Firefighting classified as carcinogenic to humans

We asked scientists how the findings apply to wildland firefighters

crew from Minnesota
A crew from Minnesota mopping up on 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 carcinogenicity of occupational exposure as a firefighter.

A Working Group of 25 international experts, including 3 Invited Specialists from 8 countries was convened by the IARC Monographs program for a meeting in Lyon, France.

After thoroughly reviewing the available scientific literature, sufficient evidence led the Working Group to classify occupational exposure as a firefighter as carcinogenic to humans.

A summary of the final evaluations has now been published. The detailed assessment will be published in The Lancet Oncology in 2023 as Volume 132 of the IARC Monographs.

Evidence for cancer in humans 
The study found that occupational exposure as a firefighter causes cancer. There was sufficient evidence for cancer in humans for mesothelioma and bladder cancer.

There was limited evidence for cancer in humans for the following cancer types: colon cancer, prostate cancer, testicular cancer, melanoma of the skin, and non-Hodgkin lymphoma.

Strong mechanistic evidence 
The evaluation of the mechanistic evidence was based on exposures associated with fighting structure and wildland fires. There was strong mechanistic evidence in exposed humans that occupational exposure as a firefighter exhibits 5 of the 10 key characteristics of carcinogens: “is genotoxic”, “induces epigenetic alterations”, “induces oxidative stress”, “induces chronic inflammation”, and “modulates receptor-mediated effects”.

Exposure of firefighters
Firefighters are exposed to a complex mixture of combustion products from fires (e.g. polycyclic aromatic hydrocarbons, volatile organic compounds, metals, and particulates), diesel exhaust, building materials (e.g. asbestos), and other hazards (e.g. heat stress, shift work, and ultraviolet and other radiation). In addition, the use of flame retardants in textiles and of persistent organic pollutants (e.g. per- and polyfluorinated substances) in firefighting foams has increased over time.

This mixture may include many agents already classified by the IARC Monographs program in Group 1 (carcinogenic to humans), Group 2A (probably 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 enhanced levels of markers of exposure to polycyclic aromatic hydrocarbons, flame retardants, and persistent organic pollutants.

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

Summary of IARC Evaluation for Wildland Firefighters
The IARC evaluation of Occupational Exposure as a Firefighter included a review of the available scientific literature on occupational exposures, cancer epidemiology and the key characteristics of carcinogens. The evaluation did not differentiate between structural and wildland firefighters in making the determination of carcinogenicity. This is because the working group was not able to differentiate structure fire exposures (and other exposures) from wildfire exposures for firefighters in at least some of the cancer cohort studies that were included the evaluation.

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

Lastly, the exposure studies reviewed supported that both structural and wildland firefighters were exposed to similar types of carcinogens. As a result, the definition of “occupational exposure as a firefighter” for the IARC evaluation was kept broad and included a variety of hazards resulting from fires (e.g., structure, wildland, and vehicle fires) and other events (e.g., vehicle accidents, medical incidents, hazardous material releases, and building collapses).

Is mesothelioma only caused by exposure to asbestos, and are wildland firefighters generally exposed to it?
Yes, mesothelioma is caused by exposure to asbestos. Asbestos exposure is generally rare among wildland firefighters, with the exception for wildland firefighters who commonly encounter built environments (especially buildings constructed before the 1970s), areas with contamination (e.g., Libby, MT) or naturally occurring asbestos. A past NIOSH Health Hazard Evaluation reported that exposure to total asbestos fibers in air were less than the lowest occupational exposure limits while conducting a prescribed burn. However, the highest concentrations measured were during tasks with greater plant and soil disturbance and where water was not used (e.g., fire line construction and dry mop-up).

Dr. Kenny Fent leads the National Firefighter Registry at NIOSH and was the chair of the exposure characterization subgroup for the IARC working group.

Dr. Kathleen Navarro leads the Wildland Firefighter Safety and Health program at NIOSH and was a Representative of a national health agency for the IARC evaluation.

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Author: Bill Gabbert

After working full time in wildland fire for 33 years, he continues to learn, and strives to be a Student of Fire.

13 thoughts on “Firefighting classified as carcinogenic to humans”

  1. If I’m reading some of these comments correctly. there are folks out there that know as much about the health hazards of smoke as research scientists and MD’s, have known it for a long time, and yet took the jobs as wildland firefighters and continued doing it? Am I missing something? The nice thing about beating your head against a wall is that it feels so good when you stop.

  2. Smoke is carcinogenic from all sources. There are many who do not want to either acknowledge or publicize this simple fact.

  3. I’m not knocking MD’s or PHD’s. This data has been languishing in files for years and was ignored. Over 30 years ago we in Cal Fire could fill out an incident data card documenting our exposures to various hazards such as smoke, bodily fluids, chemicals, etc. . In the “Fire” portion of the card we could document various types of fires including vegetation/wildland. We then mailed the card into the Union were the info was entered into our individual record. Once a year we received a printout of the data we had sent in the year before. For many years that data was ignored by various levels of management for whatever reason. If there are questions as to why it was ignored follow the money trail

  4. Wouldn’t be so hard on the MD’s or PhD’s here, it’s pretty obvious stuff but turns out you need to provide evidence of cause or nobody is sending your or your spouse anything but condolences. Glad someone looked into it..

    1. Responsible actions by the LMAs prior to this coming out would have been to employ/ contract MD and PhDs loonng ago as SMEs. Rather, Congress and the public probably needed to be harder on responsible agencies who failed or thought they had medical SMEs on staff….which in reality is more than a Safety Officer or two and a handbook..

      Time for some changes…but change is hard

  5. This confirms what we’ve all known for a long time. Wildland firefighters are clearly included in the findings.

  6. Hmmm!!!!
    That explains why I’m down to one kidney.
    I didn’t need someone with a MD, or PHD behind there name to figure that out either.

  7. Shaaaazzzaammm!!!

    We’re just now coming to this explanation?

    No one needs to wonder why the wildland fireline personnel is so sarcastic or develops it in and around year 5

    Who’d a thunk that?

    You mean since about 1903 and Gifford Pinochet, we’re just learning about this?

    Wow…. $%×!&% SCIENCE!!!

  8. 20 years forced to accept prescribed fire smoke as part of the job. “Suck it up buttercup, it’s harmless unless your the public”. As a burnboss (ifpm requirement) working for line, tell the same lie to make others breathe it in. Meanwhile I send out media releases to close your windows or leave your home it’s bad for you. “Wildfire smoke is unmanageable, prescribed is on our terms and ok to breathe ”. Paid hotel stays for public to be out of the smoke at their homes when we sucked it down. Job corp get in there! Stipend for the work I did, however I need to triple the output to save lives and property. But the more smoke I make kills more honest folks and isn’t worth the compensation to my wife. Well shit… what to do?


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