8
Surveillance and Research Programs on Cabin Air Quality

The analyses presented in previous chapters have repeatedly led to the conclusion that available air-quality data are not adequate to address specific questions on aircraft cabin air quality and its possible effects on cabin occupant health. On the basis of its review, the committee has identified the following critical questions:

  1. Do current aircraft, as operated, comply with the Federal Aviation Administration (FAA) design and operational limits for specific chemical contaminants—ozone (O3), carbon monoxide (CO), and carbon dioxide (CO2)—and for ventilation rate? Are the existing federal aviation regulations (FARs) for air quality adequate to protect health and ensure the comfort of passengers and cabin crew?

  2. What is the association, if any, between exposure to cabin air contaminants and reports or observations of adverse health effects in cabin crew and passengers?

  3. What are the frequency and severity of air-quality incidents (nonroutine conditions) that might lead to deterioration of cabin air quality by introduction of air contaminants, such as pyrolysis products of engine oil?

Studies have been published that report detailed monitoring of several aspects of aircraft air quality. However, the studies have involved a very small fraction of the total commercial aircraft flights and therefore cannot be portrayed as representing the full range of conditions during routine and nonroutine



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The Airliner Cabin Environment and the Health of Passengers and Crew 8 Surveillance and Research Programs on Cabin Air Quality The analyses presented in previous chapters have repeatedly led to the conclusion that available air-quality data are not adequate to address specific questions on aircraft cabin air quality and its possible effects on cabin occupant health. On the basis of its review, the committee has identified the following critical questions: Do current aircraft, as operated, comply with the Federal Aviation Administration (FAA) design and operational limits for specific chemical contaminants—ozone (O3), carbon monoxide (CO), and carbon dioxide (CO2)—and for ventilation rate? Are the existing federal aviation regulations (FARs) for air quality adequate to protect health and ensure the comfort of passengers and cabin crew? What is the association, if any, between exposure to cabin air contaminants and reports or observations of adverse health effects in cabin crew and passengers? What are the frequency and severity of air-quality incidents (nonroutine conditions) that might lead to deterioration of cabin air quality by introduction of air contaminants, such as pyrolysis products of engine oil? Studies have been published that report detailed monitoring of several aspects of aircraft air quality. However, the studies have involved a very small fraction of the total commercial aircraft flights and therefore cannot be portrayed as representing the full range of conditions during routine and nonroutine

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The Airliner Cabin Environment and the Health of Passengers and Crew operations. A summary and critical review of nine reports published during the last 13 years (Nagda et al. 2000) showed that the studies varied widely in sample selection, pollutants monitored, measurement methods, and quality control. The number of flights sampled ranged from less than 10 to 158; only three studies sampled at least 50 flights.1 Furthermore, only three studies claimed random selection of flights, and only one provided supporting details. Study duration ranged from 1 month to 1 year. None of the studies included more than four aircraft types. Three studies included measurements of only one contaminant; the others included measurements of six to nine contaminants or contaminant groups. For logistical reasons, state-of-the-art methods for air-quality monitoring were not used in all studies, and only one study provided a description of calibration procedures. Two additional studies (Haghighat et al. 1999; Lee et al. 2000), which were not reviewed by Nagda et al. (2000), involved 16 and 43 flights. Both appear to have limitations in sampling methods similar to those described above. Subject to those limitations, the published data lead to the tentative conclusion that the concentrations of CO and CO2 under routine operations most likely do not exceed the FAA guidelines, but O3 concentrations might exceed the guidelines on some flights. (See Chapter 3 for a more detailed critique of the O3 data.) No published reports include measurements of air quality during flights involving nonroutine events, such as leaks of hydraulic fluid or engine oil into bleed air. Because some of the constituents or pyrolysis products of those fluids have high toxicity (Wyman et al. 1993; Wright 1996; van Netten and Leung 2000), obtaining exposure data during air-quality incidents is critical. Little information is available that would permit an estimate of the frequency of such events. (See Chapter 3 for further discussion of air-quality incidents and their possible frequency.) To address the important unresolved questions regarding aircraft cabin air quality and its possible effects on occupant health, the committee recommends two complementary approaches: a surveillance program and a research program. The primary goals of the surveillance program are to determine aircraft compliance with FAA cabin air-quality regulations, to characterize air-quality characteristics and establish temporal trends in them, and to estimate the frequency of nonroutine incidents in which air quality is seriously degraded. This 1   To put the numbers of flights sampled in perspective, there were about 8 million departures of passenger jets equipped with at least 30 seats operated by U.S. domestic aircraft companies in 1999 (DOT 2001).

