[Federal Register Volume 59, Number 242 (Monday, December 19, 1994)]
[Unknown Section]
[Page 0]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 94-31016]


[[Page Unknown]]

[Federal Register: December 19, 1994]


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DEPARTMENT OF TRANSPORTATION
49 CFR Part 571

[Docket No. 93-02; Notice 06]
RIN 2127-AF14

 

Federal Motor Vehicle Safety Standards; Fuel System Integrity of 
Compressed Natural Gas Vehicles; Compressed Natural Gas Fuel Container 
Integrity

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

ACTION: Supplemental notice of proposed rulemaking (SNPRM).

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SUMMARY: This notice proposes to amend Standard No. 303, Fuel System 
Integrity of Compressed Natural Gas Vehicles, and Standard No. 304, 
Compressed Natural Gas Fuel Containers. With respect to Standard No. 
303, the notice proposes additional labeling requirements for 
compressed natural gas (CNG) vehicles. With respect to Standard No. 
304, the notice proposes to specify additional performance requirements 
that would ensure a CNG fuel container's integrity. The proposes tests 
include environmental cycling tests, an impact test, a gunfire test, a 
flaw tolerance test, a pendulum impact test, and a drop test. Along 
with the vehicle labeling requirements, the notice proposes additional 
labeling requirements for CNG containers. These tests and performance 
requirements, which are based on the Natural Gas Vehicle Coalition's 
voluntary standard, NGV2, are intended to ensure the structural 
integrity of CNG containers.

DATES: Comments on this notice must be received by the agency no later 
than February 17, 1995.

ADDRESSES: Comments on this notice should refer to the above docket and 
notice number and be submitted to: Docket Section, National Highway 
Traffic Safety Administration, Room 5109, 400 Seventh Street SW., 
Washington, D.C. 20590. Telephone: (202) 366-5267. Docket hours are 
9:30 a.m. to 4:00 p.m., Monday through Friday.

FOR FURTHER INFORMATION CONTACT:
Mr. Gary R. Woodford, NRM-01.01, Special Projects Staff, National 
Highway Traffic Safety Administration, 400 Seventh Street SW., 
Washington, D.C. 20590 (202-366-4931).

SUPPLEMENTARY INFORMATION:

Outline

I. Background
    A. General Information
    B. Previous Agency Rulemakings
II. Agency Supplemental Proposal
    A. General
    B. Environmental Cycling Test
    C. Road Salt Environmental Test
    D. Charpy Impact Test
    E. Gunfire Test
    F. Damage Tolerance Tests
    1. General Considerations
    2. Flaw Tolerance Test
    3. Pendulum Impact Test
    4. Drop Test
    G. Bonfire Test Fuel
    H. Labeling Requirements
    1. CNG Containers
    a. Labeling Information
    b. Label Location
    2. Vehicle Labeling
    I. Other Safety Issues
    J. Leadtime
    K. Benefits
    L. Costs
III. Rulemaking Analyses and Notices

I. Background

A. General Information

    Natural gas is a vapor that is lighter than air at standard 
temperature and pressure.\1\ When used as a motor fuel, natural gas is 
typically stored on-board a vehicle in cylindrical containers at a 
pressure of approximately 20,684 kPa pressure (3,000 psi). Natural gas 
is kept in this compressed state to increase the amount that can be 
stored on-board the vehicle. This in turn serves to increase the 
vehicle's driving range. Since natural gas is a flammable fuel and is 
stored under high pressure, natural gas containers pose a potential 
risk to motor vehicle safety.
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    \1\Standard temperature is 0 deg. Celsius or 32 deg. Fahrenheit 
and standard pressure is 101.4 kiloPascals (kPa) or 14.7 pounds per 
square inch (psi).
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    Vehicles powered by CNG have not been numerous to date, although 
they are increasing. The number of CNG vehicles in the United States 
has more than doubled from 10,300 in 1990 to 23,800 at the end of 1992. 
The number of CNG vehicles is projected to again double to an estimated 
50,800 vehicles in 1994. As discussed in detail in a final rule 
published on April 22, 1994, establishing Standard No. 303, Fuel System 
Integrity of Compressed Natural Gas Vehicles, recent Federal 
legislation, as well as the need to meet environmental and energy 
security goals, will lead to increased production and use of these 
vehicles. (59 FR 19648)

B. Previous Agency Rulemakings

    On October 12, 1990, NHTSA published an advance notice of proposed 
rulemaking (ANPRM) to explore whether the agency should issue Federal 
motor vehicle safety standards (FMVSSs) applicable to CNG fuel 
containers and the fuel systems of motor vehicles using CNG or 
liquefied petroleum gas (LPG) as a motor fuel. (55 FR 41561). The ANPRM 
sought comment about the crash integrity of vehicle fuel systems, the 
integrity of fuel storage containers, and pressure relief for such 
containers.
    On January 21, 1993, NHTSA published a notice of proposed 
rulemaking (NPRM) in which the agency proposed to establish a new FMVSS 
specifying performance requirements for vehicles fueled by CNG. (58 FR 
5323). The proposal was based on comments received in response to the 
ANPRM and other available information.The NPRM was divided into two 
segments: (1) vehicle requirements that focused on the integrity of the 
entire fuel system, and (2) equipment requirements that focused on the 
fuel containers alone. In that notice, the agency proposed specific 
requirements applicable to the initial strength, durability, and 
pressure relief characteristics of CNG containers. In addition, the 
agency sought comments about the effects of corrosion and cold 
temperature extremes on CNG containers, and their rupture without 
fragmentation.
    NHTSA received a large number of comments to the docket addressing 
the January 1993 proposal. The commenters included manufacturers of CNG 
containers, vehicle manufacturers, trade associations, other CNG-
oriented businesses, research organizations, State and local 
governments, the United States Department of Energy, and energy 
companies. In addition, NHTSA met with the Compressed Gas Association 
(CGA) and the Natural Gas Vehicle Coalition (NGVC) and had telephone 
conversations meetings with some of the commenters. A record of each of 
these contacts may be reviewed in the public docket.
    The commenters generally believed that a Federal safety standard 
regulating the integrity of CNG fuel systems and fuel containers is 
necessary and appropriate. In fact, some commenters, including the CGA, 
the NGVC, and CNG container manufacturers stated that NHTSA should 
issue a Federal standard as soon as possible to facilitate the safe and 
expeditious introduction of CNG fueled vehicles. With respect to the 
equipment requirements, the commenters generally believe that Federal 
requirements about the CNG fuel container integrity are needed and 
should be implemented as quickly as possible.
    In addition to comments addressing the proposed requirements for 
durability, strength, and pressure relief, some commenters favored the 
promulgation of requirements about corrosion resistance, high and low 
temperature extremes, damage tolerance, and rupture characteristics of 
CNG containers.
    As noted above, NHTSA recently established Standard No. 303. It 
specifies vehicle performance requirements for the fuel system of 
vehicles fueled by CNG. The Standard enhances the fuel system integrity 
of CNG vehicles by subjecting the vehicles to crash testing and placing 
a limit on the post-crash pressure drop in the fuel system. The 
Standard specifies frontal, rear, and lateral barrier crash tests for 
light vehicles and a moving contoured barrier crash test for school 
buses with a GVWR over 10,000 pounds.
    NHTSA has also issued a final rule that establishes a new Federal 
motor vehicle safety standard, Standard No. 304, Compressed Natural Gas 
Fuel Containers, that specifies tests and performance requirements 
applicable to a CNG fuel container's durability, strength, and pressure 
relief. A pressure cycling test evaluates a container's durability by 
requiring a container to withstand without any leakage, 18,000 cycles 
of pressurization and depressurization. This requirement helps to 
ensure that a CNG container is capable of sustaining the cycling loads 
imposed on the container during refuelings over its service life. A 
burst test evaluates a container's initial strength and resistance to 
degradation over time. This requirement helps to ensure that a 
container's design and material are appropriately strong over the 
container's life. A bonfire test evaluates a container's pressure 
relief characteristics when pressure builds in a container, primarily 
due to temperature rise. In addition, the final rule specifies labeling 
requirements for CNG fuel containers. These requirements are based on 
specifications in NGV2, a voluntary industry standard addressing CNG 
fuel containers which was adopted by the American National Standards 
Institute (ANSI)\2\.
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    \2\NGV2 was developed by an industry working group that included 
container manufacturers, CNG users, and utilities.
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    NGV2 specifies four types of container designs. A Type 1 container 
is a metallic noncomposite container. A Type 2 container is a metallic 
liner over which an overwrap such as carbon fiber or fiberglass is 
applied in a hoop wrapped pattern over the liner's cylinder wall. A 
Type 3 container is a metallic liner over which an overwrap such as 
carbon fiber or fiberglass is applied in a full wrapped pattern over 
the entire liner, including the domes. A Type 4 container is a non-
metallic liner over which an overwrap such as carbon fiber or 
fiberglass is applied in a full wrapped pattern over the entire liner, 
including the domes.

