6
Health Surveillance

At the end of its review of health data in the 1986 report The Airliner Cabin Environment: Air Quality and Safety, the National Research Council (NRC) committee concluded that “available information on the health of crews and passengers stems largely from ad hoc epidemiologic studies or case reports of specific health outcomes [and] conclusions that can be drawn from the available data are limited to a great extent by self-selection…and lack of exposure information” (NRC 1986). This chapter reviews data on possible health effects of exposure to aircraft cabin air that have emerged since the 1986 report and the emergence of data resources (e.g., surveillance systems) and studies that have particular relevance for the evaluation of potential health effects related to aircraft cabin air quality. Selected earlier sources are also reviewed. The decision to ban tobacco-smoking on domestic airline flights in 1987 and on flights into and out of the United States in 1999 reduces the relevance of some studies of exposures and reported signs and symptoms that clearly could have been related to the products of tobacco smoke.

A wide array of symptoms have been attributed to various exposures to cabin air as a result of normal aircraft operations or incidents (Table 6–1). The symptoms or health effects are grouped into four categories that are intended to be descriptive and do not imply mechanisms. The column “Health Outcomes” identifies outcomes related to chronic exposure, to cabin air, or to physiological responses in groups of people who may be at particular risk in the cabin of a commercial airliner, such as passengers with underlying cardiac or pulmonary disease. Most of the symptoms listed in the first three categories have been reported primarily by cabin crews. Very few data are available on passengers, and their symptoms are primarily drying of mucous membranes.



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The Airliner Cabin Environment and the Health of Passengers and Crew 6 Health Surveillance At the end of its review of health data in the 1986 report The Airliner Cabin Environment: Air Quality and Safety, the National Research Council (NRC) committee concluded that “available information on the health of crews and passengers stems largely from ad hoc epidemiologic studies or case reports of specific health outcomes [and] conclusions that can be drawn from the available data are limited to a great extent by self-selection…and lack of exposure information” (NRC 1986). This chapter reviews data on possible health effects of exposure to aircraft cabin air that have emerged since the 1986 report and the emergence of data resources (e.g., surveillance systems) and studies that have particular relevance for the evaluation of potential health effects related to aircraft cabin air quality. Selected earlier sources are also reviewed. The decision to ban tobacco-smoking on domestic airline flights in 1987 and on flights into and out of the United States in 1999 reduces the relevance of some studies of exposures and reported signs and symptoms that clearly could have been related to the products of tobacco smoke. A wide array of symptoms have been attributed to various exposures to cabin air as a result of normal aircraft operations or incidents (Table 6–1). The symptoms or health effects are grouped into four categories that are intended to be descriptive and do not imply mechanisms. The column “Health Outcomes” identifies outcomes related to chronic exposure, to cabin air, or to physiological responses in groups of people who may be at particular risk in the cabin of a commercial airliner, such as passengers with underlying cardiac or pulmonary disease. Most of the symptoms listed in the first three categories have been reported primarily by cabin crews. Very few data are available on passengers, and their symptoms are primarily drying of mucous membranes.

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The Airliner Cabin Environment and the Health of Passengers and Crew TABLE 6–1 Signs and Symptoms Reported to Be Related to Aircraft Cabin Air Reported Signs and Symptoms Respiratory and Mucosal Surfaces Neurological and Neurobehavioral Syndrome-Symptom Complexes Other Symptoms Health Outcomes Irritation, pain (eyes, nose, sinuses, throat) Difficulty breathing Breathing discomfort Pain in chest Coughing Dry, stuffy nose Neurotoxicity (altered vision and coordination, loss of balance, slurred speech, paresthesias) Neurobehavioral (impaired memory and ability to concentrate, trouble counting, general cognitive problems) Headache Disorientation and confusion Lightheadedness Dizziness Weakness and fatigue Feelings of intoxication Aerotoxic syndrome Irritability, neurotoxicity, chemical sensitivity Acute intoxications Neurological signs and symptoms, neurobehavioral effects, cardiovascular effects, gastrointestinal symptoms Chemical sensitivity Ozone-related Cough, chest discomfort, irritation of mucous membranes Organophosphate-induced delayed neuropathy syndrome Delayed-onset weakness, ataxia, paralysis Dry skin Rapid heart rate and palpitations Reproductive effects Cancer (unrelated to cosmic radiation) Lung function effects Signs and symptoms related to underlying disease or episodes of worsening underlying diseases (cardiovascular, chronic respiratory) Signs and symptoms related to cabin pressure and oxygen content Acute infections (1979 influenza outbreak, tuberculosis) Immunosuppression Hair loss

