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

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]

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