II. Agency Supplemental Proposal

A. General

    Based on comments to the January 1993 NPRM and other available 
information, NHTSA has decided to issue this supplemental notice of 
proposed rulemaking (SNPRM), to propose additional performance 
requirements and tests to ensure a CNG container's structural 
integrity. Among the proposed tests are environmental cycling tests, a 
low temperature impact test, a gunfire test, a flaw tolerance test, a 
pendulum impact test, and a drop test. One environmental cycling test 
would evaluate a container's resistance to internal corrosion and high 
humidity as well as the effects of high and low temperatures on a 
container. A second environmental test would evaluate a container's 
resistance to road salt and other acidic chemicals. The impact test, 
known as the Charpy test, would evaluate a metal container's brittle 
fracture characteristics under low temperatures. The gunfire test would 
evaluate container fragmentation. Three tests, the flaw tolerance test, 
the pendulum impact test, and the drop test, would evaluate a 
container's resistance to external damage. Specifically, the flaw 
tolerance test would evaluate a container's exterior resistance to 
abrasion; the pendulum impact test would evaluate a container's ability 
to withstand a sharp external blow; and the drop test would evaluate a 
container's ability to withstand a blunt external blow. This notice 
also proposes labeling requirements applicable to CNG vehicles and 
labeling requirements for CNG containers in addition to those required 
by the CNG container final rule.
    Each of the proposed performance requirements and test procedures 
are modeled after provisions in NGV2 or are similar to those 
requirements. The agency tentatively concludes that modeling the 
Federal standard after NGV2 would be the best way to regulate how a CNG 
container reacts to such conditions as corrosive substances, 
temperature extremes, external damage, and rupture. In some instances, 
the agency departed from NGV2's performance requirements and test 
criteria to be consistent with 49 U.S.C. 30111 (formerly section 103 of 
the National Traffic and Motor Vehicle Safety Act, 15 U.S.C. 
Sec. 1392). That statute commands the agency to issue ``motor vehicle 
safety standards'' that are practicable, meet the need for motor 
vehicle safety, and are stated in objective terms. One example of such 
a departure can be found in the environmental cycling performance 
requirement for internal corrosion. Instead of stating that there shall 
be no ``evidence of distortion, deterioration, or failure,'' the 
proposal states that the container ``shall not leak or be distorted.'' 
Another example can be found in the gunfire test conditions. Instead of 
stating that ``(t)he distance from firing location to test container is 
not to exceed 46 meters,'' the proposal states that ``(t)he distance 
from firing location to test container is 46 meters.'' The most 
significant differences between the proposal and NGV2 are discussed 
below.

B. Environmental Cycling Test

    Section 1-18(d)(2) of NGV2 includes an environmental cycling test 
to prevent the unreasonable corrosion of a CNG container's internal 
surface. In addition, this test evaluates the effect that high humidity 
as well as high and low temperatures have on the CNG containers.\3\
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    \3\The Charpy impact test also evaluates low temperature 
performance for metal containers and liners because some metals are 
susceptible to brittle fracture at low temperatures.
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    In the ANPRM and NPRM, NHTSA noted that the level of impurities in 
CNG (i.e., gas quality) could influence the fuel container's integrity. 
Specifically, certain compounds in CNG could lead to stress corrosion 
cracking, corrosion, fatigue or other internal harm to the container's 
integrity. Such harm could cause the CNG containers to fail. The agency 
initially decided not to propose a performance test to address a CNG 
container's ability to withstand corrosion, since the agency was not 
aware of any readily available performance test that would address the 
failure modes at issue. Nevertheless, in the NPRM, NHTSA requested 
comments about the need for a requirement addressing corrosion and, if 
so, what tests and performance levels are most appropriate. In 
particular, the agency requested comment about the practicability of 
using the NGV2's environmental cycling test. In the NPRM, the agency 
specifically asked whether, instead of adopting the first sentence of 
the test verbatim, the agency should say ``One representative container 
free of any protective coating shall be cycle tested as follows, and 
shall not leak * * *''
    Commenters on the NPRM stated that there are two principal ways to 
regulate containers to prevent unreasonable internal corrosion: (1) 
Regulating the gas quality or (2) regulating container performance. 
NGVC, Pressed Steel Tank Co., EDO, the National Fire Protection 
Association, the American Automobile Manufacturers Association (AAMA), 
Tecogen, and Ontario recommended that the agency adopt gas quality 
requirements for CNG such as those set forth in a Society of Automotive 
Engineers (SAE's) Recommended Practice SAE J1616, ``Fuel Composition 
for Natural Gas Vehicles,'' February 1994. That recommended practice 
addresses internal corrosion by limiting the amount of water and other 
impurities in CNG.
    After reviewing the comments and other available information. NHTSA 
has decided to propose a corrosion resistance requirement for CNG 
containers. The agency notes that under 49 U.S.C. 30101 et seq. 
(formerly the Safety Act, 15 U.S.C. 1381 et seq.), NHTSA is authorized 
to regulate the manufacture of motor vehicles and motor vehicle 
equipment. However, it has no authority to regulate fuel quality since 
fuel is not considered to be motor vehicle equipment. Therefore, NHTSA 
cannot issue standards regulating the quality of CNG. Nevertheless, the 
agency encourages the industry to improve gas quality for CNG vehicles 
through voluntary standards such as SA J1616.
    NHTSA has decided to propose a performance requirement to ensure 
that a CNG container resists corrosion. Such a requirement would 
prevent catastrophic failures of CNG containers due to internal 
corrosion. This is particularly important since the agency only has 
statutory authority to issue safety standards that regulate the 
condition and performance of vehicles prior to their first consumer 
purchase. The agency does not have any authority to require periodic 
inspection of containers for corrosion. NHTSA is proposing to adopt an 
environmental cycling performance requirement and test procedure 
patterned after the ones in NGV2. The proposed performance requirement 
is set forth in S7.5, and the proposed test conditions and procedures, 
in S8.5.
    NGV2 states that a ``container free of any protective coating shall 
be cycle tested, without showing evidence of distortion, deterioration 
or failure * * *'' The agency believes that while the term ``without 
distortion'' appears to be objective, the terms ``without deterioration 
or failure'' are too ambiguous and broad to permit their incorporation 
in a Federal Motor Vehicle Safety Standard. Therefore, the agency has 
decided not to include the terms ``deterioration'' and ``failure'' in 
its proposal. Instead, the agency is proposing that its pass/fail 
criteria for the environmental cycling test depart from NGV2 and state 
that, when cycle tested, the CNG container ``shall not leak or 
permanently change in external configuration or dimensions.'' NHTSA has 
added the prohibition against leakage, since the absence of leakage can 
be objectively determined. Further, the prohibition is consistent with 
the environmental cycling test's safety goal and with the pressure 
cycling test and hydrostatic burst test that the agency adopted when it 
issued Standard No. 304.
    Under today's proposal, the phrase ``shall not . . . permanently 
change in external configuration or dimensions'' throughout the test is 
intended to serve the same purpose as the NGV2 ``no distortion'' 
criterion. Thus, if there were a slight bulge in one location or if 
there were a change in the container's volume by even one tenth of one 
percent, the container would be considered to be distorted. A pass/fail 
gauge could be adjusted to fit the container before the test, and then 
used again after the test to verify that a container's dimensions had 
not changed. NHTSA requests comments about this ``zero distortion'' 
requirement, and whether some amount of distortion should be allowed. 
If so, how should the permissible amount of distortion be quantified 
and measured? The agency also invites comments on how the no distortion 
criterion might otherwise be objectively expressed. In addition, the 
agency requests comments on whether there are other terms, such as 
fiber delamination, which should be incorporated and how they could be 
objectively defined.
    As an alternative, NHTSA is considering a no leakage criterion as 
the sole pass/failure performance requirement. However, under this 
alternative, the agency would increase the two sets of 5,000 cycles to 
9,000 cycles each. Thus, the standard would specify a total of 18,000 
cycles instead of the 10,000 cycles currently specified in NGV2. The 
agency tentatively concludes that the additional cycles would be 
necessary since this alternative proposal would otherwise be less 
stringent than NGV2 which contains additional criteria to disqualify 
substandard containers, i.e., distortion, deterioration, and failure. 
The agency further notes that 18,000 cycles is consistent with the 
ambient pressure cycling in NGV2 and in FMVSS No. 304. That cycling 
represents severe service, i.e., four refuelings per day, 300 days per 
year for 15 years. The agency requests comments on this alternative, 
and on other approaches that might be more appropriate. In addition, 
the agency requests that commenters suggesting other approaches include 
measurable pass/fail performance criteria and a proposed test 
procedure.
    Section S8.5 sets forth the procedures and conditions for the 
environmental cycling test. As with the proposed performance 
requirements, these provisions are modeled after NGV2. The agency has 
tentatively adopted modified versions of certain provisions in order to 
be consistent with the criteria that are within the agency's authority.
    NGV2 further specifies that during the environmental cycling test 
the container is pressurized ``using natural gas or methane.'' This is 
part of the test's preconditioning phase in which a corrosive material 
is introduced inside the container to determine its corrosion 
resistance. The agency is proposing that only automotive grade natural 
gas be used in the environmental cycling test. The agency believes that 
specifying only one test gas would make the test more repeatable for 
enforcement purposes. Further, although the major constituent of 
natural gas is methane, natural gas does contain other minor 
constituents which could make the test performed with natural gas more 
severe than if only pure methane were used. Therefore, the use of 
natural gas would represent a more severe scenario that is closer to 
real world use. NHTSA requests comment on the appropriateness of using 
only natural gas in the environmental cycling test, rather than 
specifying both fuels.
    NHTSA has decided to propose language addressing the use of 
protective coatings that it believes is consistent with NGV2. 
Specifically, S8.5.2 states that ``A CNG fuel container free of any 
protective coating'' is cycle tested in a specified manner. The agency 
believes that the phrase ``free of any protective coating'' refers to 
temporary coatings such as oil and grease, so as not to inhibit action 
from the corrosive materials during subsequent testing. The agency 
further believes that it would be inappropriate for the agency to 
preclude permanent coatings such as paint or other materials, since 
this would discourage manufacturers from applying permanent coatings 
that increase corrosion resistance. The agency requests comments on how 
best to describe this concept. An alternative to the proposal to 
specify ``free of any protective coating,'' would be to specify ``The 
container shall be in the as manufactured condition.''
    NHTSA is also proposing relative humidity conditions during the 
environmental cycling test. Specifically, under the proposal, S8.5.2.2 
would specify ``Condition the container for 48 hours at zero pressure, 
60 deg. C (140 deg. F) and 95 percent relative humidity. To obtain the 
specified temperature and relative humidity, spray with a fine spray or 
mist of water at 60 deg. C (140 deg. F) in a chamber held at 60 deg. C 
(140 deg. F).'' NHTSA requests comments on how the phrase ``fine spray 
or mist of water'' could be made more objective, since different rates 
of spray might influence the humidity level. As an alternative, the 
agency is considering a rate of spray consistent with ANSI standard 
Z26.1-1977, which is referenced in FMVSS NO. 205, Glazing Materials. 
That provision specifies that ``The fine spray of water shall be under 
a pressure of 172 to 207 kPa (25 to 30 psi) at the nozzle and in 
sufficient volume to wet the container immediately upon impact.'' 
Another alternative would be to specify a relative humidity level of 95 
percent. This would allow manufacturers and test facilities the 
flexibility to determine how that level is achieved. The agency 
requests comments on how best to specify relative humidity in the 
environmental cycling test.
    In comments to the NPRM, Norris and NGV Systems supported an 
alternative corrosion test issued by the National Association of 
Corrosion Engineers (NACE), NACE Standard TM0177-90. The NACE voluntary 
standard includes several test methods for determining the sulfide 
stress cracking resistance of steels. Sulfide stress cracking corrosion 
can result from the presence of too much hydrogen sulfide in natural 
gas. NHTSA requests comments on the appropriateness of using the NACE 
test either in conjunction with or in lieu of NGV2's environmental 
cycling test.
    The NACE test provides a laboratory method but does not specify 
acceptable results. If the agency were to incorporate the NACE test in 
an FMVSS, it would be necessary to specify performance requirements. 
The agency believes that this could be done by making the performance 
requirements consistent with the ones already contained in the draft 
International Standards Organization (ISO) standard for CNG containers 
(Section A13). If the agency decides to adopt the NACE test, the NACE 
Standard Tensile Test method would be used and subsized tensile 
specimens (gauge diameter 2.54 mm) would be machined from the wall of a 
finished container, placed under constant tensile load, and immersed in 
the NACE test solution. Tests would be conducted to demonstrate that 
the threshold stress exceeds 20 percent of the specified minimum yield 
strength of the steel, where threshold stress is the maximum stress at 
or below which no specimen fails the test for a period of 720 hours. 
NHTSA requests comments on the need for the NACE test and various 
aspects of the test, including the appropriateness of setting threshold 
stress at 20 percent above the yield strength and the number of tests 
which should be conducted to demonstrate this.

