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


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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