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EXECUTIVE SUMMARY Each year Americans take more than 300 million plane trips, and airliner cabins are the workplace for about 70,000 flight attendants. The health and comfort of these travelers depend on the complex interplay of several factors: the adequacy of ventilation systems affecting the amount of cigarette smoke, microorganisms, and other contaminants in the cabin air; the use of fire-retardant materials in cabin equipment and furnishings; the availability and ease of use of breathing and other emergency equipment; and the clarity of special and emergency instructions. Although such devices and procedures are usually taken for granted, Congressional hearings during 1983-1984 revealed that information on airliner cabin air quality was contradictory. Flight attendants and others testified about inadequate ventilation and other problems with the cabin environment that caused discomfort. Representatives from the airline industry and federal regulatory agencies argued that present standards for the airliner cabin were adequate to protect the health and safety of travelers. Under Public Law 98-466, Congress stipulated that the National Academy of Sciences enter into a contract with the Federal Aviation Administration (FAA). The Academy was asked to determine whether such aspects of cabin air as the quantity of outside air, the quality of onboard air, the extent of pressurization, the characteristics of humidification, the presence of cosmic radiation, contaminants (such as bacteria, fungi, and other microorganisms), and pollutants (such as environmental tobacco smoke, carbon monoxide, carbon dioxide, and ozone) could be responsible for health problems in the long or short run; to recommend remedies for problems discovered; and to outline the safety 1
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2 precautions necessary to protect passengers in event of in-flight fires, which produce smoke and fumes. Accordingly, the Committee on Airliner Cabin Air Quality was established in the National Research Council's Commission on Life Sciences. This report summarizes the findings of the Committee's 18-month study of relevant issues. The investigation covered five general subjects: · Cabin air Quality: including potential health effects of reduced ventilation and of contamination by chemicals, microorganisms, other allergens, tobacco smoke, and ozone. · Cabin environment: health effects of reduced pressure and of cosmic radiation. · -Emergency procedures: control of fires and toxic fumes, use of emergency breathing equipment, and adequacy of emergency instruction given passengers. . Regulations: regulations established by U.S. and foreign agencies. · Records: statue and adequacy of medical statistics on air travel, of records on airline maintenance, and of records on operating procedures. The Committee relied heavily on published material-- articles in scientific and medical Journals and government and industry publications. FAA provided accident data and information on continuing investigations. Members of the Committee also visited government, airline, and industry groups to review fire testing, crew training facilities, and research programs on cabin ventilation. Relevant comments and information were received from the general public and other interested groups at an open hearing and were reviewed by the Committee. In formulating its conclusions and recommendations, the Committee attempted, but abandoned, the separation of issues of health from those of safety. However, under current statutes and administrative orders, no federal office has direct responsibility for health effects associated with air travel. This lack of correspondence between the issues an conceived by the Committee and the responsibilities of federal agencies
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3 contributed to the difficulty of the Committee's work. The Committee believes that the health effects associated with air travel should be within the Durview of a federal agency. CABIN AIR QUALITY In assessing the overall quality of onboard air, the Committee determined the range of outside-air ventilation rates on the U.S. fleet by reviewing manufacturers' design specifications, airline load-factor data, and operating procedures. No data were available on actual measured airflow in the fleet. The Committee found that, if the lowest rate of ventilation permitted by current equipment design were used under conditions of full or nearly full passenger loads, the resulting ventilation rate would be at the minimum determined to provide acceptable air quality when smoking is not permitted and other contaminant sources are not present. In the absence of sources of contamination, this rate does not constitute a health hazard. In particular, the Committee noted that the flow rate of outside air varied from below 7 cubic feet per minute (cfm) per economy-class passenger to 50 cfm per first-class passenger. Cockpit ventilation rates are often as high an 150 cfm per crew member; this higher rate, however, is provided to meet avionic and electronic equipment cooling loads, rather than for reduction of contaminant concentrations. These rates compare with a ventilation rate of 5-7 cfm/person established for other types of vehicular travel that have nonsmoking sections, including passenger and commuter trains and subways. It should be noted, however, that these other ventilation standards do not consider possible synergistic effects of the low relative humidity encountered in aircraft. Another important consideration is the adequacy of oxygen supply--because the normal requirement of air to meet oxygen needs for sedentary people in only 0.24 cfm/person, the amount of oxygen is sufficient in aircraft even at the lowest rate of flow of outside air . ~
