From Fire Season to Fire Year

the Synergist

DEPARTMENTS

Protecting Wildland Firefighters in an Extreme Environment

BY TIM REINHARDT, KATHLEEN NAVARRO DUBOSE, AND JOSEPH DOMITROVICH

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Pictured above: Rice Ridge Fire, 2017 (left) and Redmond Interagency Hotshot on the Cow Fire, 2019 (right). Photos by Kathleen DuBose.

Editor's note: A slideshow farther down this page contains additional wildfire images that did not appear in the print version of this article. Readers can click or tap the arrows on either side of the slideshow to move to the previous or next photo.

Wildfires are a natural part of the ecosystem in the United States, but in many areas, our cumulative risk management choices over the last century have contributed to crisis conditions that make fires more severe and far-reaching. Where we are unprepared, wildfires threaten communities, destroy neighborhoods, expose the public and workers to smoke for extended periods, and cause unnecessary loss of life. On the front lines of wildfire response are wildland firefighters (WFFs), who do arduous work under difficult conditions, frequently in remote locations.

ABOUT THE JOB WFFs are typically employed by federal or state agencies, Tribal governments, or wildland fire contract companies. They conduct diverse tasks to suppress wildfires, including operating fire engines and portable pumps, constructing firelines intended to slow or stop fires’ spread, holding firelines against fires, engaging in mop-up operations to extinguish smoldering hot spots after areas are burned, and executing firing operations that remove unburned vegetative fuels from the path of fires to stop further expansion. These tasks fall to different classifications of crews or groups of WFFs.

Engine crews, which typically comprise three to seven firefighters, manage diesel-powered pumps on a fire engine, supplying water to crews operating in the fire vicinity. The engine crew is often first on the scene in areas accessible by improved or unimproved roads. For fires in rough or inaccessible terrain, the first resources to arrive may be aerially deployed firefighters such as smokejumpers, who parachute from planes, or helitack crew members, who rappel from or are delivered by helicopters. Hand crews operating in groups of 20 perform work as a unit and may hike many miles from roads in steep terrain to reach their fire deployment locations. Hand crews also perform work on more accessible sites with support from engine crews. Firefighting resources are logistically supported by incident command posts (ICPs) that provide food, supplies, latrines and showers, and outdoor sleeping locations for hundreds to thousands of personnel per fire. But in situations where it would take too much time to return to an ICP, WFFs may stay overnight in remote conditions on the firelines or at “spike camps” in spartan conditions, sometimes surviving on prepackaged rations for days.

Fireline construction requires creating a break in the contiguous vegetation to halt the spread of the fire by removing combustible biomass “fuel” from its path. When feasible—for example, in grasslands or gentle terrain with road access—this task is mechanized and performed using bulldozers or tractor-plows to scrape all vegetation from a wide path to encircle the “head” of the fire, which refers to the part that is spreading most quickly, often with great intensity. In steeper terrain with timbered or brushy areas, fireline construction falls to firefighters with hand tools to clear the vegetation, first with chainsaws and then with shovels and specialized hand tools like Pulaskis to dig and scrape down to mineral soil. As the fire approaches, firefighters work to hold the fireline, which means keeping the active fire within the designated boundaries by extinguishing spot fires and incursions with shovels and soil, water from backpack sprayers, and fire hoses, when available.

After the fire, crews perform mop-up activities by extinguishing remaining hot spots through digging out smoldering woody debris and mixing in mineral soil, or by water application to reduce the chances of the fire reemerging. Fire operations may also entail deliberately setting fires to remove flammable vegetation in the path of a fire. For this task, WFFs commonly use drip torches that deliver a mixture of diesel and unleaded gasoline.

WFFs also work on “beneficial fires,” including prescribed burning and cultural burning, as described in a 2023 report from the Wildland Fire Mitigation and Management Commission (PDF). Beneficial fires also include wildfires managed for resource benefit, where community wildfire risk reduction or ecological restoration are among the intended positive outcomes.