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The Airliner Cabin Environment and the Health of Passengers and Crew The sources of the various reports or symptoms can be grouped into two broad categories (Table 6–2): various types of systematic presentations, only a few of which represent formal studies, and selected written documents that have not been peer-reviewed and published. Most of the reports of symptoms come from collections of case reports abstracted from various reporting systems for cabin and cockpit crew members, usually in relation to known or suspected incidents. This chapter begins with a discussion of the systematic studies that have been conducted, including those on specific exposure conditions (e.g., pesticides, infectious agents, and cabin pressure). That is followed by a brief review of other sources of health information. Finally, the current health-related data collection systems are reviewed. STUDIES OF AIRCRAFT CABIN AIR QUALITY Relatively few formal studies have evaluated the effects on passengers and cabin crew of exposure to aircraft cabin air during routine flights or during flight-related air-quality incidents. General Air-Quality Surveys Although the data were available to the 1986 NRC committee, the report of Tashkin et al. (1983) is reviewed briefly here because it has been quoted often in more recent publications and testimony (e.g., Australian Senate Rural and Regional Affairs and Transport References Committee 1999). The authors analyzed survey data collected by a flight attendants union in response to complaints of various respiratory symptoms among attendants who flew on the Boeing 747SP. Attendants were concerned that the aircraft flew at high altitudes and that increased exposure to ozone (O3) was therefore possible. O3 concentrations as high as 1.09 ppm had been measured in the cabins of 747SP aircraft on other occasions (Tashkin et al. 1983). The authors acknowledged that they did not have a role in the survey design and that considerable methodological problems existed, including the following: The response rate of the surveys was inadequate: Only 55.1% (248 of 450) of the original surveys distributed to attendants who flew on the 747SPs were returned. An attempt to obtain “control” data from cabin crew who flew on other 747s led to a response rate of only 15.3% (38 of 248). A third survey had a response rate of 7.6% (65 of 850).

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The Airliner Cabin Environment and the Health of Passengers and Crew TABLE 6–2 Sources of Data on Health Outcomes Attributed to Exposure to Aircraft Cabin Air Planned Studies, Systematic Reviews of Records, and Presentations at Conferences Respiratory Symptoms of Flight Attendants During High-Altitude Flight, Tashkin et al. (1983) —Analysis of survey conducted by flight attendant union in response to concerns about O3 exposure. —Response frequencies to surveys ranged from 7.6% to 55%. —No direct measurements of exposure. Flight Attendant Health Survey, Cone and Cameron (1984) —Flights from San Francisco to Honolulu. —Monitored ozone, nitrogen oxides, sulfur dioxide, phosphoric acid esters. —Surveyed crew for symptoms. —95% response frequency (683/720), but total eligible not given. Air Quality on Commercial Aircraft, Pierce et al. (1999) —Cabin air monitoring of 8 Boeing 777s; comfort survey included. —No sampling plan (930 (43%) of passengers; 27 (26%) of flight attendants). American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Project 957-RP, ASHRAE/CSS (1999) —Systematic monitoring of environment of Boeing 777 with recirculation and O3 converter. —Passenger and crew comfort questionnaire; 930 (43%) passengers and 27 (26%) of cabin crew completed survey. —Appendix contains literature review with references to small planned studies related to physiology. O3 and Relative Humidity on Airline Cabins on Polar Routes, De Ree et al. (2000) —Comparison of ozone-related symptoms in crew of planes with and without O3 catalytic converters. —O3 and relative humidity measurements. —Variable response rates from pilots (79–94%) and cabin crew (66–71%). —Nonsystematic survey of passengers. —Weak statistical analysis. Questionnaire Survey to Evaluate the Health and Comfort of Cabin Crew, Lee et al. (2000) —Nonsystematic sampling of cabin crew on Cathay Pacific flights. —Number eligible and response rate not reported. Passenger Comfort and the Effect of Air Quality, Rankin et al. (2000) —Self-administered survey of passengers on six types of aircraft with air recirculation of 0 to 50%. —Only 43% response rate (3,630/8,517).

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The Airliner Cabin Environment and the Health of Passengers and Crew Smoke/fumes in the Cockpit, Rayman and McNaughton (1983) —Review of 89 incidents of smoke and fumes in cockpit in U.S. Air Force aircraft. —Apparent complete ascertainment. Air Quality and Health Effects Associated with the Operation of BAe 146–200 Aircraft, van Netten (1998) —Review of clinical assessments and accident reports over 4 mo filled out by crew on two BAe 146–200 that had experienced oil-seal failures. —Completeness of data unknown. Aerotoxic Syndrome, Winder and Balouet (2000a) —Published presentation at Proceedings of the International Congress on Occupational Health, Brisbane, 2000. —Summary of “aerotoxic syndrome.” —No primary data or references. In-Cabin Trace Chemicals and Crew Health Issues, Balouet (1998); Airborne Chemicals in Aircraft Cabins, Balouet and Winder (2000a) —Data based on 350 selected reports of symptoms supposedly related to documented leak events. —No details on methods for selection of reports or documentation of leaks and exposure. —Cites common words to describe symptoms from diverse and unrelated incidence episodes in support of constellation of symptoms. —Citation of impending investigations as implicit evidence of problem. —“Aerotoxic syndrome.” Outbreak of Influenza Aboard a Commercial Airliner, Moser et al. (1979) —72% of passengers at risk became ill. —Flight was grounded for over 3 h and air-conditioning system was inoperative. Outbreak of Influenza A/Taiwan/1/86 Infections at a Naval Base and Association with Airplane Travel, Klontz et al. (1989) —Influenza among 114-member squadron within 72 h after flights from Puerto Rico to Key West, Florida. —Evidence of transmission of influenza was occurring before flights. Imported Measles in the United States, Amler et al. (1982) —Three cases of measles in children on flight from Venezuela to Miami, Florida (one child had prodromal symptoms during the flight). —No information on relationships between children, their proximity, or contact before, during, or after flight; two secondary cases could have been infected before flight. Surveillance Report of Measles Transmission in an Airport, CDC (1983) —One person appeared to infect one passenger on same flight and five others within airport.

