This story is part of a collaborative journalism project between Boulder Reporting Lab, the Center for Environmental Journalism at CU Boulder and KUNC public radio, reported and led by CU Boulder graduate students. Read the main story, No return: The unseen toll of the Marshall Fire’s ‘standing home’ survivors.
Karen Braverman stood on the back deck of her Louisville home on the afternoon of Dec. 30, 2021. A cloud of orange-tinged smoke rolled in the sky and ash fluttered around her. A hurricane of fire approached.
Braverman evacuated before Boulder County issued its mandatory orders. Although her house was saved from the flames that reached into her neighborhood of Coal Creek Ranch, the Marshall Fire claimed many of her neighbors’ homes. It would turn out flames were not the only threat to residents that day.
Everything that made up those neighborhood homes — insulation, paint, sealants, electronics, batteries, fiberglass, plastic, heavy metals, nylon carpeting, flame retardant coating and more — burned. The materials turned to ash, soot, char and gas. They rode gusting winds into Braverman’s house. The smoke infiltrated vents and cracks in siding, settled onto walls and floors and between window panes. It even absorbed into the building materials — the drywall, the wood frames, the protective siding.
Today, almost a year later, Braverman has not returned to her home in Louisville. She is living in an apartment in Boulder, awaiting the restoration of her smoke-damaged home.
“The thing about the wildfire smoke is that it swirled around in our homes in every nook and cranny from the insulation down and settled on all our furniture and our soft surfaces,” Bravermen said.
Braverman is not alone in her concerns. Like her, other homeowners, and the industrial hygienists they’ve hired, continue to discover remnants of ash, soot and char in and around their homes at levels health experts worry could be unsafe with prolonged exposure. This is often despite remediation cleaning. Some community members with standing homes still fear returning because of possible health risks associated with the smoke damage. Some never will.
“People lost their homes, and it’s horrible. And a lot of my friends and neighbors I know personally lost their homes,” Braverman said. “But I lost my home too. My home is standing but I can’t live there. It’s so toxic.”
Standing home survivors like Braverman have desperately looked for experts to tell them what to do in this situation. However, research on living in wildfire smoke-damaged homes is lacking. Most air quality science related to smoke has looked at living with second-hand smoke from cigarettes and the immediate exposure to a smoke plume outdoors, like in firefighting. Only recently have researchers begun examining how wildfire smoke affects indoor air chemistry and health over time.
Rise in WUI fires amid worsening climate change spurs research
The types of material that burned and fueled the Marshall Fire — nearly 1,100 homes plus cars and other synthetic materials across a relatively small 6,080 acres — put the disaster in a new category of wildfire: a wildland-urban interface (WUI) fire. All the incinerated urban material has made assessing the potential toxins that spewed into people’s homes, and their impact on human health, particularly complex.
“The emissions from an event like the Marshall Fire are a little different than the emissions from, let’s say, an ordinary wildland fire that happens in a more remote area,” Steven Brown, an atmospheric chemist at the National Oceanic and Atmospheric Administration (NOAA), said. “All that same stuff that comes out of the fires is the same stuff that got into the homes that really contaminated the interior environments.”
Bill Hayes, the air quality program coordinator for Boulder County Public Health, estimates that of the 13,000 to 14,000 homes that didn’t burn in and around the Marshall Fire burn area, a majority may have been damaged to varying degrees by smoke.
“With a thousand homes burning in a very small area, we weren’t just concerned with the particulates typically associated with wildfire smoke,” Hayes said, “we were concerned about the pollutants created from the burning of those synthetic materials.”
The recent spate of WUI fires amid a worsening climate crisis is spurring new scientific research to understand how, exactly, homes change when filled with smoke. The complexity of studying indoor air quality is one reason why it hasn’t received much research attention to date. Because each home or indoor space is a unique environment, it can be difficult to extrapolate broad findings. Each WUI fire is unique too, due to the different types of fuel, the total area, and how long each burns, according to Sheryl Magzamen, a respiratory epidemiologist in the Department of Environmental and Radiological Health Sciences at Colorado State University (CSU). “Really, wildfire smoke throws that entire research paradigm completely out of whack.”
Researchers have been increasingly taking on the challenge in part because the stakes are so high.
In April 2022, the National Academies of Sciences, Engineering, and Medicine (NASEM) published a report on the chemistry of wildfires in an effort to summarize existing research and identify its holes. It said that WUI fires produce pollutants that are known to be toxic to humans, including carbon monoxide, formaldehyde, hydrogen cyanide, which can all swiftly enter the lungs and bloodstream and cause tissue damage and respiratory irritation. These fires also release benzene, a known carcinogen. All these compounds, among others in the plume, are known broadly as volatile organic compounds, or VOCs, a category of chemicals commonly found in materials used to build and furnish homes.
Overall, the NASEM report said exposure to WUI smoke can be particularly harmful to the respiratory system, but it has also been found to cause cardiovascular effects, too.
