Researchers find compromised indoor air in homes following Marshall Fire
University of Colorado at Boulder
image:
Remnants of ashes across the street from the studied house in Superior, Colorado
view moreCredit: Will Dresser/CU Boulder
2021’s Marshall Fire became the most destructive fire in Colorado history, burning nearly 1,000 homes and forcing more than 37,000 residents of Boulder County to evacuate.
New research by scientists at the Cooperative Institute for Research in Environmental Sciences (CIRES) at the University of Colorado Boulder found compromised indoor air quality in homes near the burnt area for weeks after the fire, similar to pollution levels recorded in urban Los Angeles in the 1990s. According to the researchers, the findings can help individuals weigh their options when returning home after a fire.
In the aftermath of the fire, some residents found their homes burned to the ground. Others, to their relief, found their homes visibly unscathed. Yet they reported unpleasant odors that lingered indoors and found layers of black ash covering many surfaces.
In response to community concerns, CIRES scientists responded quickly to research a topic that had never been studied before: indoor air quality immediately following a fire at the Wildland Urban Interface (WUI), where human development meets forests and other natural spaces.
Ten days after the fire, researchers set up field instruments in a home bordering a block where houses burned to the ground in Superior, Colorado. Winds had blown smoke directly into the home, and residents complained the air inside smelled like a campfire.
Will Dresser, lead author and chemistry PhD student at CU Boulder, led the study with CIRES Fellows Joost de Gouw and Christine Wiedinmyer.
“No study has, in a real-world environment, gone into an indoor space and looked at indoor smoke impacts so close after a fire event,” Dresser said.
Their study, published today in ACS Environmental Science & Technology Air, confirmed what residents were smelling in their homes: Gases harmful to human health were trapped and lingered for weeks following the fire.
WUI fires have increased in recent decades, yet research looking at the impacts on air quality following these events is limited. The structures and items that burn in WUI fires — cars, roofs, furniture, and carpets — release different, sometimes more dangerous, volatile organic compounds (VOCs).
VOC gases were elevated, indicating potential health risks
Researchers set up research-grade instruments in the first-floor room of a home next to a block of burned homes. The instruments sampled indoor air continuously for five weeks, measuring over 50 gases.
Key findings of the sampling included:
- Aromatic VOCs like benzene, toluene, and naphthalene, which pose risks to human health, were highest at the beginning of data collection. VOC concentrations were much higher indoors than outdoors.
- Concentrations of aromatic VOCs were similar to those recorded in urban Los Angeles in the 1990s.
- The aromatic VOCs initially declined rapidly and then more slowly during the five-week study.
- However, the rate at which the VOCs declined was slower than expected.
The results indicate the home acted like a sponge for VOCs during the fire and slowly returned these pollutants to indoor air afterward. However, the study does not reveal where exactly the VOCs were trapped.
“Based on prior research, we had expected these VOCs to disappear from the home within hours, but it took weeks,” de Gouw said. “What this means is we don’t understand very well how and where these chemicals get trapped inside a home.”
Ventilation and mitigation help clean air, with caveats
The research team also tested ways to mitigate smells and VOC concentrations indoors.
First, they opened windows to increase the circulation of indoor and outdoor air. When windows were opened, VOC levels dropped. However, after closing the windows, the VOC concentrations went back up.
Next, they constructed home-built air cleaners made of a box fan and pleated air filters with activated carbon. These filters removed VOCs within an hour of starting the fans — but the VOCs rebounded when the fans were turned off, similar to opening windows.
Both methods, opening windows and running air cleaners, decreased gases indoors by more than 50 percent.
While the research is the first of its kind, it’s important to note the results represent a single house following one WUI fire. Different circumstances — poor outdoor air quality, high winds, or new materials burned in the process — could have different environmental impacts.
Looking to the future, scientists predict that WUI fires will increase in speed and frequency, and Dresser notes it’s important to be informed. The study’s results can help residents weigh their options when deciding whether or not to return home following a wildfire.
“I think our study brings some numbers and perspective to that story,” Dresser said. “It highlights the importance of these impacts for people returning to areas after these WUI fires.”
Journal
ACS ES&T Air
Article Publication Date
23-Dec-2024
Months after Colorado's Marshall Fire, residents of surviving homes reported health symptoms, poor air quality
Three years after blaze burned 1,000 homes, studies explore health impacts of urban wildfires
University of Colorado at Boulder
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The Marshall Fire burned more than 1,000 homes in Boulder, County, Colorado on Dec. 30, 2021. New research offers insight into how indoor air quality and health changed for returning residents.
view moreCredit: Joost de Gouw/CU Boulder
Six months after the Marshall Fire destroyed more than 1,000 houses in Boulder County, Colo., more than half of residents of surviving homes in the area reported physical symptoms— including headaches, sore throats or a strange taste in their mouth— that they attributed to poor air quality, a new CU Boulder study has found.
