container is filled with a hydraulic fluid.
    (b) The container, the surrounding environment, and the hydraulic 
fluid are at any temperature between 5.0 [deg]C and 35.0 [deg]C.
    (c) The rate of pressurization shall be less than or equal to 1.4 
MPa per second for pressures higher than 1.50 times NWP. If the rate 
exceeds 0.35 MPa per second at pressures higher than 1.50 times NWP, 
then the container is placed in series between the pressure source and 
the pressure measurement device.
    (d) The container is hydraulically pressurized until burst and the 
burst pressure of the container is recorded.
    S6.2.2.2. Pressure cycling test.
    (a) The container is filled with a hydraulic fluid.
    (b) The container surface, or the surface of the container 
attachments if present, the environment surrounding the container, and 
the hydraulic fluid are at any temperature between 5.0 [deg]C and 35.0 
[deg]C at the start of testing and maintained at the specified 
temperature for the duration of the testing.
    (c) The container is pressure cycled at any pressure between 1.0 
MPa and 2.0 MPa up to the pressure specified in the respective section 
of S5. The cycling rate shall be any rate between or equal to 5 and 10 
cycles per minute.
    (d) The temperature of the hydraulic fluid entering the container 
is maintained and monitored at any temperature between 5.0 [deg]C and 
35.0 [deg]C.
    (e) The container manufacturer may specify a hydraulic pressure 
cycle profile within the specifications of S6.2.2.2(c). Manufacturers 
shall submit this profile to NHTSA upon request, in writing, and within 
five business days, otherwise NHTSA shall determine the profile. At 
NHTSA's option, NHTSA shall cycle the container within 10 percent of 
the manufacturer's specified cycling profile.
    S6.2.3. Performance durability test.
    S6.2.3.1. Proof pressure test. The container is pressurized 
smoothly and continually with hydraulic fluid or hydrogen gas as 
specified until the pressure level is reached and held for the 
specified time.
    S6.2.3.2. Drop impact test. The container is drop tested without 
internal pressurization or attached valves. The surface onto which the 
container is dropped shall be a smooth, horizontal, uniform, dry, 
concrete pad or other flooring type with equivalent hardness. No 
attempt shall be made to prevent the container from bouncing or falling 
over during a drop test, except for the vertical drop test, during 
which the test article shall be prevented from falling over. The 
container shall be dropped in any one of the following four 
orientations described below and illustrated in Figure 2.
    (a) From a position within 5[deg] of horizontal with the lowest 
point of the container at any height between 1.800 meters and 1.820 
meters above the surface onto which it is dropped. In the case of a 
non-axisymmetric container, the largest projection area of the 
container shall be oriented downward and aligned horizontally;
    (b) From a position within 5[deg] of vertical with the center of 
any shut-off valve interface location upward and with any potential 
energy of between 488 Joules and 538 Joules. If a drop energy of 
between 488 Joules and 538 Joules would result in the height of the 
lower end being more than 1.820 meters above the surface onto which it 
is dropped, the container shall be dropped from any height with the 
lower end between 1.800 meters and 1.820 meters above the surface onto 
which it is dropped. If a drop energy of between 488 Joules and 538 
Joules would result in the height of the lower end being less than 
0.100 meters above the surface onto which it is dropped, the container 
shall be dropped from any height with the lower end between 0.100 
meters and 0.120 meters above the surface onto which it is dropped. In 
the case of a non-axisymmetric container, the center of any shut-off 
valve interface location and the container's center of gravity shall be 
aligned vertically, with the center of that shut-off valve interface 
location upward;
    (c) From a position within 5[deg] of vertical with the center of 
any shut-off valve interface location downward with any potential 
energy of between 488 Joules and 538 Joules. If a potential energy of 
between 488 Joules and 538 Joules would result in the height of the 
lower end being more than 1.820 meters above the surface onto which it 
is dropped, the container shall be dropped from any height with the 
lower end between 1.800 meters and 1.820 meters above the surface onto 
which it is dropped. If a drop energy of between 488 Joules and 538 
Joules would result in the height of the lower end being less than 
0.100 meters above the surface onto which it is dropped, the container 
shall be dropped from any height with the lower end between 0.100 
meters and 0.120 meters above the surface onto which it is dropped. In 
the case of a non-axisymmetric container, the center of any shut-off 
valve interface location and the container's center of gravity shall be 
aligned vertically, with the center of that shut-off valve interface 
location downward;
    (d) From any angle between 40[deg] and 50[deg] from the vertical 
orientation with the center of any shut-off valve interface location 
downward, and with the container center of gravity between 1.800 meters 
and 1.820 meters above the surface onto which it is dropped. However, 
if the lowest point of the container is closer to the ground than 0.60 
meters, the drop angle shall be changed so that the lowest point of the 
container is between 0.60 meters and 0.62 meters above the ground and 
the center of gravity is between 1.800 meters and 1.820 meters above 
the surface onto which it is dropped. In the case of a non-axisymmetric 
container, the line passing through the center of any shut-off valve 
interface location and the container's center of gravity shall be at 
any angle between 40[deg] and 50[deg] from the vertical orientation. If 
this results in more than one possible container orientation, the drop 
shall be conducted from the orientation that results in the lowest 
positioning of the center of the shut-off valve interface location.
    S6.2.3.3. Surface damage test. The surface damage test consists of 
surface cut generation and pendulum impacts as described below.
    (a) Surface cut generation: Two longitudinal saw cuts are made at 
any location on the same side of the outer surface of the unpressurized 
container, as shown in Figure 3, or on the container attachments if 
present. The first cut is 0.75 millimeters to 1.25 millimeters deep and 
200 millimeters to 205 millimeters long; The second cut, which is only 
required for containers affixed to the vehicle by compressing its 
composite surface, is 1.25 millimeters to 1.75 millimeters deep and 25 
millimeters to 28 millimeters long.
    (b) Pendulum impacts: Mark the outer surface of the container, or 
the container attachments if present, on the side opposite from the saw 
cuts, with five separate, non-overlapping circles each having any 
linear diameter between 100.0 millimeters and 105.0 millimeters, as 
shown in Figure 3. Within 30