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The Airliner Cabin Environment and the Health of Passengers and Crew Measles Outbreak on Flight from New York to Tel Aviv, Slater et al. (1995) —8 of 306 passengers developed measles. —No information on location of passengers in aircraft. —Waiting area was congested, and loaded plane was grounded for 2 h for repairs. Tuberculosis Transmission on a Flight from London to Minneapolis, Minnesota, McFarland et al. (1993) —Contact investigation for passenger with pulmonary tuberculosis. —Alternative explanations could be found for all cases with positive skin tests. Tuberculosis Transmission among Flight Crew, Driver et al. (1994) —Flight attendant flew for 6 mo while symptomatic. —Crew members on same flights as infected attendant were compared with control group of crew on other flights. —Greater prevalence of positive skin tests among crew that had contact with infected attendant. Tuberculosis Transmission on Airline Flights, Kenyon et al. (1996) —Symptomatic passenger flew on four flights; other passengers and crew were investigated. —Greatest number of positive skin tests were found on fourth flight. —Six passengers that had no other risk factors were seated in same section as infected person. Tuberculosis Transmission on Airline Flights, Miller et al. (1996) —Contact investigation of passengers and crew from two flights with passenger who had pulmonary tuberculosis. —Data not available on 35% of potential contacts. —Two people with positive skin test (and no other risk factors) did not sit near or have contact with infected passenger. Tuberculosis Transmission on Airline Flights, Moore et al. (1996) —Infected person flew on two short flights (about 1 h). —Contact investigation of passengers and crew. —Data available on only 53% of potential contacts. Tuberculosis Transmission on a Flight, Wang (2000) —Contact investigation of passengers and crew on flight with infected passenger. —Three subjects with skin-test conversions were not seated in same section as infected passenger. In-flight Arterial Saturation in Pilots, Cottrell et al. (1995) —Oxygen saturation was measured with continuous-reading pulse oximeters during flights of about 4 h. In-flight Arterial Saturation in Subjects with Chronic Obstructive Lung Disease, Schwartz et al. (1984)

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The Airliner Cabin Environment and the Health of Passengers and Crew —Measurements taken in unpressurized aircraft cabin before and during flight. Arterial Saturation in Subjects with Chronic Obstructive Lung Disease, Dillard et al. (1989), Naughton et al. (1995) —Simulation performed in hypobaric chamber. Air Travel in Patients with Chronic Obstructive Lung Disease, Dillard et al. (1991) —44 of 100 subjects reported traveling by air within previous 2 yr. —8 subjects reported symptoms. Oxygen Saturation in Cabin Crew, Ross (2001) —“Spot” measurements were taken periodically with pulse oximeters. —No data on saturations related to cabin altitude and work activities of crew. Testimony to Various Committees and Unpublished Summaries Commonwealth of Australia Proof Committee Hansard Senate-Air Safety—BAe 146 Cabin Air Quality, Senate Rural and Regional Affairs and Transport References Committee (1999) —Case-report testimony based on exposures to smoke, mist, fumes. —“Old socks” odors. —Association between odors and short-term irritation of mucous membranes, nausea, shortness of breath. Case Study of “Cabin Crew Syndrome” Presented to ASHRAE Aviation Subcommittee, Wright and Clarke (1999) —Suggestion, but no documentation, of an incident (sweet smell). —Single case with multiple signs and symptoms over many months. —Inference based on toxicology of organophosphates. Association of Flight Attendants (AFA) Reports of Health Effects Related to Exposure to Insecticide Spraying, Witkowski (1999); Cone and Das (2001) —Sample of cases submitted by AFA. —Lists of disability claims. Unreferenced Reports on Symptoms and Symptom Complexes by Balouet and Colleagues —Description of “aerotoxic syndrome” (Balouet and Winder 1999). —Anecdotal presentation of symptom complex. —No exposure data. —No information on how subject data were obtained. —Presentation of case studies. —Report on symptoms associated with “exposure” to chemicals in aircraft (Balouet and Winder 2000b). —Apparent tabulation of data from several databases to which reports are filed. —No information on techniques for selection of data. —No information on quality of data reports.

