Many Boulder County residents returned to their homes relieved to see them still standing, after the Marshall fire, which started Dec. 30, 2021.

But, new research from the University of Colorado shows those homes did not escape completely unscathed, and neither did their residents. The researchers found that six months after the Marshall fire, more than half of the residents who returned to their surviving homes reported physical health symptoms due to poor air quality. The Marshall fire killed two people and caused more than $2 billion damage, mostly in Louisville and Superior.

“What the concern was from an air-quality perspective was the people whose homes were not destroyed by the fire returned to their homes and they smelled different,” said Colleen Reid, CU geography professor and co-author of the study. “And there was a lot of ash in the homes.”

Reid teamed up with a group surveying those impacted by the Marshall fire and asked a few questions about physical health symptoms to those who were able to go home. The survey found that 55% of people had at least one of 12 listed physical health symptoms six months after the fire. Another survey sent out six months after that, or one year after the fire, decreased to 33% of people still experiencing symptoms.

The study found that dry cough, headache, itchy or watery eyes, sneezing, sore throat and a strange taste in the mouth were significantly higher in people who reported a home smelled different when they returned after the fire compared with people with non-smelly homes.

Reid was also able to map the locations of the survey respondents to see how many destroyed buildings the people lived near.

“We found that people whose home was closer to more destroyed buildings had significantly higher odds of reporting headache and a strange taste in their mouth than people who had fewer destroyed buildings near their home,” she said.

In addition to the survey, Reid’s colleagues measured air quality in homes led by CU professor and co-author Joost de Gouw. They found high levels of volatile organic compounds, or VOCs, such as benzene, a carcinogen found in gasoline and diesel exhaust. The authors said that VOCs are considered carcinogenic only at levels higher than what they found.

Dust samples also showed high levels of copper, zinc, arsenic and industrial pollutants called polycyclic aromatic hydrocarbons, which are known to cause eye irritation.

“A lot of time has been spent studying wildfire smoke — what you get when you burn vegetation,” de Gouw said in CU Boulder Today, a daily university newsletter. “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.”

Reid thinks this study is the first of its kind to document any physical health symptoms associated with people living in a home that had smoke or ash damage. She said she couldn’t find any other research on the topic.

The Marshall fire was different than other fires Reid has studied, she said, because of the indoor air-quality component and because most of what burned was human-made materials like homes, cars and electronics..

“This is really important to study because we’re getting more of these fires,” Reid said. “These are what we’re calling a wildland-urban interface fire. It might start in wildlands, this one started in grassland near Marshall, but then it could get to housing developments.”

However, Reid said the research doesn’t provide insight into what chemicals caused the short-term symptoms or whether it would cause any long-term health problems for people.

“Just because we did see these associations doesn’t necessarily mean there will be long-term health implications of these exposures,” Reid said. “We can’t say that, because we don’t know, and we couldn’t find any other studies that looked at people who returned to smoke-damaged homes after a wildfire.”

The findings allow researchers to provide common-sense guidance, like wearing a mask and other protective equipment when returning home. But, more research is needed, they said.

Reid also interviewed people for the study and wants to analyze that anecdotal data and look for common themes. She plans to follow up to see if the reported health symptoms improve.

She said she hopes more research is done to see if there would be similar results after other fires.

“I think it’s really important that we understand these impacts, that we look at it longer term, that we know what we can tell people to do,” Reid said. “There’s lots of research showing there’s more and more wildfires and more of them are happening within this wildland-urban interface.”