C. Road Salt Environmental Test

    NHTSA has decided to propose a road salt environmental test for CNG 
fuel containers to address the potential for container degradation due 
to road salt and other acidic chemicals. The proposed test is in 
addition to the environmental cycling test already discussed.
    NHTSA has decided to propose this requirement after learning of two 
CNG fiberglass fuel container failures which occurred in early 1994. 
NHTSA is concerned about the exposure of container exterior surfaces to 
acidic fluids, which may lead to stress corrosion cracking and 
container failure. Depending on the environmental conditions present, 
road salt or salt spray while driving in wet conditions, can be acidic 
in nature. Therefore, the agency proposes this road salt environmental 
test to address these potential safety problems.
    The number of test cycles and the pass/fail criterion are the same 
as those proposed for the environmental cycling test discussed earlier. 
However, prior to cycling, the fuel container would be exposed to salt 
spray in accordance with American Society for Testing and Materials 
(ASTM) B117-73, ``Method of Salt Spray (Fog) Testing.'' This method of 
salt spray testing is used in FMVSS NO. 108, Lamps, Reflective Devices, 
and Associated Equipment for testing the corrosion resistance of 
headlamps.
    Under the proposal, a CNG fuel container would be exposed to the 
salt spray for 240 hours, consisting of ten successive 24 hours 
periods. Within each period, the container would be exposed to the 
spray for 23 hours. During the 24th hour, the salt spray would not be 
activated. Following the 240 hours of salt spray exposure, the 
container would then be cycled for 5,000 cycles, through hydrostatic 
pressurization, from not more than 10 percent of service pressure to 
service pressure. Then it would be hydrostatically pressure cycled for 
another 5,000 cycles from not more than 10 percent of the service 
pressure to 125 percent of the service pressure. When tested in this 
way, the container would be prohibited from leaking or permanently 
changing in external configuration or dimensions.
    NHTSA requests comments on the appropriateness of using this test 
to address exterior environmental degradation of CNG fuel containers 
due to road salt and other acidic chemicals. The agency specifically 
requests comments on whether the proposed test would adequately address 
the potential for stress corrosion cracking of fiberglass overwrap in 
CNG fuel containers, and whether it should be applied to all types of 
CNG fuel containers, including all metal, hoop wrapped with metal 
liner, full wrapped with metal liner, and all composite for both 
fiberglass and carbon fiber. NHTSA also requests comments on whether 
the 240 hours of salt spray exposure appropriately reflects the amount 
of exposure which can reasonable be expected during the life of a CNG 
fuel container.
    In addition, NHTSA requests comments on the pH level of the salt 
solution used in the proposed test method. Under ASTM B-117, the pH 
level of the salt solution is in the range of 6.5 to 7.2 at 35 deg.C, 
although the method provides for an upward or downward adjustment in 
pH. A downward adjustment of pH level would make the solution more 
acidic, thereby representing more severe road chemicals which CNG 
containers may encounter. It appears possible that stress corrosion 
cracking of fiberglass may be accelerated with decreasing pH. 
Therefore, the agency requests comments on whether a lower pH range for 
the salt solution should be specified in the test method, such as three 
to four.
    NHTSA also requests comments on whether to specify the pass/fail 
criterion for the salt spray test to ``no leakage'' in lieu of ``shall 
not leak or be permanently changed in external configuration or 
dimensions.'' Concurrently, the agency would also increase the number 
of cycles during testing from two sets of 5,000 cycles each to two sets 
of 9,000 cycles each. The agency requests comments on whether these 
modifications in the number of cycles would be appropriate for the road 
salt test as well as the environmental cycling test discussed earlier. 
The agency also requests comments on the estimated cost of the salt 
spray test and the extent to which current CNG containers would comply 
with the requirements.

D. Charpy Impact Test

    Section 1-12(d) and 1-13(e) of NGV2 set forth an impact test, known 
as the Charpy test, and performance criteria to address brittle 
fracture of steel CNG containers and liners under low temperatures. 
NGV2 states that this test is an indicator of the performance of heat 
treated steels.\4\ The Charpy test evaluates marginal heat treating 
performance which can lead to poor fracture performance, degraded 
resistance to stress corrosion cracking, and lessened fatigue 
resistance.
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    \4\  The Charpy test only evaluates steel CNG containers and 
liners. The environmental cycling test evaluates composite materials 
under low temperature conditions.
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    In the NPRM, NHTSA requested comments on whether there is a safety 
problem sufficiently serious to warrant establishing a requirement for 
low temperature testing of CNG container materials. The agency 
requested these comments due to its concern that certain materials such 
as high strength steels can lose their ductility at low temperatures, a 
situation that could lead to a container's catastrophic failure. The 
agency requested specific comments on the Charpy impact test set forth 
in NGV2.
    NGV Systems, ARC, Comdyne, Pressed Steel Tank, EDO, Fiber Dynamics, 
AAMA, Minnesota Gas, Amoco, Navistar, CNG Pittsburgh, and Manchester 
commented about the need for cold temperature testing. All but 
Manchester believed that the standard should include some sort of cold 
temperature testing for containers. Manchester stated that the 
container's service environment should be examined to determine if such 
cold temperature testing is needed. Most commenters stated that 
temperature extremes should be accounted for in the standard but did 
not elaborate about the specific test. PST recommended that the agency 
include the Charpy impact test in the Federal standard. AAMA and EDO 
recommended that the containers be cycled at -40 deg. C (-40 deg. F) 
and -50 deg. C (-58 deg. F), respectively.
    After reviewing the comments, NHTSA has decided to propose amending 
Standard No. 304 to include a low temperature test patterned after the 
Charpy impact test. This test is set forth in sections 1-12(d) and 1-
13(e) of NGV2, which references Methods for Notched Bar Impact Testing 
of Metallic Materials, ASTM E 23. Section 1-13(e) states that the 
average energy absorbed by the three test specimens shall not be less 
than 100 J/cm\2\. The minimum value for any one specimen shall not be 
less than 80 J/cm\2\. Under the test, a pendulum swings down and hits a 
specimen. The test device then measures the amount of energy 
transmitted into the specimen needed to break it. If the specimen 
breaks at low levels of energy, then it would fail the test. To 
illustrate, while a substance such as glass would break at very low 
energy levels, a non-brittle metal would break only at relatively high 
energy levels. Specifically, the purpose of this test is to determine 
the brittle fracture behavior of steels. It also evaluates the 
performance of steels which have been heat treated as part of the 
manufacturing process. An improper heat treatment process can result in 
the material being brittle and thus more susceptible to fatigue and 
stress corrosion cracking. Non-steel containers and liners need not be 
tested to comply with the Charpy test because they are not heat treated 
this way. The agency requests comments about the agency's decision to 
propose the Charpy impact test. Is it appropriate to only apply these 
requirements to Type 1 containers and Type 2 and Type 3 containers with 
steel liners? In addition, NHTSA requests comments on applicable 
performance tests for fracture and fatigue assessment of liner 
materials other than steel, if such materials perform a structural 
function, e.g., aluminum liners or containers. Along with this 
information, commenters should include a description of the specific 
performance tests recommended, along with objective pass/fail criteria.
    NHTSA agrees with the recommendations by AAMA and EDO that 
containers be pressure cycled at low temperatures (e.g., -40 deg. C 
(-40 deg. F)). The agency notes that this low temperature is consistent 
with test conditions in NGV2 and NHTSA standards, including Standard 
No. 105, Hydraulic Brake Systems, Standard No. 106, Brake Hoses, and 
Standard No. 108, Lamps, Reflective Devices, and Associated Equipment. 
The agency requests comment about whether the proposed test temperature 
is appropriate.
    In response to Manchester's comment that the service environment 
should be examined to determine if cold temperature testing is needed 
for a particular container, NHTSA notes that it would be impracticable 
to determine what type of environment each individual container would 
encounter. In establishing a requirement, the agency believes that it 
is appropriate to test CNG containers in a worst case scenario, such as 
the low temperature levels being proposed.