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4 Nevertheless, a minimal ventilation rate for airplane passenger cabins is not defined under FM regulations, which specify ventilation rates only for flight crew compartments. Actual cabin airflow is seldom measured once an aircraft is in service; and flow can be reduced by deterioration in equipment performance. A data collection Program that measures airflow and contamination in airplane cabins should be implemented. CARBON DIOXIDE The Committee's efforts in evaluatlag contaminant concentrations were hampered by an almost complete absence of reliable data. The carbon dioxide concentration associated with a given ventilation rate, however, can be estimated with confidence. For a rate of 9.7 cfm/occupant, the carbon dioxide concentration would be about 0.15X, or 1,500 ppm. No adverse health effects of carbon dioxide would be noted at this concentration, but the FAA standard for aircraft allows for 20 times this concentration. This is considerably higher than standard concentrations permitted by the Occupational Safety and Health Administration (OSHA) and the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) for other types of indoor environments. The FAA standard is much hither than standards for other confined environments. The Committee recommends that FAA review its carbon dioxide standard. HUMIDITY In addition to carbon dioxide, relative humidity in the cabin at flight altitude is predictable, depending only on cabin ventilation rate, passenger load factor, temperature, and pressure. With a range of standard cabin ventilation rates, the relative humidity varied from 23% to less than 2Z. After 3 or 4 hours of exposure to relative humidity in the 5-1OX range, some passengers experience discomfort, such as dryness of the eyes, nose, and throat. However, the Committee could find no conclusive evidence of extensive or serious adverse health effects of low relative humidity on the flying population that would Justify recommending a regulation to add supplementary humidification systems to aircraft.
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5 OZONE Ozone has been measured at concentrations above 0.8 part per million by volume (ppmv) in the cabin during flight above the tropopause and during periods in which there is increased vertical air exchange between the stratosphere and the troposphere. This relatively high concentration can be reduced if ozone control equipment has been installed and is operating or if altitude and route limitations are imposed. In comparison with the observed ozone concentration of 0.8 ppmv, compliance with existing standards would limit ozone concentration to a maximum of 0.25 ppmv at equivalent sea-level pressure. Standards also limit the time-weighted average ozone concentration for any flight segment of over 4 hours to 0.1 ppmv. The Committee could find no documentation of the effectiveness of the various methods being used by the airlines to control ozone. Therefore, the Committee suggests that FAA carry out a carefully designed program to ensure that cabin ozone concentrations comply with Department of Transportation regulations. ENVIRONMENTAL TOBACCO SMOKE A contaminant in aircraft cabins that can be detected by its characteristic odor and visibility is environmental tobacco smoke (ETS)--the combination of exhaled mainstream smoke and the smoke generated by smoldering cigarettes. ETS is a hazardous substance and is the most frequent source of complaint about aircraft air quality. In the past, ventilation systems on aircraft were designed to control odor and irritation from cigarette smoke on the assumption that smokers are randomly distributed throughout the aircraft. However, separation of smokers and nonsmokers into separate zones is now federally mandated. Because of the high concentration of ETS generated in the smoking zone, it cannot be compensated for by increased ventilation in that zone. Moreover, strict separation of the airplane into smoking and nonsmoking zones does not prevent exposure of flight attendants and nonsmoking passengers to ETS, because of the location of galleys and lavatories in the smoking areas. Smoke exposure can become significant in aircraft with outside-air flow
