10. CONCLUSIONS AND RECOMMENDATIONS
10.1 CONCLUSIONS
10.1.1 Measurement Methods and Results
The flights that were randomly chosen for monitoring in this study
proved to be representative of the population of flights departing from major
U.S. airports. Distributions of the monitored flights by airline and type
of aircraft were very similar to those for all scheduled commercial jet
aircraft flights.
Levels of particle-phase ETS contaminants monitored during the study
were substantially higher in smoking sections of the aircraft than in
nonsmoking areas. Respirable suspended particle (RSP) concentrations in
the coach smoking section averaged about 175 ug/m3. The average RSP
concentration in the no-smoking section near coach smoking (i.e., boundary
region) was near 55 ug/m3, and RSP concentrations averaged about 35 ug/m3 in
other no-smoking areas and on nonsmoking flights. These averages are based on
combined results from two measurement methods -- optical and Gravimetric.
One-minute peak RSP concentrations measured with optical sensors were more
than ten times higher in the smoking section, and three times higher in the
boundary region, than in the no-smoking areas on smoking flights. Measured RSP
levels in the boundary region were most strongly correlated with observed
smoking rates in the coach smoking section (i.e., higher levels when smoking
rates were higher) and distance from the coach smoking section (i.e., higher
levels at shorter distances).
Levels of gas phase ETS contaminants that were monitored were also
highest in smoking sections. Nicotine concentrations averaged near 13.5 ug/m3
in the coach smoking section, near 0.25 ug/m3 in the boundary region within
the no-smoking section, and near or below 0.05 ug/m3 in other no-smoking areas
and on nonsmoking flights. CO concentrations averaged near 1.4 ppm in the
coach smoking section, near 0.7 ppm in no-smoking areas of smoking flights,
and 0.6 ppm on nonsmoking flights.
Levels of these ETS tracers in the boundary region were not strongly
correlated with observed smoking rates or distance from the coach smoking
section.
Two separate techniques for estimating smoking rates on each monitored
flight provided consistent results. Estimates based on technician
observations of the number of lighted cigarettes during a one-minute interval
every 15 minutes agreed well with estimates based on cigarette butts collected
by technicians at the end of most smoking flights. An average of 20 cigarettes
per hour, or 68 cigarettes per flight, was smoked by passengers in the coach
smoking section on smoking flights that were monitored; an average of 13.7
percent of passengers were assigned to the coach smoking section.
Carbon dioxide (CO2) levels on flights monitored during this study were
frequently above the level recommended by ASHRAE (1,000 ppm) to satisfy
comfort (odor) criteria. CO2 concentrations on the monitored flights
averaged above 1,500 ppm and exceeded 3,000 ppm on several occasions. Measured
concentrations were 1,000 ppm or greater on 87 percent of the monitored
flights, and the C02 levels were most strongly related to the number of
passengers in the airliner cabin; on the average, 70 percent of the seats were
occupied on the flights monitored in the study. Depending on assumed C02
exhalation rates, measured levels were as much as twice those predicted by a
cabin air quality model. Even if the measured levels were to be lowered by
half, however, C02 concentrations would still exceed 1,000 ppm on 24 percent
of the study flights.
Relative humidity levels on monitored flights were quite low, averaging
near 15 percent on smoking flights and near 20 percent on nonsmoking flights.
Humidity levels were below 25 percent, outside the range indicated by ASHRAE
for provision of adequate thermal comfort, on about 90 percent of all
monitored flights. Temperatures in the cabins of monitored aircraft averaged
near 24 oC (75 oF) for both smoking and nonsmoking flights and were within
ASHRAE's comfort range.
