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EXECUTIVE SUMMARY
Each year Americans take more than 300 million plane
trips, and airliner cabins are the workplace for about
70,000 flight attendants. The health and comfort of
these travelers depend on the complex interplay of
several factors: the adequacy of ventilation systems
affecting the amount of cigarette smoke, microorganisms,
and other contaminants in the cabin air; the use of
fire-retardant materials in cabin equipment and
furnishings; the availability and ease of use of
breathing and other emergency equipment; and the clarity
of special and emergency instructions.
Although such devices and procedures are usually
taken for granted, Congressional hearings during
1983-1984 revealed that information on airliner cabin
air quality was contradictory. Flight attendants and
others testified about inadequate ventilation and other
problems with the cabin environment that caused
discomfort. Representatives from the airline industry
and federal regulatory agencies argued that present
standards for the airliner cabin were adequate to
protect the health and safety of travelers.
Under Public Law 98-466, Congress stipulated that
the National Academy of Sciences enter into a contract
with the Federal Aviation Administration (FAA). The
Academy was asked to determine whether such aspects of
cabin air as the quantity of outside air, the quality of
onboard air, the extent of pressurization, the
characteristics of humidification, the presence of
cosmic radiation, contaminants (such as bacteria, fungi,
and other microorganisms), and pollutants (such as
environmental tobacco smoke, carbon monoxide, carbon
dioxide, and ozone) could be responsible for health
problems in the long or short run; to recommend remedies
for problems discovered; and to outline the safety
1
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precautions necessary to protect passengers in event of
in-flight fires, which produce smoke and fumes.
Accordingly, the Committee on Airliner Cabin Air Quality
was established in the National Research Council's
Commission on Life Sciences. This report summarizes the
findings of the Committee's 18-month study of relevant
issues. The investigation covered five general subjects:
· Cabin air Quality: including potential health
effects of reduced ventilation and of contamination by
chemicals, microorganisms, other allergens, tobacco
smoke, and ozone.
· Cabin environment: health effects of reduced
pressure and of cosmic radiation.
· -Emergency procedures: control of fires and
toxic fumes, use of emergency breathing equipment, and
adequacy of emergency instruction given passengers.
.
Regulations: regulations established by U.S.
and foreign agencies.
· Records: statue and adequacy of medical
statistics on air travel, of records on airline
maintenance, and of records on operating procedures.
The Committee relied heavily on published material--
articles in scientific and medical Journals and
government and industry publications. FAA provided
accident data and information on continuing
investigations. Members of the Committee also visited
government, airline, and industry groups to review fire
testing, crew training facilities, and research programs
on cabin ventilation. Relevant comments and information
were received from the general public and other
interested groups at an open hearing and were reviewed
by the Committee.
In formulating its conclusions and recommendations,
the Committee attempted, but abandoned, the separation
of issues of health from those of safety. However,
under current statutes and administrative orders, no
federal office has direct responsibility for health
effects associated with air travel. This lack of
correspondence between the issues an conceived by the
Committee and the responsibilities of federal agencies
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contributed to the difficulty of the Committee's work.
The Committee believes that the health effects associated
with air travel should be within the Durview of a federal
agency.
CABIN AIR QUALITY
In assessing the overall quality of onboard air, the
Committee determined the range of outside-air ventilation
rates on the U.S. fleet by reviewing manufacturers'
design specifications, airline load-factor data, and
operating procedures. No data were available on actual
measured airflow in the fleet.
The Committee found that, if the lowest rate of
ventilation permitted by current equipment design were
used under conditions of full or nearly full passenger
loads, the resulting ventilation rate would be at the
minimum determined to provide acceptable air quality
when smoking is not permitted and other contaminant
sources are not present. In the absence of sources of
contamination, this rate does not constitute a health
hazard.
In particular, the Committee noted that the flow
rate of outside air varied from below 7 cubic feet per
minute (cfm) per economy-class passenger to 50 cfm per
first-class passenger. Cockpit ventilation rates are
often as high an 150 cfm per crew member; this higher
rate, however, is provided to meet avionic and
electronic equipment cooling loads, rather than for
reduction of contaminant concentrations. These rates
compare with a ventilation rate of 5-7 cfm/person
established for other types of vehicular travel that
have nonsmoking sections, including passenger and
commuter trains and subways. It should be noted,
however, that these other ventilation standards do not
consider possible synergistic effects of the low
relative humidity encountered in aircraft.
Another important consideration is the adequacy of
oxygen supply--because the normal requirement of air to
meet oxygen needs for sedentary people in only 0.24
cfm/person, the amount of oxygen is sufficient in
aircraft even at the lowest rate of flow of outside air
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Nevertheless, a minimal ventilation rate for
airplane passenger cabins is not defined under FM
regulations, which specify ventilation rates only for
flight crew compartments. Actual cabin airflow is
seldom measured once an aircraft is in service; and flow
can be reduced by deterioration in equipment performance.
