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7
DESIRABILITY AND FEASIBILITY OF ADDITIONAL
DATA COLLECTION
The available empirical evidence is of insufficient
quality and quantity for a scientific evaluation of
airliner cabin air or of the probable health effects of
short or long exposure to it. The Committee believes
that this situation should be rectified and that data
should be collected on the quality of airliner cabin air
and on its health effects on passengers and crew.
There is a lack of definitive data showing
relationships between airliner cabin air quality and
health problems, except symptoms (chest pain, difficulty
of breathing, and persistent cough) presumably associated
with high ozone concentrations. Data are lacking because
adequate studies have not been performed.
Several previous chapters have addressed the
information relevant to the assessment of potential
health risks associated with airliner cabin air: Chapter
2 described the systems for controlling cabin air,
Chapter 5 described contaminants and special conditions
of cabin air and the health effects usually associated
with them, and Chapter 6 reviewed available evidence on
the manifestation of health effects in crew or
passengers. This chapter addresses the desirability and
feasibility of collecting data that could be used to
evaluate the quality of airliner cabin air and health
effects associated with it. A start at modeling the
most important factors that affect pollutant
concentrations and flows on aircraft may be found in
Appendix A. However, further model development and
verification require a variety of additional data.
214
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215
GENERAL CONCEPTS AND APPROACHES
The Committee has identified several potential
sources of environmental quality problems on aircraft,
including reduced air pressure, low humidity, ozone,
cosmic radiation, and air contaminants, such as microbial
aerosols. Although these factors are found in other
environments as well, their combination in the aircraft
cabin constitutes an environment whose uniqueness makes
it difficult to draw valid conclusions on the basis of
data on other environments. Although both the limited
data available and calculations based on aircraft design
and engineering information suggest that cabin air is
probably no worse than air in many other confined
environments, such a conclusion must remain speculative
until valid measurements are made in the airliner cabin
environment. The Committee believes that it is of
paramount importance to measure characteristics of cabin
air, to determine how they compare with conditions that
cause problems in other environments.
Simply measuring the contaminants and other relevant
variables of the airliner cabin does not address the
question of the likely health effects of short or long
exposure to that environment. The evaluation of the
health effects of exposure requires the collection and
interpretation of data very different from those on
exposure. Furthermore, because it is difficult to
detect and measure such effects, it is generally
necessary to rely on measures that indicate or are
related to the health effects of concern. The collection
of data must be discussed with respect to four
interrelated issues: potential causes of diminution in
air quality, potential health effects of diminished air
quality, actual examples of such effects, and surrogate
measures of the effects where direct measurement is not
possible. Extensive data on the operation and
maintenance of aircraft have already been collected.
The existing mechanisms of data collection should be
examined to determine whether they can be used to
satisfy these new needs.
Several parts of the federal regulations governing
commercial air carriers2 specify records and reports
that commercial operators and air carriers must keep and
submit to FAA. They include mechanical reliability
reports describing the occurrence or detection of each
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216
failure, malfunction, or defect that endangers the safe
operation of an aircraft.4 Each certificate holder
must submit a report covering each 24-h period to the
FAA maintenance inspector assigned to its operations.
In addition, summary reports on mechanical interruptions,
alterations, and repairs must be submitted regularly, 1 3
and an airworthiness log kept on each aircraft must
record all work performed on it, including maintenance,
preventive maintenance, and alterations. Given the
large numbers of aircraft in the fleets and the numbers
of flights each day, these requirements generate a
tremendous amount of data that provide a precise record
that can be examined when accidents occur.
These data are entered into computerized storage and
retrieval systems like the FAA Accident/Incident Data
System (AIDS) and Service Difficulty Reports. However,
such unfocused collection of information about almost
anything that happens to each aircraft in difficult to
use. Unless the data are classified according to
relevant categories, it is very difficult to retrieve
them in a way that is useful to answer the question
under consideration. The FAA data collection and storage
systems are oriented toward mechanical interruptions and
accidents or incidents involving potential damage or
injury, and the Committee has found the vast data
collected by FAA to be of little use in assessing the
quality of air in airliner cabins or the potential
health consequences of exposure to it. The Committee
suggests that consideration be given to adapting this
data collection system to include collection of data
relevant to the assessment of cabin air quality.
