[Federal Register Volume 61, Number 232 (Monday, December 2, 1996)]
[Rules and Regulations]
[Pages 63952-63956]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 96-30525]



[[Page 63951]]

_______________________________________________________________________

Part IV





Department of Transportation





_______________________________________________________________________



Federal Aviation Administration



Allowable Carbon Dioxide Concentration in Transport Category Airplane 
Cabins; Final Rule

  Federal Register / Vol. 61, No. 232 / Monday, December 2, 1996 / 
Rules and Regulations  

[[Page 63952]]



DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. 27704, Amdt. No. 25-89]
RIN 2120-AD47


Allowable Carbon Dioxide Concentration in Transport Category 
Airplane Cabins

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final rule.

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

SUMMARY: This amendment revises the standards for maximum allowable 
carbon dioxide (CO2) concentration in occupied areas of transport 
category airplanes by reducing the maximum allowable concentration from 
3 percent to 0.5 percent. This action is in response to a 
recommendation from the National Academy of Sciences to review the 
CO2 limit in airplane cabins, and provides a cabin CO2 
concentration level representative of that recommended by some 
authorities for buildings.

EFFECTIVE DATE: January 2, 1997.

FOR FURTHER INFORMATION CONTACT: Kristin L. Larson, FAA, Flight Test 
and Systems Branch, ANM-111, Transport Airplane Directorate, Aircraft 
Certification Service, 1601 Lind Avenue SW., Renton, Washington 98055-
4056; telephone (206) 227-1760, facsimile (206) 227-1100.

SUPPLEMENTARY INFORMATION:

Background

    This amendment is based on Notice of Proposed Rulemaking No. 94-14, 
published in the Federal Register on May 2, 1994 (59 FR 22718). As 
discussed in that notice, this action reduces the maximum allowable 
carbon dioxide concentration level from 3 percent to 0.5 percent.
    In October 1984, the Department of Transportation was directed by 
Congress (Public Law 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. 
One of the recommendations in the report 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 
rule, the term ``cabin'' is meant to include the passenger cabin, the 
flight deck, lower lobe galleys, crew rest areas, and any other areas 
occupied by passengers or crew members in a transport category 
airplane.

Discussion

    Carbon dioxide is the product of normal human metabolism, which is 
the predominant source in airplane 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. 
Carbon dioxide is also generated by sublimation of dry ice used to cool 
food in the galleys, and to preserve certain cargo carried in the cargo 
compartments. 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 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 4b6 on March 5, 1952. This 
limit was carried over into 14 CFR part 25 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 
airplanes with built-in carbon dioxide fire extinguishing systems, safe 
carbon dioxide concentration levels would not be exceeded in the 
occupied areas 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, the 
American Society of Heating, Refrigerating, and Air-Conditioning 
Engineers (ASHRAE), in their Standard 62-1989, recommends an outside 
air ventilation rate of 15 cubic feet per minute for vehicles. Based on 
the ASHRAE calculations, this equates to a CO2 limit of 1,000 
parts per million (PPM), or 0.1 percent, if the occupants have a low 
physical activity level. As most of the airplane occupants are 
passengers who are not active, this is a reasonable parallel. ASHRAE 
standards such as the 0.1 percent CO2 limit are frequently quoted 
in magazine and newspaper articles when reporting on airliner cabin air 
quality.
    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, occasionally, 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. As noted above, according to 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 previous edition of the 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 ASHRAE standard is intended to be used as 
a comfort standard rather than a health and safety standard. ASHRAE has 
recognized that the 0.1 percent CO2 concentration limit may not be 
appropriate for airliner cabins, and has formed an aviation 
subcommittee, the charter of which is to develop a transport airplane 
cabin air quality standard. While this subcommittee is not an FAA 
advisory committee, industry often uses ASHRAE standards in designing 
systems. The subcommittee will sponsor research studies to determine 
the quality of the ambient air and quantify the correlation between 
measurable contaminants and passenger perception of air quality. As 
noted above, ASHRAE standards were intended to be used for buildings 
rather than vehicles such as airplanes, and they consider it 
appropriate to establish a new standard for airplanes at this time.
    The Occupational Safety and Health Administration (OSHA), in 
Sec. 1910.1000 of part 1910 (CFR 29), sets an interim (transitional) 
limit for CO2 at 5,000 ppm or 0.5 percent, with a final rule limit 
of

