Post-Marshall Fire: Residents Face Ongoing Health Struggles and Indoor Air Quality Concerns

Half a year following the Marshall Fire that obliterated over 1,000 homes in Boulder County, Colorado, more than 50% of inhabitants in intact residences in the vicinity reported physical ailments—such as migraines, throat irritation, or an unusual taste in their mouths—that they linked to subpar air quality, a recent study from CU Boulder has uncovered.

A related study indicated that the indoor air quality of one residence post-fire resembled that of downtown Los Angeles during the 1990s on a day with high pollution, with dangerous gases persisting for weeks.

“Our investigations indicate that there could be significant health consequences for individuals returning to homes affected by smoke or ash after a fire, and that we need to establish systems to safeguard them,” stated Colleen Reid, associate professor of geography and co-author of the research.

The documents, released this week in ACS Environmental Science & Technology Air, are the first to investigate indoor air quality in homes impacted by smoke and ash and to evaluate the health effects on their occupants. They arise as incidents in the Wildland-Urban Interface, similar to those in Paradise, California, in 2018 and Lahaina, Hawaii, in 2023, become increasingly frequent.

“Much effort has gone into studying wildfire smoke—what you get when vegetation burns. But what do you inhale when a house is burned, with all its furniture, electronics, and vehicles? Up until now, little was known,” remarked co-author Joost de Gouw, a professor of chemistry and a fellow with the Cooperative Institute for Research in Environmental Sciences (CIRES).

A historic winter inferno

As residents returned to their homes, scientists from CU Boulder, situated just 4 miles from the fire’s origin, began receiving inquiries.

“Initially, they felt fortunate, but upon entering their residences, they noticed ash everywhere and a different odor—similar to a campfire or chemicals,” explained Reid. “They inquired: What should we do? We’re uncertain if it’s safe to re-enter.”

With scant research providing answers, the scientists commenced their investigations.

Ten days post-fire, de Gouw’s team set up field instruments in an undamaged house adjacent to a block where residences were reduced to ashes. Over a span of five weeks, they consistently monitored the presence of 50 gases. (Find out more about the study here.)

Simultaneously, Reid and her team devised a survey to distribute to residents within the burn zone, along with a random selection of those living within a 2-mile radius.

At the six-month interval, 642 participants had responded; 413 had answered by the one-year mark.

Approximately 55% of respondents indicated symptoms they associated with the fire at the six-month juncture, and survey results were largely contingent on the state of their homes upon returning.

For example, individuals who discovered ash indoors were three times more likely to report migraines compared to those who found no ash; those noting an unusual odor were four times more likely to mention migraines than those who did not detect any odd scents.

Individuals with similar symptoms often clustered together, as observed through computer mapping analyses. For instance, those residing near destroyed properties, particularly downwind on the day of the fire, reported a strange taste in their mouth at significantly higher rates.

“These results align with chemical exposures and imply that residents of homes affected by smoke and ash may have faced lasting air quality and health issues months subsequent to the fire,” stated Reid.

Long-lasting effects uncertain

The authors cannot determine which specific chemicals resulted in the health issues reported by survey participants. However, findings in one residence revealed elevated levels of volatile organic compounds (VOCs) such as benzene, a carcinogen present in gasoline and diesel emissions.

Dust analysis also indicated high concentrations of copper, zinc, arsenic, and industrial pollutants known as polycyclic aromatic hydrocarbons (PAHs), which are recognized for causing eye irritation.

“If your residence survives, and the neighboring house two doors down burns, all those melted substances can enter the air and infiltrate your home,” accumulating in furniture, carpets, and drywall, noted Reid.

The authors emphasize that VOCs are only classified as carcinogenic at significantly higher concentrations than what they discovered, and individuals are commonly exposed to low levels of these compounds daily through environmental pollution.

Their study showed that uncomplicated actions, such as opening windows and utilizing affordable, carbon-activated air filters, can considerably enhance air quality.

One year post-fire, the percentage of residents reporting symptoms had reduced to merely 33%, and most expressed increased confidence in the air quality of their homes.

Until further research is conducted, the scientists cannot ascertain whether such exposures may result in long-term health concerns.

Nonetheless, Reid advises anyone entering a smoke- or ash-affected home shortly after a wildland urban interface (WUI) fire to exercise caution by wearing KN95 masks and gloves.

They aspire that their ongoing research can inform clearer directives for policymakers and insurance firms regarding the appropriate timing for individuals to safely return to smoke-affected residences.

“This wasn’t just any fire. It felt personal,” said de Gouw. “Knowing that we could at least begin to offer some answers to our community has made this work exceptionally meaningful.”