[Federal Register Volume 59, Number 83 (Monday, May 2, 1994)]
[Unknown Section]
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From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 94-9759]


[[Page Unknown]]

[Federal Register: May 2, 1994]


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Part II





Department of Transportation





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Federal Aviation Administration



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14 CFR Part 25




Allowable Carbon Dioxide Concentration in Transport Category Airplane 
Cabins; Proposed Rule
DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. 27704; Notice No. 94-14]
RIN 2120-AD47

 
Allowable Carbon Dioxide Concentration in Transport Category 
Airplane Cabins

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of proposed rulemaking.

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SUMMARY: This notice proposes to revise the standards for maximum 
allowable carbon dioxide (CO2) concentration by reducing the 
allowable maximum concentration from 3 percent to 0.5 percent in 
occupied areas of transport category airplanes. This action is in 
response to a recommendation from the National Academy of Sciences to 
review the CO2 limit in airplane cabins, and would provide a cabin 
CO2 concentration equivalent to that recommended for buildings.

DATES: Comments must be received on or before August 30, 1994.

ADDRESSES: Send comments on this notice in triplicate to: Federal 
Aviation Administration, Office of the Chief Counsel, Attn: Rules 
Docket (AGC-200), Docket No. 27704, 800 Independence Avenue SW., 
Washington, DC 20591; or deliver comments in triplicate to: Federal 
Aviation Administration, room 915G, 800 Independence Avenue SW., 
Washington, DC 20591. Comments must be marked Docket No. 27704. 
Comments may be examined in the Rules Docket weekdays, except Federal 
holidays, between 8:30 a.m. and 5 p.m. In addition, the FAA is 
maintaining an information docket of comments in the Office of the 
Assistant Chief Counsel (ANM-7), Federal Aviation Administration, 
Northwest Mountain Region, 1601 Lind Avenue SW., Renton, Washington 
98055-4056. Comments in the information docket may be examined in the 
Office of the Assistant Chief Counsel weekdays, except Federal 
holidays, between 7:30 a.m. and 4 p.m.

FOR FURTHER INFORMATION CONTACT:
Bob McCracken, FAA, Flight Test and Systems Branch, ANM-111, Transport 
Airplane Directorate, Aircraft Certification Service, 1601 Lind Avenue 
SW., Renton, Washington 98055-4056; telephone (206) 227-2118.

SUPPLEMENTARY INFORMATION: 

Comments Invited

    Interested persons are invited to participate in this proposed 
rulemaking by submitting such written data, views, or arguments as they 
may desire. Comments relating to any environmental, energy, federalism, 
or economic impacts that might result from adoption of the proposal 
contained in this notice are also invited. Substantive comments should 
be accompanied by cost estimates. Commenters should identify the 
regulatory docket or notice number and submit comments in triplicate to 
the Rules Docket address above. All comments received on or before the 
closing date for comments will be considered by the Administrator 
before taking action on this proposed rulemaking. The proposal 
contained in this notice may be changed in light of comments received. 
All comments received will be available in the Rules Docket, both 
before and after the closing date for comments, for examination by 
interested persons. A report summarizing each substantive public 
contact with FAA personnel concerning this rulemaking will be filed in 
the docket. Persons wishing the FAA to acknowledge receipt of their 
comments must submit with those comments a self-addressed, stamped 
postcard on which the following statement is made: ``Comments to Docket 
No. 27704.'' The postcard will be date stamped and returned to the 
commenter.

Availability of NPRM

    Any person may obtain a copy of this Notice of Proposed Rulemaking 
(NPRM) by submitting a request to the Federal Aviation Administration, 
Office of Public Affairs, Attention: Public Inquiry Center, APA-230, 
800 Independence Avenue SW., Washington, DC 20591; or by calling (202) 
267-3484. Communications must identify the notice number of this NPRM. 
Persons interested in being placed on the mailing list for future NPRMs 
should also request a copy of Advisory Circular No. 11-2A, Notice of 
Proposed Rulemaking Distribution System, which describes the 
application procedure.