[[Page 63953]]

10,000 ppm or 1 percent, 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 a 
limit, but ACGIH recommends this value as a time-weighted average limit 
for repeated daily exposure by workers. The FAA is 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 the establishment of a lower value.
    Copies of the pertinent documents from ASHRAE, OSHA, and ACGIH have 
been placed in the public docket for this 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. 
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 airplanes, 
there is no significant reduction in the percentage of oxygen, or 
increase in the amount of water vapor in the cabin due to respiration. 
However, the design parameters for the ventilation systems are driven 
by operation on the ground during hot days. 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 rule 
adopts a new maximum allowable carbon dioxide concentration of 0.5 
percent. According to ASHRAE, for sedentary people this concentration 
can be maintained by a fresh air flow rate of 2.25 cfm per person, 
which is lower than that currently measured in transport category 
airplanes.
    Section 25.831(b)(2) currently reads, ``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 has removed the 
reference to crewmembers. In addition, Sec. 25.831(b)(2) also specifies 
that, ``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, cabin, or cargo compartment. 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. Therefore, that 
sentence in Sec. 25.831(b)(2) is removed because it is no longer 
considered necessary or appropriate.
    Section 25.831(b)(1) 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 action does 
not change this limit.

Discussion of Comments

    Comments were received from foreign and domestic airplane 
manufacturers through their respective trade associations, foreign 
airworthiness authorities, trade organizations representing flight 
attendants and US and Canadian pilots, one US operator, an organization 
representing airline passengers, and several individuals.
    Two commenters support the proposed change as it appears in the 
notice. Five commenters wrote to register dissatisfaction with the air 
quality on airplanes, mentioning both comfort for passengers and 
illnesses believed to be associated with inadequate fresh air flow. One 
commenter urges the FAA to ``make the changes necessary so that we can 
fly in reasonable health.'' Another commenter is of the opinion that 
``very poor recirculation of air in planes is costing a lot of money in 
medical terms, not to mention suffering.'' Two commenters state that 
the FAA should perform tests on existing airplanes. The FAA infers from 
these comments that the commenters are in favor of revising the 
requirements to ensure acceptable air quality. Studies conducted by the 
FAA and others do not indicate that there is a health hazard associated 
with cabin air quality. As none of these commenters suggest specific 
changes to the proposal, there are no changes to the final rule in 
response to the comments.
    One commenter misread the proposal as to the allowable 
concentration currently in the regulations and that proposed in the 
notice. This commenter states that the standards for cabin air quality 
should be better than the standard set for buildings, because the 
population density is higher in an airplane, and in an office building 
people may exit periodically. While the commenter made no specific 
recommendations, the FAA infers that the commenter advocates lower 
limits than proposed in the notice. The FAA does not concur that these 
factors justify a requirement for a lower carbon dioxide concentration. 
The existing standards are all based on a ventilation rate per 
occupant. To meet the same requirements with a higher population 
density, a greater volume of fresh air ventilation is required. It is 
not clear how this concern can be addressed by the airline industry or 
the FAA when the studies conducted indicate that the air quality in 
airplanes does not present a hazard to the health of the travelers.
    Two commenters state that the proposed 0.5 percent carbon dioxide 
concentration limit is too high. One commenter suggests that the FAA 
``set a limit of 800 parts per million (ppm), the same level proposed 
by the Occupational Safety and Health Administration for indoor air 
quality,'' which is 0.08 percent. Another commenter recommends that the 
FAA adopt an airplane cabin carbon dioxide maximum concentration of 0.1 
percent. Both commenters express concerns about the effect of higher 
carbon dioxide levels and increased recirculation on the spread of 
disease and on people with respiratory difficulties. One commenter 
notes that concentrations above 0.1 percent may result in complications 
for persons with an existing respiratory difficulty, noting that 12.4 
million Americans have asthma.
    Another commenter states that flight attendants who are repeatedly 
exposed to carbon dioxide levels above 0.1 percent develop a tolerance, 
while passengers do not. Another commenter states that flight 
attendants are at a greater risk because of this same

