Personal PM_2.5 Exposure Among Wildland Firefighters Working at Prescribed Forest Burns in Southeastern United States

Abstract

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/m³ on burn days. Geometric mean PM_2.5 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 PM_2.5 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 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/m³ 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.

Keywords:

• exposure
• firefighters
• particulate matter
• prescribed burn
• wildland
• woodsmoke

ACKNOWLEDGMENTS

We acknowledge the support of John Blake, Dan Shea, Jason Demas, Mark Frizzel, Paul Linse, and Jeff Prevey of the United States Forest Service and David Macintosh of the Environmental Resource Management Inc., Needham, Massachusetts. Funding was provided by the Department of Energy–Savannah River Operations Office through the U.S. Forest Service Savannah River under Interagency Agreement DE-AI09-00SR22188.

The findings and conclusions in this article are those of the author(s) and do not necessarily represent the views of the Centers for Disease Control and Prevention (CDC). Mention of company names or products does not constitute endorsement by the CDC.