September 19, 2019

NIOSH Finds Overexposures to Carbon Monoxide, Noise, Other Hazards among Wildland Firefighters

A NIOSH evaluation of health hazards encountered by firefighters for a state-based wildland fire management program found overexposures to carbon monoxide, noise, wood dust, and vibration during “fuel reduction” activities such as thinning trees and removing underbrush. The evaluation, which was recently made available on the NIOSH website (PDF), involved confidential medical interviews conducted on two occasions in 2015 and a follow-up visit in 2016 during which NIOSH personnel evaluated work tasks and administered a questionnaire covering work history.

The fuel reduction activities evaluated by NIOSH included tasks performed by sawyers, who use gasoline-powered handheld chainsaws to cut trees, and “swampers,” who help sawyers by clearing brush, limbs, and smaller trees. The National Park Service considers these tasks to be effective in protecting developed areas against wildfires by removing fuels so that a wildfire can be more easily contained and suppressed.

Personal air sampling results for carbon monoxide were below full-shift occupational exposure limits, but NIOSH found brief, intermittent exposures that exceeded the agency’s ceiling limit of 200 ppm. The maximum length of these exposures was 25 seconds.

Six of nine air sampling results for wood dust, which NIOSH considers a potential carcinogen, were above the NIOSH recommended exposure limit and the ACGIH threshold limit value of 1.0 mg/m3. As with carbon monoxide, exposures to wood dust varied with wind speed and direction.

For noise, exposures to five workers over two days of monitoring exceeded the NIOSH REL and the OSHA action level of 85 dBA over an eight-hour work shift. Sound levels for swampers, who were working in the vicinity of chainsaws, were similar to those of sawyers. One sawyer experienced a short-term exposure of 110 dBA. Workers who were operating or working near wood chippers had short-duration noise exposures of around 100 dBA. Of the 42 firefighters who had a baseline audiogram, nine exhibited a hearing threshold shift as defined by NIOSH. The agency defines a threshold shift as an increase in the hearing threshold level of at least 15 dB relative to the baseline audiogram.

NIOSH personnel measured vibration for two sawyers using four different chainsaw models. Estimates based on these measurements indicated that the sawyers would exceed daily limit values for vibration after a few hours of use, based on limits published in ANSI S2.70, American National Standard Guide for the Measurement and Evaluation of Human Exposure to Vibration Transmitted to the Hand. Seventy-three percent of firefighters who participated in the medical evaluations reported symptoms that could be consistent with hand-arm vibration syndrome, or HAVS.

NIOSH made several recommendations to address overexposures, including regular sharpening of chainsaws, adjusting work schedules so that sawyers’ daily vibration exposures remain below the ANSI limit values, requiring double hearing protection for firefighters operating the wood chipper, and requiring N95 filtering facepiece respirators for fuel reduction activities until wood dust exposures can be reduced.