[[Page 63954]]

repeated exposure. The FAA does not concur with these views. The 
documented studies contained in the docket for this rule indicate that 
the air quality currently present in the airliner cabins is comparable 
to that found in other indoor environments. The OSHA recommendation 
proposed in the Federal Register on April 5, 1994 (59 FR 16035), which 
has not been adopted at this time, addresses the carbon dioxide 
concentration as a comfort factor to be used in determining the need to 
verify proper operation of heating and ventilating equipment. Further, 
this proposal addresses non-industrial work environments and 
specifically excludes vehicles. A copy of the OSHA proposed amendment 
has been included in the docket for this rulemaking. There is no 
evidence that concentrations up to 0.5 percent present any health 
hazard in terms of general health or the spread of disease. In the 
economic evaluation conducted by the FAA, the higher costs associated 
with requiring a carbon dioxide concentration limit below 0.5 percent 
do not present a favorable cost/benefit ratio and cannot be justified. 
Further, there appears to be no specific concentration level, even at 
levels down to 0.1 percent, at which at least some passengers might not 
be affected. This rule, which will be contained in the airworthiness 
requirements of part 25, is intended to provide safe flight and landing 
for transport category airplanes. Because carbon dioxide in 
concentrations below 0.5 percent do not have adverse safety effects, 
the FAA has determined that a concentration limit of 0.5 percent 
provides a reasonable balance between cost and benefit, and provides a 
significant improvement over the existing allowable concentration.
    Several commenters note that the OSHA and ACGIH standards are for 
an average concentration over a specific time period. ACGIH, for 
instance, recommends 5,000 ppm (0.5 percent) as a time-weighted average 
for a normal 8-hour workday or a 40-hour workweek. They note in their 
1991 report that Australia, Germany, Sweden, and the United Kingdom all 
recommend a time-weighted value of 0.5 percent for carbon dioxide 
concentration. OSHA's limits also reflect the average airborne exposure 
in any 8-hour work shift of a 40-hour workweek. The FAA infers that the 
commenters advocate providing both a time weighted and a short term 
concentration limit. The FAA does not concur that the carbon dioxide 
level should be averaged over the entire flight for several reasons. 
Many flights exceed eight hours in duration, and the occupants are not 
able to leave the airplane as are workers in an office. Also, there are 
added stresses involved in being in an airplane cabin. The cabin 
pressure altitude is significantly above sea level, usually at 6,000 to 
8,000 feet. The relative humidity is lower than is usually found in 
ground-based environments. There are unquantified stresses associated 
with being in a crowded airplane cabin. Many people experience anxiety 
from the mere fact that they are aloft. While most of these factors 
cannot be controlled, the FAA has determined that the present part 25 
limit on carbon dioxide concentration does not reflect industry 
standards and should be reduced accordingly.
    One commenter suggests that the average concentration should be 
limited to 0.5 percent, but ``a limit of 3 percent by volume (sea level 
concentration) may be allowed for short term durations.'' The commenter 
points out that the 3 percent limit for short term durations 
corresponds to the short term exposure limit (STEL) adopted by the 
ACGIH, and having two limits should be similar to the two limits on 
cabin ozone concentration specified in Sec. 25.832. Again, the FAA does 
not concur. The adverse health and safety effects of ozone are defined 
in available literature and Sec. 25.832 of the FAR addresses that 
concern. There appears to be no reason to phrase the two requirements 
similarly.
    The FAA has determined, however, that some short term excursions to 
values higher than 0.5 percent at some locations in the airplane may 
occur during normal, inflight operations when airplane pressurization 
and air conditioning systems are controlling the environment in the 
cabin. One commenter notes that the area in close proximity to the 
galley may experience higher carbon dioxide levels because meals are 
often cooled by dry ice, which releases gaseous carbon dioxide. Another 
commenter states that cabin air can be contaminated on the ground by 
exhaust ingestion or self ingestion during certain wind conditions. The 
FAA does not agree that this presents a problem. In one survey, 
conducted by the Harvard University School of Public Health, carbon 
dioxide levels were measured during boarding and deboarding operations. 
The typical levels reported were 2,000 to 2,550 ppm, or 0.2 to 0.25 
percent, well below the 0.5 percent proposed by the FAA. However, the 
FAA does concur that it is not appropriate for the certification 
standards to apply to operations on the ground when the airplane 
systems are not operating (e.g., at the gate or during ``push-back''). 
The final rule is changed to reflect this determination.
    The same commenter expresses concern that the use of carbon dioxide 
hand-held fire extinguishers in the cabin could result in local 
concentrations exceeding 0.5 percent, noting that the present Halon 
extinguishers might be replaced by carbon dioxide devices now that 
production of Halon is banned, and suggests a higher short-term 
exposure limit. The FAA does not concur that this is a justification 
for a higher limit. The use of carbon dioxide fire extinguishers is not 
envisioned, although there are no prohibitions against their use in 
airplanes. When Halon is no longer available, the replacement 
extinguishers will be required to be safe in the concentrations 
predicted for use in occupied areas. Further, the use of fire 
extinguishers in the cabin is, by its nature, an emergency situation. 
This is not, in the context of the previous paragraph, normal in-flight 
operations. Therefore, there appears to be no need for the higher limit 
on carbon dioxide.
    Two commenters state that the utilization of building criteria for 
establishing carbon dioxide concentration limits for airplane cabins is 
not appropriate. Both commenters add that the statement in the proposal 
that concentrations above 0.5 percent are hazardous is not justifiable. 
The FAA concurs with the general statement that carbon dioxide 
concentrations above 0.5 percent may not be hazardous for most people. 
Many standards in use today allow higher concentrations. As noted by 
one commenter, the World Health Organization considers 12,000 ppm (1.2 
percent) to be a safe level. In any case, the final rule has been 
changed and no longer contains the word ``hazardous.'' Both of these 
commenters note that the rule, as proposed, would limit carbon dioxide 
concentrations in lower lobe galleys, accessible cargo compartments 
where animals are carried, cockpits, and other occupied areas. They 
express concern that local carbon dioxide concentrations in the galley 
areas where food is cooled with dry ice might exceed 0.5 percent. The 
FAA concurs in part with these comments. The ventilation requirements 
associated with this rule change are intended to address areas that are 
normally occupied. Cargo compartments accessible in flight, whether in 
all cargo or ``combi'' airplanes with main deck cargo compartments, are 
not ``normally occupied.'' The final rule has been changed to reflect 
this determination.
    One commenter disagrees with the statement in the preamble of the 
proposed rule that ``This low ventilation rate is also sufficient to 
dissipate the water vapor * * *,'' noting that water