[[Page 27554]]

minutes following preconditioning for any duration from 12 hours to 24 
hours in an environmental chamber at any temperature between -45.0 
[deg]C and -40.0 [deg]C, impact the center of each of the five areas 
with a pendulum having a pyramid with equilateral faces and square 
base, and the tip and edges being rounded to a radius of between 2.0 
millimeters and 4.0 millimeters. The center of impact of the pendulum 
shall coincide with the center of gravity of the pyramid. The energy of 
the pendulum at the moment of impact with each of the five marked areas 
on the container is any energy between 30.0 Joules and 35.0 Joules. The 
container is secured in place during pendulum impacts and is not 
pressurized above 1 MPa.
    S6.2.3.4. Chemical exposure and ambient temperature pressure 
cycling test.
    (a) Each of the 5 areas preconditioned by pendulum impact in 
S6.2.3.3(b) is exposed to any one of five solutions:
    (1) 19 to 21 percent by volume sulfuric acid in water;
    (2) 25 to 27 percent by weight sodium hydroxide in water;
    (3) 5 to 7 percent by volume methanol in gasoline;
    (4) 28 to 30 percent by weight ammonium nitrate in water; and
    (5) 50 to 52 percent by volume methyl alcohol in water.
    (b) The container is oriented with the fluid exposure areas on top. 
A pad of glass wool approximately 0.5 centimeters thick and 100 
millimeters in diameter is placed on each of the five preconditioned 
areas. A sufficient amount of the test fluid is applied to the glass 
wool to ensure that the pad is wetted across its surface and through 
its thickness for the duration of the test. A plastic covering shall be 
applied over the glass wool to prevent evaporation.
    (c) The exposure of the container with the glass wool is maintained 
for at least 48 hours and no more than 60 hours with the container 
hydraulically pressurized to any pressure between 125.0 percent NWP and 
130.0 percent NWP. During exposure, the temperature surrounding the 
container is maintained at any temperature between 5.0 [deg]C and 35.0 
[deg]C.
    (d) Hydraulic pressure cycling is performed in accordance with 
S6.2.2.2 at any pressure within the specified ranges according to 
S5.1.2.4 for the specified number of cycles. The glass wool pads are 
removed and the container surface is rinsed with water after the cycles 
are complete.
    S6.2.3.5. Static pressure test. The container is hydraulically 
pressurized to the specified pressure in a temperature-controlled 
chamber. The temperature of the chamber and the container surface, or 
the surface of the container attachments if present, are held at the 
specified temperature for the specified duration.
    S6.2.3.6. Extreme temperature pressure cycling test.
    (a) The container is filled with hydraulic fluid for each test;
    (b) At the start of each test, the container surface, or the 
surface of the container attachments if present, the hydraulic fluid, 
and the environment surrounding the container are at any temperature 
and relative humidity (if applicable) within the ranges specified in 
S5.1.2.6 and maintained for the duration of the testing.
    (c) The container is pressure cycled from any pressure between 1.0 
MPa and 2.0 MPa up to the specified pressure at a rate not exceeding 10 
cycles per minute for the specified number of cycles;
    (d) The temperature of the hydraulic fluid entering the container 
shall be measured as close as possible to the container inlet.
    S6.2.4. Test procedures for expected on-road performance.
    S6.2.4.1. Ambient and extreme temperature gas pressure cycling 
test.
    (a) In accordance with the Table to S5.1.3.2, the specified ambient 
conditions of temperature and relative humidity, if applicable, are 
maintained within the test environment throughout each pressure cycle. 
When required in accordance with the Table to S5.1.3.2, the CHSS 
temperature shall be in the specified initial system equilibration 
temperature range between pressure cycles.
    (b) The CHSS is pressure cycled from any pressure between 1.0 MPa 
and 2.0 MPa up to any pressure within the specified peak pressure range 
in accordance with the Table to S5.1.3.2. The temperature of the 
hydrogen fuel dispensed to the container is controlled to within the 
specified temperature range within 30 seconds of fueling initiation. 
The specified number of pressure cycles are conducted.
    (c) The ramp rate for pressurization shall be greater than or equal 
to the ramp rate given in the Table to S6.2.4.1(c) according to the 
CHSS volume, the ambient conditions, and the fuel delivery temperature. 
If the required ambient temperature is not available in the table, the 
closest ramp rate value or a linearly interpolated value shall be used. 
The pressure ramp rate shall be decreased if the gas temperature in the 
container exceeds 85 [deg]C.