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The Airliner Cabin Environment and the Health of Passengers and Crew No O3 concentrations were measured on any flight for which survey data were available. The association with possible O3 exposure during flight was based on the subjective assessment of three experts who decided which reported symptoms were most likely due to O3 exposure. The only objective measurements were of pulmonary function in 21 attendants (no criteria for selection given). All results were normal. The possibility of selection bias in the study means that the results cannot be interpreted as supporting or refuting the relation of symptoms to O3 exposure on high-altitude flights. Moreover, many of the symptoms considered “definitely” or “probably” related to O3 exposure are nonspecific and prevent use of the study as an assessment tool for estimating effects of O3 exposure. The Occupational Health Clinic of San Francisco General Hospital was commissioned by the AFA and American Airlines to conduct a study of the cause of symptoms reported by flight crews on flights between San Francisco and Honolulu in association with an odor described as that of “dirty socks” (Cone and Cameron 1984). Three types of aircraft—Boeing 747, DC-10–10, and DC 10–30—were evaluated. Questionnaires were distributed to crew members. A wide array of symptoms were reported more frequently on the B747 and the DC-10–10 (eye, nose, throat, and sinus irritation; dry or watery eyes; shortness of breath; dizziness; and lightheadedness). Symptoms of eye, nose, and sinus irritation; headache; and chest symptoms (burning, difficulty in breathing, and cough) were reported more frequently when odors were noted. Of the agents monitored—O3, nitrogen oxides, sulfur dioxide, and phosphoric acid esters—only episodic increases in nitrogen oxides were observed, and association with odor was reported only on one occasion. No other exposure data were related to symptoms. The authors concluded that there was evidence of exposure to a “powerful mucous membrane irritant” whose etiology could not be determined from the study. They speculated that vaporization and pyrolysis products of aircraft fluids were a possible cause. Although a high response rate was reported (95%, 683 of 720), the total number of eligible crew members was not provided, nor were any data provided on the relation of chronic respiratory symptoms to smoking (32% were current smokers) or allergy (36% had unspecified allergy). The statistical analysis did not take into account crew differences in the factors that could have contributed to the results. The ASHRAE commissioned a study to monitor the cabin air of Boeing 777s (Pierce et al. 1999). A cabin-comfort survey administered to passengers

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The Airliner Cabin Environment and the Health of Passengers and Crew and cabin crew had a number of components, one of which related specifically to symptoms. For virtually every symptom, cabin crews were more likely to report the presence of a symptom and greater severity than passengers (Table 6–3). The study has several serious problems that make it difficult to interpret the data. The response rates of passengers and crew were very low (Table 6–2). The percentages for the reported symptoms do not add to 100% (Table 6–3), so it is difficult to know what is being reported. Finally, no formal analysis links the environmental measurements with the symptom reports. In response to complaints from cabin and cockpit crews of a variety of symptoms thought to be related to O3 exposure, DeRee and colleagues (2000) carried out a monitoring and symptom study in two European airlines. The planes of airline A were fitted with O3 converters but lacked humidifiers; airline B had humidifiers but no O3 converters. O3 and relative-humidity measurements were made on the flight deck. Symptom questionnaires were completed by flight and cabin crew at the beginning and end of 24 polar flights (12 flights per airline) monitored in February-May 1998. Cabin crews were “encouraged” to record symptoms reported by passengers, but no systematic surveillance was conducted. Background information on smoking and upper respiratory symptoms was obtained. Participation rates of cabin crews were 71% (187) on airline A and 66% (222) on airline B.Mean O3 concentrations during cruise on airlines A and B were 2–40 and 43–177 ppb (not stated if sea- TABLE 6–3 Report of Selected Symptoms by Passengers and Cabin Crew   Passengers (n=930)a Cabin Crew (n=27)a Symptoms Great Extent Somewhat Not At All Great Extent Somewhat Not At All Dry, itchy, or irritated eyes 7.3 17.3 33.0 22.2 37.0 3.7 Dry, stuffy nose 9.7 19.9 30.5 29.6 37.0 7.4 Sore, dry throat 4.8 12.8 37.0 11.1 33.3 22.2 Shortness of breath 0.9 3.8 45.3 3.7 22.2 37.0 Sinus pain 2.9 7.3 41.9 18.5 7.5 44.4 Skin dryness or irritation 4.4 10.5 38.4 37.0 33.3 0.0 aPercentages do not add to 100% for each symptom and no explanation given in Pierce et al. (1999) or ASHRAE/CSS (1999). Source: Adapted from Pierce et al. (1999).

