Wildland firefighter smoke exposure and risk of lung cancer and cardiovascular disease mortality.

Wildland firefighters are exposed to wood smoke, which contains hazardous air pollutants, by suppressing thousands of wildfires across the U. S. each year. We estimated the relative risk of lung cancer and cardiovascular disease mortality from existing PM2.5 exposure-response relationships using measured PM4 concentrations from smoke and breathing rates from wildland firefighter field studies across different exposure scenarios. To estimate the relative risk of lung cancer (LC) and cardiovascular disease (CVD) mortality from exposure to PM2.5 from smoke, we used an existing exposure-response (ER) relationship. We estimated the daily dose of wildfire smoke PM2.5 from measured concentrations of PM4, estimated wildland firefighter breathing rates, daily shift duration (hours per day) and frequency of exposure (fire days per year and career duration). Firefighters who worked 49 days per year were exposed to a daily dose of PM4 that ranged from 0.15 mg to 0.74 mg for a 5- and 25-year career, respectively. The daily dose for firefighters working 98 days per year of PM4 ranged from 0.30 mg to 1.49 mg. Across all exposure scenarios (49 and 98 fire days per year) and career durations (5-25 years), we estimated that wildland firefighters were at an increased risk of LC (8 percent to 43 percent) and CVD (16 percent to 30 percent) mortality. This unique approach assessed long term health risks for wildland firefighters and demonstrated that wildland firefighters have an increased risk of lung cancer and cardiovascular disease mortality.

Factors affecting smoke and crystalline silica exposure among wildland firefighters.

Smoke exposure data among U.S. wildland firefighters for carbon monoxide, respirable particulate and respirable crystalline silica are presented from a field surveillance program between 2009 and 2012. Models to predict fireline-average exposure to each inhalation hazard were developed and fit to the available data. The models identify factors to consider when defining similar exposure groups and designing future data collection. Task-based rather than shift-average data collection is important because the work activity representing the majority of fireline time, the position up- or downwind of the fire, and the proportion of time this combination represented were significant factors in the model for carbon monoxide, and all but wind position were significant for respirable particulate matter. The wind position versus the fire was not important for respirable quartz exposure. The crew type was an important factor in each model.

Review of the health effects of wildland fire smoke on wildland firefighters and the public.

Each year, the general public and wildland firefighters in the US are exposed to smoke from wildland fires. As part of an effort to characterize health risks of breathing this smoke, a review of the literature was conducted using five major databases, including PubMed and MEDLINE Web of Knowledge, to identify smoke components that present the highest hazard potential, the mechanisms of toxicity, review epidemiological studies for health effects and identify the current gap in knowledge on the health impacts of wildland fire smoke exposure. Respiratory events measured in time series studies as incidences of disease-caused mortality, hospital admissions, emergency room visits and symptoms in asthma and chronic obstructive pulmonary disease patients are the health effects that are most commonly associated with community level exposure to wildland fire smoke. A few recent studies have also determined associations between acute wildland fire smoke exposure and cardiovascular health end-points. These cardiopulmonary effects were mostly observed in association with ambient air concentrations of fine particulate matter (PM2.5). However, research on the health effects of this mixture is currently limited. The health effects of acute exposures beyond susceptible populations and the effects of chronic exposures experienced by the wildland firefighter are largely unknown. Longitudinal studies of wildland firefighters during and/or after the firefighting career could help elucidate some of the unknown health impacts of cumulative exposure to wildland fire smoke, establish occupational exposure limits and help determine the types of exposure controls that may be applicable to the occupation.

Baseline measurements of smoke exposure among wildland firefighters.

Extensive measurements of smoke exposure among wildland firefighters are summarized, showing that firefighters can be exposed to significant levels of carbon monoxide and respiratory irritants, including formaldehyde, acrolein, and respirable particulate matter. Benzene was also measured and found to be well below permissible exposure limits, with the highest concentrations occurring among firefighters working with engines and torches burning petroleum-based fuel. Exposures to all pollutants were higher among firefighters at prescribed burns than at wildfires, while shift-average smoke exposures were lowest among firefighters who performed initial attack of wildfires in the early stages of the fires. Smoke exposure reaches its highest levels among firefighters maintaining fire within designated firelines and performing direct attack of spot fires that cross firelines. These events and the associated smoke exposures were positively correlated with increasing ambient wind speeds, which hamper fire management and carry the convective plume of the fire into firefighters' breathing zone. The pollutants measured in smoke were reasonably well-correlated with each other, enabling estimation of exposure to multiple pollutants in smoke from measurements of a single pollutant such as carbon monoxide.

Association between lung function and exposure to smoke among firefighters at prescribed burns.

We investigated the short-term effects of exposures to PM3.5, acrolein, formaldehyde, and carbon monoxide on lung function in a group of firefighters performing prescribed burns. Spirometric measurements were made on 65 firefighters at the beginning, midpoint, and end of their work shift, while exposure was measured over the entire day. The interquartile range (IQR) of daily personal PM3.5 exposures was 235 micrograms/m3 to 1317 micrograms/m3, with an average daily exposure of 882 micrograms/m3. Concentrations of acrolein (IQR: [0.002, 0.018] ppm), formaldehyde (IQR: [0.008, 0.085] ppm), and carbon monoxide (IQR: [2.10, 10.48] ppm) were similarly elevated. In this group of firefighters, FEV1 changed by -0.125 L from preshift to postshift (p < .001). We examined the association between this cross-shift lung function decrement and smoke exposure. A 1000 micrograms/m3 increase in PM3.5 was associated with a -0.030 L change in the cross-shift FEV1 (95% CI [-0.087, 0.026]). Acrolein, formaldehyde, and carbon monoxide exposure were also not significantly associated with changes in FEV1, FVC, or FEF25-75. We concluded that while firefighters' lung function significantly decreased from preshift to postshift, firefighters exposed to greater concentrations of respiratory irritants did not experience greater lung function decrements. We could not establish a significant link to any of the individual toxic components of smoke we measured.

A screening-level assessment of the health risks of chronic smoke exposure for wildland firefighters.

A screening health risk assessment was performed to assess the upper-bound risks of cancer and noncancer adverse health effects among wildland firefighters performing wildfire suppression and prescribed burn management. Of the hundreds of chemicals in wildland fire smoke, we identified 15 substances of potential concern from the standpoints of concentration and toxicology; these included aldehydes, polycyclic aromatic hydrocarbons, carbon monoxide, benzene, and respirable particulate matter. Data defining daily exposures to smoke at prescribed burns and wildfires, potential days of exposure in a year, and career lengths were used to estimate average and reasonable maximum career inhalation exposures to these substances. Of the 15 substances in smoke that were evaluated, only benzene and formaldehyde posed a cancer risk greater than 1 per million, while only acrolein and respirable particulate matter exposures resulted in hazard indices greater than 1.0. The estimated upper-bound cancer risks ranged from 1.4 to 220 excess cancers per million, and noncancer hazard indices ranged from 9 to 360, depending on the exposure group. These values only indicate the likelihood of adverse health effects, not whether they will or will not occur. The risk assessment process narrows the field of substances that deserve further assessment, and the hazards identified by risk assessment generally agree with those identified as a concern in occupational exposure assessments.