Average levels of other pollutants (ozone, bacteria, and fungi) were
relatively low on virtually all monitored flights. Measured levels of
ozone did not exceed the FAA 3-hour standard of 0.1 ppm or the current EPA
standard of 0.12 ppm on any of the monitored flights. The highest ozone level
measured was 0.08 ppm, and the average measured level was between 0.01 and
0.02 ppm. Measured bacteria levels were somewhat higher in the smoking than
no-smoking sections of monitored smoking flights, and the average level in the
no-smoking section on these flights was nearly identical to that on nonsmoking
flights. Measured fungi levels were somewhat higher on nonsmoking flights than
smoking flights, but the bacteria and fungi levels in all cases were low,
relative to those that have been measured in other environments.
The method used in the study to measure air exchange rates was generally
adequate for aircraft with recirculation but was inadequate for other types of
aircraft. The measurement method, involving release and sampling of
perfluorocarbon tracers, was less effective on aircraft without recirculation
because of the limited extent of lateral air movement on such aircraft. This
limitation could have been overcome by increasing the number of tracer release
and sampling locations, but such a strategy was deliberately avoided in this
study in order to remain unobtrusive to passengers and flight attendants
during monitoring.
The strategy of monitoring at multiple seat locations provided important
insights regarding spatial variations in cabin air quality, particularly for
ETS contaminants. This strategy provided some indications that the
boundary region in the no-smoking section was affected by coach smoking, in
addition to the distinct effects in the smoking section itself, and that
spatial variations were relatively minor for CO2 and other pollutants (ozone,
bacteria, and fungi) that were monitored.
The strategy of continuous monitoring where practical, combined with
integrated sampling, also provided some important insights concerning cabin
air quality. Continuous monitoring results provided the strongest
indication of an effect of smoking in the no-smoking boundary region.
10.1.2 Risk Assessment
The risks faced by cabin crew members and passengers depend on such factors
as frequency of flying, number of years flown, specific routes flown, and, in
the case of ETS exposures, seat locations and prevailing smoking rates. The
study conclusions pertaining to cancer risks are based on specific scenarios
relating to number of hours per year in flight, number of years flown, and, in
the case of ETS exposures, proportion of time spent in the smoking section,
boundary region near smoking, and other no-smoking areas. Detailed
descriptions of the scenarios and calculations underlying the risk estimates
given herein are provided in Section 7.0 for ETS and in Section 8.0 for cosmic
radiation. Estimates for cabin crew members relating to ETS exposure pertain
only to flight attendants and do not include the cockpit crew.
ETS
Estimated lifetime lung cancer risks ascribable to ETS exposure for
nonsmoking cabin crew members flying 960 hours per year on smoking flights for
20 years range from 12 to 15 premature cancer deaths per 100,000 nonsmoking
cabin crew members for domestic flights and from 13 to 17 premature cancer
deaths per 100,000 for international flights. The range of estimates was
derived from two different cancer risk models (a phenomenological model and a
multistage model) that assume different durations of exposure.) Applying these
risk estimates to the entire U.S. cabin crew population results in an
estimated 0.18 premature lung cancer deaths per year for domestic flights
(that is, approximately 4 premature deaths can be expected every 20 years) and
0.16 premature deaths per year for international flights.
Estimated Lifetime lung cancer risks due to ETS exposure for nonsmoking
passengers flying 480 hours per year on smoking flights for 30 years
range from 0.3 to 0.8 premature cancer deaths per 100,000 nonsmoking
passengers for domestic flights and from 0.2 to 0.6 premature cancer deaths
per 100,000 for international flights. The range of estimates was derived
from the two cancer risk models mentioned above, and the relatively broad
range is due to differences in assumed durations of exposure and the
sensitivity of the multistage model to assumptions concerning the age at which
exposure begins.
Estimated lifetime lung cancer risks due to ETS exposure for nonsmoking
passengers flying 48 hours per year on smoking flights for 40 years are
approximately 0.1 premature cancer deaths per 100,000 for both domestic and
international flights. Applying these risk estimates to the U.S. flying
population results in an estimated 0.24 premature lung cancer deaths per year
for domestic flights (that is, approximately 10 premature deaths can be
expected every 40 years) and 0.12 premature deaths per year for international
flights.
