When Kate Gammon and her family fled their home in Santa Monica, California, during the recent wildfires, she wasn’t sure what they would find when they returned.
Although there was no evacuation order in effect, Gammon, who suffers from asthma, told CBC News that the air quality deteriorated quickly and the fires were volatile. So they left on January 8, when the fires were about six kilometers away. When she returned four days later, she found the house had been spared from the flames, but was alarmed to see a layer of ash all over her yard.
“It just rains down on us at night,” she said. “They resemble large, white, chunky pieces of ash.”
Researchers now say that because of the enormous scale of these wildfires and the nature of the buildings burning, people returning home when the initial fire threat has passed may still be exposed to health problems from airborne compounds contained in the ash and smoke can.
Firefighters in the state are still working to extinguish the two largest fires in Altadena and Pacific Palisades, which have killed at least 27 people and destroyed more than 12,000 structures, including homes, schools and banks. On Thursday, the Los Angeles County health officer banned any removal of fire debris until hazardous materials inspections are completed.
Ash and dirt in debris from residential and building fires could contain asbestos, heavy metals and other hazardous substances, the health official said, noting that people can be exposed to the toxic substances through inhalation of ash or fire dust particles or through contact with the toxic substances Skin or contaminated drinking water.
As an environmental journalist, Gammon has previously reported on the health threats posed by ash, not just from brush but also from thousands of charred structures. That’s why she says she avoids touching the ashes and wears a mask when outdoors.
Earlier this week, scientists published their findings on how wildfires that burn both wildland and urban areas can affect indoor air. They studied the 2021 Marshall Fire in Boulder, Colorado, which burned about 1,000 buildings in eight hours, which could help shed light on urban fires like the one in LA
Headache after the burn, itchy eyes
Colleen Reid, a professor at the University of Colorado, studied the health effects on people who returned to unburned homes after this fire. She and her colleagues interviewed residents who lived near burned buildings.
Over a period of about five weeks, they also measured volatile organic compound (VOC) levels in a home that survived the fires but was heavily affected by smoke.
They found that the higher-than-average VOC levels inside the home persisted for nearly a month before returning to typical indoor levels.
“People who said their home smelled different after the fire were more likely to have headaches, dry cough, itchy, watery eyes, strange taste in mouth and sneezing six months after the fire,” said Reid, an environmental epidemiologist.
As evacuees in Los Angeles begin to consider returning home, research suggests that the toxic aftermath of urban wildfires can linger for months in buildings that withstand the flames.
Reid and her team also surveyed people six months after the fire (642 respondents) and again a year later (413 respondents). The results included:
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65 percent of those surveyed reported ash in their homes after the fire.
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Most respondents were less confident about the air quality in both their home and their neighborhood six months after the fire. Most regained their confidence by a year.
Cleaning tips after wildfires
Delphine Farmer, a Canadian scientist at Colorado State University, studies indoor air as part of an experiment at the U.S. National Institute of Standards and Technology in Gaithersburg, Maryland, where she and her team analyzed the composition of particles in a converted home. Lab after they introduced wildfire smoke.
VIEW | The science of indoor air after wildfires:
Farmer noted that smoke burrows into painted surfaces and then slowly releases back into the air, meaning residents remain exposed to indoor pollutants for a long time after a fire.
To guide people who need to clean after a fire, scientists are also studying how different air purifiers work and how surface cleaning affects air quality.
Based on their findings, Farmer’s cleaning recommendations include:
- Open the windows as soon as the smoke subsides. The sooner you clear the smoke, the better.
- Wash fabrics such as bedding, clothing and curtains that may contain smoke.
- Vacuum floors. Be sure to wear an N95 mask as this can stir up soot or smoke particles.
- Mop floors with soap and water and wipe down all surfaces you can reasonably reach, including walls, if there is a lot of smoke in your area. Clean ceiling fans and other rarely cleaned surfaces. Change the water when it gets dirty.
- Clean the “hidden spaces” of your home such as attics, basements, closets and garages.
- If your HVAC system has been in use, you should consider having it professionally cleaned. Change the filters on your home HVAC system or air purifiers and run the fans constantly.
- Vacuum and wash furniture as quickly as possible. If you still smell smoke, consider a thorough cleaning or replacement.