A data collection Program that measures airflow and
contamination in airplane cabins should be implemented.
CARBON DIOXIDE
The Committee's efforts in evaluatlag contaminant
concentrations were hampered by an almost complete
absence of reliable data. The carbon dioxide
concentration associated with a given ventilation rate,
however, can be estimated with confidence. For a rate
of 9.7 cfm/occupant, the carbon dioxide concentration
would be about 0.15X, or 1,500 ppm. No adverse health
effects of carbon dioxide would be noted at this
concentration, but the FAA standard for aircraft allows
for 20 times this concentration. This is considerably
higher than standard concentrations permitted by the
Occupational Safety and Health Administration (OSHA) and
the American Society of Heating, Refrigerating, and
Air-Conditioning Engineers (ASHRAE) for other types of
indoor environments. The FAA standard is much hither
than standards for other confined environments. The
Committee recommends that FAA review its carbon dioxide
standard.
HUMIDITY
In addition to carbon dioxide, relative humidity in
the cabin at flight altitude is predictable, depending
only on cabin ventilation rate, passenger load factor,
temperature, and pressure. With a range of standard
cabin ventilation rates, the relative humidity varied
from 23% to less than 2Z. After 3 or 4 hours of exposure
to relative humidity in the 5-1OX range, some passengers
experience discomfort, such as dryness of the eyes,
nose, and throat. However, the Committee could find no
conclusive evidence of extensive or serious adverse
health effects of low relative humidity on the flying
population that would Justify recommending a regulation
to add supplementary humidification systems to aircraft.
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OZONE
Ozone has been measured at concentrations above 0.8
part per million by volume (ppmv) in the cabin during
flight above the tropopause and during periods in which
there is increased vertical air exchange between the
stratosphere and the troposphere. This relatively high
concentration can be reduced if ozone control equipment
has been installed and is operating or if altitude and
route limitations are imposed. In comparison with the
observed ozone concentration of 0.8 ppmv, compliance
with existing standards would limit ozone concentration
to a maximum of 0.25 ppmv at equivalent sea-level
pressure. Standards also limit the time-weighted
average ozone concentration for any flight segment of
over 4 hours to 0.1 ppmv.
The Committee could find no documentation of the
effectiveness of the various methods being used by the
airlines to control ozone. Therefore, the Committee
suggests that FAA carry out a carefully designed program
to ensure that cabin ozone concentrations comply with
Department of Transportation regulations.
ENVIRONMENTAL TOBACCO SMOKE
A contaminant in aircraft cabins that can be
detected by its characteristic odor and visibility is
environmental tobacco smoke (ETS)--the combination of
exhaled mainstream smoke and the smoke generated by
smoldering cigarettes. ETS is a hazardous substance and
is the most frequent source of complaint about aircraft
air quality. In the past, ventilation systems on
aircraft were designed to control odor and irritation
from cigarette smoke on the assumption that smokers are
randomly distributed throughout the aircraft. However,
separation of smokers and nonsmokers into separate zones
is now federally mandated. Because of the high
concentration of ETS generated in the smoking zone, it
cannot be compensated for by increased ventilation in
that zone. Moreover, strict separation of the airplane
into smoking and nonsmoking zones does not prevent
exposure of flight attendants and nonsmoking passengers
to ETS, because of the location of galleys and
lavatories in the smoking areas. Smoke exposure can
become significant in aircraft with outside-air flow
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rates as low as 7 cfm/pansenger. Even a ventilation
(airflow) rate of 14-15 cfm/passenger consists of as
much as 50% recirculated, and possibly smoky, cabin air
It is not known how often operating procedures are
used that can decrease actual ventilation rates and
increase contaminant concentrations. The Committee
found no published peer-reviewed data on ETS
concentrations in cabins. Although the adverse effects
of ETS are still under investigation, the Committee
feels that this potential threat to the health of
nonsmoking passengers and flight attendants should not
be ignored, especially because flight attendants on some
airlines can fly up to the twenty-eighth week of
pregnancy. It is highly probable that eye, nose, and
throat irritation will increase among airline passengers
as outside-air ventilation rates are decreased and
recirculation is increased to improve fuel efficiency.
.