HAZARDS AND RISKS WFFs face many risks and hazards, including slips, trips, and falls; falling trees, rocks, and debris; heat-related illnesses and injuries; injuries related to vehicle and aircraft accidents; and exposure to smoke, dust, and ash. Exposure to exhaust from vehicles, water pumps, and generators is an additional concern. And when fires race across the landscape, WFFs may become trapped and face a “burnover,” which refers to situations in which firefighters are unable to escape to safety and must use emergency shelters to attempt to survive as the flames pass through their location.

Natural wildland fire smoke is a mixture of gas and particulate-phase air contaminants, including carbon monoxide (CO), volatile organic compounds (VOCs) such as formaldehyde and acrolein, polycyclic aromatic hydrocarbons (PAHs), and ultrafine to respirable particulate matter (PM), which can contain amorphous carbon or soot. (Further discussion of wildland fire smoke composition can be found in a review article published in 2016 in Inhalation Toxicology. The article is listed as a resource below.) According to a NIOSH Science Blog post on wildland firefighter health, factors such as vegetation type, fire behavior, and meteorological conditions can affect the contents of wildfire smoke, which in turn affects firefighters’ exposures. Smoke particulate matter has also been shown to vary in composition depending on burning conditions and can be quite toxic (see research published in 2018 in Environmental Health Perspectives). Past exposure assessments focused on wildland fire smoke have documented concentrations over occupational exposure limits for CO; PM4, or respirable particulate matter with a mass median aerodynamic diameter of four micrometers; and the irritant mixture of the aldehydes acrolein and formaldehyde. Along with smoke exposure on the firelines, WFFs may be exposed to smoke from nearby fires at ICPs while off duty.

Burning vegetation is the best-characterized exposure concern from wildland fires, but NIOSH notes that compounds similar to those produced during structure fires may also be found in the smoke from fires that occur in the wildland-urban interface, or WUI. The consensus study report “The Chemistry of Fires at the Wildland-Urban Interface” from the National Academies of Sciences, Engineering, and Medicine describes the WUI as “the area where structures and other human development meet undeveloped wildland or vegetation fuels.” Vehicles and structures found in the WUI contain a variety of plastics and human-made organic materials. WFFs suppressing WUI fires may be exposed via smoke to additional compounds including VOCs, derivatives from flame retardants, a suite of low- to higher-molecular-weight chlorinated and brominated species of flame retardants, and PAHs more hazardous than those typically found in wildland fire smoke. Composition of smoke from WUI fires represents a critical knowledge gap that deserves further applied research by the industrial hygiene community.

Wildfire in Idaho. Photo by Brett Story.

In addition to smoke, WFFs work in ash and dry soils, causing exposure to soil-borne hazards. The main concern with this exposure is respirable crystalline silica (RCS), concentrations of which were shown to exceed permissible exposure limits fairly frequently through research described in an article published in the Journal of Occupational and Environmental Hygiene (JOEH) in 2019. Literature published in 2023 in Nature Communications identified an additional hazard—hexavalent chromium, or Cr(VI)—in the ash in wildfire-burnt areas. Based on the reported Cr(VI) concentrations and dust exposures measured during wildfires, exposure to Cr(VI) poses a minor risk among all the hazards faced by WFFs. However, soil-derived hazards present additional concerns in areas with naturally occurring asbestiform minerals. And in regions where the fungi Coccidioides immitis or Coccidioides posadasii are endemic, industrial hygienists and others should protect WFFs from coccidiomycosis, or Valley Fever, a disease caused by the inhalation of fungal spores. Valley Fever concerns exist regardless of whether a fire has occurred in areas where WFFs must disturb soil for fireline construction and fire management.

Finally, noise-induced hearing loss is another documented hazard among those operating and working near chainsaws as well as WFFs operating wildland fire engines and portable gas-powered water pumps, which are commonly deployed to support fireline and mop-up operations at both wildfires and prescribed burns. An article published in 2017 in the Journal of the Acoustical Society of America contains further discussion of noise exposure among federal WFFs.