                                                                 Table 5 to S6.2.4.1(c)
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                      CHSS pressurization rate (MPa/min)
                                                     ---------------------------------------------------------------------------------------------------
                                                        50.0 [deg]C to 55.0       5.0 [deg]C to 35.0     -30.0 [deg]C to -25.0    -30.0 [deg]C to -25.0
                   CHSS volume (L)                         [deg]C ambient           [deg]C ambient           [deg]C ambient           [deg]C ambient
                                                      conditions -33.0 [deg]C  conditions -33.0 [deg]C  conditions -33.0 [deg]C   conditions 15.0 [deg]C
                                                        to -40.0 [deg]C fuel     to -40.0 [deg]C fuel     to -40.0 [deg]C fuel     to 25.0 [deg]C fuel
                                                        delivery temperature     delivery temperature     delivery temperature     delivery temperature
--------------------------------------------------------------------------------------------------------------------------------------------------------
50..................................................                      7.6                     19.9                     28.5                     13.1
100.................................................                      7.6                     19.9                     28.5                      7.7
174.................................................                      7.6                     19.9                     19.9                      5.2
250.................................................                      7.6                     19.9                     19.9                      4.1
300.................................................                      7.6                     16.5                     16.5                      3.6
400.................................................                      7.6                     12.4                     12.4                      2.9
500.................................................                      7.6                      9.9                      9.9                      2.3
600.................................................                      7.6                      8.3                      8.3                      2.1
700.................................................                      7.1                      7.1                      7.1                      1.9
1,000...............................................                      5.0                      5.0                      5.0                      1.4
1,500...............................................                      3.3                      3.3                      3.3                      1.0
2,000...............................................                      2.5                      2.5                      2.5                      0.7
2,500...............................................                      2.0                      2.0                      2.0                      0.5
--------------------------------------------------------------------------------------------------------------------------------------------------------


[[Page 27555]]

    (d) The de-fueling rate shall be any rate greater than or equal to 
the intended vehicle's maximum fuel-demand rate. Out of the 500 
pressure cycles, any 50 pressure cycles are performed using a de-
fueling rate greater than or equal to the maintenance de-fueling rate.
    S6.2.4.2. Gas permeation test.
    (a) A CHSS is filled with hydrogen gas to any SOC between 100.0 
percent and 105.0 percent and placed in a sealed container. The CHSS is 
held for any duration between 12 hours and 24 hours at any temperature 
between 55.0 [deg]C and 60.0 [deg]C prior to the start of the test.
    (b) The permeation from the CHSS shall be determined hourly 
throughout the test.
    (c) The test shall continue for 500 hours or until the permeation 
rate reaches a steady state. Steady state is achieved when at least 3 
consecutive leak rates separated by any duration between 12 hours and 
48 hours are within 10 percent of the previous rate.
    S6.2.5. Test procedures for service terminating performance in 
fire. The fire test consists of two stages: a localized fire stage 
followed by an engulfing fire stage. The burner configuration for the 
fire test is specified in S6.2.5.1. The overall test configuration of 
the fire test is verified using a pre-test checkout in accordance with 
S6.2.5.2 prior to the fire test of the CHSS. The fire test of the CHSS 
is conducted in accordance with S6.2.5.3.
    S6.2.5.1. Burner Configuration.
    (a) The fuel for the burner shall be liquefied petroleum gas (LPG).
    (b) The width of the burner shall be between 450 millimeters and 
550 millimeters.
    (c) The length of the burner used for the localized fire stage 
shall be between 200 millimeters and 300 millimeters.
    (d) The length of the burner used for the engulfing fire stage 
shall be in accordance with S6.2.5.3(m).
    (e) The burner nozzle configuration and installation shall be in 
accordance with the Table below. The nozzles shall be installed 
uniformly on six rails.

                           Table 6 to S6.2.5.1
------------------------------------------------------------------------
                  Item                             Description
------------------------------------------------------------------------
Nozzle type............................  Liquefied petroleum gas fuel
                                          nozzle with air pre-mix.
LPG orifice in nozzle..................  0.9 to 1.1 millimeter inner
                                          diameter.
Air ports in nozzle....................  Four (4) holes, 5.8 to 7.0
                                          millimeter inner diameter.
Fuel/Air mixing tube in nozzle.........  9 to 11 millimeter inner
                                          diameter.
Number of rails........................  6.
Center-to-center spacing of rails......  100 to 110 millimeter.
Center-to-center nozzle spacing along    45 to 55 millimeter.
 the rails.
------------------------------------------------------------------------

    S6.2.5.2. Pre-test Checkout.
    (a) The pre-test checkout procedure in this section shall be 
performed to verify the fire test configuration for the CHSS tested in 
accordance with S6.2.5.3.
    (b) A pre-test container is a 12-inch Schedule 40 Nominal Pipe Size 
steel pipe with end caps. The cylindrical length of the pre-test 
container shall be equal to or longer than overall length of the CHSS 
to be tested in S6.2.5.3, but no shorter than 0.80 m and no longer than 
1.65 m.
    (c) The pre-test container shall be mounted over the burner:
    (1) At any height between 95 millimeters and 105 millimeters above 
the burner;
    (2) Such that the nozzles from the two center rails are pointing 
toward the bottom center of the pre-test container; and
    (3) Such that its position relative to the localized and engulfing 
zones of the burner are consistent with the positioning of the CHSS 
over the burner in S6.2.5.3.
    (d) For outdoor test sites, wind shielding shall be used. The 
separation between the pre-test container and the walls of the wind 
shields shall be at least 0.5 meters.
    (e) Temperatures during the pre-test check-out shall be measured at 
least once per second using 3.2 millimeter diameter or less K-type 
sheath thermocouples.
    (f) The thermocouples shall be located in sets to measure 
temperatures along the cylindrical section of the pre-test container. 
These thermocouples are secured by straps or other mechanical 
attachments within 5 millimeters from the pre-test container surface. 
One set of thermocouples consists of:
    (1) One thermocouple located at the bottom surface exposed to the 
burner flame,
    (2) One thermocouple located mid-height along the left side of the 
cylindrical surface,
    (3) One thermocouple located mid-height along the right side of the 
cylindrical surface, and
    (4) One thermocouple located at the top surface opposite to the 
burner flame.
    (g) One set of thermocouples shall be centrally located at the 
localized fire zone of the CHSS to be tested as determined in S6.2.5.3. 
Two additional sets of thermocouples shall be spread out over the 
remaining length of the engulfing fire zone of the CHSS to be tested 
that is not part of the localized fire zone of the CHSS to be tested.
    (h) Burner monitor thermocouples shall be located between 20 
millimeters and 30 millimeters below the bottom surface of the pre-test 
container in the same three horizontal locations described in 
S6.2.5.2(g). These thermocouples shall be mechanically supported to 
prevent movement.
    (i) With the localized burner ignited, the LPG flow rate to the 
burner shall be set such that the 60-second rolling averages of 
individual temperature readings in the localized fire zone shall be in 
accordance with the localized stage row in the table below.
    (j) With the entire burner ignited, the LPG flow rate to the burner 
shall be set such that the 60-second rolling averages of individual 
temperature readings shall be in accordance with the engulfing stage 
row in the table below.

