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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
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
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.
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.
218 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
219 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.
220 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
221 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
222 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
223 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.