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.