HEALTH EFFECTS So far, health assessments of wildland firefighters have typically focused on acute effects during work shifts or an entire fire season. These studies, including the previously mentioned Inhalation Toxicology article from 2016, revealed significant declines in lung function and increased airway responsiveness. Other studies examining biomarkers of effects—such as one on working in smoke published in Clinics in Chest Medicine in 2020—reported systemic inflammatory and oxidative stress responses in firefighters. A risk assessment published in 2019 in Environmental Research estimated increased risks of lung cancer mortality (8 to 43 percent) and cardiovascular disease (16 to 30 percent) for WFFs across various exposure scenarios and career durations.

Few studies have measured health effects over multiple fire seasons. For this reason, NIOSH partnered with the U.S. Forest Service and National Park Service to measure exposure to smoke and acute, sub-chronic, and chronic health outcomes for six wildland fire crews across two fire seasons. Researchers assessed WFFs’ cardiovascular health, pulmonary function and inflammation, kidney function, workplace exposures, and noise-induced hearing loss by collecting self-reported risk factors and symptoms through questionnaires, taking measurements from serum and urine, and conducting audiometric testing. Results are forthcoming and are expected to contribute to the evidence regarding occupational risk factors and exposures that can impact WFF health as well as guide future research on the wildland fire community. Further information on this study is available from the Northern Rockies Fire Science Network and from the Annals of Work Exposures and Health.

Then, in 2022, the International Agency for Research on Cancer conducted a review of existing scientific literature and determined that there was sufficient evidence to classify occupational exposure as a firefighter as carcinogenic to humans. While the agency’s working group did not distinguish between structural and wildland firefighter exposures in relation to cancer risk, numerous studies providing mechanistic evidence of carcinogenicity focused on WFFs who showed heightened levels of inflammation and oxidative stress.

The landscape of wildfires is changing: WFFs and the larger responder workforce are experiencing fires of increasing scale, complexity, and severity, and fire seasons are lengthening, turning into “fire years.” Assessing exposures and health effects in the wildfire environment is logistically difficult due to the extreme work conditions, remote locations, and the high variability of exposure conditions in the fire environment. These challenges also affect industrial hygienists’ approach to controlling exposures and protecting workers responding to wildfires.