Background

    In October 1984, the Department of Transportation was directed by 
Congress (Pub. L. 98-466) to commission the National Academy of 
Sciences (NAS) to conduct an independent study on the cabin air quality 
in transport category airplanes. The NAS formed the Committee on 
Airliner Cabin Air Quality to study all safety aspects of airliner 
cabin air quality, and submitted its report, ``The Airliner Cabin 
Environment--Air Quality And Safety,'' to the FAA on August 12, 1986. 
The report includes 19 recommendations for legislative, regulatory, and 
air transport industry changes in relation to airliner cabin air 
quality. One of the recommendations relates to the allowable carbon 
dioxide (CO2) concentration in the airplane cabin. This action is 
a result of that recommendation. For the purposes of this notice, the 
term, ``cabin'' is meant to include the passenger cabin, the flight 
deck, lower lobe galleys, crew rest areas, and any other occupied areas 
in a transport category airplane.

Discussion

    Carbon dioxide is the product of normal human metabolism, which is 
the predominant source in aircraft cabins. The CO2 concentration 
in the cabin depends on the ventilation rate, the number of people 
present, and their individual rates of CO2 production, which 
varies with activity and (to a smaller degree) with diet and health. 
The carbon dioxide concentration level is frequently used as an 
indication of general air quality. At concentrations above a given 
level, complaints of poor air quality or ``stuffiness'' begin to 
appear.
    The current maximum CO2 limit of Sec. 25.831(b)(2) of the 
Federal Aviation Regulations (FAR) is 3 percent by volume, sea level 
equivalent. This 3 percent limit was incorporated into Sec. 4b.371 of 
the Civil Air Regulations (CAR) by Amendment 4b-6 on March 5, 1952. 
This limit was carried over into 14 CFR part 25 of the FAR when this 
part was codified in 1965. This high limit was established to allow for 
increases in the carbon dioxide levels in the crew compartment to 
ensure that, in aircraft with built-in carbon dioxide fire 
extinguishing systems, safe carbon dioxide concentrations would not be 
exceeded in the crew compartment when combating fires in cargo 
compartments.
    The American Conference of Governmental Industrial Hygienists 
(ACGIH) has adopted a short-term exposure limit (STEL) for CO2 of 
30,000 parts per million (3 percent). The 3 percent limit specified in 
part 25 may therefore be satisfactory as a short-term limit, but is 
inappropriate for a steady-state condition. However, the NAS Committee 
notes in their report that this 3 percent limit is much higher than the 
limits adopted by the air conditioning industry for buildings and other 
types of interior environments, and recommends that the limit specified 
in part 25 be revised to more closely match the currently acceptable 
limits. The FAA concurs.
    In contrast to the 3 percent limit specified in part 25, Standard 
62-1989, prepared by the American Society of Heating, Refrigerating, 
and Air-Conditioning Engineers (ASHRAE), recommends a CO2 limit of 
1,000 parts per million (PPM), or 0.1 percent. As CO2 
concentration in the air increases, there is an increase in both the 
rate and the depth of breathing, reaching twice the normal rate at 3 
percent concentration. At 3 percent concentration, there is some 
discomfort; at higher concentrations, headache, malaise, and fatigue 
occur, and the air is reported by those affected as being stale. People 
can function for long periods of time at levels of CO2 as high as 
1 percent (as in nuclear submarines), but it is generally felt by 
ASHRAE that 0.1 percent is a better limit. This value, however, is 
based on the dissipation of smoke and odors and not on health 
considerations. According to the ASHRAE Standard 62-1989, a steady-
state CO2 concentration of 0.1 percent would require a fresh-air 
ventilation rate of 15 cubic feet per minute (cfm) per person. In the 
old standard (62-1981), ASHRAE recommended a limit of 0.5 percent for 
office buildings and other occupied spaces, but suggested that 0.25 
percent would provide an additional safety factor.
    The Occupational Safety and Health Administration (OSHA), in 29 CFR 
1910.1000, sets an interim (transitional) limit for CO2 at 5,000 
ppm or 0.5 percent, with a final rule limit of 10,000 ppm or 1 percent, 
which becomes effective December 31, 1993. The increase to 1 percent is 
apparently in deference to operators of commercial bakeries and 