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The Airliner Cabin Environment and the Health of Passengers and Crew program also includes a health surveillance component to determine the incidence of health effects in cabin crew and passengers and to identify possible associations between air quality and health effects. The research program is designed to focus more narrowly on specific unresolved issues of cabin air quality. The two approaches are described in more detail on the following pages. AIR-QUALITY SURVEILLANCE A program of systematic surveillance of air quality is needed to determine compliance with FARs for air quality and to establish temporal trends in air-quality measures. Accurate characterization of the variation in air-quality characteristics during routine operations, coupled with health-surveillance information, would provide insight into the possible association between air quality and reported health effects in cabin occupants. At a minimum, the surveillance program should include continuous monitoring and recording of O3, CO, CO2, fine particulate matter (PM), cabin pressure, temperature, and relative humidity. An adequate surveillance program must be extensive and sample a large number of flight segments over a relatively short period. Estimates based on the studies reviewed to date (Nagda et al. 2001) reveal that, depending on the specific design of the surveillance program, samples from at least 100 flight segments over 1–2 years might be needed. Steps should be taken to ensure that a variety of aircraft types, aircraft companies, and routes are represented in the flights monitored. A standard instrument package should be developed that incorporates continuous monitors and data-recording hardware suitable for installation on commercial aircraft. (See Chapter 7 for a discussion of current technology that is adequate for accomplishing this goal.) Because aircraft equipment design and operating procedures evolve continuously, a continuing program will be required to characterize air quality in contemporary aircraft and to evaluate changes in air quality as aircraft equipment ages or is upgraded. The air-quality surveillance program must be coupled with a health surveillance program. HEALTH SURVEILLANCE As described in Chapter 6, the current systems for reporting signs and symptoms, which could reflect health-related responses to the cabin environ-

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The Airliner Cabin Environment and the Health of Passengers and Crew ment or the cabin air, are not standardized with respect to the methods of surveying potentially affected individuals or how specific data are obtained. Among the relevant databases maintained by the federal government, only the National Aeronautics and Space Administration (NASA) Aviation Safety Reporting System focuses on health-related data. However, as noted in Chapter 6, the data are collected as unstandardized narratives that do not appear to be abstracted in a standardized manner and stored in a format that would facilitate analysis. The committee also notes that the survey instrument released recently by the Association of Flight Attendants has a number of design flaws that could impede its use (see Chapter 6). Although implementing all the details of an ideal system might not be practical, defining the minimal characteristics of a rigorous system for collecting, storing, analyzing, and disseminating health outcomes related to routine or nonroutine conditions is essential (see Table 8–1). Such definition should provide the guidance to improve the completeness and validity of current data on cabin air quality and health. On the basis of exposure and self-interest, the cabin crew appears to be the logical vehicle through which a routine health surveillance system should operate. Self-interest should work to minimize nonparticipation and to mitigate problems of selection bias that severely compromise current systems for data collection. Securing unbiased estimates of passenger symptoms on any continuing basis seems less practical, although a serious marketing effort to educate passengers on the need for this information could make sampling passengers possible. Ideally, passengers would be surveyed on flights on which the crew is scheduled to be surveyed. Central to any valid surveillance system are a plan for systematic sampling across all possible exposures under routine flight conditions and a set of standardized procedures for reporting all suspected incidents. Because many different aircraft are used on many flight routes, some form of multistage sampling would be required for monitoring health-related symptoms under routine flight conditions. However sophisticated the sampling scheme, the validity of the data will ultimately depend on the thoroughness with which the final-stage sampling units complete the requisite forms (cabin crew for routine conditions, and cabin crew, cockpit crew, and passengers for incident conditions). All data forms must be relatively short, have few or no text fields, and permit direct entry through scanning. The use of personal digital assistants was considered, but it probably is not practical because of cost, limitations of programming, and the need to have a network that ensures easy access. Some combination of options would most likely be necessary to generate

