Firefighting is classified as a human carcinogen

We asked scientists how to apply the findings to firefighters in the wild

Crew from Minnesota
A Minnesota crew tours the King Fire east of Placerville, California in 2014. Incident management team photo.

The International Agency for Research on Cancer (IARC), the cancer agency of the World Health Organization (WHO), has evaluated the possibility of developing cancer as a result of occupational exposure as a firefighter.

The IARC Monographs Program convened a working group of 25 international experts, including 3 invited specialists from 8 countries, for a meeting in Lyon, France.

After a thorough review of the available scientific literature, sufficient evidence led the working group to. Occupational exposure as a firefighter is classified as a human carcinogen.

A summary of the final evaluations has now been published. Detailed evaluation will be published in Oncology Lancet in 2023 as volume 132 of IARC Monographs.

Evidence for cancer in humans
The study found that occupational exposure as a firefighter causes cancer. There has been insufficient evidence of carcinogenicity in humans in relation to mesothelioma and bladder cancer.

There has been limited evidence of cancer in humans for the following types of cancer: colon cancer, prostate cancer, testicular cancer, melanoma, and non-Hodgkin’s lymphoma.

Strong mechanical guides
The assessment of automated evidence was based on exposures associated with combat structure and wildland fires. There has been strong mechanistic evidence in exposed humans that occupational exposure as a firefighter exhibits 5 of the 10 main characteristics of carcinogens: “genotoxic,” “inducing epigenetic changes,” “inducing oxidative stress,” “inducing chronic inflammation,” and “modulating future mediated effects.

firefighter exposure
Firefighters are exposed to a complex mixture of combustion products from fires (such as PAHs, VOCs, metals and particulates), diesel exhaust, building materials (such as asbestos) and other hazards (such as heat stress, shift work, UV rays, etc.). Additionally, the use of flame retardants in textiles and persistent organic pollutants (such as perfluorinated and polyfluorinated substances) in firefighting foams has increased over time.

This mixture may include many agents already classified by IARC Monographs into Group 1 (possibly carcinogenic to humans), Group 2A (possibly carcinogenic to humans), and Group 2B (possibly carcinogenic to humans). Dermal exposure, inhalation, and ingestion are common routes of exposure, and biomarker studies among firefighters have found improved levels of exposure markers for PAHs, flame retardants, and POPs.

Most firefighter health studies evaluate structural firefighters. We asked Dr. Kenny Vint and Dr. Kathleen Navarro of the National Institute for Occupational Safety and Health (NIOSH) questions about how these findings might apply to wildland firefighters. Here is their common response:

Summary of the IARC assessment of wildland firefighters
The International Agency for Research on Cancer (IARC) assessment of occupational exposure as a firefighter included a review of the available scientific literature on occupational exposure, cancer epidemiology and key characteristics of carcinogens. The evaluation did not differentiate between construction firefighters and prairie firefighters in determining carcinogenicity. This is because the working group was unable to differentiate structural fire exposures (and other exposures) from wildfire exposures for firefighters in at least some of the cancer cohort studies that were included in the assessment.

In addition, many of the studies that provided evidence of carcinogenicity included assessment of the main characteristics of carcinogens (intermediate health outcomes on the cancer pathway). These included studies of prairie firefighters working on wildfires and prescribed fires.

Finally, the exposure studies reviewed supported that construction and wildland firefighters were exposed to similar types of carcinogens. As a result, the definition of “occupational exposure as a firefighter” was kept to the IARC as broad-based and included a variety of hazards from fires (for example, fires of structures, land and vehicles) and other events (for example, vehicular accidents, medical accidents, and fires Hazardous materials, building collapses).

Is mesothelioma caused solely by exposure to asbestos, and are prairie firefighters generally exposed to it?
Yes, mesothelioma is caused by exposure to asbestos. Exposure to asbestos is generally rare among wildfirefighters, with the exception of wildfirefighters who typically encounter built environments (particularly buildings constructed prior to the 1970s), contaminated areas (eg Libby, MT) or natural asbestos. A previous NIOSH health risk assessment reported that exposure to total asbestos fibers in air was below the lowest occupational exposure limits during the prescribed incineration procedure. However, the highest concentrations measured were during tasks involving greater plant and soil disturbance and where no water is used (eg, setting up fire lines and dry mopping).

Dr. Kenny Vint leads the National Register of Firefighters at NIOSH and was chair of the exposure characterization subgroup of the IARC working group.

Dr. Kathleen Navarro leads the Wildland Firefighter Safety and Health Program at NIOSH and was a representative of the National Health Agency for IARC Assessment.

author: Bill Jaber

After working full-time in prairie fires for 33 years, he continues to learn, striving to be a student of fire. View all posts by Bill Gabert

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