The potential health effects of cabin air considered
by the Committee to be of greatest concern are
reproductive effects, chronic pulmonary disease, chronic
heart disease, cancer (including leukemia), and
infectious disease. These effects are often hard to
detect, measure, and attribute to specific causes. The
numerous reasons include the lack of baseline
observations on most persons who fly, the lack of
equivalent groups with which to compare them,
difficulties of measuring individual exposures, ethical
constraints on and practical infeasibility of
experimentation with various characteristics of cabin
air, imprecision of signs and symptoms of acute effects
(such as chest tightness), and the rarity of most
effects of concern.
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217
The Committee has identified several measures that
are related to the health effects of concern, including
reproductive function (e.g., abortion and birth-defect
rates), pulmonary function (e.g., chronic obstructive
pulmonary disease and disability), myocardial-infarction
rates, use of onboard medical kits, and concentrations
of specific contaminants (ozone, cosmic radiation,
carbon monoxide, respirable suspended particles, and
microorganisms). However, none of these measures has a
one-to-one relationship with any of the health effects
of concern, and most of the effects have several sources.
Furthermore, data collected on health effects in
airliner passengers or cabin crew will be extremely
difficult to interpret, because of the difficulty of
determining appropriate control groups. We know that
the socioeconomic profile of the typical airline
passenger is different from that of the general public,
so we cannot be certain that the health effects observed
in airline passengers are different from those in
nonflyers, until they are compared with those in a
similar group of nonflyers.
Despite these difficulties, the Committee concludes
that appropriate data collection is not only possible,
but highly desirable. The following sections describe
the Committee's recommendations for research on airliner
cabin air quality, the health effects of exposure to the
cabin environment, and other topics.
MEASURES OF AIRLINER CABIN AIR QUALITY
The principal air quality problems on aircraft
involve tobacco smoke, ozone, cosmic radiation, humidity,
and microbial aerosols. Because ventilation rate and
cabin pressure are the controlling factors for cabin air
quality, actual ventilation rates should be measured
under routine flight conditions in all types of
commercial aircraft. The factors that influence
pollutant concentrations and distribution within the
cabin should be carefully considered, as well as the
requirement of measuring concentrations over small
spatial and temporal spans. If significant variations
are found in an initial study, continual monitoring
should be instituted.
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Ozone is virtually the only source of degradation in
air quality of which extensive measurements in aircraft
have been reported. Exposure to ozone is regulated.
Compliance can be achieved either through installation
of filtration equipment (generally a catalytic
converter), through the routing of flights so an to
avoid areas of high ozone concentration (as detected by
satellite), or through the choice of flight altitudes
below those at which ozone is highly concentrated. The
Committee feels that an evaluation of cabin air quality
would be incomplete without a determination of the
degree of compliance and the ozone concentrations to
which passengers and cabin crew are exposed. The
Committee accordingly recommends that FAA analyze cabin
ozone concentrations. The analysis need not involve
permanent monitoring, but should include sufficient data
to provide a statistically representative sample of
aircraft types, routes, and other factors relevant to
the alternative ways of complying. Studies could be
conducted in altitude chambers to determine whether
ozone and the hypoxia induced by cabin pressurization to
the equivalent of an 8,000-ft altitude are associated.
Exposure to cosmic radiation is a matter of concern.
The Committee feels that FAA should periodically review
flight routes and altitudes, to assess their implications
for exposure to cosmic radiation. Regular representative
sampling should be performed to estimate the exposure of
the flying public. A special effort should be made to
alert the medical profession to the hazards to groups
that might be at increased risk, such as pregnant women
and patients receiving particular medical therapy. Those
who live at high altitudes should perhaps avoid further
chronic exposure to cosmic rays in high-altitude flights.
But such decisions require more reliable data than are
available on the effects of chronic exposure to cosmic
rays on the long-term incidence of neoplastic disease.
Because routes change, FAA should measure exposure to
cosmic rays on a representative sample of current
flights.