[[Page 27556]]



                                               Table 7 to S6.2.5.2
----------------------------------------------------------------------------------------------------------------
                               Temperature range on
         Fire stage             bottom of pre-test     Temperature range on sides    Temperature range on top of
                                    container             of pre-test container          pre-test container
----------------------------------------------------------------------------------------------------------------
Localized..................  450 [deg]C to 700        less than 750 [deg]C........  less than 300 [deg]C.
                              [deg]C.
Engulfing..................  Average temperatures of  Not applicable..............  Average temperatures of the
                              the pre-test container                                 pre-test container surface
                              surface measured at                                    measured at the three top
                              the three bottom                                       locations shall be at least
                              locations shall be                                     100 [deg]C, and when
                              greater than 600                                       greater than 750 [deg]C,
                              [deg]C.                                                shall also be less than the
                                                                                     average temperatures of the
                                                                                     pre-test container surface
                                                                                     measured at the three
                                                                                     bottom locations.
----------------------------------------------------------------------------------------------------------------

    S6.2.5.3. CHSS Fire Test.
    (a) The CHSS to be fire tested shall include TPRD vent lines.
    (b) The CHSS to be fire tested shall be mounted at any height 
between 95 millimeters and 105 millimeters above the burner.
    (c) CHSS shall be positioned for the localized fire test by 
orienting the CHSS such that the distance from the center of the 
localized fire exposure to the TPRD(s) and TPRD sense point(s) is at or 
near maximum.
    (d) When the container is longer than the localized burner, the 
localized burner shall not extend beyond either end of the container in 
the CHSS.
    (e) The CHSS shall be filled with compressed hydrogen gas to any 
SOC between 100.0 percent and 105.0 percent.
    (f) For outdoor test sites, the same wind shielding shall be used 
as was used for S6.2.5.2. The separation between the CHSS and the walls 
of the wind shields shall be at least 0.5 meters.
    (g) Burner monitor temperatures shall be measured below the bottom 
surface of the CHSS in the same positions as specified in S6.2.5.2(h).
    (h) The allowable limits for the burner monitor temperatures during 
the CHSS fire test shall be established based on the results of the 
pre-test checkout as follows:
    (1) The minimum value for the burner monitor temperature during the 
localized fire stage (TminLOC) shall be calculated by 
subtracting 50 [deg]C from the 60-second rolling average of the burner 
monitor temperature in the localized fire zone of the pre-test 
checkout. If the resultant TminLOC exceeds 600 [deg]C, 
TminLOC shall be 600 [deg]C.
    (2) The minimum value for the burner monitor temperature during the 
engulfing fire stage (TminENG) shall be calculated by 
subtracting 50 [deg]C from the 60-second rolling average of the average 
of the three burner monitor temperatures during the engulfing fire 
stage of the pre-test checkout. If the resultant TminENG 
exceeds 800 [deg]C, TminENG shall be 800 [deg]C.
    (i) The localized fire stage is initiated by starting the fuel flow 
to the localized burner and igniting the burner.
    (j) The 10-second rolling average of the burner monitor temperature 
in the localized fire zone shall be at least 300 [deg]C within 1 minute 
of ignition and for the next 2 minutes.
    (k) Within 3 minutes of the igniting the burner, using the same LPG 
flow rate as S6.2.5.2(i), the 60-second rolling average of the 
localized zone burner monitor temperature shall be greater than 
TminLOC as determined in S6.2.5.3(h)(1).
    (l) After 10 minutes from igniting the burner, the engulfing fire 
stage is initiated.
    (m) The engulfing fire zone includes the localized fire zone and 
extends in one direction towards the nearest TPRD or TPRD sense point 
along the complete length of the container up to a maximum burner 
length of 1.65 m.
    (n) Within 2 minutes of the initiation of the engulfing fire stage, 
using the same LPG flow rate as S6.2.5.2(j), the 60-second rolling 
average of the engulfing burner monitor temperature shall be equal or 
greater than TminENG as determined in S6.2.5.3(h)(2).
    (o) The fire testing continues until the pressure inside the CHSS 
is less than or equal to 1.0 MPa or until:
    (1) A total test time of 60 minutes for CHSS on vehicles with a 
GVWR of 10,000 pounds or less or;
    (2) A total test time of 120 minutes for CHSS on vehicles with a 
GVWR over 10,000 pounds.
    S6.2.6. Test procedures for performance durability of closure 
devices.
    S6.2.6.1. TPRD performance tests. Unless otherwise specified, 
testing is performed with hydrogen gas with a purity of at least 99.97 
percent, less than or equal to 5 parts per million of water, and less 
or equal to 1 part per million particulate. All tests are performed at 
any temperature between 5.0 [deg]C and 35.0 [deg]C unless otherwise 
specified.
    S6.2.6.1.1. Pressure cycling test. A TPRD undergoes 15,000 internal 
pressure cycles at a rate not exceeding 10 cycles per minute. The table 
below summarizes the pressure cycles. Any condition within the ranges 
specified in the table may be selected for testing.
    (a) The first 10 pressure cycles shall be from any low pressure of 
between 1.0 MPa and 2.0 MPa to any high pressure between 150.0 percent 
NWP and 155.0 percent NWP. These cycles are conducted at any sample 
temperature between 85.0 [deg]C to 90.0 [deg]C.
    (b) The next 2,240 pressure cycles shall be from any low pressure 
between 1.0 MPa and 2.0 MPa to any high pressure of between 125.0 
percent NWP and 130.0 percent NWP. These cycles are conducted at any 
sample temperature between 85.0 [deg]C to 90.0 [deg]C.
    (c) The next 10,000 pressure cycles shall be from any low pressure 
of between 1.0 MPa and 2.0 MPa to any high pressure between 125.0 
percent NWP and 130.0 percent NWP. These cycles are conducted at a 
sample temperature between 5.0 [deg]C to 35.0 [deg]C.
    (d) The final 2,750 pressure cycles shall be from any low pressure 
between 1.0 MPa and 2.0 MPa to any high pressure between 80.0 percent 
NWP and 85.0 percent NWP. These cycles are conducted at any sample 
temperature between -45.0 [deg]C to -40.0 [deg]C.