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The Airliner Cabin Environment and the Health of Passengers and Crew level equivalent), respectively. Mean relative humidity was 8–12% and 5–28% on airlines A and B, respectively. Of the 16 symptoms included in the questionnaire, four were considered to be O3-related (coughing, tightness of the chest, shortness of breath, and “breathing hurts”). Symptoms were reported equally by cabin crew of the two airlines before flight (68%) and similarly after flight (A, 95%; B, 91 %). Symptom reporting was also similar in percentages of cabin-crew members who reported worsening (about 30%) and improvement in preflight O3-related symptoms. Similar findings were observed for aggregate nonspecific symptoms (e.g., headache and watery and stinging eyes); however, no data are provided on symptoms specifically related to mucosa irritation. No correlation (Pearson product-moment) was observed for changes in O3-related or nonspecific symptoms and measured O3 concentrations (it was not stated which O3 metric was used—mean or maximum) on airline A; weak, statistically nonsignificant correlations were observed for O3-related (0.18) and nonspecific (0.21) symptoms on airline B. The authors concluded that there was “not a straightforward relationship between O3 levels and relative humidity on the one hand and reported symptoms on the other.” Although the study had a reasonable design, the presentation of the data is problematic. The assumption that the four symptoms were O3-related was not unreasonable, given findings from controlled human exposure in environmental chambers (Folinsbee et al. 1988, 1994). However, those symptoms are not specific for O3 exposure. No data are provided on the specific symptoms, and the basic data analysis is weak. The use of Pearson correlations probably is not justified, given the distributional characteristics of the symptom data (binomial). Other analytic strategies, such as logistic regression, would have been more appropriate and could have been used to evaluate symptom response in relation to O3, relative humidity, smoking, and preflight medical conditions. Moreover, that there were so few measurements of independent O3 and relative humidity gave the study relatively little precision in estimating health effects related to O3. A survey of symptoms among 185 cabin-crew members of an Asian airline was carried out from September 1996 to March 1997 (Lee et al. 2000). The number of crew members eligible to participate and the method of flight selection are not provided, although the authors state that the survey was “compulsory.” Various mucosal, respiratory and nonspecific symptoms (e.g., headache and faintness) were evaluated. Air quality (carbon dioxide, relative humidity, temperature, noise level, PM10, and carbon monoxide [CO]) was monitored on all flights on which questionnaires were distributed. The monitoring instruments were placed in the center of the economy class, but the details

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The Airliner Cabin Environment and the Health of Passengers and Crew of the monitoring protocol are not provided. Flights were 1.5–18 h long, and smoking was permitted. The results are presented in terms of acceptability ratings of various components of air quality and health symptoms; no formal analysis plan is provided. Table 6–4 summarizes the reported symptoms. Over 50% of the crew members reported at least one symptom of skin or mucosal irritation during the flight. No data are reported on any of the following: the relationship between monitoring data and reports of symptoms or ratings of air-quality acceptability, the presence of and relationship between preflight symptoms and symptoms experienced during flight, the relationship between flight duration and symptoms, and the relationship between the amount of smoking on each flight and the reports of symptoms. A survey of passenger comfort and cabin air quality on standard and wide-body aircraft with and without recirculated air was carried out by an aircraft manufacturer (Rankin et al. 2000). A series of health-related questions were included in the survey. Self-administered questionnaires were completed by 3,630 passengers (43% of 8,517 distributed) on 71 flights in March, April, and June 1997. Of the questionnaires completed, 57% were from flights of 2–3 h, 32% from flights of 6–7 h, and 11 % from flights of 10–12 h. The contribution of the flight to the presence of symptoms was rated on a scale of 1 (great extent) to 7 (not at all). Figure 6–1 summarizes the data. Overall health before the flight (no data given on responses and on the format of the variable) was most closely correlated with overall health during the flight (R=0.80; type of correlation coefficient not specified). A regression analysis showed that only TABLE 6–4 Frequency of Symptoms Reported by Cabin Crew Symptoms None to Mild, % Moderate to Severe, % Dry, stuffy nose 26 74 Irritation, dryness, itchiness in eyes 36 64 Dry, sore throat 41 59 Dry, irritated skin 43 57 Stomach discomfort (indigestion, gas) 57 43 Ear problems 66 34 Dizziness, faintness, lightheadedness 67 33 Headache 68 32 Nausea, motion sickness 71 29 Shortness of breath 73 27   Source: Adapted from Lee et al. (2000).

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The Airliner Cabin Environment and the Health of Passengers and Crew Cabin Air Pressure and Health Risks Current standards permit pressurization of the cabins of commercial aircraft up to an equivalent altitude of 2,450 m (about 8,000 ft) under normal operating conditions (FAR 25.841). The health concerns associated with current cabin pressurization are reviewed in Chapter 5. The 1986 NRC report summarized the effects of altitude on partial pressure of oxygen (PO2) and recommended that passengers with heart, lung, and middle ear diseases be educated about the potential risks of flight. However, that 1986 committee had few direct data on the oxygen (O2) saturation that might be expected in passengers and cabin crew under normal conditions of modern commercial airline flight. Cottrell and colleagues (1995) used continuous-reading pulse oximeters to measure O2 saturation in 38 pilots on 21 flights about 4 h long. Maximal and minimal O2 saturations were 95–99% (mean, 97%) and 80–93% (mean, 88.6% ±2.9%), respectively. Of the subjects, 53% developed an O2 saturation of less than 90% at some time during the flight (duration below 90% was not given). Schwartz et al. (1984) studied subjects with severe chronic obstructive pulmonary disease (COPD) (average resting arterial PO2, 68.0±7.3 mm Hg) during flights at altitudes of 1,650–2,250 m (about 5,400 to 7,400 ft) in unpressurized aircraft cabins. PO2 decreased to an average of 51.0±9.1 mm Hg at an altitude of 1,650 m and little further change at 2,250 m. Several simulation studies have been carried out in hypobaric chambers with COPD patients and healthy subjects (Dillard et al. 1989; Naughton et al. 1995). Declines in PO2 were observed in all patients at rest; it fell to below 50 mm Hg in many subjects and was made worse by light exercise. Of 100 COPD patients, 44 reported traveling by air in the 2 yr before the interview (Dillard et al. 1991). Eight of the patients reported increased symptoms during flight (no direct physiological measurements were available); five of these patients experienced shortness of breath when walking in the cabin, and two requested supplemental O2 for their symptoms. As part of a study for British Airways, Building Research Establishment Ltd. examined the effects of cabin air pressure on O2 saturation in cabin crew (Ross 2001). Saturation in cabin crew of Boeing 777s and 747s was measured with a pulse oximeter. Cabin pressure was measured hourly during flights, and oximetry readings in cabin crews were “instantaneous spot measurements.” On each of 16 flights, 10–15 crew members were studied. Cabin altitudes were 1,585–2,286 m (5,200–7,500 ft). Symptom questionnaires were distrib-

