Personal PM(2.5) 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 PM(2.5) and 149 individual person-day CO samples were collected; during non-burn activities, 37 person-day PM(2.5) 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 PM(2.5) ranged from 5.9-2673 μg/m(3) on burn days. Geometric mean PM(2.5) exposure was 280 μg/m(3) (95% CL = 140, 557 μg/m(3), n = 177) for burn day samples, and 16 μg/m(3) (95% CL = 10, 26 μg/m(3), n = 35) on non-burn days. Average measured PM(2.5) differed across levels of the firefighters' categorical self-assessments of exposure (p < 0.0001): none to very little = 120 μg/m(3) (95% CL = 71, 203 μg/m(3)) and high to very high = 664 μg/m(3) (95% CL = 373, 1185 μg/m(3)); p < 0.0001 on burn days). Time-weighted average PM(2.5) and personal CO averaged over the run times of PM(2.5) 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/m(3) for respirable particulate matter in a few extreme situations. Self-assessed exposure levels agreed with measured concentrations of PM(2.5). Correlation analysis shows that either PM(2.5) or CO could be used as a surrogate measure of exposure to woodsmoke at prescribed burns.