                                              Table 8 to S6.2.6.1.1
----------------------------------------------------------------------------------------------------------------
                                                                                          Sample temperature for
          Number of cycles                Low pressure              High pressure                 cycles
----------------------------------------------------------------------------------------------------------------
First 10...........................  1.0 MPa to 2.0 MPa....  150.0% NWP to 155.0% NWP...  85.0 [deg]C to 90.0
                                                                                           [deg]C.

[[Page 27557]]

 
Next 2,240.........................  1.0 MPa to 2.0 MPa....  125.0% NWP to 130.0% NWP...  85.0 [deg]C to 90.0
                                                                                           [deg]C.
Next 10,000........................  1.0 MPa to 2.0 MPa....  125.0% NWP to 130.0% NWP...  5.0 [deg]C to 35.0
                                                                                           [deg]C.
Final 2,750........................  1.0 MPa to 2.0 MPa....  80.0% NWP to 85.0% NWP.....  -45.0 [deg]C to -40.0
                                                                                           [deg]C.
----------------------------------------------------------------------------------------------------------------

    S6.2.6.1.2. Accelerated life test.
    (a) Two TPRDs undergo testing; one at the manufacturer's specified 
activation temperature, and one at an accelerated life temperature, TL, 
given in [deg]C by the expression:
[GRAPHIC] [TIFF OMITTED] TP17AP24.017

Where b = 273.15 [deg]C, TME is 85 [deg]C, and Tf is the 
manufacturer's specified activation temperature in [deg]C.

    (b) The TPRDs are placed in an oven or liquid bath maintained 
within 5.0 [deg]C of the specified temperature per S6.2.6.1.2(a). The 
TPRD inlets are pressurized with hydrogen to any pressure between 125.0 
percent NWP and 130.0 percent NWP and time until activation is 
measured.
    S6.2.6.1.3. Temperature cycling test.
    (a) An unpressurized TPRD is placed in a cold liquid bath 
maintained at any temperature between -45.0 [deg]C and -40.0 [deg]C. 
The TPRD shall remain in the cold bath for any duration not less than 2 
hours and not more than 24 hours. The TPRD is removed from the cold 
bath and transferred, within five minutes of removal, to a hot liquid 
bath maintained at any temperature between 85.0 [deg]C and 90.0 [deg]C. 
The TPRD shall remain in the hot bath for any duration not less than 2 
hours and not more than 24 hours. The TPRD is removed from the hot bath 
and, within five minutes of removal, transferred back into the cold 
bath maintained at any temperature between -45.0 [deg]C and -40.0 
[deg]C;
    (b) Step (a) is repeated until 15 thermal cycles have been 
achieved.
    (c) The TPRD remains in the cold liquid bath for any duration not 
less than 2 and not more than 24 additional hours, then the internal 
pressure of the TPRD is cycled with hydrogen gas from any pressure 
between 1.0 MPa and 2.0 MPa to any pressure between 80.0 percent NWP 
and 85.0 percent NWP for 100 cycles. During cycling, the TPRD remains 
in the cold bath and the cold bath is maintained at any temperature 
between -45.0 [deg]C and -40.0 [deg]C.
    S6.2.6.1.4. Salt corrosion resistance test.
    (a) Each closure device is exposed to a combination of cyclic 
conditions of salt solution, temperatures, and humidity. One test cycle 
is equal to any duration not less than 22 and not more than 26 hours, 
and is in accordance with the table below.