In terms of acute effects based on CO concentrations as a proxy for ETS
levels, it is estimated that on one-third of smoking flights about 1 in 8
persons seated in the smoking section would experience irritation due to ETS
exposure. Further, it is estimated that on about one-third of domestic smoking
flights, ETS levels in the smoking section (based on nicotine concentrations
as a proxy ) would be sufficiently high to evoke a marked sensory response in
the eye and nose of an airliner cabin occupant.
Differential effects of ETS and its constituents on such sensitive
populations as asthmatics, children, and persons with ischaemic heart disease
or other cardiovascular disease could not be estimated.
Cosmic Radiation
Estimated lifetime cancer risks due to cosmic radiation exposure for cabin
crew members flying 960 hours per year range from 90 to 1,026 premature deaths
per 100,000 individuals flying for 20 years on domestic flight: and from 220
to 512 premature deaths per 100,000 individuals flying for 10 years on
international flights. The estimates, which pertain to cockpit crew
members as well as cabin crew members, are lowest for relatively short
north-south domestic flights and higher for coast-to-coast flights involving
higher altitudes. The highest estimates are for relatively long, circumpolar
international flights which also occur at high altitudes.
Estimated lifetime cancer risks due to cosmic radiation exposure for
passengers flying 480 hours per year range from 45 to 513 premature deaths per
100, 000 individuals flying for 20 years on domestic flights and from 110 to
256 premature deaths per 100,000 individuals flying for 10 years on
international flights. Like the above estimates for cabin crew, the range
is governed largely by flight altitudes and latitudes. Another concern is the
effect of cosmic radiation on a fetus, particularly during the first
trimester.
Other Pollutants
The levels of bacteria and fungi measured in the airliner cabin air in this
study were found to be below the levels generally thought to pose risk of
illness. Because quantitative dose-response information on the health
risks of biological aerosols was not available, the evaluation of the
concentration data was performed by placing the prevalence of individual
genera that were identified in rank order, and comparing the prevalence to
biological aerosols in other indoor environments. The levels and genera
measured in the cabin environment were similar to or lower than those commonly
encountered in indoor environments characterized as "normal."
It was unnecessary to perform a risk assessment for ozone because measured
levels on all monitored flights were well below the current FAA and EPA
standards.
10.1.3 Mitigation
Among the methods evaluated for reducing risks due to ETS, a total ban on
airliner cabin smoking would eliminate ETS exposure in airliner cabins and
yield the greatest benefit to flight attendants and nonsmoking passengers.
A total ban on smoking on domestic flights is estimated to result in an annual
benefit of approximately 3 million to cabin crew and passengers, based on
reduced mortality risks. In conducting this benefit/cost analysis, reduction
in mortality and associated economic benefits were considered but benefits
relating to reduced morbidity were not. Possible costs related to smokers'
inconvenience and discomfort or to displacement of smokers to other modes of
transportation were not considered due to limited data.
Beyond the two-hour ban that reduces ETS exposures on domestic flights
by approximately 45 percent, more restrictive bans could be implemented to
reduce exposures by as much as 98 percent. Restricting smoking to flights of a
6-hour or greater duration would reduce ETS exposures by approximately 98
percent. and a restriction for flights of 4 hours or longer would reduce
exposures by about 86 percent. A different type of strategy to curtail
smoking, such as allowing smoking for a 10-minute period every two hours,
could reduce average exposures to ETS by as much as 70 percent. Such a
strategy, however, could substantially increase the risks of health effects
from acute exposure during the brief periods when smoking would be allowed.
Two other mitigation measures -- increased ventilation and improved filter
efficiency -- would reduce ETS exposures by lesser amounts, ranging from 5 to
33 percent. Annual costs of increased ventilation ( 6 to 50 million),
which could reduce ETS exposures by as much as 33 percent, are substantially
higher than the benefits ( 0.7 to 1.0 million) that could be calculated within
the constraints of this study. Costs related to improved filter efficiency
were not available, but improved efficiency would provide only a marginal
reduction (5 percent) in ETS exposures.