[[Page 63955]]

buildup in insulation blankets is significant with present airplane 
fresh air inflow rates, especially in hot day ground conditions. The 
FAA concurs and the statement has been removed from the preamble. In 
stating this view, the commenter did not recommend any changes in the 
rule.
    One commenter states that the term ``sea level equivalent'' should 
be clarified. The commenter suggests that the clarification include 
technical and/or medical rationale, including referenced sources, and 
provide an explanation of the methodology by which this value is to be 
calculated. If this rationale is not provided, the commenter states 
that the FAA should delete the phrase. The FAA does not concur that the 
term ``sea level equivalent'' is not defined, although the definition 
appears in reference to another gas. In FAA Advisory Circular 120-38, 
``Transport Category Airplanes Cabin Ozone Concentrations,'' sea level 
equivalent is defined as ``* * * concentration in ppmv referenced to 
standard conditions of 25 deg. C and 760 millimeters of mercury 
pressure.'' Based on this definition, and calculations provided in the 
AC, the maximum measured concentration, sea level equivalent, for a 
cabin altitude of 8,000 feet would be 0.5 percent multiplied by 0.74 
(the ratio of air pressure at 8,000 feet to air pressure at sea level), 
or 0.37 percent. Values of this ratio for other cabin altitudes are 
provided in the AC. As the term sea level equivalent is defined, the 
rule is adopted as proposed.
    The same commenter also notes that the statement in the preamble 
that control of carbon dioxide buildup due to respiration is the factor 
that dictates the design parameters for ventilation systems is 
incorrect. Operation on the ground during high ambient temperatures 
generally dictates the ventilation system design parameters. The FAA 
concurs and the preamble has been changed accordingly.
    One commenter recommends that the new standards for carbon dioxide 
concentration not be applied to all-cargo airplanes. The commenter 
notes that measured carbon dioxide levels on the flight decks of these 
airplanes are well below both the current standard and that proposed in 
Notice 94-14. The commenter goes on to state that lowering the limit on 
carbon dioxide is a comfort issue, and would place a burden on the 
manufacturers of transport category airplanes that is not commensurate 
with any safety benefit that might result. The FAA does not concur. As 
noted elsewhere in this preamble, the FAA has determined that the 
existing concentration limit of 3 percent for carbon dioxide is not 
appropriate because many passengers and crewmembers are adversely 
affected at that level. The lower levels adopted by this amendment will 
provide a standard that, when met, will ensure that passengers and 
crewmembers, including those on all-cargo airplanes, will not be 
subjected to levels of carbon dioxide that would reduce their ability 
to perform their assigned duties. There are no costs associated with 
lowering the limit as proposed.
    With the exception of the changes noted above, this final rule is 
adopted as proposed in Notice 94-14.

