As California reels, study shows Marshall fire made air in nearby homes hazardous for months

Direct neighbors of houses burned in the Marshall fire suffered measurable increases in volatile organic compounds from toxic smoke in their homes, and hundreds more residents reported headaches and other health problems, according to companion University of Colorado studies published in late December. 

Smoke-weary Los Angeles County residents may want to study up as they sit in limbo during evacuations from the Pacific Palisades/Malibu and Pasadena wildfires sweeping the area this week. The twin CU studies show toxins from burned homes drift into still-standing neighboring homes and create tangible health symptoms for months after fires are put out. 

Los Angeles media are warning residents even relatively far from the fires that the basin monitors show air pollution warnings well into danger zones for vulnerable categories of people. 

The CU-based studies add to a growing body of Colorado-led research into the increasing hazards in the wildland-urban interface, or WUI. Driving winds carry not just wood ash into homes, but also the residue of countless plastics, carpets, paints and construction materials from suburban structures. 

The potentially harmful particles require concerted efforts from nearby homeowners to clean up, and can even return in force if countermeasures, such as filtered box fans, are switched off. 

CU researchers were inundated with public questions soon after the fire swooped in on 100-mph winds and destroyed more than 1,000 homes Dec. 30, 2021, in southeastern Boulder County.  

Callers reported “intense smells that lingered for days, and that really got them worrying ‘Is this a space that I can go back to and take my family to with a clear head, or do I need to take some extra precautions? And what’s the time frame, if any, that it would be OK to come back into these spaces?’” recounted Will Dresser, a Ph.D. candidate. Dresser led the air quality half of the studies for CU’s Cooperative Institute for Research in Environmental Sciences, or CIRES. 

The CIRES study set up air monitoring equipment in the homes of worried Marshall-area neighbors, from full-room tanks and computer terminals to small pieces that could sit in a corner while families stayed in place. The researchers, publishing in ACS Environmental Science & Technology Air, call it the first study of its kind in lived-in homes, rather than test-model homes, conducted so close to a fire and so soon afterward. 

What they found were spikes in volatile organic compounds blown in with ash and other residues, including benzene, toluene and naphthalene. The chemicals could have come from burned cars, flooring, cleaning fluids and paints, or household materials that burned up just across the street. 

The first few days of VOCs measured indoors were as bad as the outdoors smog in the Los Angeles basin in the 1990s, Dresser said. The levels dropped after a few days, but then lingered and dropped more slowly after that, raising further concerns, Dresser said. Homeowners could lower the numbers with affordable, jury-rigged solutions like furnace filters taped around a box fan, but some of the VOCs came back if the rigs were turned off. 

That parallels findings from a previous Colorado State University study using model homes, showing that filtering the air is not enough to clean up wood smoke toxins. The CSU researchers recommended hearty and repeated scrub-downs of walls, floors and other surfaces, in addition to filtering air. 

The second CU study, on health impacts, surveyed hundreds of neighbors whose homes were intact, but suffering from blown-in smoke and ash. 

On a check-in six months after the fire, more than half of respondents spoke of more headaches, sore throats or “a strange taste in their mouth,” according to CU. The study, with lead researcher and associate professor of geography Colleen Reid, was also published in December in the ACS journal. 

“Those who found ash inside were three times as likely to report headaches compared to those who didn’t find ash; those who reported an odd odor were four times as likely to report headaches compared to those who did not pick up an unusual scent,” according to CU’s account of the study. 

Survey answers were similar in geographic clusters, and those findings are “consistent with chemical exposures,” Reid said, in a CU summary. 

Dresser said in an interview that it’s difficult to link specific ailments to specific VOC readings, but it’s clear the chemicals detected were high, and that they came in with the smoke and ash. The companion studies should be seen as a launching point for more research on resident hazards in areas where neighborhoods meet wildlands, the scientists said. 

“I just want to add,” Dresser said, “that it was really amazing for these homeowners to open their spaces to us, and that really was what allowed us to do this work.”