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The Airliner Cabin Environment and the Health of Passengers and Crew uted. Ross (2001) reported that O2 saturations of 90% or less occurred in 16 of the subjects (maximal number of crew was 240, but the exact number sampled not given) and often were followed or preceded by readings above 90%. This study, as presented, is of little value for several reasons: The collection method for the oximetry data is not adequate. Spot measurements are not useful unless related specifically to the cabin altitude in the aircraft and the activities of the crew when the measurement is made. No quality-control criteria are given to ensure that the recorded readings represent a stable measurement over some prespecified number of heart-beats. In fact, the data on subjects who had at least one saturation value of 90% or less suggest that no such criteria were applied; that is, the readings were preceded or followed by much higher readings. The data are presented as average 1-h values, apparently representing the averaging of data on several people over a given period in that only spot measurements were made for each crew member. No data are presented on the relationship between saturation and cabin altitude during various flight segments or during various work activities of the crew. Those data gaps preclude an assessment of the relationship between cabin altitude and O2 saturation in crew members during the course of the flights. Under ordinary conditions of commercial flight, it is clear that reductions in PO2 to the point of hypoxia can take place at rest or in situations of minimal exertion. As discussed in Chapter 5, PO2 levels are such that reduced arterial O2 content could pose a definite health risk for persons with underlying pulmonary or cardiac disease or untreated or partially treated anemia. OTHER SOURCES OF HEALTH EFFECTS INFORMATION A considerable amount of material was submitted to the committee in support of health effects related to incidents of smoke, fumes, and unusual odors in the cabins of commercial aircraft both in association with and independent of known or suspected episodes of leaks of hydraulic fluid, engine oil, or other sources of contaminants in the cabin. Those materials consisted primarily of testimony and summaries of unpublished data. Three examples are presented here as typical of the data presented.

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The Airliner Cabin Environment and the Health of Passengers and Crew The Australian Senate Rural and Regional Affairs and Transport Committee (1999, 2000) conducted an inquiry into reported cabin air quality and health-related consequences related to incidents of engine oil leaks that involved British Airways BAe 146 aircraft. The Senate committee summarized testimony on symptoms related to oil fumes in aircraft cabin air, the “aerotoxic syndrome.” The report (Australian Senate 2000) cited testimony that questioned the specificity of this symptom complex and the fact that such nonspecific symptoms “are present at any one time in 10 percent of the population.” The report also highlighted other testimony that questioned the validity of claims of chronic symptoms related to acute exposures to products of engine oil leaks and fumes. In relation to health effects, the Australian Senate (2000) concluded the following: It appears to the Committee that contamination of cabin aircraft air on the BAe 146 aircraft has led to short-term and medium-term health problems…. Some scientists link these health problems to contaminants, although the link has not yet been definitively established…. This remains a question to be further investigated and assessed. The Committee is also convinced that there is sufficient evidence before this inquiry to justify further examination of the following factors: the effects on human health of the introduction into the aircraft cabin…of engine oil, by-products of engine oil combustion and other compounds as a result of leaking seals and bearings; and the cumulative physical effect of exposure to these substances which can affect particular individuals. However, the Australian Senate went on to recommend that “aerotoxic syndrome” be included “in appropriate codes as a matter of reference for future Workers Compensation and other insurance cases,” although this appeared to contradict its summary of the evidence. Two sets of unpublished data illustrate the difficulty with the data used to link specific symptoms to putative incident exposures in aircraft cabin air. The first set of unpublished data provided a review of the evidence of health effects related to cabin air incidents (C.Witkowski, Association of Flight Attendants, unpublished data, January 24, 1999), including all incidents reported in relation to a particular airline with a focus on the MD-80 aircraft. Flight reports, insurance claims, OSHA reports, medical records, and mechanical reports were evaluated. The criteria for the selection of specific reports were not provided. An air-quality incident was defined as “a specific mechanical

