Researchers find prescribed fire smoke to be less harmful than that from wildfires

Therefore, prescribed fires to protect communities can protect residents in more ways than one

Wolf Trap National park prescribed fire
Prescribed fire at Wolf Trap National Park, April, 2018. NPS photo by Nathan King.

Researchers studying the effects of smoke on children found prescribed fire smoke to be less harmful than smoke from wildfires. The Stanford University study looked at three groups of children:

  • Those who were exposed to smoke from a prescribed fire;
  • Children exposed to smoke from a wildfire in which no structures burned; and,
  • Children that were not exposed to smoke.

Sometimes fire personnel refer to a prescribed fire as “good fire”. Now they may call smoke from a planned burn as “good smoke”. A way to look at this research is that removing hazardous fuels near a community is a way to reduce the threat of a wildfire spreading into the town and burning structures or entrapping and killing people. And, removing the fuels with good fire rather than allowing a wildfire to burn the same area, exposes residents to less harmful smoke. For fire-prone areas, it is not IF it burns, it’s WHEN. Do you want your smoke now under controlled conditions or later, possibly under extreme conditions?

From Stanford University:

…The study was published May 30 in the European Journal of Allergy and Clinical Immunology. It was conducted in Fresno, California, a city with high air pollution levels due to its topography and other sources, including traffic and agriculture.

“This study suggests that exposure to wildfire smoke is detrimental above and beyond poor air quality,” said the lead author, Mary Prunicki, MD, PhD, an instructor of medicine.

The study’s senior author is Kari Nadeau, MD, PhD, professor of medicine and of pediatrics and director of the Sean N. Parker Center for Allergy & Asthma Research at Stanford.

Native Americans traditionally used controlled burns to manage California’s forests, but throughout the early 20thcentury, wildfires were widely suppressed. This began to change in the 1960s and 1970s, when scientists recognized fire as a normal part of forest ecology. Recent wildfires have brought more attention to the possible benefits of prescribed burns as a way to reduce fuel levels and wildfire risk, but not everyone is enthusiastic.

Opposition to controlled burns
“We know that there’s some public opposition to doing prescribed burning,” Prunicki said. “It’s our feeling that prescribed burning, because it’s so controlled, may expose people to fewer health effects than wildfires.” Prescribed burns are of lower intensity and are permitted only when weather conditions allow the fire to be contained.

In the study, the researchers compared blood samples from three groups of children, all of whom were 7 or 8 years old. One group of 32 children had been exposed to smoke from a 553-acre prescribed burn that occurred in March 2015; a second group of 36 children had been exposed to smoke from a 415-acre wildfire in September 2015. Both fires were about 70 miles away from Fresno, and blood samples were collected from the children within three months of each fire.

The study also included blood samples from a control group of 18 children who lived in the San Francisco Bay Area and had not been exposed to wildfire or prescribed-burn smoke.

The researchers measured air pollution levels recorded at four monitoring stations in Fresno and estimated pollution levels at the children’s homes during the fires based on how far they lived from the stations.

Pollutant exposures were higher in the wildfire group compared to the prescribed-burn group.  The air pollutants measured included nitrogen dioxide, polycyclic aromatic hydrocarbons, elemental carbon, carbon monoxide and particulate matter.

Wildfire smoke exposure was associated with lower blood levels of type-1 T helper cells, a group of immune cells that are involved in the immune response. Among children exposed to wildfire smoke, the researchers also saw increased methylation of the Foxp3 gene, indicating reduced activity of this gene, which is broadly involved in modulating allergic and other immune responses. The finding of greater Foxp3 methylation is congruent with earlier studies of the effects of air pollution on the immune system, Prunicki noted.

Significance of particulate matter
One important aspect of the study was that the September 2015 wildfire was confined to forested areas and did not burn any structures.

“Particulate matter from wildfires is different from region to region and depends on what is burning,” Prunicki said. “When a wildfire is going through a town, there are a lot of concerns about what happens to the chemicals in people’s homes and cars when they go up in flames.” Smoke from wildfires that burn inhabited areas almost certainly has worse health effects than those found in the current study, she said.

