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Personal PM2.5 Exposure Among Wildland Firefighters Working at Prescribed Forest Burns in Southeastern United States

This study investigated occupational exposure to wood and vegetative smoke in a group of 28 forest firefighters at prescribed forest burns in a southeastern U.S. forest during the winters of 2003–2005. During burn activities, 203 individual person-day PM2.5 and 149 individual person-day CO samples were collected; during non-burn activities, 37 person-day PM2.5 samples were collected as controls. Time-activity diaries and post-work shift questionnaires were administered to identify factors influencing smoke exposure and to determine how accurately the firefighters’ qualitative assessment estimated their personal level of smoke exposure with discrete responses: “none” or “very little,” “low,” “moderate,” “high,” and “very high.” An average of 6.7 firefighters were monitored per burn, with samples collected on 30 burn days and 7 non-burn days. Size of burn plots ranged from 1–2745 acres (avg = 687.8). Duration of work shift ranged from 6.8–19.4 hr (avg = 10.3 hr) on burn days. Concentration of PM2.5 ranged from 5.9–2673 μg/m3 on burn days. Geometric mean PM2.5 exposure was 280 μg/m3 (95% CL = 140, 557 μg/m3, n = 177) for burn day samples, and 16 μg/m3 (95% CL = 10, 26 μg/m3, n = 35) on non-burn days. Average measured PM2.5 differed across levels of the firefighters’ categorical self-assessments of exposure (p < 0.0001): none to very little = 120 μg/m3 (95% CL = 71, 203 μg/m3) and high to very high = 664 μg/m3 (95% CL = 373, 1185 μg/m3); p < 0.0001 on burn days). Time-weighted average PM2.5 and personal CO averaged over the run times of PM2.5 pumps were correlated (correlation coefficient estimate, r = 0.79; CLs: 0.72, 0.85). Overall occupational exposures to particulate matter were low, but results indicate that exposure could exceed the ACGIH®-recommended threshold limit value of 3 mg/m3 for respirable particulate matter in a few extreme situations. Self-assessed exposure levels agreed with measured concentrations of PM2.5. Correlation analysis shows that either PM2.5 or CO could be used as a surrogate measure of exposure to woodsmoke at prescribed burns.