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The Airliner Cabin Environment and the Health of Passengers and Crew TABLE 8–1 Desirable Properties of a Health Surveillance System for Commercial Aircraft Under Routine Flight Conditions Systematic sampling of cabin crew Multistage cluster sampling could be conducted with aircraft type as primary unit and flight type as secondary unit. Sampling could also be conducted with airline as primary unit, aircraft type as secondary unit, and flight type as tertiary unit. All cabin crew on sampled flights must complete preflight and postflight surveys. Collection of data Standardized pencil-and-paper forms: Structured to be completed within 5 min. Formatted to be scanned into database. Formatted for self-return to centralized data processing center. Management of database and reporting Central data center receives, edits, and processes all data; prepares reports at regular intervals by type of aircraft and flight; and distributes reports to airlines, FAA, manufacturers, flight attendant unions, and pilot union. Mechanisms to release data to public and organization to release data to be determined. Actions based on surveillance data To be decided by interested regulatory agencies, airlines, and crew. Under Incident Conditions Ad hoc sampling survey for suspected incident Would supplement routine health surveillance monitoring. Collection of data All cabin and cockpit crew complete surveys. Standardized pencil-and-paper form for incident description (same properties as above). Standardized health form to supplement incident form. Standardized supplemental form to be distributed to all passengers to report incident-related symptoms. Standardized form for health followup of crew. Standardized maintenance evaluation form to be linked to database.

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The Airliner Cabin Environment and the Health of Passengers and Crew Management of database and reporting Same procedure as above. Central data manager sends followup health form at 6 and 12 mo. Findings are distributed to groups noted above plus responsible maintenance monitoring databases (FAA Accident/Incident Data System and Service Difficulty Reporting System). Actions based on surveillance data To be decided by interested regulatory agencies, airlines, and crew. an effective solution to the problem of passenger and crew complaints of cabin air quality and its possible association with health effects. As noted above, air-quality monitoring remains an essential approach and must be coordinated with the health surveillance system to address the questions regarding possible links between air quality and health effects. AIR-QUALITY RESEARCH Apart from the surveillance program, the committee recommends a series of research investigations, each aimed at a specific aspect of cabin air quality. The investigations would have a more limited scope than the surveillance program, but could involve more intensive air sampling for one or two contaminants in selected aircraft or on selected flights. The research program must be coordinated with the surveillance program discussed above. When it is appropriate, data collected in the surveillance program can be used to formulate research questions. The following pages outline seven research topics on which further information is critical for assessing cabin air quality. Suggestions for collecting data on exposure to biological agents and related health effects were provided in Chapter 4. Ozone The committee identified several questions relevant to O3 in aircraft cabins that should be addressed. How is the concentration of O3 in aircraft cabins affected by factors such as ambient O3 concentration, deposition on surfaces

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The Airliner Cabin Environment and the Health of Passengers and Crew in the aircraft, the presence and effectiveness of the catalytic converter, the maintenance and replacement schedule for the converter, and chemical reactions of O3 with component surfaces in the cabin? What is the strength of the relationship between cabin O3 concentration, both short-term and averaged over the duration of a flight, and health effects in the occupants? (See Chapter 3 for discussion of factors affecting O3 concentration and Chapter 5 for discussion of health effects of O3.) O3 concentrations for this study should be monitored in both supply and exhaust air. Cabin Pressure and Oxygen Partial Pressure The committee identified several critical unanswered questions regarding cabin pressure: Is a maximal cabin pressure altitude of 2,440 m (8,000 ft) appropriate for avoiding hypoxia? Are passengers with pulmonary or cardiovascular disease exposed to unacceptable risk at that pressure? How does cabin pressure vary with factors such as flight duration, altitude, and aircraft type? Because partial pressure of oxygen (PO2) in air is proportional to air pressure, continuous monitoring and recording of cabin pressure altitude is sufficient to determine the temporal variation in inhaled PO2. However, the relationship between inhaled and arterial PO2, and therefore hemoglobin saturation, are influenced by the functional status of the cardiovascular and respiratory systems (Slonim and Hamilton 1971; Murray 1976; Robson et al. 2000). Therefore, use of pulse oximetry to assess hemoglobin saturation in crew and passengers should be considered. (See Chapters 5 and 6 for further discussion of cabin pressure and health risk.) Outside-Air Ventilation The committee was unable to resolve several questions related to ventilation on aircraft: Is the current FAA design requirement for outside-air ventilation (FAR 25.831) adequate to minimize complaints? Are environmental control systems (ECSs) in aircraft operated so that they meet the outside air-ventilation rate in the FAA design requirements at all times during normal operation? To what extent are complaints from passenger and crew associ