The researchers plan to conduct larger, more detailed studies of the effects of wildfire smoke on health. They will be enrolling healthy people in a trial at Stanford later this summer to collect baseline data from blood samples. When future wildfires affect Bay Area air quality, the participants will be asked to provide follow-up blood samples.

The scientists also plan to research the health effects of using home air purifiers during wildfires, as well as measure the protection offered by N95 masks, with the aim of developing recommendations for when masks should be used by different populations, such as healthy adults, elderly people, children and people with chronic illnesses.

The study’s other Stanford co-authors are biostatistician Justin Lee; life science researcher Xiaoying Zhou, PhD; Francois Haddad, MD, clinical associate professor of medicine; and Joseph Wu, MD, PhD, professor of medicine and of radiology.

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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.

14 thoughts on “Researchers find prescribed fire smoke to be less harmful than that from wildfires”

  1. Is there a way to get the title of the article? Guessing its free to read but a title would at least give us the chance to track it down. Thanks!

  2. The EPA long ago stated that there is no safe level of smoke. Any type can have huge health impacts. Sometimes prescribed burn fires and smoke continue for weeks or months at a time. Remember, children’s lungs are still developing. Damaging them has lifelong consequences.

    It should be noted that, following research done by the Pacific Northwest National Laboratory, the opening paragraph of a 2009 news release states, “…The results from the new study also suggest that smoldering fires may produce more toxins than wildfires — a reason to keep human exposures to a minimum during controlled burns.”

  3. prescribed fires ARE needed, but the smoke and flames are not harmless…. just ask any career firefighter

    1. I am with bobby george on this one. WAY more study is needed before anyone can make that conclusion.
      As the career firefighters know, it is all about the fuel type being burned and how much is consumed.
      Byram’s Intensity Formula does not care if the grass fire was lit by a drip torch or a lightning strike. If the burning conditions are equal, a “combustion event” will produce the same smoke regardless of the ignition source.

  4. You have misquoted the study findings. This is dangerous and misleading.
    Smoke is always injurious to health. Please do not compare these two types of Fire events unless always saying that smoke is dangerous. This is propaganda.
    Repeating that First people’s used fire is like saying European colonizers kept salves. Just because it was done in the past does not convey any special virtue to it. Some historical comparisons are not helpful or useful in modern contexts.

    1. Can you give me a specific example of a misquote of the study findings? Since you obviously read the original study.

      Comparing the relative health impacts of smoke from different fire events is perfectly reasonable information. Nowhere does it say that smoke isn’t harmful, just that it appears to be “less” harmful — data points that would useful for decision makers.

      The early use of fire by native peoples wasn’t a point about health effects, it was a point about historic context of using fire to manage fuels and plant communities — a realization that has taken some time to come back into favor following a period of all out war against all fire and the negative impacts that had.

      There is always risk — health and safety risks from using fire and from not using fire. We tried not using and fire and while that works in the short-term, the long-term ecosystem changes increase the severity of the eventual return of fire to those systems and the people living nearby.

      1. Cy, you are right. The study was not misquoted. Ms. Bibb has commented multiple times on this site about what she sees as the evils of prescribed fire.

        1. The study is not mis-quoted, but the study is limited and the exposure assessment of smoke is flawed. The researchers only used one prescribed fire and one wildfire as points of comparison. Both fires were located quite a long distance from Fresno. In previous, case studies of smoke in the Sierras, we see that the smoke is generally transported to the eastern Sierra and down the Kern River drainage, not into Fresno. Additionally, Sept. 2015 wildfire exposure the researchers use was at the same time as the Rough Fire ~150,000 acres (not mentioned in the study) in Sequoia and Sierra NF.

      2. Sorry to take so long to respond. I object to calling any smoke “good smoke”. There is no “good smoke”.
        The authors were not suggesting that smoke is good. It’s just not as bad as wildfire smoke.
        Yes, I am opposed to lighting fires especially since some of these fires go rogue and some kill people. Already 85%+ fires are human-caused. More fire is not necessarily good.
        The fire-industrial complex would suggest that more fire is good. We just need to be aware that although we suppressed fires in the past starting fires also has consequences, both good and bad. Our forests now are predominately second, third growth monocultures. Our climate is different. The number of people causing fires has increased.


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