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The Airliner Cabin Environment and the Health of Passengers and Crew problem resulting in smoke, mist, odors, fumes or smells, or those incidents where there was a complaint made regarding symptoms experienced by flight attendants or passengers.” The results of the review are presented in Table 6–6. Although an association between reports of various symptoms and incidents on flights is inferred, few data are provided in terms of the persons at risk, the percentage who reported symptoms, or the temporal pattern of onset and recovery. Moreover, no data are provided on similar symptoms reported on flights during which no odors were detected and no observable conditions occurred or on the health status of those affected. It is not possible to distinguish symptoms reported by passengers and those reported by flight attendants. The second set of unpublished data centered on a case study of a flight attendant with acute and chronic symptoms that occurred in relation to a presumed leak of hydraulic fluid (“hydraulic pressure light illuminated in flight”) (Wright and Clarke 1999). Details of a variety of neurological symptoms over a 6-mo period are reported and related, by analogy, to those which might be expected in connection with exposure to toxic concentrations of organophosphates—specifically organophosphate-induced delayed neuropathy (see Chapter 5 for more information on this toxic effect). No specific exposure data are provided. The criteria for selection and the representativeness of this single anecdote are impossible to determine. Allegedly, the “entire crew” were ill, and passengers reported nausea and vomiting (the number at risk and the percentage with symptoms were not provided). CURRENT HEALTH-RELATED DATA COLLECTION SYSTEMS The federal government maintains several databases that are potentially relevant to the identification of health-related problems associated with cabin air; a database summary is available at the Federal Aviation Administration (FAA) web site (http://intraweb.nasdac.faa.gov/learn_about/dat_learn.asp). Several databases of particular relevance are reviewed below. FAA Accident/Incident Data System (AIDS): Collects descriptive data on incidents (e.g., fumes, smoke, and odors) that do not meet aircraft-damage or personal-injury thresholds for the National Transportation Safety Board definition of an accident. Includes steps taken for remediation. Data are available on 1978 to the present. No health-related data are provided.

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The Airliner Cabin Environment and the Health of Passengers and Crew TABLE 6–6 Summary of 760a Incidents Reported by the Association of Flight Attendants Source of Incident Reports Passenger report of symptoms (9.9%) Flight-attendant report of symptoms (64.7%) Reports of observable conditions, such as smoke and mist fumes in cabin (25.4%) Reported Incidence of Episodes for Airline 7.6 incidents per 10,000 flights for airline under consideration from July 1989 to August 1998 Character of Odor Reported in Incidents with Observed Conditions (data from 83% of incidents): Unusual (29%),b burning (18.6%), sweet (12.9%), nail polish (9.3%), toxic (7.7%), dirty socks (5.1%), 17.6% of incidents identified as hydraulic fluid or oil Symptom Reports (based on 925 flight attendants involved in 760 incidents)c 97.2% of incidents involved reports of disorientation, confusion, “spacey,” euphoria for incidents with smoke or haze Landing: difficulty in breathing, coughing, irritation of eyes, throat, and lungs Mid-flight: headaches, disorientation, giddiness, difficulty in concentrating, nausea, vomiting Ground and takeoff: same as for mid-flight aSee text for definition of “incident.” bNumber of fight attendants and/or passengers involved not given. Not clear whether percentage refers to proportion of people or events. cReports prepared by 492 people. Specific percentages and number of persons involved for each symptom for various flight segments not provided. Source: C.Witkowski, Association of Flight Attendants, unpublished data, January 24, 1999. FAA Service Difficulty Reporting System (SDRS): Repository of Service Difficulty Reports, Malfunction and Defect Reports, and Maintenance Difficulty Reports. Data are available on 1986 to the present. No health-related data are provided. Aviation Safety Reporting System (ASRS): Voluntary confidential incident reporting system administered by National Aeronautics and Space Administration (NASA). Has narrative descriptions of the conditions of an incident and any health-related information that the people who filed the reports chose to provide. The data summaries do not indicate any systematic data recording structure. ASRS data are anonymous and confidential and

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The Airliner Cabin Environment and the Health of Passengers and Crew therefore are not useful for retrospective assessments of health effects of reported incidents. Moreover, because the data are reported as unstructured narratives, they are not particularly useful even when linked to more specific information about incidents in the AIDS and SDRS databases. Finally, given that reporting to ASRS is voluntary, the database is not useful as a numerator to estimate what fraction of incidents reported to the other databases are associated with reports of adverse health outcomes. Data are available on 1988 to the present. No information was available to the committee on the details of operation of incident reporting systems or maintenance record reporting systems for any commercial airline. AFA has distributed a standard event reporting form to its members as part of its Safety and Health Database Initiative (AFA 2001). The form is intended to be completed primarily by cabin crew, but may also be completed by passengers, pilots, or mechanics in response to a perceived air-quality incident, including required pesticide spraying on international flights. Form submission to the database (which will eventually be available on line) is voluntary. It is not designed to obtain nonincident data (“baseline” symptom frequency under ordinary operating conditions of flight) against which incident-related symptoms could be evaluated, but rather will function to provide AFA with a tabulation of problems reported by its members. The listing of health-related symptoms sometimes requires that the person completing the form make what amounts to a diagnosis (e.g., “allergic reaction,” “ear inflammation…/damage,” “infectious agent”), which is a less than optimal way to collect such data. On the basis of the little information available to the committee, this data system is not intended to and will not remedy the need for more systematic data on health-related symptoms under nonincident conditions. Moreover, the system does not have a built-in systematic sampling strategy to ensure comprehensive assessment of health effects on crew and passengers under incident-related conditions (J Murawski, AFA, personal communication, 2001). CONCLUSIONS None of the current systems for reporting signs and symptoms that could reflect health-related responses to aircraft cabin air quality are standardized with regard to how potentially affected individuals are surveyed. There is also a lack of standardization with respect to how specific data are obtained.