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The Airliner Cabin Environment and the Health of Passengers and Crew ated with the outside-air ventilation rate? How do factors such as passenger loading and recirculation of cabin air affect the amount of outside-air ventilation needed? Can the conclusion drawn in Chapter 4 that infectious-disease agents are transmitted primarily between people in close proximity be verified? What effects, if any, do outside-air ventilation rate, total airflow (outside air plus recirculation air), and airflow patterns in the cabin have on disease transmission? Is American Society of Heating, Refrigerating and Air-Conditioning Engineers Standard 62 (ASHRAE 1999) appropriate for aircraft, and is it adequate to avoid air-quality complaints on aircraft? The CO2 concentration in an aircraft cabin depends primarily on the outside-air ventilation rate per occupant and, in the absence of confounding factors (e.g., dry ice in galleys), may be used as a surrogate for outside-air ventilation rate. Outside-air ventilation flow rates may be measured directly, but this would be extremely difficult on an aircraft. Monitoring should be conducted continuously from “crew on” to “crew off” and in conjunction with corresponding evaluations of cabin occupant comfort and health variables, as noted above. Air-Quality Incidents Questions identified by the committee regarding contaminants entering bleed air because of oil leaks or equipment malfunctions include the following: How does the frequency vary with the type of engine or bleed-air system? What is the toxicity of the constituents and pyrolyzed products of the materials? What is their relationship to reported health effects? How are the oil, fluids, and pyrolyzed products distributed from the engines, into the ECS, and throughout the cabin environment? A complex approach to monitoring may be required to evaluate these questions and may include careful evaluation of maintenance records to identify aircraft in which fluid is lost or aircraft components that require frequent service of fluid seals and cabin air monitoring to detect airborne products of leakage, such as fine PM and CO. Fine PM could indicate a leak in which aerosols are produced, and CO could indicate a leak in which incomplete combustion of fluids occurs at high temperatures. Integrated filter sampling of airborne particles during flight would be necessary for determination of the chemical composition of the materials released by oil leaks or equipment mal

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The Airliner Cabin Environment and the Health of Passengers and Crew functions.2 The samples could be stored and analyzed later. Because nonroutine conditions appear to be rare, sampling a large number of flight segments may be required to accumulate sufficient data to characterize the role of fluid leaks in affecting cabin air quality. For example, if the frequency of the events is no more than 1 per 1,000 flights, acquiring data from 100 events would involve sampling a minimum of 100,000 flight segments. Sampling such a large number of flights is not feasible, and more appropriate approaches are discussed below. Focus on “problem” aircraft. Use surveillance data to identify aircraft types in which problems are especially frequent, and conduct intensive air monitoring on them. Only a few aircraft or engine types may be responsible for most serious health complaints reported to date in nonroutine incidents. Intensive sampling with all the techniques outlined in Chapter 7 may be possible for investigating the aircraft and thus identifying the causes and remedies of problems. Review maintenance and repair records. Identify aircraft that have recurrent problems (e.g., excessive loss of engine oil or hydraulic fluids and failed fluid seals) that might be associated with deterioration in cabin air quality. Linking the results of such an investigation to the health surveillance program might make it possible to evaluate the reported association between cabin air quality and health problems. Investigate the need for additional air-contaminant control devices. The goal is to capture contaminants that might enter through the ECS before they can enter the aircraft cabin. Potential approaches could include additional air-cleaning devices in the air supply lines upstream of the points where bleed air is mixed with recirculated air or upstream of the points where air is directed to the cabin in aircraft without recirculation. When the air contaminant control devices are being investigated, some objective measures of their performance must be defined to validate expected improvements in cabin air quality. Investigate only aircraft or flights on which health complaints have been reported. This approach could be based on the health surveillance 2   The committee has not suggested sampling for volatile organic compounds or semivolatile organic compounds because no available sampling techniques are practical or feasible on aircraft (see Appendix D). However, if new techniques become available, their application to this research should be considered.