“Although they likely evacuated due to the fire that was in their community,” Magzamen said of those affected by the Marshall Fire, “the homes might be exposed, and there might be some kind of retention of those exposures over time.”
Downwind of the Marshall Fire, people were immediately exposed to pollutants in the smoke plume as they evacuated their homes. But for those whose homes didn’t burn, a secondary type of exposure, not as apparent, occurred in the weeks and months following the fire. Heat from the initial blaze warmed the building materials inside standing homes, opening pores in their siding and wood frames. Once these pores opened, they filled with gas and particulates from the plume. The gas and particulates got trapped inside as the temperature cooled again. The small pores closed up. As winter gave way to spring and summer, those pores reopened and released trace amounts of gasses back into the air. Odor is one telling sign of this exposure.
“Most of the air quality concerns that residents have raised are smells, and the smells are most likely from VOCs that were part of the smoke,” said Colleen Reid, a professor at CU Boulder who studies the human health impacts of wildfire smoke. “And we know that with hotter temperatures, those VOCs will off-gas more. Some of the things that we’ve heard from residents is that they’ll get those smells returning periodically.”
How long are VOCs off-gassed into homes? No one knows.
A house is not a sealed ecosystem separate from the outdoor environment, but a dynamic structure that breathes. Through its chimneys, vents in the attic and porous materials invisible to the eye, a house is continuously pulling air and dust in from the outdoors. Homes directly downwind of the Marshall Fire breathed in the VOCs and particulates from the plume.
Once inside, “these molecules from the smoke burrow into things, and fabric is really good at holding onto scents and compounds,” Delphine Farmer, an atmospheric chemist at CSU, said.
It’s not just textiles — carpet, clothing, bedding and furniture — that can hold these toxins. Any surface can end up coated in residue after a fire. “This sort of residue creates this muck that layers your house,” Farmer said.
Those substances can then off-gas, the process that makes indoor air potentially unsafe, in which solid material — like residue, plastic, paint — emits gas into the air. This process is responsible for that well-known “new car smell,” for instance, when the seat furnishings and the plastic coverings of a new vehicle emit small amounts of gas.
The same thing happens in a house. The particulate matter produced by a fire (soot, ash, and char) can off-gas VOCs into the home long after the fire has been extinguished.
“At this point, we don’t know for how long and at what concentration these VOCs are going to be off-gassed by materials in people’s homes,” Reid said.
What level of cleaning is needed? ‘Just beginning to understand’
Because there’s not a clear understanding about how VOCs might be affecting air quality inside standing homes, it’s also unclear what level of cleaning is needed to make the home safe again.
“I was shocked at how little information we have,” said Christiene Wiedinmyer, who studies emissions and air quality at the University of Colorado Boulder.
Wiedinmyer is part of a CU Boulder team of scientists that is using the Marshall Fire to study smoke impacts in homes. This team deployed mass spectrometers, instruments that measure molecules in the air, inside standing homes to see how long harmful levels of VOCs (like benzene) stuck around inside the house.
“Right after the fire these compounds were enhanced inside homes more than you would usually see,” Joost de Gouw, a chemist at the Cooperative Institute for Research in Environmental Sciences at CU Boulder who is leading the project, said. “But three, four weeks later, it had come down to more normal levels.”
With time, the substances will eventually stop off-gassing, as de Gouw witnessed in the data collected by the mass spectrometers. But the fact that these compounds lingered indoors weeks after the fire surprised de Gouw. He thought the VOCs would be gone in a matter of days. “We saw them stick around for a month and so that really changes our understanding of how pollutants interact with our homes.”
How long a compound sticks around may depend on what type of material the smoke residue landed on — for instance, whether it was porous enough to capture large quantities of smoke or whether it can be deeply cleaned to remove wildfire particles and residue. Solid surfaces, like treated wood floors, painted walls and countertops should be smooth and solid enough to thoroughly clean. But porous materials like textiles (carpets and furniture), untreated wood and plastics are very porous and can absorb smoke easily.
“It is going to depend on the compound and it’s going to depend on where you’re cleaning,” Farmer, the CSU atmospheric scientist, said. “ If you can actually remove all the compound that is off-gassing, in theory you could remove the entire reservoir” of toxins, she added. “I think we are just beginning to understand how hard it is to clean environments and how important that is for real people.”
Braverman is one of those people who remains stuck in the purgatory of a smoke-damaged home. At the time of this reporting, Braverman is scheduled to have her home recleaned and retested, with the hopes of finally moving back into a place that feels safe.
“When someone asks ‘how are you,’ I just say that I’m trying to be okay,” said Braverman. “It’s hard to share how bad every day is. I keep thinking that in a year maybe it will be better, but I don’t know.”
Helen Driesen, Amber Carlson, Josh Couture, Elise Ertll and Zain Iqbal contributed reporting to this story.