E. Gunfire Test

    Section 1-18(j) of NGV2 includes a gunfire test that evaluates 
whether a fully pressurized container fragments upon suffering a high 
impact puncture. A similar puncture could occur in a motor vehicle 
crash, causing the propulsion of container fragments at high speeds. 
The gunfire test assures that a container will instead essentially 
remain in one piece.
    In the NPRM, the agency discussed a specific test criterion in 
which the container would be permitted to rupture only if there were no 
fragmentation. The container industry refers to this situation as 
``leak before burst.'' Containers that leak before bursting are 
designed to release their contents through the sidewall without 
explosive fragmentation when the container becomes overpressurized. The 
industry tests for this characteristic by piercing the pressurized 
container with a gunshot. The area around the container is then 
examined for fragmentation. The container is supposed to be designed so 
that no fragments will break off during this failure. In the NPRM, the 
agency requested comments about how to define the term ``without 
fragmenting'' for regulatory and compliance purposes.
    Brunswick, NGV Systems, PST, EDO, CNG Pittsburg, and AAMA commented 
about container fragmentation. These commenters stated that in the 
event of a rupture, the CNG fuel containers should be designed to 
release their contents through their sidewalls without fragmentation. 
Brunswick, AAMA, NGV Systems, EDO, and PST commented about how to 
define the phrase ``without fragmenting.'' EDO recommended that the 
container be required to remain ``in one piece.'' NGV Systems stated it 
should be defined as ``no separation of parts such that projectiles are 
possible.'' AAMA stated that it should be defined as ``no separation of 
pieces exceeding one gram in mass from the fuel tank.'' Brunswick 
stated that it should be defined as loss of small pieces not exceeding 
30 grams (one ounce) in weight. PST also indicated that 30 grams (one 
ounce) is an acceptable size.
    Based on the comments and other available information, NHTSA has 
decided to propose amending Standard No. 304 to include a gunfire test 
similar to the one set forth in NGV2, with some modifications. The 
agency believes that if a CNG container is punctured in a crash, the 
failure should result in a controllable situation, e.g., fuel leakage, 
rather than a catastrophic explosion of the container. A catastrophic 
failure would present a much more serious failure mode than fuel 
leakage through the sidewall, since fragments could be propelled in all 
directions at high speeds and with tremendous force. Such fragments 
could pose a significant safety risk to vehicle occupants and others 
near the vehicle.
    With respect to the performance criteria for the gunfire test, NGV2 
states that ``The tested container shall reveal no evidence of a 
fragmentation failure'' and ``Loss of small pieces of composite 
material which would not have sufficient momentum to penetrate sheet 
metal typically found in automobile construction shall not constitute 
failure of the test.'' Under the second phrase, NGV2 allows the 
fragmentation of small pieces, even though the gunfire test is intended 
to prevent fragmentation.
    NHTSA has tentatively concluded that some of NGV2's performance 
requirements and test conditions are insufficiently objective for use 
in a FMVSS. In order to establish objective, safety criteria, NHTSA has 
decided to propose incorporating the recommendations by Brunswick and 
PST to prohibit fragments exceeding 30 grams (one ounce) in mass. 
Although the intent of the gunfire test is to demonstrate no 
fragmentation, the agency understands that small composite pieces or 
fragments are considered normal. Therefore, the agency has tentatively 
concluded that to prohibit all fragmentation, as recommended by EDO and 
NGV Systems would not be practicable. Similarly, the agency believes 
that AAMA's recommendation to prohibit the separation of pieces 
exceeding one gram (0.035 ounce) would not be practicable and would 
involve very small pieces that could be difficult to measure. NHTSA has 
tentatively concluded that prohibiting pieces in excess of 30 grams 
would provide for a practicable, objective, and safe performance 
criterion for the gunfire test. However, the agency requests comments 
on the proposed size, and whether the standard should prohibit all 
fragmentation or whether some smaller level of fragmentation would be 
measurable and safe. What is the lightest container fragment that would 
be readily measurable and would not pose an unreasonable risk to the 
safety of motorists? NHTSA also seeks comment on whether the container 
should be pressurized with nitrogen or air, since only one gas should 
be used to assure consistency of testing.
    NHTSA has tentatively determined that it is necessary to depart 
from certain aspects of the gunfire test in NGV2 to make the agency's 
proposed requirement objective and ensure repeatable test results. As 
proposed in this notice, these modifications include specifying the 
precise muzzle velocity, the projectile's path, and the precise 
distance.

F. Damage Tolerance Tests

1. General Considerations
    NGV2 addresses damage tolerance with three separate tests: a flaw 
tolerance test, a pendulum impact test, and a drop test. In general, 
the damage tolerance tests serve to evaluate damage caused by 
incidental contact with other objects. Such contact can occur in a 
variety of ways. For instance, containers mounted underneath the 
vehicle could be damaged by road debris. Similarly, containers mounted 
in the bed of a pickup truck could be damaged by cargo or tools being 
thrown on them. The flaw tolerance test evaluates abrasive damage to 
composite overwraps such as scratches and small cuts on the container. 
If the overwraps are cut or gouged, they may unravel or delaminate, 
possibly causing container failure. The pendulum impact evaluates sharp 
blows to the container. The drop test evaluates blunt impacts to the 
container.
    NHTSA did not address damage tolerance in the January 1993 NPRM. 
Nevertheless, CGA, Tecogen, Comdyne, ARC, and Brunswick commented that 
a container's resistance to mechanical damage from incidental contact 
or road debris should be tested. Of these commenters, only Brunswick 
suggested a specific test procedure to determine container damage 
tolerance. Brunswick stated that NGV2 adequately addresses resistance 
to mechanical damage with the flaw tolerance, pendulum impact, and drop 
tests. In addition, it stated that the effects of more severe damage, 
such as a puncture, are addressed with the gunfire test.
    NHTSA has decided to propose the three damage tolerance tests in 
NGV2 because the agency has tentatively concluded that, during normal 
use, CNG containers may be exposed to each type of external damage 
addressed by these tests. This may be especially true for containers 
sold in the aftermarket, since vehicle manufacturers would presumably 
be more likely than vehicle converters to design their vehicles to 
protect containers from exposure to road debris and other damage. This 
is so because vehicle manufacturers can design a CNG vehicle with 
container placement in mind. Converters are not involved in the 
original designing of the vehicles they convert and may have to place a 
container in a relatively vulnerable location given space limitations.
    NHTSA is proposing to subject Type 1 containers to the drop test, 
but not to the other two tests, since noncomposite metal containers are 
generally not affected by the proposed damage evaluated by those tests. 
Type 2, 3, and 4 composite containers would be subject to all three 
damage tolerance tests. The agency requests comments about the 
appropriateness of applying the proposed damage tolerance tests to the 
different types of CNG containers.
    In NGV2, the criterion for each damage tolerance test is that the 
container, after having a cut made into the container or being 
impacted, must sustain 1,500 pressure cycles without evidence of 
failure such as distortion or leakage. The only exception to this is 
the drop test. The drop test in NGV2 requires two alternative sets of 
cycling tests. If the container sustains damage that would cause its 
rejection at a three year inspection interval specified by NGV2, the 
container is tested for 1,500 cycles. In contrast, if the container 
sustains damage that would cause it not to be rejected at a three year 
inspection, it is tested for 18,000 cycles. The 1,500 cycles in NGV2 
apparently corresponds to the maximum number of fills expected during 
the three year inspection interval. Because NGV2 requires reinspection 
every three years, it is structured to permit a level of damage to the 
container that would keep it in service until the maximum inspection 
interval of three years is completed. In contrast, NHTSA has no 
statutory authority to require container inspection after the first 
consumer purchase of the container.\5\
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    \5\The agency is proposing labeling requirements to encourage 
the periodic inspection of containers every 12 months, as explained 
below.
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    In today's notice, NHTSA is proposing 1,500 cycles for the flaw 
tolerance and pendulum impact tests, and the more severe alternative of 
18,000 cycles for the drop test. This is consistent with the manner of 
cycles specified in NGV2, after which the agency is patterning its 
proposal. However, since NHTSA has no authority to require the periodic 
inspection of CNG containers, the agency requests comments on whether 
1,500 cycles is adequate to assure the safety of a CNG container 
throughout its life. As a alternative, the agency is considering 
requiring 18,000 cycles for the flaw tolerance and pendulum impact 
tests. This is consistent with the pressure cycling test in FMVSS No. 
304 and with the drop test where no inspection would be involved. It 
would also represent the worst case scenario for a container which 
sustains damage early in its service life, but may not be subsequently 
inspected, since 18,000 cycles represents four refuelings per day, 300 
days per year for 15 years. The agency requests comments on the 
appropriate number of cycles for the flaw tolerance, pendulum impact, 
and drop tests to assure the safety of the traveling public.
2. Flaw Tolerance Test
    Section 1-18(f)(1) of NGV2 sets forth a flaw tolerance test, which 
evaluates a container's ability to withstand external damage caused by 
abrasive material scratching a container, NHTSA is proposing to adopt 
the flaw tolerance test in NGV2 with some minor modifications. The 
agency's adaptation of these performance requirements and test 
conditions and procedures is set forth in sections S7.8 and S8.8 of 
this notice's regulatory text.
    NGV2's flaw tolerance test specifies that the container shall be 
tested ``without evidence of distortion, deterioration or failure'' and 
``show no evidence of flaw propagation\6\ or other physical damage 
likely to weaken the container appreciably.'' as explained in the 
earlier discussion on the environmental cycling test, these performance 
requirements contain subjective criteria that the agency believes need 
to be modified to be objective and enforceable. The agency believes 
that the terms ``without deterioration or failure'' and ``other 
physical damage likely to weaken the container appreciably'' are 
unreasonably ambiguous and broad. Therefore, the agency has decided not 
to include, in the proposed requirement, the terms ``deterioration'' 
and ``failure'' and the phrase ``other physical damage likely to weaken 
the container appreciably'' since these terms are not sufficiently 
objective to include in a Federal standard and would not provide 
measurable criteria for enforcement. The agency welcomes comments about 
ways to refine terms to make them objective. In addition, the agency 
requests comments on whether there are other terms, such as fiber 
delamination, which should be incorporated and how they could 
objectively be defined.
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    \6\Propagation is defined as ``enlargement or extension (as of a 
crack) in a solid body. (Webster's Ninth New Collegiate Dictionary)
---------------------------------------------------------------------------