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The Airliner Cabin Environment and the Health of Passengers and Crew system described above. Although air-quality measurements might not be available for the particular flights in question, careful review of the aircraft itinerary, operations log, maintenance history, and other characteristics might reveal information that would suggest a cause of the complaints and a suitable remedy. Although the implementation of a health surveillance system for routine conditions of flight is relatively straightforward, some unique complexities exist for the evaluation of incidents. Given the concerns of cabin crew, the most important need would be to develop a standard procedure for followup of cabin crew who have worked on a flight on which an incident has been reported. The intervals for data collection, the mechanisms to maximize compliance and to protect privacy, and the total duration of followup after an incident all require consideration. The need to link data collected in an incident surveillance system with existing data systems (FAA’s Accident/Incident Data System, NASA’s Aviation Safety Reporting System, FAA’s Service Difficulty Reporting System) and the need to link maintenance findings and corrective actions to the system also require consideration. A simple sampling protocol for incident conditions and the responsibility for the maintenance and updating of a central data repository would be required. The repository would be responsible for the maintenance of data accuracy and privacy. Pesticide Exposure The committee identified several questions related to pesticide exposure: What exposure concentrations and chemical constituents are observed in commercial aircraft as a result of disinsection? How do the exposures depend on the pesticide application method (blocks away, top of descent, on arrival, residual treatment, and preembarkation; see Chapter 3)? What health risks, if any, are associated with such exposures? Evaluation of pesticide exposure may require air monitoring and other analytic techniques. For the airborne route, analysis of integrated PM samples would indicate exposure to airborne particles resulting from direct spraying or resuspension of settled material. Methods available to assess the noninhalation routes include analysis of samples removed from aircraft surfaces and from skin and sampling of body fluids or tissues. (See Chapter 7 and Appendix D for further discussion of the sampling techniques.)

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The Airliner Cabin Environment and the Health of Passengers and Crew Relative Humidity The committee identified several questions regarding the issue of relative humidity: What is the contribution of low relative humidity to the perception of dryness? Do other factors cause or contribute to the irritation attributed to the dry cabin environment during flight? As noted previously in this report, low relative humidity occurs on nearly all flights during cruise. Therefore, the focus of this research effort is to determine the relationship between relative humidity and the complaints of irritation of eyes and mucous membranes among passengers and crew, not to determine the cabin relative humidity itself. Fine Particulate Matter Although fine PM is not a major focus of the research program, the committee identified several questions related to fine PM: What is the role of fine PM in inducing complaints and health effects in cabin occupants? What are the probable sources of the fine PM? What are the important chemical or biological components of fine PM in the cabin? To what extent do filters or other air-cleaning devices reduce PM concentrations in aircraft cabins? What factors influence the effectiveness of those devices? Careful study of this topic requires reliable monitoring of fine PM that is both continuous and time-integrated (averaged over the period of a flight). (See Chapter 7 for a discussion of techniques for monitoring fine PM.) STAGING Feasibility Demonstration of Air-Quality Monitoring Program Air-quality monitoring will be required for both surveillance and research. One possible approach to implementing the necessary monitoring is a feasibility study. A prototype instrument package could be assembled by using commercial instruments with modifications as necessary to meet power, space, and safety requirements. The package should include direct-reading monitors for temperature, cabin pressure, relative humidity, O3, CO, CO2, and fine PM. It could be installed in nonrevenue-generating space in selected commercial