The Committee strongly recommends that, so long as
smoking is permitted in airplanes, the Congress mandate
a program to monitor onboard carbon monoxide and
respirable suspended particles. The Committee believes
that, except for emergency situations involving fire,
the most pervasive threat to airliner cabin air quality
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is cigarette smoke. Carbon monoxide and respirable
suspended particles are two components of environmental
tobacco smoke that are relatively easily measured, but
the only empirical data have been collected on an ad hoc
and nonrepresentative basis. There is a deficiency of
information regarding hypoxia, which might result from
synergism between altitude effects (decreased partial
pressure of oxygen) and formation of carboxyhemoglobin
(due to increased molar concentration of carbon
monoxide). Studies are beginning to evaluate this
interaction, but at higher ambient carbon monoxide
concentrations than reportedly occur in the aircraft
cabin. Patients with cardiorespiratory problems might
be at greater risk, as might cabin attendants who must
work and rest in these conditions.
Many people believe that one is more likely to catch
cold or contract a respiratory infection in an airplane
than in most other common environments, but no evidence
has been produced to establish this. In view of the
degree of expressed concern about microbial contamination
in aircraft and the possibility that serious acute health
effects could result from such contamination, it is
important to collect baseline data on background
concentrations of microbial aerosols during normal
flight conditions. It is also important to collect data
on microbial aerosols in aircraft with known emission
sources and under conditions of decreased ventilation.
The Congress should authorize and appropriate funds for
studies to measure volumetrically bioaerosol
concentrations and associated variables in aircraft in
flight--such as temperature, relative humidity,
ventilation rate, filtration modes, and number of
passengers on board--and bioaerosol concentrations in
intake air in aircraft on the ground.
The purpose of gathering data on the various
potential contaminants of airliner cabin air is to
compare the concentrations measured with those believed
to cause health problems in other environments. Even
though the combination of environmental conditions found
on aircraft is unique, such comparisons can identify
possible problems, which can then be examined in greater
detail.
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MEASURES OF HEALTH EFFECTS
The previous section identified several potential
contaminants of airliner cabin air on which the Committee
recommends collection of additional data. As pointed
out earlier in this chapter, data on the potential
health effects of these contaminants in the airliner
environment must also be collected, but they must be
collected and interpreted in ways that differ
considerably from those for data on the contaminants.
The Committee attempted to identify measures for
each of the health effects of concern: reproductive
effects, chronic obstructive pulmonary disease, chronic
heart disease, cancer, and infectious disease. However,
direct measurement of these health effects is often not
possible; therefore, collection of data on a series of
suggestive measures is recommended.
Appropriately designed studies of selected health
effects among crew members would be useful and ought to
be performed, but finding valid comparison groups will
be more difficult than in other industrial epidemiologic
studies. For example, comparing disease rates of male
employees in a particular factory with rates in the
general population usually shows the workers to be
healthier, because the total population includes all
sick people. It might be better to compare the workers
in one factory with those in another. But it is not
possible to determine from the data on health alone
which group of workers is exposed to the greater risk.
That requires accompanying measures of exposure as
well. Data on health effects of airliner cabin air in
passengers pose even more problems, because relatively
little is known about the characteristics of the flying
public and it is not clear how to identify an equivalent
group of people who do not fly. Even though the
relevant characteristics of cabin crews are much better
known, it is still difficult to find a group of nonflyers
or infrequent flyers with whom appropriate comparisons
can be made.
The Committee feels that, given the nature of the
exposures and resulting health effects and the special
occupational setting, it is unrealistic to expect that
feasible epidemiologic studies will be able to determine
conclusively the health hazards associated with exposure
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to airliner cabin air. Nevertheless, even though such
studies cannot prove the degree of hazard associated
with such exposure, they can produce data that are
suggestive and that identify potential problems for
further analysis.
The Committee recommends studies to examine rates of
spontaneous abortion and birth defects among cabin crew
members. Cabin crew members are subject to longer
exposure than the flying public in general, and in
examining reproductive effects it is not necessary to
wait many years for chronic effects to emerge. In
addition, reproductive effects are often sensitive
indicators of other effects that are more difficult to
measure. The only way to determine with accuracy
whether the observed reproductive effects were due to
exposure during flight, as opposed to exposure in the
home or exposure to other personal variables, would be
to assign new employees at random to cabin crews, as
opposed to, say, work at ticket counters. The rates
exhibited over time by the two groups would then be
directly compared, to assess the reproductive hazards of
exposure during flight. Such random assignment of
employees in not practical. In lieu of it, comparisons
would need to be made with several groups of similar
ages, places of residence, family status, and other
characteristics. Even then, the results could be
considered only suggestive, and more detailed
examinations would be required if problems were
revealed. Care would need to be exercised to ensure
that the groups examined were large enough to permit
statistically significant analyses, and it could prove
extremely difficult to find groups that include enough
people with appropriate characteristics. In addition,
careful measurements of exposure (or appropriate
surrogates) should be made. Despite the difficulties in
interpreting results, the Committee recommends that a
feasibility study be undertaken to determine whether
these conditions can be met.