    Instead, the agency is proposing a modified version of the NGV2 
pass/fail criteria for the flaw tolerance test that states that when 
cycle tested, the CNG container ``shall not leak or permanently change 
in external configuration or dimension.'' In addition, NHTSA is 
proposing an additional performance provision to prohibit the growth of 
a longitudinal cut made in the container. NHTSA has added the 
prohibitions against leakage and increase in the size of cut since 
compliance with them can be objectively determined. It is also 
consistent with the flaw tolerance test's safety goal and with the 
performance requirements for the presence cycling test and the 
hydrostatic burst test in Standard No. 304. The agency previously 
discussed the no distortion criterion in the environmental cycling 
section and request similar comments here. In addition, the other 
requirement being proposed for the flaw tolerance test is that the 
``cut made in accordance with S8.8 for the purpose of this test shall 
not increase in length, width or depth as a result of this test.''
    NHTSA has tentatively determined that it is also necessary to 
depart from certain aspects of NGV2's flaw tolerance test procedures 
and conditions to make agency's flaw tolerance test objective and 
repeatable. As proposed in this notice, these modifications include 
specifying the precise dimensions and location of the flaw.
    NGV2 specifies that a cut be made in the other wall at 
approximately midlength and that the cut be not less than 0.75 mm 
(0.030 inches) in depth. The agency is proposing additional provisions 
to make the proposed FMVSS more precise, thereby increasing the test 
procedure's objectivity and repeatability. For instance, the agency is 
proposing to amend the standard to specify that the cut be 0.75 mm 
wide. The agency tentatively believes that these dimensions represent 
abrasions that containers may experience as a result of contacting road 
debris. However, the agency requests comments on the cut's dimensions, 
including the appropriate width, and whether the length, width, and 
number of such cuts should be increased.
3. Pendulum Impact Test
    Section 1-18(f)(2) of NGV2 sets forth a pendulum impact test which 
evaluates a container's ability to withstand a sharp external blow. 
NHTSA is proposing to adopt the pendulum impact test in NGV2 with some 
minor modifications. The agency's adoption of these performance 
requirements and test conditions is set forth in sections S7.9 and S8.9 
of this notice's regulatory text.
    NGV2 specifies that ``The tests shall be made on the points of the 
container which are regarded as vulnerable. The points regarded as 
vulnerable are those which are most exposed or weakest having regard to 
the shape of the container and/or the way in which it is installed on 
the vehicle.''
    NHTSA has decided to propose modifying this provision since it is 
not objective. Instead, the agency is proposing to require that the 
pendulum impact test be conducted at ``any point and any angle.'' NHTSA 
anticipates that to be able to certify compliance with the requirement, 
manufacturers would direct the test impacts to the container's most 
vulnerable points. Such a test procedure would be consistent with the 
regulatory language specified in Standard No. 301's moving contoured 
barrier test. The agency requests comments about whether such a test 
condition would be appropriate for pendulum impact testing of CNG 
containers.
4. Drop Test
    Section 1-18(g) of NGV2 sets forth a drop test, which evaluates a 
container's ability to withstand a blunt external blow. NHTSA is 
proposing to adopt the drop test in NGV2 with some minor modifications. 
The agency's adoption of these performance requirements and test 
procedures is set forth in sections S7.10 and S8.10 of this notice's 
regulatory text.
    As with NGV2, NHTSA is proposing to specify that a container be 
dropped at ambient temperature without internal pressurization or 
attached valves. In the test, the container is held in a horizontal 
position with the container's bottom 3.05 meters (10 feet) above the 
surface onto which it is dropped.
    Today's proposal, consistent with NGV2, specifies that the surface 
onto which the CNG container is dropped ``shall be a smooth, horizontal 
concrete pad or flooring.'' NHTSA notes that this definition of the 
surface is not fully objective. As an alternative, the agency is 
considering specifying that the surface be made of concrete that is at 
least four inches thick. NHTSA requests comments on this alternative, 
and on how the surface could otherwise be more objectively defined.

G. Bonfire Test Fuel

    In the NPRM, NHTSA proposed that the fire for the bonfire tests be 
generated by No. 2 diesel fuel. This fuel type was proposed so that the 
standard would be consistent with the bonfire test in NGV2, which 
specifies this type of fuel.
    NGVC, CGA, AAMA, and Norris commented that the agency should 
specify a different fuel to generate a bonfire that is more 
environmentally sound. CGA stated that the large amounts of smoke that 
would be created by burning diesel fuel are contrary to the 
environmental objectives of developing CNG vehicles. NGVC and Norris 
suggested using a CNG or propane grill for the test.
    In the final rule, NHTSA decided to specify the use of No. 2 diesel 
fuel. The agency explained that it was aware of the environmental 
problems associated with this type of fuel and would further study 
whether other fuels should be used to generate the bonfire test. 
However, the agency stated that until it could determine that a 
different fuel is an appropriate (e.g., generates a fire of comparable 
heat and intensity) replacement for No. 2 diesel fuel, that fuel will 
be specified for generating the bonfire.
    NHTSA has decided to propose to amend the bonfire test conditions 
to allow alternative types of fuel, given the environmental 
difficulties resulting from No. 2 diesel fuel. One alternative would be 
to allow manufacturers to conduct the test with any fuel that generates 
a flame temperature equivalent to that of No. 2 diesel fuel. Under this 
alternative, any fuel that generates a flame temperature of 850 deg. to 
900 deg. C (the flame temperature of No. 2 diesel fuel) for the 
duration of the test, would be permitted. To verify the flame 
temperature of 850 deg. to 900 deg. C for a period of 20 minutes, or 
until the container is fully vented or fails, three thermocouples would 
be located on the container's bottom, 102 mm above the fuel surface, as 
measured before the fire is started. The thermocouples would be placed 
so that one would be at the center of the container's bottom and one on 
each side of the container where the dome and sidewall intersect. NHTSA 
requests comments about the appropriateness of this alternative, 
including the use of flame temperature to define ``equivalence'' among 
fuel types. Would a different fuel characteristic such as Btu/lb be 
more appropriate? If a commenter believes that an alternative approach 
would be more appropriate, it should submit the test procedures 
associated with such an alternative.