CONTROLLING EXPOSURES IN AN EXTREME ENVIRONMENT Inhalation hazards are just one of many risks and hazards to control in the wildland fire environment. The approach to mitigating exposures will depend on fire behavior, available resources and personnel, operational objectives, and the prioritization of inhalation and physical agent exposures in the context of all identified risks. Current recommendations include establishing mop-up criteria to allow WFFs to secure their area based on fire behavior, fuels, and topography rather than a specified distance from containment lines; rotating fire personnel in areas of high unavoidable smoke exposure (which may still result in high acute exposures); using air resource advisors to monitor and address smoke concerns at ICPs; and locating ICPs and remote camps in areas that are not prone to smoke exposure. Outreach and education to promote better understanding of exposure risks and health hazards from wildland firefighting are also recommended. Although some training and discussion on the inhalation hazards of smoke is available, there is little focus on RCS from dust, despite existing data showing an even higher hazard index than that from smoke components (see “Factors Affecting Smoke and Crystalline Silica Exposure among Wildland Firefighters” in JOEH). More work is needed to understand WFF exposures (especially to RCS), develop and implement administrative controls, and assess the effectiveness of exposure controls. Lack of Respiratory Protection There is currently no respirator available for WFFs that meets the National Fire Protection Association’s standard for respiratory protection for WFF personnel (NFPA 1984), is certified by NIOSH, will provide protection for all inhalation hazards, and is able to be worn in the extremes of the wildfire environment. Although NFPA 1984 has been available since 2011, to date no manufacturer has submitted a respirator to NIOSH for certification. (Please note that NFPA is working to consolidate standards, and the new edition of NFPA 1984 will be called NFPA 1985.) Wildland fire agencies have recommendations for administrative controls, but respiratory protection is a needed option for this dynamic and changing environment that now frequently includes the WUI. To help address this issue, the Department of Homeland Security (DHS) is supporting the development of a wildland firefighter respirator device. According to the operational field assessment report published in December 2022 by DHS (PDF), this device is a powered air-purifying respirator (PAPR) designed for wildland firefighting operations that is intended to protect firefighters from both gas and particulate respiratory hazards as well as “withstand extreme environmental conditions associated with wildland firefighting operations.” The PAPR is also meant to be easy to use, lightweight, and low-profile for long-duty shifts in remote locations. Past exposure assessments indicate that WFFs do not usually need respirators for their full shifts, but when they do (approximately one to 30 percent of all shifts), they need protection against RCS and soil-borne particulate matter hazards as well as ultrafine vegetative fire smoke particles and gases (mainly CO and aldehydes, plus the typically lesser hazards of sulfur dioxide, SO2, and nitrogen oxides, NOx). These hazards prompt the need for an end-of-service-life indicator for at least CO or a well-planned cartridge change schedule. Another aspect to consider is whether WFFs should use full-face or half-mask respirators. Acrolein and formaldehyde irritate mucous membranes, as do SO2 and NOx. But protecting the eyes against these hazards introduces added heat stress and fogging issues. We believe the cardiovascular impact of air-purifying respirators is surmountable but needs further research in this already stressed workforce. One example of a groundbreaking effort to bring respirators to WFFs is currently underway at the California Division of Occupational Safety and Health. Cal/OSHA is developing a standard it says will “protect firefighters from inhalation exposures during WUI/wildland deployments.” The standard, Respiratory Protection for Wildland Firefighter and Wildland Urban Interface Operations, draws from NFPA 1984 and includes requirements for administrative and engineering controls as well as respiratory protection to prevent or significantly reduce harmful inhalation exposures. Although none are currently available on the market, the standard requires the use of NIOSH-approved, full-face, Class 3 PAPRs certified under NFPA 1984. This is an evolving effort that will likely inform future efforts to develop respiratory protection programs for WFFs once a respirator becomes available that is both NIOSH-approved and certified under NFPA 1984. Proper implementation of a respiratory protection program for all WFFs will require cultural change and substantial commitment to funding, oversight, and logistical support. No OEL for Smoke Controlling exposures in this dynamic environment is complicated by the lack of an OEL for smoke. Comparing exposures to an OEL is an important component of industrial hygiene practice when developing and implementing control strategies. Most exposure assessments of WFFs have focused on measuring CO; fine particulate matter, or PM2.5; and PM4 (for example, see the 2020 study in Clinics in Chest Medicine listed in the resources section). The PELs set by OSHA are 50 ppm for CO and 5 mg/m3 measured as the respirable fraction for particulates not otherwise regulated (PNOR), which applies to PM4. However, particulate matter from wildfire smoke is a complex mixture and is not analogous to PNOR. An article published in JOEH in 2019 makes the case that OSHA’s PNOR PEL is insufficient for wildland fire smoke due to its toxicity and carcinogenic potential. The states of Oregon, Washington, and California have promulgated wildfire smoke standards for outdoor workers that are based on public health studies. Washington’s regulation specifically states, “Given the diverse array of adverse health effects caused by PM2.5 exposure from wildfire smoke, this regulatory threshold [for PNOR] is not appropriate to address the hazard caused by particulate pollution from wildfire smoke.” The National Wildfire Coordinating Group has recommended exposure limits for CO (16 ppm) and PM4 (0.7 mg/m3) that are more conservative than the OSHA PELs and account for workplace factors such as long work shifts and the chemical mixture of smoke. But since there is no robust regular exposure monitoring, these limits are not being used to control exposures administratively. One option to improve administrative control compliance would be to utilize some combination of CO and PM4 real-time dosimetry, as CO has been shown in studies to be correlated with most products of incomplete combustion in wildland fire smoke. Future of Wildfires and WFF Health Dramatically increasing the use of beneficial fire will be critical in restoring natural processes for fire-adapted ecosystems, protecting communities, and reducing the risk of severe wildfires. With this comes an urgent need to expand and care for the workers who will be exposed as they suppress wildfires and conduct prescribed burning to return beneficial fire to fire-adapted lands. Significant legislative direction that recognizes the need to address the mental and physical health of WFFs was passed recently under the Infrastructure Investment and Jobs Act, also known as the Bipartisan Infrastructure Law (BIL), and the National Defense Authorization Act (NDAA) for fiscal year 2023. The BIL directs the Department of the Interior (DOI) and the U.S. Forest Service to establish mental health programs and develop and adhere to recommendations for mitigation strategies to minimize WFFs’ exposure to line-of-duty environmental hazards. The FY 2023 NDAA “established that certain illnesses and diseases are to be deemed to be proximately caused by employment in federal fire protection activities,” as explained on the Department of Labor’s (DOL) website. This includes certain types of cancers, heart disease, and lung disease. The FY 2023 NDAA also calls for DOI and the Department of Agriculture, in consultation with DOL and NIOSH, to study the long-term health effects experienced by federal WFFs who are exposed to fires, smoke, and toxic fumes on the job. Although this legislative direction represents a monumental effort to improve the health and well-being of WFFs, IH solutions are needed to overcome the challenges presented here and experienced by WFFs in this extreme and dynamic work environment. TIM REINHARDT, MS, CIH, is a vice president environmental scientist with WSP USA Environment & Infrastructure and has worked in fire emissions characterization and lead exposure assessments among wildland firefighters for several decades. Reinhardt worked two summers as a wildland firefighter with the U.S. Forest Service. KATHLEEN NAVARRO DUBOSE, PhD, MPH, is the Wildland Firefighter Health and Wellbeing Program coordinator for the Department of the Interior, Office of Wildland Fire. DuBose has worked in this area both as an industrial hygienist and as a wildland firefighter. JOSEPH DOMITROVICH, PhD, is a supervisory program manager for the Forest Service National Technology and Development Program. Domitrovich’s work has focused on heat stress, smoke exposure, and the physiological demands of PPE. He has also worked as an operational wildland firefighter and is now a member of an incident management team. Send feedback to The Synergist.