A companion study showed that the air quality inside one home post-fire equaled that of downtown Los Angeles in the 1990s on a high pollution day, with hazardous gases lingering for weeks.
“Our research suggests that there could be important health impacts for people returning to smoke- or ash-damaged homes after a fire and that we need to have systems in place to protect them,” said Colleen Reid, associate professor of geography and co-author of the studies.
The papers, published this week in ACS Environmental Science & Technology Air, are the first to explore air quality inside smoke- and ash-damaged homes and to assess the health impacts on people who live in them. They come as fires in the Wildland-Urban Interface, like in Paradise, California, in 2018 and Lahaina, Hawaii, in 2023 grow more common.
“A lot of time has been spent studying wildfire smoke – what you get when you burn vegetation. But what do you get when you burn a home, with all its furniture and electronics and cars? Until now, there has been very little known,” said co-author Joost de Gouw, a professor of chemistry and fellow with the Cooperative Institute for Research in Environmental Sciences (CIRES) at CU Boulder.
A record winter blaze
Fueled by 100-mile-per-hour winds and record dry conditions, the Dec. 30, 2021, Marshall Fire burned 1,084 buildings in densely populated areas, took two lives and forced 37,000 people to evacuate.
Once residents returned home, scientists at CU Boulder, just 4 miles from the fire’s ignition, started getting calls.
“At first, they felt really lucky, but when they went into their homes they saw ash everywhere and it smelled differently – like a campfire or chemicals,” said Reid. “They asked: What should we do? We don’t know if it’s safe to go back in.”
With little research offering answers, the scientists began to investigate.
Ten days after the fire, de Gouw’s team erected field instruments in an intact home bordering a block where houses burned down. Over five weeks, they continually measured the presence of 50 gases.
Meanwhile, Reid and colleagues developed a survey to send to residents within the burn perimeter, as well as a random sample of those within 2 miles.
At six months, 642 people had responded; 413 had responded at the one-year mark.
Some 55% of respondents reported symptoms that they attributed to the fire at the six- month mark, and survey answers depended largely on the condition of their home when they returned home.
For instance, 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.
People with the same symptoms tended to cluster together, according to computer mapping analyses. For example, those living near destroyed homes, especially in the direction the wind was blowing the day of the fire, were far more likely to report a strange taste in their mouth.
“These findings are consistent with chemical exposures and suggest that residents of smoke- and ash-damaged homes may have experienced lingering air quality and physical health challenges months after the fire,” said Reid.
Long-term impacts uncertain
The authors cannot say which chemicals caused the health impacts that survey respondents reported. But measurements in one home found high levels of volatile organic compounds (VOCs) like benzene, a carcinogen found in gasoline and Diesel exhaust.
Dust samples also showed high levels of copper, zinc, arsenic and industrial pollutants called polycyclic aromatic hydrocarbons (PAHs), which are known to cause eye irritation.
“If your home survives, and the neighbor two doors down burns, all those melted things can get into the air and find their way into your home” settling into furnishings, carpets and drywall, said Reid.
The authors stress that VOCs are only considered carcinogenic at levels much higher than what they found, and people are regularly exposed to low levels daily through pollution.
Their research found that simple measures, like opening windows and using low-cost, carbon-activated air filters, can substantially improve air quality.
One year after the fire, the number of residents reporting symptoms had declined to just 33% and most said confidence in their home’s air quality had improved.
Until more studies are done, the researchers cannot say whether such exposures can lead to long-term health problems.
Nonetheless, Reid urges anyone going inside a smoke- or ash-damaged home just after a wildland urban interface (WUI) fire to use caution, wearing KN95 masks and gloves.
They hope their ongoing research can lead to clearer guidelines for policymakers and insurance companies about when it is safe for people to return to smoke-damaged homes.
“This wasn’t just any fire. It felt personal,” said de Gouw. “Knowing that we could at least begin to provide some answers to our community has made the work extra meaningful.”
A lone chimney remains after the Marshall Fire ripped through a Boulder County, Colorado neighborhood on Dec. 30, 2021.
Credit
Glenn Asakawa/CU Boulder
ptionThe Marshall Fire burned more than 1,000 homes in Boulder, County Colorado on Dec. 30, 2023.
Credit
Glenn Asakawa/CU Boulder
Journal
ACS ES&T Air
Method of Research
Survey
Subject of Research
People
Article Title
Physical Health Symptoms and Perceptions of Air Quality among Residents of Smoke-Damaged Homes from a Wildland Urban Interface Fire
Article Publication Date
23-Dec-2024
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