breweries, both of which generate a significant amount of CO2 in 
their processes. The FAA does not believe it is appropriate to base the 
allowable CO2 concentration in transport category airplanes on the 
needs of specific manufacturing processes. Other commercial enterprises 
have no difficulty in meeting the existing OSHA limit of 0.5 percent.
    The American Conference of Governmental Industrial Hygienists, in 
its ``Documentation of the Threshold Limit Values and Biological 
Exposure Indices--Sixth Edition,'' also recommends 0.5 percent as the 
time weighted average limit for repeated daily exposure by workers. The 
FAA proposes adopting this value as a limit. A concentration limit of 
0.5 percent is considered to be appropriate because there are no 
documented safety or health benefits associated with a lower value. 
Parties reviewing this document are encouraged to comment on values 
between 0.1 percent and the existing 3 percent limit, and to provide 
justification for any recommendations. The FAA may determine, based on 
the comments, that a limit different from 0.5 percent is appropriate 
and change the final rule accordingly.
    Copies of the pertinent documents from ASHRAE, OSHA, and ACGIH have 
been placed in the public docket for this proposed rulemaking.
    Cabin ventilation provides air for dilution of airborne 
contaminants, and supplies oxygen for passengers and crew. Oxygen 
requirements for sedentary adults can be met with a fresh-air 
ventilation rate of only 0.24 cubic feet per minute (CFM) per person. 
This low ventilation rate is also sufficient to dissipate the water 
vapor produced by cabin occupants. Ventilation rates for current 
transport category airplanes vary from a low of approximately 7 cfm per 
person (with one or more air conditioning packs turned off for 
economy), to over 20 cfm per person (which includes up to 50 percent 
filtered, recirculated air). Thus, even at the lowest ventilation rates 
available on current aircraft, there is no significant reduction in the 
percentage of oxygen, or increase in the amount of water vapor in the 
cabin due to respiration. Ventilation for the control of CO2 
buildup due to respiration is therefore the factor that dictates design 
parameters for ventilation systems, although many airplane systems are 
sized much larger than the minimum required for passenger comfort. 
Contamination of air with CO2 varies inversely with the 
ventilation rate, because CO2 production by sedentary people is 
nearly constant.
    In order to bring the maximum allowable carbon dioxide 
concentration into concert with accepted modern limits, this NPRM 
proposes to reduce the maximum allowable carbon dioxide concentration 
from the current value of 3 percent to 0.5 percent. According to 
ASHRAE, for sedentary people, this concentration can be maintained by a 
fresh air flow rate of 2.25 cfm, which is lower than that currently 
measured in transport category aircraft.
    Section 25.831(b)(2) currently states that ``Carbon dioxide in 
excess of three percent * * * is considered hazardous in the case of 
crewmembers.'' The health and comfort considerations discussed earlier 
are equally valid for passengers. Therefore, the FAA proposes to remove 
the reference to crewmembers. In addition, Sec. 25.831(b)(2) currently 
contains the following sentence: ``Higher concentrations of carbon 
dioxide may be allowed in crew compartments if appropriate protective 
breathing equipment is available.'' This sentence was incorporated when 
the 3 percent limit was established in CAR 4b.371 in 1952. As noted 
above, the origins of the 3 percent limit are unclear, but it is likely 
that the limit was set at this high level to account for the discharge 
of CO2 fire extinguishers in the flight deck or cabin. This thesis 
is supported by the mention of protective breathing in the existing 
rule. However, most CO2 extinguishers have been replaced by Halon 
or other types of fire extinguishers. Further, the rule is not intended 
to cover the short-duration rise in CO2 concentration that would 
accompany discharge of a fire extinguisher. Removal of the sentence 
from Sec. 25.831(b)(2) is proposed because it is no longer considered 
necessary or appropriate.
    Section 25.831 also specifies a limit for carbon monoxide (CO) 
concentration of 1 part in 20,000 parts air (0.005 percent). This limit 
is the same as currently recommended by ASHRAE and the Occupational 
Safety and Health Administration (OSHA), and therefore this notice does 
not propose to change this limit.

