Smoke from home fires can pose health risks that last for months – tips for cleaning and staying secure

As fires spread through neighborhoods, they burn all kinds of materials found in cars and homes and everything around them – electronics, paint, plastics, furniture.

Research shows that the mixture chemicals released the combustion of such man-made materials is different from the combustion emitted during a vegetation fire and is potentially more toxic. Smoke and ash can billow under the doors and around windows of nearby homes, introducing chemicals that soak into furniture, walls and other interior surfaces and off-gas for weeks or months.

As people return to smoke-damaged homes after a fire, they exist some steps they can take to protect your health before cleaning.

Increased levels of metals and VOCs

In 2021, as the Marshall Fire swept through neighborhoods near Boulder, Colorado, my colleagues and I at Colorado universities and labs heard from many residents who were concerned about ash and lingering odors in their homes that would otherwise endure flames.

In homes that my colleagues could quickly test, they discovered increased levels of metals and PAHs – polycyclic aromatic hydrocarbons – in the ash. We also found increased concentrations of VOCs – volatile organic compounds – in airborne samples. Some VOCs, e.g dioxins, benzene, formaldehyde AND PAHsmay be toxic to humans. There is benzene known carcinogen.

At that time, we found no information about the physical health consequences of people who returned to smoke-damaged homes after the fire. So, looking for patterns, we surveyed residents affected by the fire six months, one year and two years after the fire.

We found it even six months after the fire many people reported symptoms which are consistent with the health risks associated with smoke and ash from wildfires.

More than half (55%) reported experiencing at least one symptom six months after the fire, which they attributed to the Marshall Fire. The most common symptoms reported were itchy or watery eyes (33%), headache (30%), arid cough (27%), sneezing (26%), and sore throat (23%).

All of these symptoms, as well as a strange taste in the mouth, were associated with people reporting that their home smelled different when they returned a week after the fire.

Many survey respondents said odors fade over time. Most attributed the improved odor to the passage of time, cleaning surfaces and air ducts, replacing furnace filters, and removing carpets, textiles, and furniture from the home. Despite this, many people still had symptoms.

We also found that living near a enormous number of burned buildings was associated with these health symptoms. We found that for every 10 additional buildings destroyed within 250 meters of a person’s home, there was a 21% boost in headaches and a 26% boost in a strange taste in the mouth.

These symptoms are consistent with what can be expected from exposure to chemicals we found in the ash and measured in the air in several smoke-damaged homes that we were able to examine in depth.

Persistent symptoms and questions

There are still many unanswered questions about the health risks of homes damaged by smoke and ash.

For example, we don’t yet know what the long-term health consequences might be for people living with home gases caused by fire smoke and ash. We found significant decrease in the number of people reporting symptoms one year after the fire. However, 33% of people whose homes were damaged and who responded to a subsequent 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 levels of VOCs or metals to which each person was exposed. However, we believe that reports of a change in odor in an individual’s home one week after the fire indicate the likely presence of VOCs in the home. This likely has consequences for the health of people whose homes are exposed to smoke or ash from the fire.

Tips on how to protect yourself after wildfires

There are fires houses and other structures burning more and more often as more people move to the intersection of wild and urban areas, temperatures are rising and the fire season is getting longer.

If your home survived a fire nearby, here are some of them steps to think about before cleaning:

• When you’re ready to pristine your house, start by protecting yourself. Wear at least an N95 (or KN95) mask. and gloves, glasses and clothing that covers the skin. Cleaning may cause some gases and ash to be released back into the air.

• Keep people with heart or lung disease, the elderly, pregnant women, children and pets away from cleaning activities.

• Vacuum floors, curtains and furniture. A recent scientific study documents how cleaning all surfaces in your home can reduce VOC build-up and lower VOC concentrations in indoor air. Once the air outside has cleared, open the windows to let in pristine air.

• Avoid harsh chemical cleaners as they may react with the chemicals in the ash.

• Tidy the filter and HVAC ducts to prevent further spread of ash, and replace filters monthly until the odor disappears. Portable air purifiers with carbon filters can lend a hand remove volatile organic compounds and particles.

• If your car smells of smoke, consider replacing the cabin filter.

This is an update to an article first published on December 23, 2024.