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The Airliner Cabin Environment and the Health of Passengers and Crew aircraft before their initial delivery or during a periodic overhaul. The presence of passengers and crew in the aircraft during flight will be necessary to evaluate the performance of the monitors in the presence of human sources of several important contaminants. Hardware and software for data collection and storage should be included in the demonstration system. It may ultimately be feasible to incorporate the data generated by the monitoring systems into the flight data recording system already in place on all commercial aircraft. It will be especially important to demonstrate that the air-quality monitoring package, including all pumps and air-sampling tubing, can be installed and operated without disrupting normal aircraft operation. The committee recognizes that the visibility of the monitoring equipment in the passenger cabin must be minimized to avoid raising health and safety concerns among passengers. Development of Standard Monitoring Package When the prototype package has been developed and tested on selected flights, a standard package can be designed for installation on any commercial aircraft. The committee emphasizes that the collection of monitoring data from a large number of flights for the air-quality characteristics described will have great value for compliance and enforcement of existing air-quality regulations, as well as for research on the safety and comfort goals of aircraft ECSs. The ability to evaluate correlations between objective measurements of exposure to contaminants or their surrogates and reports or measures of health and comfort problems in aircraft cabin occupants would facilitate a considerable advance over current knowledge. This information would answer many of the questions that have arisen about the causes and frequencies of relatively rare but possibly severe health events in commercial aviation. Another advantage of the committee’s recommended surveillance program is that continuous monitoring data could provide justification for cockpit and cabin crew to try to minimize excessive exposures in flight. For example, if CO2 were found to be high in the cabin, the pilot could increase the ventilation rate. However, when in-flight corrections cannot be made, off-specification or unexpected performance of the ECS can be documented, and appropriate maintenance can be promptly scheduled. That practice would minimize exposures that would otherwise continue or worsen during later flights. The committee, however, notes that adding instrumental indicators in the cockpit that might draw cockpit-crew attention may place an unreasonable additional bur

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The Airliner Cabin Environment and the Health of Passengers and Crew den on those responsible for safe operation during the flight. An appropriate balance must be sought between automated monitoring and recording without crew attention and the need for human observation and evaluation of the data as they emerge. Finally, the capacity for collection and storage of extensive air-quality monitoring data would prove useful in the investigation of events and complaints. Airline companies and FAA could use the data to verify performance of aircraft ECSs or to develop appropriate solutions to environmental problems that might be revealed only through routine continuous monitoring. However, access to data and the duration of its storage are important issues, and a clear policy on these matters should be developed before an air-quality monitoring program begins. CONCLUSIONS Existing air-quality data are inadequate for evaluating the possible association between air contaminants in routine operations and health problems or complaints from crew and passengers. Measurements have been made on a very small fraction of the total flight segments with methods that often lack acceptable accuracy and precision. Although CO and CO2 concentrations do not appear to exceed FAA guidelines under routine operating conditions, O3 concentrations probably do exceed the guidelines on some flights. Virtually no air-quality measurements are available for assessing the nature, severity, or frequency of nonroutine incidents aboard aircraft. Although complaints of foul odor and a variety of more serious health conditions have been reported, any relationship to deterioration in cabin air quality cannot be determined. There is some information on various possible toxic components produced by pyrolysis of aircraft fluids, but their presence in cabin air has not been documented. Equipment for control of airborne contaminants is available. Examples include high-efficiency particle filters and charcoal adsorbers. Systematic collection of continuous monitoring data on selected contaminants would reveal cases in which proper selection of additional control equipment can be made. In addition to the lack of exposure information, a major difficulty in the evaluation of the potential effects of cabin air quality on the health of passengers and cabin crew is the lack of standardized health surveillance systems for obtaining health-related data during normal and nonroutine operating conditions.