H. Labeling Requirements

1. CNG Containers
    a. Labeling information. In the NPRM, NHTSA proposed to require 
that container manufacturers certify that each of their containers 
comply with the proposed equipment requirements by permanently labeling 
the container with the following information: The symbol ``DOT'' to 
constitute a certification by the manufacturer that the container 
conforms to all requirements of the standard; the date of manufacture 
of the container; the name and address of the container manufacturer; 
and the maximum service pressure. The agency stated that labeling the 
container would provide vehicle manufacturers and consumers with 
assurance that they are purchasing containers that comply with the 
Federal safety standards. In addition, the agency believed that the 
proposed requirement would facilitate the agency's enforcement efforts 
by providing a ready means of identifying the container and its 
manufacturer.
    EDO, NGVC, Thomas, NYCFD, and Volvo GM addressed the proposed 
labeling requirements. EDO and NYCFD stated that the label should 
include the maximum fill pressure at a location close to the fill 
receptacle. NGVC recommended that a blank area for the container 
installation date be included in the label to be filled in by the 
installer. Volvo GM stated that only containers manufactured after the 
standard's effective date should be entitled to display the DOT symbol. 
Thomas stated, without elaboration, that the labeling requirements of 
NGV2 should be adopted. NHTSA's proposal did not include certain 
information specified in NGV2, including the type of container, 
inspector symbols, trademarks, manufacturers's part number, and serial 
numbers.
    In the CNG container final rule, NHTSA decided to adopt the 
proposed labeling requirements with a slight modification from the 
proposed format. In item (a), the agency modified the proposal which 
states ``The tank manufacturer's name and address'' to state the 
following: include the statement that ``If there is a question about 
the proper use, installation, or maintenance of this container, contact 
[manufacturer's name, address, and telephone number].'' In the final 
rule, the agency decided not to require the other additional items of 
information in NGV2 since the agency had not proposed requiring such 
information. Notwithstanding the agency's decision not to require this 
additional information, the agency explained that a manufacturer may 
list such information on the label, provided that the additional 
information does not obscure or confuse the required information. In 
particular, NHTSA urged manufacturers to include the container type, 
e.g., Type 1, 2, 3 or 4, since the agency had adopted NGV2's design and 
material specifications in the final rule. The agency believed that 
specifying the type of container would facilitate oversight of 
compliance tests since each type of container is required to undergo a 
hydrostatic burst test with a safety factor unique to that type.
    In the final rule, NHTSA also explained that it anticipated 
proposing additional requirements about the CNG fuel container's label. 
The agency is now proposing to amend S7.4 to specify that CNG 
containers be labeled with the following additional information:
    (1) The container designation (Type 1, 2, 3, or 4),
    (2) The statement ``CNG ONLY,''
    (3) The statement: ``This container should be visually inspected 
after a motor vehicle accident or fire and at least every 36 months for 
damage and deterioration in accordance with the Compressed Gas 
Association (CGA) guidelines C-6 and C-6.1 for Type 1 containers and C-
6.2 for Types 2, 3, and 4 containers.''
    (4) The statement: ``Do Not Use After ____________,'' inserting the 
year that is the 15th year beginning after the year in which the 
container is manufactured.
    NHTSA believes that it would be in the interest of motor vehicle 
safety to add this information to the CNG container label. Adding 
information about container type, e.g., Type 1, 2, 3 or 4 would be 
consistent with the agency's adoption of NGV2's design and material 
specifications in the CNG final rule. The agency believes that 
specifying the type of container would facilitate oversight of 
compliance tests since each type of container is required to undergo a 
hydrostatic burst test with a safety factor unique to that type. Adding 
the phrase ``CNG ONLY'' would assure that CNG containers are used only 
for CNG and are not used for other fuels for which the containers were 
not designed, such as liquefied petroleum gas (LPG).
    Since NHTSA has no statutory authority to require the periodic 
inspection of CNG containers after the first consumer purchase, adding 
information about periodic inspections would help assure their safe use 
after this time. Such statements would alert owners to the desirability 
for reinspection over time or in the event of an accident. The agency 
notes that the proposed requirement is consistent with NGV2's 
guidelines for visual inspection of CNG containers every 36 months. 
Reference to the CGA guidelines would provide standardized criteria by 
which to inspect containers built by different manufacturers. The 
agency is proposing use of the visual inspection guidelines contained 
in CGA C-6, C-6.1, and C-6.2, and not those for hydrostatic testing. In 
addition to the proposal that the container be inspected after an 
accident or at least every 36 months, NHTSA requests comments about the 
need to specify both a time interval and a mileage interval (e.g., the 
agency could require the following statement: ``This container should 
be visually inspected after a motor vehicle accident or fire, and for 
damage or deterioration at least every 36 months or 36,000 miles, 
whichever comes first, in accordance with . . .''). What time and 
mileage intervals would be most appropriate? Would an agency 
requirement for inspection every 12 months be appropriate?
    NHTSA is proposing to require information about the container's 
service life in the belief that this information would help assure that 
a CNG container is removed from service after its design service life 
expires. As commenters on the NPRM stated, this is especially important 
since there is a finite period during which CNG containers can be used 
safely. The agency is proposing 15 years because CNG containers built 
to follow NGV2 have a design service life of 15 years. Nevertheless, 
since containers may be built for a service life other than 15 years, 
the agency would allow a manufacturer to specify the service life 
length appropriate to its containers.
    The agency requests comments about the need for each of these 
proposed items of information and alternative ways to specify this 
information.
    b. Label location. In response to the NPRM, EDO and NYCFD stated 
that the label should include certain labeling information such as the 
maximum fill pressure at a location close to the fill receptacle.
    NHTSA has decided to propose requirements related to the label's 
location. Accordingly, the agency has decided to propose that the 
containers be installed in a manner that ensures the visibility of the 
container labeling. Specifically, the agency is proposing to require 
the label to be near the end of the container containing the outlet 
valve, since such a location would help ensure that the label would be 
more visible during refueling. The agency notes that NGV2 contains a 
similar requirement.
2. Vehicle labeling
    The CNG vehicle final rule did not specify requirements for the 
labeling of CNG fueled vehicles. In this SNPRM, the agency is proposing 
to amend Standard No. 303 to include two items of information.
    S5.3.1  The statement: ``Maximum service pressure ________ kPa 
(________ psig).''
    S5.3.2  The statement ``See instructions on fuel container for 
inspection and service life.''
    The agency believes that the first item of information would help 
assure that CNG containers are not overfilled during refueling. The 
second item is intended to assure that vehicle owners and operators are 
informed about the important safety information on container 
inspection. In addition, the agency is proposing that for vehicles 
manufactured or converted prior to the first sale to the consumer, the 
manufacturer provide this information in writing to the consumer, 
either in the owner's manual or on a one page statement. The agency 
requests comments about the need for vehicle labeling and written 
information bearing this and other information.

I. Other Safety Information

    NHTSA requests comments on the following additional issues related 
to the safe performance of CNG containers. What are the safety 
implications of fast-filling CNG containers during refueling, which can 
result in pressure levels of 125 percent of service pressure due to the 
heat of pressurization? Do the initial permeation rates of CNG 
containers constructed of nonmetallic liners remain constant over the 
life of the container? What are the consequences of gas permeation from 
vehicles fueled by multiple CNG containers? What are the degradation 
characteristics of vinyl esters and thermoplastic resins for composite 
material? Should containers and container liners have longitudinal or 
circumferential welds?

J. Leadtime

    NHTSA is proposing to make the requirements in this notice 
effective one year after publication of the final rule in the Federal 
Register. The agency believes this would be a reasonable time period 
for container manufacturers to test their containers and certify 
compliance to the additional tests being proposed in this notice. The 
agency anticipates that container manufacturers would readily be able 
to certify compliance to the proposed requirements. This is because 
container manufacturers already certify compliance with NGV2, which is 
essentially consistent with the proposed requirements. The one 
exception is the proposed salt spray test. The agency requests comments 
about the leadtime. Does one year provide sufficient time for 
manufacturers to certify compliance to the proposed requirements? Would 
the addition of the proposed salt spray test require a longer leadtime 
than one year?
    In the meantime, prior to the standard's effective date, the 
industry is free to advertise containers as meeting the CNG equipment 
standard that will take effect in one year. Manufacturers have sought 
to achieve early compliance with other agency requirements\7\ such as 
those relating to dynamic side impact protection and air bags. The 
agency encourages manufacturers to seek, to the extent feasible, to 
manufacture their CNG containers to meet these new requirements before 
the date the standard takes effect.
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    \7\However, the agency emphasizes that a manufacturer may not 
certify a container as meeting the equipment standard until the 
standard goes into effect. Under the statte, a certification is a 
statement that a vehicle or item of equipment meets all applicable 
Federal Motor Vehicle Standards that are then in effect. Therefore, 
until a standard is effective, manufacturers may not certify 
compliance with it.
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K. Benefits

    As explained earlier, NHTSA anticipates that the number of CNG fuel 
vehicles will increase greatly in the near future, in light of 
directives by the Clinton Administration and legislation by Congress to 
develop vehicles powered by cleaner burning fuels. This notice will 
enhance the safety of this growing population of vehicles, since CNG 
containers will be required to comply with the tests in Standard No. 
304. The necessity for certifying compliance with the Federal 
requirements will provide added assurance that the containers are safe. 
The benefits of the proposal to issue additional requirements 
applicable to CNG containers are to provide assurances of the 
structural integrity of the CNG containers. The agency is adding one 
test not currently part of NGV2 (the salt spray test) to simulate 
environmental roadway conditions. In addition, by helping to minimize 
any safety concerns associated with CNG vehicles, this rule should 
result in positive environmental impacts.