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6 rates as low as 7 cfm/pansenger. Even a ventilation (airflow) rate of 14-15 cfm/passenger consists of as much as 50% recirculated, and possibly smoky, cabin air It is not known how often operating procedures are used that can decrease actual ventilation rates and increase contaminant concentrations. The Committee found no published peer-reviewed data on ETS concentrations in cabins. Although the adverse effects of ETS are still under investigation, the Committee feels that this potential threat to the health of nonsmoking passengers and flight attendants should not be ignored, especially because flight attendants on some airlines can fly up to the twenty-eighth week of pregnancy. It is highly probable that eye, nose, and throat irritation will increase among airline passengers as outside-air ventilation rates are decreased and recirculation is increased to improve fuel efficiency. . The Committee considered several ways of reducing ETS concentrations in aircraft. Any solution requiring structural or engineering changes--such as markedly increasing ventilation, moving lavatories and galleys, and separating smoking compartments with physical barriers--appears economically infeasible. Increasing ventilation of the smoking zone to the point where it is in compliance with ASHRAE guidelines and eliminating recirculation on existing aircraft does not appear technically feasible. The amount of air that would be required could exceed the engine bleed capacity and in all cases would reduce the range of the aircraft, the payload, or both. Injection of large volumes of air into the cabin would create unacceptable air velocities and result in passenger discomfort. In contrast, the Committee feels that a return to the random distribution of smokers throughout the cabin to reduce overall ETS concentration would be unacceptable to a majority of the traveling public. Cigarette-smoking has been implicated in a small number of in-flight fires, and thus presents a potential threat to safety. The Committee recommends a ban on smoking on all domestic commercial flights, for four major reasons: to lessen irritation and discomfort to passengers and crew, to reduce potential health hazards to cabin crew
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7 associated with ETS, to eliminate the possibility of fires caused by cigarettes, and to bring the cabin air Quality into line with established standards for other closed environments. AEROSOLS Evaluation of the degree of health hazard associated with exposure to biologic aerosols was impossible, because of the lack of data on their concentrations in aircraft cabins. There is an urgent need for studies of potentially infectious airborne agents under routine flight conditions. In the meantime, the Committee's recommendations regarding control of infection through ventilation must be based on similar occupancies (trains and subway cars) for which ventilation standards have been established. Because a likelihood of occurrence of epidemic disease when forced-air ventilation is not available on the ground has been demonstrated, the Committee recommends that a regulation be established that requires removal of passengers from an airplane within 30 minutes or less after a ventilation failure or shutdown on the ground and maintenance of full ventilation whenever onboard or around air-conditionine is available. The Committee also recommends that maximal airflow be used with full passenger complements to decrease the potential for microbial exposure and that recirculated air be filtered (to remove particles larder than 2-3 ~m] to reduce microbial aerosol concentrations. The Committee found no studies of the concentrations of other contaminants--such as volatile organic compounds or substances that might be emitted from disinfectants or cleaning materials--and therefore cannot assess their potential health hazard to passengers or crew members. Because the Committee found only sparse data on air quality and contaminants in aircraft, it undertook to have a multizone computer model of an aircraft ventilation system developed for its use in calculating contaminant, water vapor, and carbon dioxide
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8 concentrations in various cabin zones. The model was used to calculate average and peak concentrations of contaminants in smoking and nonsmoking zones. The effects of reduced flow, recirculation, and filter efficiency were analyzed. Cabin smoke from various onboard cabin fire scenarios can be evaluated with models of this type to develop optimal procedures for control of smoke under emergency conditions. This model is available to FAA. CABIN ENVIRONMENT Two unrelated factors of the cabin environment affect airline passengers: pressure and cosmic radiation. Pressurization of the cabin to equivalent altitudes of up to 8,000 ft. as well as changes in the normal rates of pressure during climb and descent, might pose a risk to or create discomfort for some segments of the population. At an altitude of 8,000 ft (or above if a mistake were made), people with cardiopulmonary disease might be at some risk. Persons suffering from upper respiratory or sinus infections, children, and infants might experience some discomfort or pain because of pressure changes during climb and descent. InJury to the middle ear can occur in susceptible people, but is rare. Other groups that could be at various degrees of risk include those with chronic pulmonary problems, anemia or sickle-cell disease, gastrointestinal problems, neurop~ychiatric symptoms, or recent abdominal or eye surgery. Pregnant women should not fly beyond 240 days; pregnant women with a history of spontaneous abortions should not fly; and scuba divers should not fly sooner than about 12-24 hours after diving. The Committee concluded that current Pressurization criteria and regulations are generally adequate to Protect the traveling Dublic. However, the medical Profession should use a more efficient system to warn those with existing medical conditions who are more susceptible to chances in Pressure or to lone exposure to low pressure that there might be some hazard to their health.