                                              Table 9 to S6.2.6.1.4
----------------------------------------------------------------------------------------------------------------
                    Accelerated cyclic corrosion conditions (1 cycle = 22 hours to 26 hours)
-----------------------------------------------------------------------------------------------------------------
          Cycle condition                Temperature            Relative humidity            Cycle duration
----------------------------------------------------------------------------------------------------------------
Ambient stage.....................  22.0 [deg]C to 28.0    35 percent to 55 percent..  470 minutes to 490
                                     [deg]C.                                            minutes.
----------------------------------------------------------------------------------------------------------------
                                           Transition 55 min to 60 min
----------------------------------------------------------------------------------------------------------------
Humid stage.......................  47.0 [deg]C to 51.0    95 percent to 100 percent.  410 minutes to 430
                                     [deg]C.                                            minutes.
----------------------------------------------------------------------------------------------------------------
                                      Transition 170 minutes to 190 minutes
----------------------------------------------------------------------------------------------------------------
Dry stage.........................  55.0 [deg]C to 65.0    less than 30 percent......  290 minutes to 310
                                     [deg]C.                                            minutes.
----------------------------------------------------------------------------------------------------------------

    (b) The apparatus used for this test shall consist of a fog/
environmental chamber as defined in ISO 6270-2:2017 (incorporated by 
reference, see Sec.  571.5), with a suitable water supply conforming to 
Type IV requirements in ASTM D1193-06(R2018) (incorporated by 
reference, see Sec.  571.5). The chamber shall include a supply of 
compressed air and one or more nozzles for fog generation. The nozzle 
or nozzles used for the generation of the fog shall be directed or 
baffled to minimize any direct impingement on the closure devices.
    (c) During ``wet-bottom'' generated humidity cycles, water droplets 
shall be visible on the samples.
    (d) Steam generated humidity may be used provided the source of 
water used in generating the steam is free of corrosion inhibitors and 
visible water droplets are formed on the samples to achieve proper 
wetness.
    (e) The drying stage shall occur in the following environmental 
conditions: any temperature not less than 60 [deg]C and not greater 
than 65 [deg]C and relative humidity no more than 30 percent with air 
circulation.
    (f) The impingement force from the salt solution application shall 
not remove corrosion and/or damage the coatings of the closure devices.
    (g) The complex salt solution in percent by mass shall be as 
specified below:
    (1) Sodium Chloride: not less than 0.08 and not more than 0.10 
percent.
    (2) Calcium Chloride: not less than 0.095 and not more than 0.105 
percent
    (3) Sodium Bicarbonate: not less than 0.07 and not more than 0.08 
percent
    (4) Sodium Chloride must be reagent grade or food grade. Calcium 
Chloride must be reagent grade. Sodium Bicarbonate must be reagent 
grade. For the purposes of S6.2.6.1.4, water must meet ASTM D1193-
06(R2018) Type IV requirements (incorporated by reference, see Sec.  
571.5).
    (5) Either calcium chloride or sodium bicarbonate material must be 
dissolved separately in water and added to the solution of the other 
materials.
    (h) The closure devices shall be installed in accordance with the

[[Page 27558]]

