When wildfires spread through neighborhoods, they burn all kinds of materials in cars and houses and everything around them—electronics, paint, plastic, furniture.
Research shows that the mix of chemicals released when man-made materials such as these are burned is different than that released during a plant fire and is potentially more toxic. Smoke and ash can blow under doors and around windows in nearby homes, carrying chemicals that are absorbed into furniture, walls and other interior surfaces and continue to be released for weeks to months.
As people return to their smoke-damaged homes after a wildfire, there are a few steps they can take to protect their health before they start cleaning up.
Elevated levels of metals and VOCs
In 2021, after the Marshall Fire swept through neighborhoods near Boulder, Colorado, my colleagues and I at Colorado Universities and Laboratories heard from many residents who were concerned about ash and lingering odors in their homes that had otherwise survived the flames. .
In homes that my colleagues were able to quickly test, they found elevated levels of metals and PAHs—polycyclic aromatic hydrocarbons—in the ash. We also found elevated VOCs – volatile organic compounds – in the air samples. Some volatile organic compounds, such as dioxins, benzene, formaldehyde and PAHs, can be toxic to humans. Benzene is a known carcinogen.
At that time, we were unable to find information on the physical health effects of people who returned to smoke-damaged homes after a wildfire. So to look for patterns, we surveyed residents affected by the fire six months, one year, and two years after the fire.
Even six months after the fire, we found that many people were reporting symptoms consistent with the health risks associated with fire smoke and ash.
More than half (55%) reported experiencing at least one symptom six months after the fire that they attributed to the Marshall Fire. The most common symptoms reported were itchy or watery eyes (33%), headache (30%), dry cough (27%), sneezing (26%) and sore throat (23%).
All of these symptoms, as well as the presence of a strange taste in the mouth, are associated with people reporting that their home smells different when they return to it a week after the fire.
Many respondents said that odors diminish over time. Most attribute the improvement in odor to the passage of time, cleaning surfaces and ducts, replacing furnace filters, and removing carpets, textiles, and furniture from the home. However, many of them still had symptoms.
We also found that living near a large number of burned structures was associated with these health symptoms. We found that for every 10 additional destroyed buildings within 820 feet (250 meters) of a person’s home, there was an associated 21 percent increase in headaches and a 26 percent increase in bad taste in the mouth.
These symptoms are consistent with what might be expected from exposure to the chemicals we found in the ash and measured in the air in the few smoke-damaged homes we were able to study in depth.
Persistent symptoms and questions
There are still many unanswered questions about the health risks of smoke and ash damaged homes.
For example, we don’t yet know what the long-term health effects might look like for people living with lingering wildfire smoke and ash gases in the home. We found a significant drop in the number of people reporting symptoms one year after the fire. However, 33% percent of people whose homes were affected and responded to a later survey still reported at least one symptom they attributed to the fire. About the same percentage also reported at least one symptom two years after the fire.
We also could not measure the level of VOCs or metals to which each person was exposed. But we believe that reports of a change in odor in a person’s home one week after the fire indicate the likely presence of VOCs in the home. This likely has health implications for people whose homes are exposed to wildfire smoke or ash.
Tips for protecting yourself after wildfires
Wildfires are increasingly burning homes and other structures as more people move into the wilderness-urban fringes, temperatures rise and fire seasons lengthen.
If your home experiences a nearby bushfire, here are some steps to think about before you start cleaning up:
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When you’re ready to clean your home, start by protecting yourself. Wear at least an N95 (or KN95) mask and gloves, goggles, and clothing that covers your skin. Cleaning can send some of these gases and ash back into the air.
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Keep people with heart or lung disease, the elderly, pregnant women, children and pets away from cleaning activities.
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Vacuum floors, curtains and furniture. A recent scientific study documents how cleaning all surfaces in the home can reduce VOC reservoirs and reduce indoor VOC concentrations. After the air outside has cleared, open the windows to let in fresh air.
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Avoid harsh chemical cleaners because they can react with the chemicals in the ash.
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Clean your HVAC filter and ducts to avoid further spreading of ash, and replace the filters monthly until the odor disappears. Portable air purifiers with carbon filters can help remove VOCs and particulate matter.
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If your car smells like smoke, consider replacing the cabin air filter.
This is an update to an article first published on December 23, 2024.
This article has been republished by The Conversation, an independent not-for-profit news organization that brings you facts and reliable analysis to help you make sense of our complex world. Written by: Colleen E. Reid, University of Colorado Boulder
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Colleen E. Reid receives research funding from the US EPA, NSF, and NIH, and has received funding in the past from the CDC, the Health Effects Institute, the JPB Foundation, and the Robert Wood Johnson Foundation.