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The Airliner Cabin Environment and the Health of Passengers and Crew Although airlines require frequent medical evaluations of pilots, regular health evaluations of cabin crew are not required. Lack of such data precludes any systematic assessment of the extent to which occupational exposures of cabin crew are associated with chronic health conditions that follow acute exposures during incident conditions. RECOMMENDATIONS Air quality in commercial aircraft should be monitored with a dual approach that includes a routine surveillance program and a more focused research program. Routine surveillance of a number of air-quality characteristics (O3, CO, CO2, fine PM, cabin pressure, relative humidity, and temperature) should be implemented in a continuing program to characterize the range of air quality found in aircraft. A detailed research program is needed to investigate specific questions about the possible association between air contaminants and observed or reported health effects. Relevant subjects include factors that affect O3 concentrations in cabin air, the need to lower cabin pressure altitude to prevent hypoxia in susceptible cabin occupants, the adequacy of outside-air ventilation flow rates, the severity of events in which contaminants enter bleed air from oil-seal leaks or other equipment malfunctions, the potential for pesticide exposure due to current disinsection practices, the contribution of low relative humidity to the perception of dryness, and the role of fine PM in generating health complaints. Health surveillance should be integrated into the air monitoring programs. Health surveillance is needed for the systematic collection, analysis, and reporting of health outcomes related to routine and nonroutine conditions in commercial aircraft. On the basis of self-interest and exposure, the cabin crew should be the vehicle through which the surveillance system would operate. Congress should designate a lead federal agency and provide sufficient funds to conduct or direct the research program that is aimed at filling major knowledge gaps identified in this report. An independent advisory committee with appropriate scientific, medical, and engineering expertise should be constituted to oversee the research program to ensure that its objectives are met.

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The Airliner Cabin Environment and the Health of Passengers and Crew REFERENCES ASHRAE (American Society of Heating Refrigerating and Air-Conditioning Engineers). 1999. Chapter 9 in Aircraft in 1999 ASHRAE Handbook: Heating, Ventilating, and Air-Conditioning Applications. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Atlanta, GA. DOT (U.S. Department of Transportation). 2001. Airport Activity Statistics of Certificated Air Carriers, Summary Tables, Twelve Months Ending December 31, 1999. BTS01–03. Office of Airline Information, Bureau of Transportation Statistics, U.S. Department of Transportation, Washington, DC. [Online]. Available: http://www.bts.gov/publications/airactstats/index.html [October 18, 2001]. Haghighat, F., F.Allard, and R.Shimotakahara. 1999. Measurement of thermal comfort and indoor air quality aboard 43 flights on commercial airlines. Indoor Built Environ. 8(1):58–66. Lee, S., C.Poon, X.Li, F.Luk, M.Chang, and S.Lam. 2000. Air quality measurements on sixteen commercial aircraft. Pp. 45–60 in Air Quality and Comfort in Airliner Cabins, N.Nagda, ed. West Conshohocken, PA: American Society for Testing and Materials. Murray, J.F. 1976. Pp. 223–276 in The Normal Lung: The Basis for Diagnosis and Treatment of Pulmonary Disease. Philadelphia: Saunders. Nagda, N.L., H.E.Rector, Z.Li, and E.H.Hunt. 2001. Determine Aircraft Supply Air Contaminants in the Engine Bleed Air Supply System on Commercial Aircraft. ENERGEN Report AS20151. Prepared for American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Atlanta, GA, by ENERGEN Consulting, Inc., Germantown, MD. March 2001. Nagda, N., H.Rector, Z.Li, and D.Space. 2000. Aircraft cabin air quality: a critical review of past monitoring studies. Pp. 215–239 in Air Quality and Comfort in Airliner Cabins, N.Nagda, ed. West Conshohocken, PA: American Society for Testing and Materials. Robson, A.G., T.K.Hartung, and J.A.Innes. 2000. Laboratory assessment of fitness to fly in patients with lung disease: a practical approach. Eur. Respir. J. 16(2):214– 219. Slonim, N., and L.Hamilton. 1971. Pp. 150–174 in Respiratory Physiology, 2nd Ed. St. Louis: Mosby. Van Netten, C., and V.Leung. 2000. Comparison of the constituents of two jet engine lubricating oils and their volatile pyrolytic degradation products. Appl. Occup. Environ. Hyg. 15(3):277–283. Wright, R. 1996. Formation of the neurotoxin TMPP from TMPE-phosphate formation. Tribology Transactions 39:827–834. Wyman, J., E.Pitzer, F.Williams, J.Rivera, A.Durkin, J.Gehringer, P.Serve, D. von Minden, and D.Macys. 1993. Evaluation of shipboard formation of a neurotoxicant (trimethyolpropane phosphate) from thermal decomposition of synthetic aircraft engine lubricant. Am. Ind. Hyg. Assoc. J. 54(10):584–592.