 L. Costs

    For six of the seven tests proposed, there would be no additional 
costs of upgrading current containers to comply with the proposed 
requirements, since CNG container manufacturers already comply with 
NGV2. Similarly, there would be no additional compliance test costs for 
these six tests, since the manufacturers already meet the NGV2 tests. 
Testing and container costs for these six tests are estimated to range 
from $13,800 to $30,650 per container size and type. The agency does 
not know whether existing containers can meet the proposed salt spray 
test, and what costs might be incurred if the containers do not meet 
the proposed test. The agency estimates that the testing and container 
cost for the salt spray test to range from $1,220 to $4,130. Total 
testing and container cost for the proposal are $15,020 to $34,780. The 
agency has made the criteria in some of the tests more objective than 
NGV2 by changing unacceptably subjective and broad terms to more 
measurable and therefore more objective criteria.

Rulemaking Analyses and Notices

A. Executive Order 12866 (Federal Regulation) and DOT Regulatory 
Policies and Procedures

    NHTSA has considered the impact of this rulemaking action under 
Executive Order 12866 and the Department of Transportation's regulatory 
policies and procedures. This rulemaking document was not reviewed 
under E.O. 12866, ``Regulatory Planning and Review.'' This action has 
been determined to be ``nonsignificant'' under the Department of 
Transportation's regulatory policies and procedures. NHTSA has 
estimated the costs of the amendments in a Preliminary Regulatory 
Evaluation (PRE) which has been placed in the docket for this 
rulemaking. As discussed in that document, NHTSA estimates that total 
testing and container costs for this proposal are $15,020 to $34,780 
per container size and type. The agency believes that a CNG container 
which meets the current industry standard, NGV2, would also comply with 
the requirements of this proposal, with the exception of the salt spray 
test.

B. Regulatory Flexibility Act

    NHTSA has also considered the effects of this rulemaking action 
under the Regulatory Flexibility Act. Based upon the agency's 
evaluation, I certify that this rule would not have a significant 
economic impact on a substantial number of small entities. For six of 
the seven tests, there will be no small business impacts since the 
proposed standards are already being met. Comments are requested on 
current compliance with the salt spray test and whether this would have 
small business impacts. Information available to the agency indicates 
that the businesses manufacturing CNG fuel containers are not small 
businesses.

C. Executive Order 12612 (Federalism)

    NHTSA has analyzed this rulemaking action in accordance with the 
principles and criteria contained in Executive Order 12612. NHTSA has 
determined that the rule would not have sufficient Federalism 
implications to warrant the preparation of a Federalism Assessment. No 
state has adopted requirements regulating CNG containers.

D. National Environmental Policy Act

    In accordance with the national Environmental Policy Act of 1969, 
NHTSA has considered the environmental impacts of this rule. The agency 
has determined that this rule would have no adverse impact on the 
quality of the human environment. On the contrary, because NHTSA 
anticipates that ensuring the safety of CNG vehicles would encourage 
their use, NHTSA believes that the rule would have positive 
environmental impacts since CNG vehicles are expected to have near-zero 
evaporative emissions and the potential to produce very low exhaust 
emissions as well.

E. Civil Justice Reform

    The proposal does not have any retroactive effect. Under 49 U.S.C. 
30103, whenever a Federal motor vehicle safety standard is in effect, a 
State may not adopt or maintain a safety standard applicable to the 
same aspect of performance which is not identical to the Federal 
standard, except to the extent that the State requirement imposes a 
higher level of performance and applies only to vehicles procured for 
the State's use. 49 U.S.C. 30161 sets forth a procedure for judicial 
review of final rules establishing, amending or revoking Federal motor 
vehicle safety standards. That section does not require submission of a 
petition for reconsideration or other administrative proceedings before 
parties may file suit in court.
Public Comments
    Interested persons are invited to submit comments on the proposal. 
It is requested but not required that 10 copies be submitted.
    All comments must not exceed 15 pages in length. (49 CFR 553.21). 
Necessary attachments may be appended to thee submissions without 
regard to the 15-page limit. This limitation is intended to encourage 
commenters to detail their primary arguments in a concise fashion.
    If a commenter wishes to submit certain information under a claim 
of confidentiality, three copies of the complete submission, including 
purportedly confidential business information, should be submitted to 
the Chief Counsel, NHTSA, at the street address given above, and seven 
copies from which the purportedly confidential information has been 
deleted should be submitted to the Docket Section. A request for 
confidentiality should be accompanied by a cover letter setting forth 
the information specified in the agency's confidential business 
information regulation. 49 CFR Part 512.
    All comments received before the close of business on the comment 
closing date indicated above for the proposal will be considered, and 
will be available for examination in the docket at the above address 
both before and after that date. To the extent possible, comments filed 
after the closing date will also be considered. Comments received too 
late for consideration in regard to the final rule will be considered 
as suggestions for further rulemaking action. The NHTSA will continue 
to file relevant information as it becomes available in the docket 
after the closing date, and it is recommended that interested persons 
continue to examine the docket for new material.
    Those persons desiring to be notified upon receipt of their 
comments in the rules docket should enclose a self-addressed, stamped 
postcard in the envelope with their comments. Upon receiving the 
comments, the docket supervisor will return the postcard by mail.

List of Subjects in 49 CFR Part 571

    Imports, Incorporation by reference, Motor vehicle safety, Motor 
vehicles, Rubber and rubber products, Tires.

    In consideration of the foregoing, the agency proposes to amend 
Standard No. 303; Fuel System Integrity of Compressed Natural Gas 
Vehicles and Standard No. 304: Compressed Natural Gas Fuel Container 
Integrity, in Title 49 of the Code of Federal Regulations at Part 571 
as follows:

PART 571--[AMENDED]

    1. The authority citation for Part 571 would continue to read as 
follows:

    Authority: 49 U.S.C. 322, 30111, 30115, 30117 and 30166; 
delegation of authority at 49 FR 1.50.


Sec. 571.303  [Amended]

    2. In Sec. 571.303, S5 would be amended to add S5.3 through S5.3.2 
and S5.4 which would read as follows:
* * * * *
    S5.3  Each CNG vehicle shall be permanently labeled, near the 
vehicle refueling connection, with the information specified in S5.3.1 
and S5.3.2. The information shall be visible during refueling, in 
English, and in letters and numbers that are not less than 4.76 mm (3/
16 inch) high.
    S5.3.1  The statement: ``Maximum service pressure ________ kPa 
(________ psig).''
    S5.3.2  The statement ``See instructions on fuel container for 
inspection and service life.''
    S5.4  When a motor vehicle is delivered to the first purchaser for 
purposes other than resale, the manufacturer shall provide the 
purchaser with a written statement of the information in S5.3.1 and 
S5.3.2 in the owner's manual, or, if there is no owner's manual, on a 
one-page document. The information shall be in English and in not less 
than 10 point type.
* * * * *
    3. Section 571.304, Standard No. 304; Compressed Natural Gas Fuel 
Container Integrity, would be amended by revising S7.4, adding S7.5 
through S7.11, revising S8.3.2 through S8.3.4, S8.3.6, and S8.3.7, and 
adding S8.5 through S8.11.3, to read as follows:


Sec. 571.304  Standard No. 304, Compressed natural gas fuel container 
integrity.