Regulatory Evaluation

    This section summarizes the full regulatory evaluation that 
provides more detailed estimates of the economic consequences of this 
regulatory action. This summary and the full evaluation quantify, to 
the extent practicable, estimated costs and anticipated benefits to the 
private sector, consumers, and Federal, State and local governments.
    Proposed changes to Federal regulations must undergo several 
economic analyses. First, Executive Order 12866 directs that each 
Federal agency shall propose or adopt a regulation only upon a reasoned 
determination that the benefits of the intended regulation justify its 
costs. Second, the Regulatory Flexibility Act of 1980 requires agencies 
to analyze the economic impact of regulatory changes on small entities. 
Finally, the Office of Management and Budget directs agencies to assess 
the effects of regulatory changes on international trade. In conducting 
these analyses, the FAA has determined that this proposed rule: (1) 
Would generate benefits that would justify its costs and is not a 
``significant regulatory action'' as defined in the Executive Order; 
(2) is not significant as defined in Department of Transportation 
Regulatory Policies and Procedures; (3) would not have a significant 
impact on a substantial number of small entities; and (4) would not 
have a negative impact on international trade. These analyses, 
available in the docket, are summarized below.

Costs

    Carbon dioxide (CO2) is a byproduct of human metabolism and is 
expelled through respiration. The proposed rule would reduce the 
maximum allowable CO2 concentration, as specified in 
Sec. 25.831(b)(2), from 3 percent to 0.5 percent in occupied areas of 
transport category airplanes.
    In a confined space, the production of CO2 is a function of 
the number of people present, their activity levels, and, to a lesser 
extent, their diet and health. The concentration of CO2 in an 
aircraft is controlled by ventilation of the cabin through the 
introduction of outside air through the aircraft's environmental 
control system. For a given set of production and ventilation 
conditions, the resulting CO2 concentration can be calculated 
reliably. In addition, engineering analyses have been conducted to 
determine the fuel that is consumed in providing a unit rate of 
ventilation.
    Taken together, these functional relationships make it possible to 
calculate the costs necessary to maintain CO2 concentrations at a 
given level under established conditions. It is estimated that the 
current 3 percent CO2 concentration limit can be maintained at a 
cost of .3 cents per passenger-hour. The lower proposed 0.5 percent 
limit would cost approximately 2.1 cents per passenger-hour, and would 
constitute an increase of 1.8 cents per passenger-hour. It should be 
noted that these are ``zero baseline'' estimates, and do not take into 
account the cost associated with the fresh air already introduced into 
the airplane for pressurization and other purposes. In actuality, 
existing and probable new airplanes currently have and will in the 
future be designed to have fresh air inflow rates that provide air with 
a CO2 concentration well below the proposed 0.5 percent. For this 
reason, there are no actual costs associated with this proposal.

Benefits

    CO2 is naturally present at low concentration (.03 percent) in 
outdoor air. When CO2 is inhaled in progressively elevated 
concentrations, it may act to produce stimulation of the respiratory 
center, mild narcotic effects, and asphyxiation, depending on the 
concentration and the duration of exposure. Numerous studies have been 
conducted to determine the effects of exposure to elevated CO2 
concentrations. At concentrations of 2 to 3 percent, CO2 produces 
effects such as headaches, breathing difficulty, and increases in blood 
pressure and pulse. By comparison, no symptoms are induced at the 
proposed 0.5 percent level.