Exposure management is the only viable option for reducing cabin crew
member and passenger exposures to cosmic radiation. In the case of crew
members, this strategy would involve careful scheduling of personnel to avoid
persistent exposure to higher cosmic radiation levels generally associated
with high-altitude flights and flight paths toward extreme northern or
southern latitudes.
On aircraft with recirculation, C02 could be removed by sorption on
solid adsorbent beds whose adsorbent capacity for C02 can be regenerated by
heating. Increased ventilation could also bring C02 levels closer to the
guidelines specified by ASHRAE. Cost or reliability data for a sorption
system were not available for comparison with costs of additional ventilation.
In view of the low levels observed for ozone and biological aerosols,
mitigation strategies were not assessed for these pollutants.
10.2 RECOMMENDATIONS
10.2.1 Actions for Improving Cabin Air Quality
Considerations should be given to a total ban on smoking on all flights
departing from or arriving at U.S. airports as a means of eliminating the ETS
risks currently faced by nonsmoking passengers and nonsmoking cabin crew
members. The estimated benefits of such a strategy exceed the costs, based on
currently available data. In considering this ban, consideration will need to
be given to smokers inconvenience and discomfort, possible economic
consequences of displacement of smokers to alternative transportation modes,
and other potential consequences such as smoker withdrawal symptoms. Possible
alternatives include limiting smoking to longer-duration flights or
restricting the time periods when smoking is allowed on flights. In the latter
case, further study would be needed of the potential health effects from acute
exposure that could occur during the limited periods when smoking would be
allowed.
Airlines should implement exposure management strategies to reduce risks
faced by cabin crew members, particularly those related to cosmic radiation.
Such strategies would include careful scheduling of personnel, especially
those at highest risk, to avoid persistent higher exposures associated with
flight paths at extreme northern/southern latitudes and higher altitudes.
Sorption should be considered as a means of reducing C02 levels in airliner
cabins. The feasibility of implementing this approach needs
to be further explored, along with potential costs, benefits, and practical
considerations. Such an approach, or increased ventilation, could also reduce
levels of other potentially hazardous chemicals, such as volatile organic
compounds that were not measured during this study.
No actions need to be taken to reduce currently prevailing levels of
ozone or biological aerosols. The types of preventive strategies that are
currently in place for ozone, which may be partly responsible for the
relatively low levels measured during this study, should be continued.
10.2.2 Information Needs
Due to constraints of unannounced and unobtrusive monitoring required to
meet study objectives, this study could not take full advantage of the
currently available state-of-the-art instrumentation for pollutant monitoring.
Based on observations and conclusions from this study, the following areas of
further study are recommended:
Additional measurements of C02 should be performed in commercial
airliner cabins. Such measurements need to be conducted with continuous
monitoring devices on different types of aircraft and at different levels of
passenger occupancy.
A study of flight attendants' exposures with personal monitors should be
conducted if a total ban on smoking is not enacted. Due to study
limitations, flight attendants' exposures could not be estimated directly. A
personal monitoring study of flight attendants would improve estimates of
exposures by accounting for the different breathing height from that of
passengers and time spent in areas such as galleys, which were not monitored
during this study.
Further measurements of prevailing air exchange rates on aircraft should be
performed. Due to the need to remain unobtrusive during this study, it was
not possible to widely deploy sources and samplers to obtain more reliable
measurements. Improved estimates will provide a stronger basis for cabin air
quality modeling which is crucial to assessment of mitigation strategies
related to ventilation.
Further information on special populations and short-term health effects
would support improved risk assessments. The information required includes
(1) the flying frequency of children and sensitive individuals such as
asthmatics, (2) dose-response functions relating various types of short-term
health effects (e.g., eye/nose/throat irritation) to levels of various ETS
tracers, and (3) quantitative measures of ETS effects on the cardiovascular
system of individuals with pre-existing cardiovascular disease.
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