Regulatory Evaluation

    Changes to Federal regulations must undergo several economic 
analyses. First, Executive Order 12866 directs Federal agencies to 
promulgate new regulations or modify existing regulations only if the 
potential benefits to society 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 
assessments, the FAA has determined that this rule: (1) will generate 
benefits exceeding its costs and is not ``significant'' as defined in 
Executive Order 12866; (2) is not ``significant'' as defined in DOT's 
Policies and Procedures; (3) will not have a significant impact on a 
substantial number of small entities; and (4) will not constitute a 
barrier to international trade. These analyses, available in the 
docket, are summarized below, following FAA's disposition of comments 
on the economic aspects of the NPRM.

Response to Comments

    One commenter calculates that it would cost about $0.076 per person 
per hour to provide 100 percent fresh air in the cabin of a typical 
300-seat widebody airplane. The FAA disagrees with this commenter and 
estimates that the cost of 100 percent fresh air would be $0.095 per 
person per hour.
    Another commenter states that the FAA did not account for the 
potential costs of applying the rule to all occupiable sections of the 
airplane because it evaluated only the passenger cabin area and ignored 
the flight deck and lower lobe galleys. The FAA concurs in part with 
this comment. The carbon dioxide concentration requirements are 
intended to apply to areas that are normally occupied. The final rule 
has been changed to reflect this intent. Thus, the commenter's 
statement does not alter the FAA's economic analysis.
    Another commenter states that the FAA did not evaluate the 
possibility that ground-air contamination (ingestion of other 
airplanes' exhausts) may temporarily push the CO2 level above the 
0.5 percent limit. The FAA does not agree that this presents a problem. 
In one survey, conducted by the Harvard University School of Public 
Health, CO2 levels were measured during boarding and deboarding 
operations. The typical levels reported were 0.2 percent to 0.25 
percent, well below the 0.5 percent in this rule. However, the FAA does 
concur that it is not appropriate for the certification standards to 
apply to ground operations when the airplane systems are not 
functioning. As a result, the final rule has been changed to reflect 
this determination. Consequently, there is no economic impact as a 
result of this remote possibility.
    Two commenters state that if live animal cargo areas are included 
under the definition of ``inhabited'' areas, there would be 
considerable potential costs. The FAA partly concurs with these 
comments in that cargo compartments accessible in flight, whether in 
all cargo or ``combi'' airplanes with main deck cargo compartments, are 
not normally occupied and the final rule has been changed to reflect 
this determination. As a result, there is no economic impact from 
excluding live animal cargo areas from this rule.

Costs

    Airplane cabin CO2 levels can be reliably calculated from the 
number of passengers and the ventilation rate. In addition, engineering 
analyses have determined the amount of fuel used to provide a unit 
ventilation rate. These functional relationships allow the calculation 
of the costs to maintain a given cabin CO2 level. The FAA 
estimates that the 3 percent CO2 limit under the current rule 
costs about 0.27 cents per person per hour while the new 0.5 percent 
limit will cost about 1.7 cents per person per hour. Thus, the amended 
limit constitutes a 1.43 cent increase per person per hour, or about 
$4,475 per (newly certificated) airplane per year.
    In point of fact, however, the ventilation rates in current 
transport category airplanes currently maintain cabin CO2 levels 
below 0.5 percent. As the FAA expects that the minimum ventilation 
rates of future aircraft designs will also maintain CO2 levels 
below 0.5 percent in order to control

[[Page 63956]]

odors, temperature, water vapor, etc., no actual incremental costs or 
benefits will result from the rule change. However, codification of 
this limit will ensure that future designs maintain the 0.5 percent 
level.