RESOURCES

Annals of Work Exposures and Health: “The Wildland Firefighter Exposure and Health Effect (WFFEHE) Study: Rationale, Design, and Methods of a Repeated-Measures Study” (2022).

Clinics in Chest Medicine: “Working in Smoke: Wildfire Impacts on the Health of Firefighters and Outdoor Workers and Mitigation Strategies” (2020).

Environmental Health Perspectives: “Mutagenicity and Lung Toxicity of Smoldering vs. Flaming Emissions from Various Biomass Fuels: Implications for Health Effects from Wildland Fires” (2018).

Environmental Research: “Wildland Firefighter Smoke Exposure and Risk of Lung Cancer and Cardiovascular Disease Mortality” (2019).

Inhalation Toxicology: “Review of the Health Effects of Wildland Fire Smoke on Wildland Firefighters and the Public” (2016).

International Agency for Research on Cancer: “Occupational Exposure as a Firefighter” (2023).

Journal of Occupational and Environmental Hygiene: “Factors Affecting Smoke and Crystalline Silica Exposure among Wildland Firefighters” (2019).

Journal of the Acoustical Society of America: “Noise Exposure among Federal Wildland Fire Fighters” (2017).

National Academies of Sciences, Engineering, and Medicine: “The Chemistry of Fires at the Wildland-Urban Interface” (2022).

National Wildfire Coordinating Group.

Nature Communications: “Metal Toxin Threat in Wildland Fires Determined by Geology and Fire Severity” (2023).

NIOSH Science Blog: “Wildland Firefighter Health: Some Burning Questions” (2020).

Northern Rockies Fire Science Network: “The Wildland Firefighter Exposure and Health Effect (WFFEHE) Study.”

U.S. Department of Agriculture: “On Fire: The Report of the Wildland Fire Mitigation and Management Commission” (PDF, 2023).

U.S. Department of Homeland Security: “Wildland Firefighter Respirator Device: Operational Field Assessment Report” (PDF, 2022).

U.S. Department of Labor: “Information Related to Federal Firefighter Claims.”