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9 Although the dose-equivalent rate of cosmic radiation in significantly higher at airplane cruise altitudes and above than at ground level, cosmic radiation associated with subsonic commercial flights does not pose a serious health risk to the general public. However, it is likely that some flight and cabin crew members will receive 100-200 mrems/yr. That is below the 500-mrem/yr recommended maximum for any member of the general public. Inasmuch as radiation exposures are additive and assumed to be linear, the additional radiation received during high-altitude flying should be considered in the estimates of total dose, which includes the radiation that might be received as a result of living at high altitude or from medical or dental x rays. This report draws attention to the potential hazard to full-time flight attendants flying high-latitude routes, who might be exposed to cosmic radiation equivalent to radiation from thoracic or abdominal medical x rays. Such medical x rays are to be avoided during pregnancy. FAA should consider rule-makina that restricts exposure of Pregnant flight crew and cabin crew members. In addition, FAA should investigate total radiation exposure of flight crew and cabin crew members through the use of a statistical sample of full-time emoloveen and should require airlines to Provide precautionary information to their flight attendants about radiation exposure. EMERGENCY SITUATIONS AND PROCEDURES The Committee reviewed emergency procedures and cabin crew training for evacuation of the cabin in emergencies or after survivable crashes and the procedures for use after cabin Repressurization. Several members of the Committee participated in an emergency evacuation exercise. The Committee also investigated fire test procedures for cabin materials, firefighting techniques, and emergency breathing equipment for cabin crews. As any air traveler can observe, many passengers ignore or pay little attention to passenger safety briefings, in spite of the fact that retention of the information presented can mean the difference between
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10 survival and death in emergency situations. The Committee approves of current efforts to base passenger safety briefings and written materials on empirical testing of comprehension and retention. However, the Committee believes that it is also important to understand how passengers recall that information and respond under the stress of emergencies. The Committee suggests that FAA or appropriate industry organizations consider the advisability of developing an empirical research program to examine Passenger response to safety instructions under routine and emergency conditions and revise them as appropriate. Consideration should be given to running some quizzes during a flight to see, for example, what proportion of passengers have retained the key features of the safety briefing. The Committee recommends that FAA require that information on proper response to fire emergencies be included in oral and written passenger safety information. In general, the FAA program on flammability testing is excellent, and its research efforts to improve testing methods are appropriate and valuable. The recently issued F. M flammability standards for seat cushions and cargo compartment liners will reduce in-flight and postcrash fire hazards. The Committee feels that continuing research is also needed in materials development. Although FAA standards are met by currently available materials, other materials exist that, with further development, would far exceed current standards and would provide substantially increased fire protection in aircraft. The Committee noted that current emergency Procedures for smoke removal recommend that the cabin be denressurized to 10,000 ft. This procedure is ineffective and should be discontinued. FAA recently proposed standards that would require that protective breathing devices be available to airliner crew members for firefighting. One such device is to be stored within 3 ft of each required fire extinguisher. However, there are generally more crew members than fire extinguishers, and the Committee recommends that FAA review the proposed rule on Protective breathing devices for crew members to
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11 ascertain the desirability of supplying such equipment for all crew members, rather than limiting it to the persons expected to be involved in firefiahtin~. In addition, the Committee suggests further evaluation of the potential of emergency breathing equipment for all cabin crew members to improve safe and expeditious evacuation of Passengers in fire emergencies. A rule requiring protective breathing devices for passengers was proposed by FAA in 1969, but later withdrawn. These devices have since been further developed and evaluated. The Committee recommends that FAA re-examine passenger protective breathing devices and consider requiring that such equipment be available in case of in-fli~ht and postcrash fires. WORLDWIDE AIRLINE REGULATIONS The Committee was charged with performing a comparison of foreign industry practices, regulations, and standards, and has gathered relevant information applicable to the issues addressed in this study. Although some differences from those in the United States have been noted, they do not appear to be significant. The Committee feels that greater effort along these lines is not warranted. FEASIBILITY OF DATA COLLECTION Empirical evidence is lacking in quality and quantity for a scientific evaluation of the quality of airliner cabin air or of the probable health effects of short or long exposure to it. Standards directly applicable to commercial aircraft have not been established for cabin ventilation rates, environmental conditions, and air contaminants, and adequate data on these factors are not available. The Committee therefore recommends that FAA establish a program for the systematic measurement, by unbiased independent Groups, of the concentrations of carbon monoxide, respirable suspended ~articles, microbial aerosols, and ozone and the measurement of actual ventilation rates, cabin Pressures, and cosmic radiation on a representative sample of routine commercial flights' These findings should be subjected to Deer review. This
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12 would provide a basis for establishing appropriate standards if justified Add for requiring regular monitoring if necessa ". The Committee recognizes the extreme difficulty of interpreting data on the health effects of air travel, but believes thee several kinds of data can be collected. The Committee recommends that FAA establish a program to monitor selected health effects on airliner crews. Air carriers are required to report to FAA all uses of the recently mandated medical kits during the first 24 months. The Committee recommends that FAA collect these data in such a wav as to permit comparison of onboard incidents with those in other settinRe.
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