Cost-Benefit Comparison

    A strict cost-benefit evaluation of the proposed rule change 
itself, without consideration of the fact that operators currently 
comply with the proposed standard, concludes that the cost of the 
increased ventilation necessary to reduce CO2 concentration from 3 
percent to 0.5 percent would be 1.8 cents per passenger-hour. The 
proposed reduction would prohibit CO2 concentration levels known 
to produce effects such as headaches, breathing difficulty, and 
increases in blood pressure and pulse. While no precise economic value 
has been assigned to this benefit, the FAA believes that it would be 
worth more than 1.8 cents per hour per passenger to avoid such ill 
effects.
    The evaluation described above looks solely at the proposed change 
in the rule. In fact, the minimum ventilation in current transport 
category aircraft maintains CO2 concentrations below the proposed 
0.5 percent concentration. Accordingly, it is estimated that no direct 
incremental costs or benefits would result from this proposed rule. The 
rule would, however, preclude future certificated airplane models from 
being designed to operate at CO2 concentrations above the 0.5 
percent level. Because this dictates a minimum design requirement for 
CO2 concentration in new airplane types, and any airplane must be 
operated in accordance with its type design, this minimum concentration 
would be maintained in actual operation unless a system failure occurs. 
In addition, an intangible benefit would accrue from the fact that the 
proposal would make the CO2 concentration limit for aircraft 
consistent with the standards of other agencies and advisory 
authorities.

Regulatory Flexibility Determination

    The FAA has determined that under the criteria of the Regulatory 
Flexibility Act (RFA) of 1980, the proposed amendment to part 25 
contained in the notice would not have a significant economic effect on 
a substantial number of small entities. The RFA requires agencies to 
review rules which may have a ``significant economic impact on a 
substantial number of small entities.'' The FAA has adopted criteria 
and guidelines for determining whether a proposed or existing rule has 
a significant economic effect on a substantial number of small 
entities. Since no actual incremental costs are expected to be incurred 
to comply with the requirements of the proposal, it would not have a 
significant economic impact.

Trade Impact Statement

    Since the certification rules apply to both foreign and domestic 
manufacturers that sell aircraft in the United States, there would be 
no competitive advantage to either. Since no actual costs are expected 
to be imposed by this rule, it would not result in a competitive trade 
disadvantage for U.S. manufacturers in foreign markets or for foreign 
manufacturers in the United States.

Federalism Implications

    The regulations proposed herein would not have substantial direct 
effects on the 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. Therefore, in 
accordance with Executive Order 12612, it is determined that this 
proposal would not have sufficient federalism implications to warrant 
the preparation of a Federalism Assessment.

Conclusion

    Because the proposed revised standards for maximum allowable carbon 
dioxide concentration are not expected to result in a substantial 
economic cost or have a significant adverse effect on competition, the 
FAA has determined that this proposed regulation is not significant 
under Executive Order 12866. In addition, the FAA has determined that 
this action is not significant as defined in Department of 
Transportation Regulatory Policies and Procedures (44 FR 11034, 
February 26, 1979). Since no actual incremental costs are expected to 
be incurred to comply with the requirements of this proposal, the FAA 
certifies, under the criteria of the Regulatory Flexibility Act, that 
this proposed regulation, if adopted, will not have a significant 
economic impact, positive or negative, on a substantial number of small 
entities. A copy of the initial regulatory evaluation prepared for this 
proposal may be examined in the public docket or obtained from the 
person identified under the caption, FOR FURTHER INFORMATION CONTACT.

List of Subjects in 14 CFR Part 25

    Aircraft, Aviation safety, Reporting and recordkeeping 
requirements.

The Proposed Amendment

    Accordingly, the Federal Aviation Administration (FAA) proposes to 
amend 14 CFR part 25 of the Federal Aviation Regulations (FAR) as 
follows:

PART 25--AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES

    1. The authority citation for part 25 continues to read as follows:

    Authority: 49 U.S.C. app. 1344, 1354(a), 1355, 1421, 1423, 1424, 
1425, 1428, 1429, 1430; 49 U.S.C. 106(g); and 49 CFR 1.47(a).

    2. Section 25.831(b)(2) is revised to read as follows:


Sec. 25.831  Ventilation.

* * * * *
    (b) * * *
    (2) Carbon dioxide in excess of 0.5 percent by volume (sea level 
equivalent) is considered hazardous.
* * * * *
    Issued in Washington, DC, on April 11, 1994.
Thomas E. McSweeny,
Director, Aircraft Certification Service.
[FR Doc. 94-9759 Filed 4-29-94; 8:45 am]
BILLING CODE 4910-13-M