manufacturer's recommended procedure and exposed to the 100 daily 
corrosion cycles, with each corrosion cycle in accordance with the 
table above.
    (i) For each salt mist application, the solution shall be sprayed 
as an atomized mist, using the spray apparatus to mist the components 
until all areas are thoroughly wet and dripping. Suitable application 
techniques include using a plastic bottle, or a siphon spray powered by 
oil-free regulated air to spray the test samples. The quantity of spray 
applied should be sufficient to visibly rinse away salt accumulation 
left from previous sprays. Four salt mist applications shall be applied 
during the ambient stage. The first salt mist application occurs at the 
beginning of the ambient stage. Each subsequent salt mist application 
should be applied not less than 90 and not more than 95 minutes after 
the previous application.
    (j) The time from ambient to the wet condition shall be any 
duration not less than 60 and not more than 65 minutes and the 
transition time between wet and dry conditions shall be any duration 
not less than 180 and not more than 190 minutes.
    S6.2.6.1.5. Vehicle environment test.
    (a) The inlet and outlet connections of the closure device are 
connected or capped in accordance with the manufacturer's installation 
instructions. All external surfaces of the closure device are exposed 
to each of the following fluids for any duration between 24 hours and 
26 hours. The temperature during exposure shall be any temperature 
between 5.0 [deg]C and 35.0 [deg]C. A separate test is performed with 
each of the fluids sequentially on a single closure device.
    (1) Sulfuric acid: not less than 19 and not more than 21 percent by 
volume in water;
    (2) Ethanol/gasoline: not less than 10 and not more than 12 percent 
by volume ethanol and not less than 88 and not more than 90 percent by 
volume gasoline; and
    (3) Windshield washer fluid: not less than 50 and not more than 52 
percent by volume methanol in water.
    (b) The fluids are replenished as needed to ensure complete 
exposure for the duration of the test.
    (c) After exposure to each fluid, the closure device is wiped off 
and rinsed with water.
    S6.2.6.1.6. Stress corrosion cracking test.
    (a) All components exposed to the atmosphere shall be degreased. 
For check valves and shut-off valves, the closure device shall be 
disassembled, all components degreased, and then reassembled.
    (b) The closure device is continuously exposed to a moist ammonia 
air mixture maintained in a glass chamber having a glass cover. The 
exposure lasts any duration not less than 240 hours and not more than 
242 hours. The aqueous ammonia shall have any specific gravity not less 
than 0.940 and not more than 0.941. Aqueous ammonia shall be located at 
the bottom of the glass chamber below the sample at any volume not less 
than 20 mL and not more than 22 mL of aqueous ammonia per liter of 
chamber volume. The bottom of the sample is positioned any distance not 
less than 30 and not more than 40 millimeters above the aqueous ammonia 
and supported in an inert tray.
    (c) The moist ammonia-air mixture is maintained at atmospheric 
pressure and any temperature not less than 35 [deg]C and not more than 
40 [deg]C.
    S6.2.6.1.7. Drop and vibration test.
    (a) The TPRD is aligned vertically to any one of the six 
orientations covering the opposing directions of three orthogonal axes: 
vertical, lateral and longitudinal.
    (b) A TPRD is dropped in free fall from any height between 2.00 
meters and 2.02 meters onto a smooth concrete surface. The TPRD is 
allowed to bounce on the concrete surface after the initial impact.
    (c) Any sample with damage from the drop that results in the TPRD 
not being able to be tested in accordance with S6.2.6.1.7(d) shall not 
proceed to S6.2.6.1.7(d) and shall not be considered a failure of this 
test.
    (d) Each TPRD dropped in S6.2.6.1.7(a) that did not have damage 
that results in the TPRD not being able to be tested is mounted in a 
test fixture in accordance with manufacturer's installation 
instructions and vibrated for any duration between 30.0 minutes and 
35.0 minutes along each of the three orthogonal axes (vertical, lateral 
and longitudinal) at the most severe resonant frequency for each axis.
    (1) The most severe resonant frequency for each axis is determined 
using any acceleration between 1.50 g and 1.60 g and sweeping through a 
sinusoidal frequency range from 10 Hz to 500 Hz with any sweep time 
between 10.0 minutes and 20.0 minutes. The most severe resonant 
frequency is identified by a pronounced increase in vibration 
amplitude.
    (2) If the resonance frequency is not found, the test shall be 
conducted at any frequency between 35 Hz and 45 Hz.
    S6.2.6.1.8. Leak test. Unless otherwise specified, the TPRD shall 
be thermally conditioned to the ambient temperature condition, then 
checked for leakage, then conditioned to the high temperature 
condition, then checked for leakage, then conditioned to low 
temperature, then checked for leakage.
    (a) The TPRD shall be thermally conditioned at test temperatures in 
each of the test conditions and held for any duration between 1.0 hour 
and 24.0 hours. The TPRD is pressurized with hydrogen at the inlet. The 
required test conditions are:
    (1) Ambient temperature: condition the TPRD at any temperature 
between 5.0 [deg]C and 35.0 [deg]C; test in accordance with 
S6.2.6.1.8(b) at any pressure between 1.5 MPa and 2.5 MPa and then at 
any pressure between 125.0 percent NWP and 130.0 percent NWP.
    (2) High temperature: condition the TPRD at any temperature between 
85.0 [deg]C and 90.0 [deg]C; test in accordance with S6.2.6.1.8(b) at 
any pressure between 1.5 MPa and 2.5 MPa and then at any pressure 
between 125.0 percent NWP and 130.0 percent NWP.
    (3) Low temperature: condition the TPRD at any temperature between 
-45.0 [deg]C and -40.0 [deg]C; test in accordance with S6.2.6.1.8(b) at 
any pressure between 1.5 MPa and 2.5 MPa and then at any pressure 
between 100.0 percent NWP and 105.0 percent NWP.
    (b) Following conditioning at each of the specified test 
temperature ranges, the TPRD is observed for leakage while immersed in 
a temperature-controlled liquid at the same specified temperature range 
for any duration between 1.0 minutes and 2.0 minutes at each of the 
pressures ranges listed above. If no bubbles are observed for the 
specified time period, it is not considered a failure. If bubbles are 
detected, the leak rate is measured.
    S6.2.6.1.9. Bench top activation test.
    (a) The test apparatus consists of either a forced air oven or 
chimney with air flow. The TPRD is not exposed directly to flame. The 
TPRD is mounted in the test apparatus according to the manufacturer's 
installation instructions.
    (b) The temperature of the oven or chimney is at any temperature 
between 600.0 [deg]C and 605.0 [deg]C for any duration between 2 
minutes and 62 minutes prior to inserting the TPRD.
    (c) Prior to inserting the TPRD, pressurize the TPRD to any 
pressure between 1.5 MPa and 2.5 MPa.
    (d) The pressurized TPRD is inserted into the oven or chimney, the 
temperature within the oven or chimney is maintained at any temperature 
between 600.0 [deg]C and 605.0 [deg]C, and the time for the TPRD to 
activate is recorded. If the TPRD does not activate within 120 minutes 
from the time of insertion into the oven or chimney, the TPRD shall be 
considered to have failed the test.

[[Page 27559]]