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The Airliner Cabin Environment and the Health of Passengers and Crew Of the relevant databases maintained by the federal government, only the NASA ASRS has health-related data as a focus. Although acute health effects potentially stem from incidents involving exposure to engines oil, hydraulic fluids, and their pyrolysis products, the existing database is inadequate to ascertain adequately any of the following in relation to documented incidents: the frequency of individual symptoms or constellations of symptoms, the characteristics of the cabin crew and passengers who might be at greatest risk from these exposures, and the long-term sequelae of single high-exposure incidents or recurrent low-level exposure. With respect to repeated exposure of cabin crew to cabin air during routine conditions of flight (nonincidents) and in the absence of smoking, the situation is even more difficult to assess, inasmuch as there are very few valid systematic surveys. The data that are available are insufficient to quantify the risk posed by cabin air-quality conditions with regard to acute symptoms or chronic sequelae. Data on exposure of passengers and related health effects are so sparse that further comment is not warranted. Data that have become available since the 1986 NRC report raise questions about the safety of current regulations related to cabin pressure, especially in light of the increased number of older and younger people flying, including children, infants, and adults with cardiovascular or pulmonary disease. RECOMMENDATIONS Because the committee concludes that there is insufficient evidence to warrant designation of a specific syndrome related to exposure to leaks of engine oil or hydraulic fluids, the committee recommends that the term aerotoxic syndrome not be used for symptoms associated with incidents of cabin air contamination. Current regulations for cabin pressure should be reviewed to determine whether they are adequate for protecting people who might be unusually susceptible to changes in air pressure, such as the elderly, infants, children, and people with cardiovascular or pulmonary disease. Consideration should be given to whether air pressure regulations can be adjusted and to what management options are available to deal with potential problems (e.g., equipping some seats with supplemental oxygen). FAA and the airlines should work with

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The Airliner Cabin Environment and the Health of Passengers and Crew medical organizations, such as the American Medical Association and the Aerospace Medical Association, to improve health professionals’ awareness of the need to advise patients of the risks that might be posed by flying. Current systems for the collection of health data in relation to cabin air quality are woefully inadequate and do not permit any quantitative assessment of the relationship between cabin exposure and potential health effects on cabin crew or passengers. A program for the systematic collection, analysis, and reporting of health data in relation to cabin air quality needs to be implemented to resolve many of the issues raised in this report. REFERENCES AFA (Association of Flight Attendants). 2001. AFA Aircraft Air Quality Reporting Form. Association of Flight Attendants Safety and Health Initiative. Amler, R.W., A.B.Bloch, W.A.Orenstein, K.J.Bart, P.M.Turner Jr, and A.R.Hinman. 1982. Imported measles in the United States. JAMA 248(17):2129–2133. ASHRAE/CSS (American Society of Heating Refrigerating and Air-conditioning Engineers and/Consolidated Safety Services). 1999. Relate Air Quality and Other Factors to Symptoms Reported by Passengers and Crew on Commercial Transport Category Aircraft. Final Report. ASHRAE Research Project 957-RP. Results of Cooperative Research Between the American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc., and Consolidated Services, Inc. February 1999. Australian Senate. 1999. Air Safety-BAe 146 Air Quality. The Proof and Official Hansard transcripts of Senate Rural and Regional Affairs and Transport References Committee, Commonwealth of Australia Senate, Canberra, Australia. November 1, 1999. Australian Senate. 2000. Air Safety and Cabin Air Quality in the BAe 146 Aircraft. Report by the Senate Rural and Regional Affairs and Transport References Committee, Parliament House, Parliament of the Commonwealth of Australia, Canberra. October 2000. Balouet, J.C. 1998. In-Cabin Trace Chemicals and Crew Health Issues. Presentation at Annual Meeting of the Aerospace Medical Association, Seattle, WA, May 20, 1998. Balouet, J.C., and C.Winder. 1999. Aerotoxic syndrome in air crew as a result of exposure to airborne contaminants in aircraft. American Society of Testing and Materials Symposium on Air Quality and Comfort in Airliner Cabins, New Orleans, October 27–28, 1999. Balouet, J.C., and C.Winder. 2000a. Airborne Chemicals in Aircraft Cabins. Presentation to Aerospace Medical Association. Air Transport Medicine Symposium, Houston, May 7, 2000.

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