The Committee considered several ways of reducing
ETS concentrations in aircraft. Any solution requiring
structural or engineering changes--such as markedly
increasing ventilation, moving lavatories and galleys,
and separating smoking compartments with physical
barriers--appears economically infeasible. Increasing
ventilation of the smoking zone to the point where it is
in compliance with ASHRAE guidelines and eliminating
recirculation on existing aircraft does not appear
technically feasible. The amount of air that would be
required could exceed the engine bleed capacity and in
all cases would reduce the range of the aircraft, the
payload, or both. Injection of large volumes of air
into the cabin would create unacceptable air velocities
and result in passenger discomfort. In contrast, the
Committee feels that a return to the random distribution
of smokers throughout the cabin to reduce overall ETS
concentration would be unacceptable to a majority of the
traveling public.
Cigarette-smoking has been implicated in a small
number of in-flight fires, and thus presents a potential
threat to safety.
The Committee recommends a ban on smoking on all
domestic commercial flights, for four major reasons: to
lessen irritation and discomfort to passengers and crew,
to reduce potential health hazards to cabin crew
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associated with ETS, to eliminate the possibility of
fires caused by cigarettes, and to bring the cabin air
Quality into line with established standards for other
closed environments.
AEROSOLS
Evaluation of the degree of health hazard associated
with exposure to biologic aerosols was impossible,
because of the lack of data on their concentrations in
aircraft cabins. There is an urgent need for studies of
potentially infectious airborne agents under routine
flight conditions. In the meantime, the Committee's
recommendations regarding control of infection through
ventilation must be based on similar occupancies (trains
and subway cars) for which ventilation standards have
been established.
Because a likelihood of occurrence of epidemic
disease when forced-air ventilation is not available on
the ground has been demonstrated, the Committee
recommends that a regulation be established that
requires removal of passengers from an airplane within
30 minutes or less after a ventilation failure or
shutdown on the ground and maintenance of full
ventilation whenever onboard or around air-conditionine
is available.
The Committee also recommends that maximal airflow
be used with full passenger complements to decrease the
potential for microbial exposure and that recirculated
air be filtered (to remove particles larder than 2-3
~m] to reduce microbial aerosol concentrations.
The Committee found no studies of the concentrations
of other contaminants--such as volatile organic
compounds or substances that might be emitted from
disinfectants or cleaning materials--and therefore
cannot assess their potential health hazard to
passengers or crew members.
Because the Committee found only sparse data on air
quality and contaminants in aircraft, it undertook to
have a multizone computer model of an aircraft
ventilation system developed for its use in calculating
contaminant, water vapor, and carbon dioxide
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concentrations in various cabin zones. The model was
used to calculate average and peak concentrations of
contaminants in smoking and nonsmoking zones. The
effects of reduced flow, recirculation, and filter
efficiency were analyzed. Cabin smoke from various
onboard cabin fire scenarios can be evaluated with
models of this type to develop optimal procedures for
control of smoke under emergency conditions. This model
is available to FAA.
CABIN ENVIRONMENT
Two unrelated factors of the cabin environment
affect airline passengers: pressure and cosmic radiation.
Pressurization of the cabin to equivalent altitudes
of up to 8,000 ft. as well as changes in the normal
rates of pressure during climb and descent, might pose a
risk to or create discomfort for some segments of the
population. At an altitude of 8,000 ft (or above if a
mistake were made), people with cardiopulmonary disease
might be at some risk. Persons suffering from upper
respiratory or sinus infections, children, and infants
might experience some discomfort or pain because of
pressure changes during climb and descent. InJury to
the middle ear can occur in susceptible people, but is
rare.
Other groups that could be at various degrees of
risk include those with chronic pulmonary problems,
anemia or sickle-cell disease, gastrointestinal
problems, neurop~ychiatric symptoms, or recent abdominal
or eye surgery. Pregnant women should not fly beyond
240 days; pregnant women with a history of spontaneous
abortions should not fly; and scuba divers should not
fly sooner than about 12-24 hours after diving.
The Committee concluded that current Pressurization
criteria and regulations are generally adequate to
Protect the traveling Dublic. However, the medical
Profession should use a more efficient system to warn
those with existing medical conditions who are more
susceptible to chances in Pressure or to lone exposure
to low pressure that there might be some hazard to their
health.
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Although the dose-equivalent rate of cosmic
radiation in significantly higher at airplane cruise
altitudes and above than at ground level, cosmic
radiation associated with subsonic commercial flights
does not pose a serious health risk to the general
public. However, it is likely that some flight and
cabin crew members will receive 100-200 mrems/yr. That
is below the 500-mrem/yr recommended maximum for any
member of the general public. Inasmuch as radiation
exposures are additive and assumed to be linear, the
additional radiation received during high-altitude
flying should be considered in the estimates of total
dose, which includes the radiation that might be
received as a result of living at high altitude or from
medical or dental x rays.