Benefits

    Although outdoor air contains CO2 at the 0.03 percent level, 
CO2 may produce respiratory center stimulation, mild narcotic 
effects, and asphyxiation under high levels and high exposure duration. 
At concentrations of 2 to 3 percent, CO2 can produce headaches, 
breathing difficulty, and increases in blood pressure and pulse. By 
comparison, no ill-effects have been observed at the 0.5 percent level.

Cost-Benefit Comparison

    From a strict cost-benefit evaluation of the rule change itself, 
isolated from actual practice, the FAA concludes that it would cost 
about 1.43 cents per person per hour to increase the ventilation to 
reduce cabin CO2 levels from 3 percent to 0.5 percent. By 
comparison, this reduction eliminates the cabin CO2 levels known 
to produce headaches, breathing difficulty, and increases in blood 
pressure and pulse. While no precise economic value has been assigned 
to the benefit from avoiding these ill effects, the FAA has determined 
that they are worth more than 1.43 cents per person per hour.

Regulatory Flexibility Determination

    The Regulatory Flexibility Act of 1980 (RFA) was enacted by 
Congress to ensure that small entities are not unnecessarily or 
disproportionately burdened by Government regulations. The RFA requires 
a Regulatory Flexibility Analysis if a proposed or final rule would 
have a significant economic impact, either detrimental or beneficial, 
on a substantial number of small entities. FAA Order 2100.14A, 
Regulatory Flexibility Criteria and Guidance, prescribes standards for 
complying with RFA review requirements in FAA rulemaking actions. The 
Order defines ``small entities'' in terms of size, ``significant 
economic impact'' in terms of annualized costs, and ``substantial 
number'' as eleven or more and which is more than one-third of the 
small entities subject to the proposed or final rule.
    The final rule would affect manufacturers of transport category 
airplanes produced under future new airplane type certificates. For 
manufacturers, Order 2100.14A defines a small entity as one with 75 or 
fewer employees. Since no part 25 airplane manufacturer has 75 or fewer 
employees, the rule would not have a significant economic impact on a 
substantial number of small entities.

International Trade Impact Assessment

    As the certification rules apply to both foreign and domestic 
manufacturers that market airplanes in the United States, neither group 
will receive a competitive advantage. As no incremental compliance 
costs are expected, there will be no competitive trade disadvantage or 
advantage for U.S. manufacturers in foreign markets or for foreign 
manufacturers in the United States.

Federalism Implications

    The regulations adopted herein will 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 final 
rule will not have sufficient federalism implications to warrant the 
preparation of a Federalism Assessment.

International Civil Aviation Organization (ICAO) and Joint Aviation 
Regulations

    In keeping with U.S. obligations under the Convention on 
International Civil Aviation , it is FAA policy to comply with ICAO 
Standards and Recommended Practices to the maximum extent practicable. 
The FAA has determined that this rule does not conflict with any 
international agreement of the United States.

Paperwork Reduction Act

    In accordance with the Paperwork Reduction Act of 1990 (44 U.S.C. 
3501 et seq.), there are no reporting or recordkeeping requirements 
associated with this rule.

Conclusion

    Because the 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 final rule 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 rule, the FAA certifies, under the criteria of the 
Regulatory Flexibility Act, that this regulation will not have a 
significant economic impact, positive or negative, on a substantial 
number of small entities. A copy of the regulatory evaluation prepared 
for this final rule has been placed in the public docket. A copy may be 
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.

Adoption of the Amendment

    In consideration of the foregoing, the Federal Aviation 
Administration (FAA) amends 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. 106(g), 40113, 44701-44702, 44704.

    2. Section 25.831 is amended by revising paragraph (b)(2) to read 
as follows:


Sec. 25.831  Ventilation.

* * * * *
    (b) * * *
    (2) Carbon dioxide concentration during flight must be shown not to 
exceed 0.5 percent by volume (sea level equivalent) in compartments 
normally occupied by passengers or crewmembers.
* * * * *
    Issued in Washington, D.C., on November 21, 1996.
Linda Hall Daschle,
Acting Administrator.
[FR Doc. 96-30525 Filed 11-29-96; 8:45 am]
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