The Committee feels that it is important to test
pulmonary function among crew members and perhaps among
selected passengers. In particular, chronic obstructive
pulmonary disorders and pulmonary disability should be
identified. The Committee feels that both flow-loop
volume tests and forced expiratory volume (FEY) tests
should be used. Plow-loop tests require more
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sophisticated computer equipment and are less susceptible
to intentional or unintentional manipulation by subject
or observer. However, FEV tests have been used
successfully in many epidemiologic studies and would
permit comparison with results under other conditions.
Flight attendants have consistently reported respiratory
effects, probably because their activity is greater than
that of passengers. Studies in which subjects are
exposed to ozone and carbon monoxide clearly indicate
that the combination of exposure and increased exercise
results in increased effects on cardiopulmonary function
The Committee feels that data concerning effects on
pulmonary function would be vital in evaluating the
health effects of airliner cabin air and recommends that
appropriate before-and-after testing be undertaken.
It is difficult to determine an appropriate approach
to the gathering of data on the incidence of myocardial
infarction associated with air travel. The onset of
myocardial infarction might be a response more to the
stress of flying than to exposure to cabin air.
Furthermore, the period at hazard may extend from before
boarding to after deplaning. Most large airports have
emergency medical facilities of some sort, so it might
be possible to gather data on the incidence of myocardial
infarction in or near airports and compare that incidence
with the incidence during flight. The Committee feels
that such a study is important enough to require a
feasibility study to determine whether accurate data in
sufficient quantity could be collected.
Measures for cancer are impractical, because of the
long period of latency between exposure and onset.
Although shorter, the incubation period for most
infectious diseases precludes development of measures of
them as well. However, from the standpoint of
occupational health, it is entirely feasible and
important to undertake a prospective monitoring of
exposures and eventual mortality based on the National
Death Index.
OTHER SUBJECTS
On January 9, 1986, FAA published a final rule
requiring an approved medical kit to be carried on all
passenger flights, training to familiarize crew members
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with the kit, and the reporting to FM of each medical
emergency during flight that results in use of the kit
for the first 24 ma after the effective date of the
rule. 5 The Committee recommends that F. M --in conjunction
with physicians, statisticians, and epidemiologists--
establish a clear protocol for reporting data on the use
of emergency medical kits. If collection procedures are
properly designed, the resulting data can be analyzed to
identify the pattern of medical incidents during flight
and to compare these patterns with the incidence of
emergencies in other settings.
The Committee also feels that it would be advisable
to monitor scientific literature relevant to various
aspects of airliner cabin air quality or its health
effects. Available computer-based bibliographic
databases, such an MEDLINE, could be easily and
inexpensively searched regularly to identify new
scientific developments relevant to the topics addressed
in this report.
REFERENCES
1. Airworthiness release or aircraft log entry. Code
of Federal Regulations, Title 14, Pt. 121.709.
Washington, D.C.: U.S. Government Printing Office,
1985.
2. Certification and operations: Domestic, flag and
supplemental air carriers and commercial operators
of large aircraft. Code of Federal Regulations,
Title 14, Pt. 121. Washington, D.C.: U.S.
Government Printing Office, 1985.
3. Mechanical interruption summary report. Code of
Federal Regulations, Title 14, Pt. 121.705.
Washington, D.C.: U.S. Government Printing Office,
1985.
4. Mechanical reliability reports. Code of Federal
Regulations, Title 14, Pt. 121.703. Washington,
D.C.: U.S. Government Printing Office, 1985.
5. U.S. Federal Aviation Administration. Emergency
medical equipment: Final rule. Federal Register
51(Jan. 9~:1218-1223, 1986.
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Representative terms from entire chapter:
airliner cabin