    S6.2.6.1.10. Flow rate test.
    (a) At least one new TPRD is tested to establish a baseline flow 
rate.
    (b) After activation in accordance with S6.2.6.1.9, and without 
cleaning, removal of parts, or reconditioning, the TPRD is subjected to 
flow testing using hydrogen, air or an inert gas;
    (c) Flow rate testing is conducted with any inlet pressure between 
1.5 MPa and 2.5 MPa. The outlet is at atmospheric pressure.
    (d) Flow rate is measured in units of kilograms per minute with a 
precision of at least 2 significant digits.
    S6.2.6.2. Check valve and shut-off valve performance tests. Unless 
otherwise specified, testing shall be performed with hydrogen gas with 
a purity of at least 99.97 percent, less than or equal to 5 parts per 
million of water, and less or equal to 1 part per million particulate. 
All tests are performed at any temperature between 5.0 [deg]C and 35.0 
[deg]C unless otherwise specified.
    S6.2.6.2.1. Hydrostatic strength test.
    (a) The outlet opening is plugged and valve seats or internal 
blocks are made to assume the open position.
    (b) Any hydrostatic pressure between 250.0 percent NWP and 255.0 
percent NWP is applied using water to the valve inlet for any duration 
between 180.0 seconds and 185.0 seconds. The unit is examined to ensure 
that burst has not occurred.
    (c) The hydrostatic pressure is then increased at a rate of less 
than or equal to 1.4 MPa/sec until component failure. The hydrostatic 
pressure at failure is recorded.
    S6.2.6.2.2. Leak test.
    Each unit shall be thermally conditioned to the ambient temperature 
condition, then checked for leakage, then conditioned to the high 
temperature condition, then checked for leakage, then conditioned to 
low temperature, then checked for leakage.
    (a) Each unit shall be pressurized to any pressure between 2.0 MPa 
and 3.0 MPa and held for any duration between 1.0 hours and 24.0 hours 
in the specified temperature range before testing. The outlet opening 
is plugged. The test conditions are:
    (1) Ambient temperature: condition the unit at any temperature 
between 5.0 [deg]C and 35.0 [deg]C; test at any pressure between 1.5 
MPa and 2.5 MPa and at any pressure between 125.0 percent NWP and 130.0 
percent NWP.
    (2) High temperature: condition the unit at any temperature between 
85.0 [deg]C and 90.0 [deg]C; test at any pressure between 1.5 MPa and 
2.5 MPa and any pressure between 125.0 percent NWP and 130.0 percent 
NWP.
    (3) Low temperature: condition the unit at any temperature between 
-45.0 [deg]C and -40.0 [deg]C; test at any pressure between 1.5 MPa and 
2.5 MPa and any pressure between 100.0 percent NWP and 105.0 percent 
NWP.
    (b) While within the specified temperature and pressure range, the 
unit is observed for leakage while immersed in a temperature-controlled 
liquid held within the same specified temperature range as the test 
condition for any duration between 1.0 minutes and 2.0 minutes at each 
of the test pressures. If no bubbles are observed for the specified 
time period, the sample passes the leak test. If bubbles are detected, 
the leak rate is measured.
    S6.2.6.2.3. Extreme temperature pressure cycling test.
    (a) The valve unit is connected to a test fixture.
    (b) For a check valve, the pressure is applied in six incremental 
pulses to the check valve inlet with the outlet closed. The pressure is 
then vented from the check valve inlet. The pressure is lowered on the 
check valve outlet side to any pressure between 55.0 percent NWP and 
60.0 percent NWP prior to the next cycle;
    (c) For a shut-off valve, the specified pressure is applied through 
the inlet port. The shut-off valve is then energized to open the valve 
and the pressure is reduced to any pressure less than 50 percent of the 
specified pressure range. The shut-off valve shall then be de-energized 
to close the valve prior to the next cycle.
    S6.2.6.2.4. Chatter flow test. The valve is subjected to between 
24.0 hours and 26.0 hours of chatter flow at a flow rate that causes 
the most valve flutter.
    S6.2.6.2.5. Electrical Tests. This section applies to shut-off 
valves only.
    (a) The solenoid valve is connected to a variable DC voltage 
source, and the solenoid valve is operated as follows:
    (1) Held for any duration between 60.0 and 65.0 minutes at any 
voltage between 0.50 V and 1.5 times the rated voltage.
    (2) The voltage is increased to any voltage between 0.5 V to two 
times the rated voltage, or between 60.0 V and 60.5 V, whichever is 
less, and held for any duration between 60.0 seconds and 70.0 seconds.
    (b) Any voltage between 1,000.0 V DC and 1,010.0 V DC is applied 
between the power conductor and the component casing for any duration 
between 2.0 seconds to 4.0 seconds.
    S6.2.6.2.6. Vibration test.
    (a) The valve is pressurized with hydrogen to any pressure between 
100.0 percent NWP and 105.0 percent NWP, sealed at both ends, and 
vibrated for any duration between 30.0 and 35.0 minutes along each of 
the three orthogonal axes (vertical, lateral and longitudinal) at the 
most severe resonant frequencies.
    (b) The most severe resonant frequencies are determined using any 
acceleration between 1.50 g and 1.60 g and sweeping through a 
sinusoidal frequency range from 10 Hz to 500 Hz with any sweep time 
between 10.0 minutes and 20.0 minutes. The resonance frequency is 
identified by a pronounced increase in vibration amplitude.
    (c) If the resonance frequency is not found, the test shall be 
conducted at any frequency between 35 Hz and 45 Hz.
BILLING CODE 4910-59-P

[[Page 27560]]

[GRAPHIC] [TIFF OMITTED] TP17AP24.018

Figure 1. Performance Durability Test; (for Illustration Purposes Only)
[GRAPHIC] [TIFF OMITTED] TP17AP24.019

Figure 2. The Four Drop Orientations; (for Illustration Purposes Only)

[[Page 27561]]

[GRAPHIC] [TIFF OMITTED] TP17AP24.020

Figure 3. Locations of Surface Damage for S6.2.3.3(a) and Pendulum 
Impacts for S6.2.3.3(b); (for Illustration Purposes Only)

    Authority: 49 U.S.C. 322, 30111, 30115, 30117, 30122 and 30166; 
delegation of authority at 49 CFR 1.95 and 501.5.

Sophie Shulman,
Deputy Administrator.
[FR Doc. 2024-07116 Filed 4-16-24; 8:45 am]
BILLING CODE 4910-59-C