* * * * *
    S7.4. Labeling. Each CNG fuel container shall be permanently 
labeled, within 30.5 cm (12 inches) of the end of the container 
containing the outlet valve, with the information specified in 
paragraphs (a) through (h) of this section. The information shall be in 
English and in letters and numbers that are at least 12.7 mm (\1/2\ 
inch) high.
    (a) The statement: ``If there is a question about the proper use, 
installation, or maintenance of this container, contact 
______________,'' inserting the CNG fuel container manufacturer's name, 
address, and telephone number.
    (b) The statement: ``Manufactured in ________,'' inserting the 
month and year of manufacture of the CNG fuel container.
    (c) The statement: ``Maximum service pressure ________ kPa, ______ 
psig).''
    (d) The symbol DOT, constituting a certification by the CNG 
container manufacturer that the container complies with all 
requirements of this standard.
    (e) The container designation (e.g., Type 1, 2, 3, 4).
    (f) The statement: ``CNG Only.''
    (g) The statement: ``This container should be visually inspected 
after a motor vehicle accident or fire and at least every 36 months for 
damage and deterioration in accordance with the Compressed Gas 
Association (CGA) guidelines C-6 and C-6.1 for Type 1 containers and C-
6.2 for Types 2, 3, and 4 containers.''
    (h) The statement: ``Do Not Use After ____________,'' inserting the 
year that is the 15th year beginning after the year in which the 
container is manufactured.
* * * * *
    S7.5  Environmental cycling test. Each CNG fuel container shall not 
leak or permanently change in external configuration or dimensions, 
when tested in accordance with S8.5.
    S7.6  Charpy impact test. Each steel container and each steel liner 
shall comply with the requirements of this section. When three 5 x 10 
mm specimens of a steel container or steel liner are tested in 
accordance with S8.6--
    S7.6.1  Each specimen shall absorb not less than 80 J/cm\2\ before 
breaking.
    S7.6.2  The average of the amounts of energy absorbed by the three 
specimens before breaking shall be not less than 100 J/cm\2\.
    S7.7  Gunfire test. Each CNG fuel container shall comply with this 
section. When a container is tested in accordance with S8.7, no piece 
exceeding 30 grams in mass shall separate from the container.
    S7.8  Flaw tolerance test. When tested in accordance with S8.8, 
each Type 2, Type 3, and Type 4 CNG fuel container shall not leak or 
permanently change in external configuration or dimensions. In 
addition, the cut made in accordance with S8.8 for the purpose of this 
test shall not increase in length, width or depth as a result of this 
test.
    S7.9  Pendulum impact test. Each Type 2, Type 3, and Type 4 CNG 
container shall not leak, when tested in accordance with S8.9.
    S7.10  Drop test. Each CNG fuel container shall not leak, when 
tested in accordance with S8.10.
    S7.11  Road salt environmental test. Each CNG fuel container shall 
not leak or permanently change in external configuration or dimensions, 
when tested in accordance with S8.11.
* * * * *
    S8.3.2  The CNG fuel container is positioned so that its 
longitudinal axis is horizontal. Attach three thermocouples to measure 
temperature on the container's bottom side along a line parallel to the 
container longitudinal centerline. Attach one at the midpoint of the 
container, and one at each end at the point where the dome end 
intersects the container sidewall. Subject the entire length to flame 
impingement, except that the flame shall not be allowed to impinge 
directly on any pressure relief device. Shield the pressure relief 
device with a metal plate.
    S8.3.3  If the test container is 165 cm (65 inches) in length or 
less, place it in the upright position. Attach three thermocouples to 
measure temperature on the container's bottom side along a line which 
intersects the container longitudinal centerline. Attach one at the 
midpoint of the bottom of the container, and one each at the point 
where the dome end intersects the container sidewall. Subject the 
container to total fire engulfment in the vertical. The flame shall not 
be allowed to impinge directly on any pressure relief device. For 
containers equipped with a pressure relief device on one end, the 
container is positioned with the relief device on top. For containers 
equipped with pressure relief devices on both ends, the bottom pressure 
relief device shall be shielded with a metal plate.
    S8.3.4  The lowest part of the container is suspended at a distance 
above the fire such that the container bottom surface temperatures 
specified in S8.3.6 are achieved.
* * * * *
    S8.3.6  The fire is generated by any fuel that generates a flame 
temperature between 850  deg. and 900  deg.C for the duration of the 
test, as verified by each of the three thermocouples in S8.3.2 or 
S8.3.3.
    S8.3.7  The fuel specified in S8.3.6 is such that there is 
sufficient fuel to burn for at least 20 minutes. To ensure that the 
sides of the fuel container are exposed to the flame, the surface area 
of the fire on a horizontal plane is such that it exceeds the fuel 
container projection on a horizontal plane by at least 20 cm (8 inches) 
but not more than 50 cm (20 inches).
* * * * *
    S8.5  Environmental cycling test procedures.
    S8.5.1  Adjust a pass/fail gauge to fit the container before the 
test.
    S8.5.2  After the removal of any protective coating or temporary 
coating such as oil or grease, a CNG fuel container is cycle tested as 
follows:
    S8.5.2.1  Precondition the container's interior as follows: Fill 
container \1/2\ full with water, pressurize container to 1.0 psi with 
hydrogen sulfide, increase pressure to 50 psi with carbon dioxide, then 
increase pressure to 67 percent of the service pressure with automotive 
grade natural gas. Maintain the pressure at room temperature for 15 
days, then increase the room temperature to 60  deg.C (140  deg.F) and 
hold for 15 days. Depressurize the container, drain and dry. Add an 
amount of compressor oil sufficient to coat the interior surfaces of 
the container. Pressurize to 67 percent of the service pressure using 
automotive grade natural gas and hold for 15 days at 60  deg.C (140 
deg.F) room temperature. Depressurize the container.
    S8.5.2.2  Condition the container for 48 hours at zero pressure, 60 
 deg.C (140  deg.F) and 95 percent relative humidity. To obtain the 
specified temperature and relative humidity, spray with a fine spray or 
mist of water at 60  deg.C (140  deg.F) in a chamber held at 60  deg.C 
(140  deg.F).
    S.8.5.2.3  For 5,000 cycles at 60  deg.C (140  deg.F) and 95 
percent relative humidity, hydrostratically pressurize the container 
from (1) a level not more than 10 percent of the service pressure, to 
(2) 125 percent of the service pressure.
    S8.5.2.4 Stabilize at zero pressure and ambient conditions.
    S8.5.2.5  For 5,000 cycles at -40  deg.C (-40  deg.F), 
hydrostatically pressurize the container from (1) a level not more than 
10 percent of the service pressure to (2) the service pressure.
    S8.5.2.6  The cycling rate does not exceed 10 cycles per minute.
    S8.5.3  Determine that the container has not leaked or permanently 
changed in external configuration or dimension. With respect to changes 
in the container's external configuration or dimension, adjust a pass/
fail gauge to fit the container. Compare the measurement with the one 
in S8.5.1.
    S8.6  Charpy impact test procedures.
    S8.6.1  Cut one set of three longitudinal 5X10 mm Charpy Vee notch 
specimens from one container or liner. Each specimen is then tested at 
-40 deg. C (-40 deg. F) in accordance with the Methods for Notched Bar 
Impact Testing of Metallic Materials, ASTM E 23.
    S8.7  Gunfire test procedures. A container is pressurized with 
nitrogen or air to service pressure. The container is then impacted by 
a 0.30 caliber armor-piercing projectile having a muzzle velocity of 
853 meter/second (2,800 feet/second). The container is positioned so 
that the projectile impact point is in the container sidewall, with the 
trajectory passing through the container longitudinal centerline at an 
angle of 45 degrees and exiting through the opposite sidewall. The 
distance from the muzzle to the test container is 46 m (50 yards).
    S8.8  Flaw tolerance test procedures.
    S8.8.1  Adjust a pass/fail gauge to fit the container before the 
test.
    S8.8.2  Make a 25.4 mm (1 inch) long longitudinal cut into the 
outer wall of a CNG test container at its midlength. The cut's depth is 
0.75 mm (0.030 inch) and width is 0.75 mm.
    S8.8.3  For 1,5000 cycles at ambient temperature, hydrostatically 
pressurize the container from (1) a level not more than 10 percent of 
the service pressure, to (2) the service pressure.
    S8.8.4  Determine that the container has not leaked or permanently 
changed in external configuration or dimension. With respect to changes 
in the container's external configuration or dimension, adjust a pass/
fail gauge to fit the container. Compare the measurement with the one 
in S8.5.1 or S8.81.
    S8.9  Pendulum impact test procedures.
    S8.9.1  The container is empty and at 21  deg.C (70  deg.F).
    S8.9.2  A pendulum impact testing fixture is used for the test. The 
impact body is a steel pyramid with equilateral triangle faces and a 
square base. The summit and the edges of the pyramid are rounded to a 
radius of 3 mm (0.12 inch). The center of percussion of the pendulum 
coincides with the center of gravity of the pyramid. The center's 
distance from the axis of rotation of the pendulum is 1 meter (40 
inches). The total mass of the pendulum referred to its center of 
percussion is 15 kg (33 pounds). The energy of the pendulum at the 
moment of impact is not less than 30 Nm (22.1 ft-lbf).
    S8.9.3  During the test, the container is held in position by the 
end bosses or by the mounting brackets.
    S8.9.4  The impact body strikes the test container at any point and 
any angle on the container.
    S8.9.5  For 1,500 cycles at ambient temperature, hydrostatically 
pressurize the container from (1) a level not more than 10 percent of 
the service pressure to (2) the service pressure.
    S8.9.6  Determine that the container has not leaked.
    S8.10  Drop test procedures.
    S8.10.1  The container is drop tested at ambient temperature 
without internal pressurization or attached valves. The container is 
held in a horizontal position with the bottom 3.05 meters (10 feet) 
above the surface onto which it is dropped. The surface is a smooth, 
horizontal concrete pad or flooring that is 4 inches thick.
    S8.10.2  For 5,000 cycles at ambient temperature, hydrostatically 
pressurize the container from (1) a level not more than 10 percent of 
the service pressure to (2) 125 percent of the service pressure, and 
then for 13,000 cycles from (1) a level not more than 10 percent of the 
service pressure to (2) the service pressure.
    S8.10.3  Determine that the container has not leaked.
    S8.11  Road salt environmental test procedures.
    S8.11.1  Adjust a pass/fail gauge to fit the container before the 
test.
    S8.11.2  A CNG fuel container, free of any protective coating, is 
cycle tested as follows:
    S8.11.2.1  Subject the container to a salt spray (fog) test in 
accordance with ASTM B-117-73, ``Method of Salt Spray (Fog) Testing,'' 
for 240 hours consisting of ten successive 24 hour periods. During each 
period, the container shall be mounted in the middle of the chamber and 
exposed for 23 hours to the salt spray. The spray is not activated 
during the 24th hour.
    S8.11.2.2  For 5,000 cycles at ambient conditions, hydrostatically 
pressurize the container from (1) a level not more than 10 percent of 
the service pressure to (2) 125 percent of the service pressure.
    S8.11.2.3  Stabilize at zero pressure and ambient conditions.
    S8.11.2.4  For 5,000 cycles at -40 deg. C (-40 deg. F), 
hydrostatically pressurize the container from (1) a level not more than 
10 percent of the service pressure to (2) the service pressure.
    S8.11.2.5  The cycling rate does not exceed 10 cycles per minute.
    S8.11.3  Determine that the container has not leaked or permanently 
changed in external configuration or dimension. With respect to changes 
in the container's external configuration or dimension, adjust a pass/
fail gauge to fit the container. Compare the measurement with the one 
in S8.11.1.

    Issued on: December 9, 1994.
Barry Felrice,
Associate Administrator for Rulemaking.
[FR Doc. 94-31016 Filed 12-16-94; 8:45 am]
BILLING CODE 4910-59-P