This report draws attention to the potential hazard
to full-time flight attendants flying high-latitude
routes, who might be exposed to cosmic radiation
equivalent to radiation from thoracic or abdominal
medical x rays. Such medical x rays are to be avoided
during pregnancy. FAA should consider rule-makina that
restricts exposure of Pregnant flight crew and cabin
crew members. In addition, FAA should investigate total
radiation exposure of flight crew and cabin crew members
through the use of a statistical sample of full-time
emoloveen and should require airlines to Provide
precautionary information to their flight attendants
about radiation exposure.
EMERGENCY SITUATIONS AND PROCEDURES
The Committee reviewed emergency procedures and
cabin crew training for evacuation of the cabin in
emergencies or after survivable crashes and the
procedures for use after cabin Repressurization.
Several members of the Committee participated in an
emergency evacuation exercise. The Committee also
investigated fire test procedures for cabin materials,
firefighting techniques, and emergency breathing
equipment for cabin crews.
As any air traveler can observe, many passengers
ignore or pay little attention to passenger safety
briefings, in spite of the fact that retention of the
information presented can mean the difference between
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survival and death in emergency situations. The
Committee approves of current efforts to base passenger
safety briefings and written materials on empirical
testing of comprehension and retention. However, the
Committee believes that it is also important to
understand how passengers recall that information and
respond under the stress of emergencies. The Committee
suggests that FAA or appropriate industry organizations
consider the advisability of developing an empirical
research program to examine Passenger response to safety
instructions under routine and emergency conditions and
revise them as appropriate. Consideration should be
given to running some quizzes during a flight to see,
for example, what proportion of passengers have retained
the key features of the safety briefing.
The Committee recommends that FAA require that
information on proper response to fire emergencies be
included in oral and written passenger safety
information.
In general, the FAA program on flammability testing
is excellent, and its research efforts to improve
testing methods are appropriate and valuable. The
recently issued F. M flammability standards for seat
cushions and cargo compartment liners will reduce
in-flight and postcrash fire hazards. The Committee
feels that continuing research is also needed in
materials development. Although FAA standards are met
by currently available materials, other materials exist
that, with further development, would far exceed current
standards and would provide substantially increased fire
protection in aircraft.
The Committee noted that current emergency
Procedures for smoke removal recommend that the cabin be
denressurized to 10,000 ft. This procedure is
ineffective and should be discontinued.
FAA recently proposed standards that would require
that protective breathing devices be available to
airliner crew members for firefighting. One such device
is to be stored within 3 ft of each required fire
extinguisher. However, there are generally more crew
members than fire extinguishers, and the Committee
recommends that FAA review the proposed rule on
Protective breathing devices for crew members to
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ascertain the desirability of supplying such equipment
for all crew members, rather than limiting it to the
persons expected to be involved in firefiahtin~. In
addition, the Committee suggests further evaluation of
the potential of emergency breathing equipment for all
cabin crew members to improve safe and expeditious
evacuation of Passengers in fire emergencies.
A rule requiring protective breathing devices for
passengers was proposed by FAA in 1969, but later
withdrawn. These devices have since been further
developed and evaluated. The Committee recommends that
FAA re-examine passenger protective breathing devices
and consider requiring that such equipment be available
in case of in-fli~ht and postcrash fires.
WORLDWIDE AIRLINE REGULATIONS
The Committee was charged with performing a
comparison of foreign industry practices, regulations,
and standards, and has gathered relevant information
applicable to the issues addressed in this study.
Although some differences from those in the United
States have been noted, they do not appear to be
significant. The Committee feels that greater effort
along these lines is not warranted.
FEASIBILITY OF DATA COLLECTION
Empirical evidence is lacking in quality and
quantity for a scientific evaluation of the quality of
airliner cabin air or of the probable health effects of
short or long exposure to it. Standards directly
applicable to commercial aircraft have not been
established for cabin ventilation rates, environmental
conditions, and air contaminants, and adequate data on
these factors are not available. The Committee
therefore recommends that FAA establish a program for
the systematic measurement, by unbiased independent
Groups, of the concentrations of carbon monoxide,
respirable suspended ~articles, microbial aerosols, and
ozone and the measurement of actual ventilation rates,
cabin Pressures, and cosmic radiation on a
representative sample of routine commercial flights'
These findings should be subjected to Deer review. This
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would provide a basis for establishing appropriate
standards if justified Add for requiring regular
monitoring if necessa ".
The Committee recognizes the extreme difficulty of
interpreting data on the health effects of air travel,
but believes thee several kinds of data can be collected.
The Committee recommends that FAA establish a program to
monitor selected health effects on airliner crews.
Air carriers are required to report to FAA all uses
of the recently mandated medical kits during the first
24 months. The Committee recommends that FAA collect
these data in such a wav as to permit comparison of
onboard incidents with those in other settinRe.
Representative terms from entire chapter:
ventilation rates
