The Marshall Fire: Health effects persisted a year later

Yesterday we reported on the indoor air quality of a home that had survived a neighbourhood fire shortly after the fire was extinguished. The team behind that research returned six months later. This is what they found.

In 2021, what is now known as the Marshall Fire swept through Boulder County in Colorado, destroying nearly 1,000 homes and forcing the evacuation of over 37,000 residents.

Quickly on the scene were a team from the Cooperative Institute for Research in Environmental Sciences (CIRES) at the University of Colorado Boulder who monitored the indoor air quality of a building which had survived the blaze almost untouched, while houses across the street were razed.

After five weeks the team returned to the University to examine their findings but, six months later, launched a companion study to examine the effects of the blaze over a longer period of time.

The team developed a survey which was sent to all addresses within the Marshall Fire boundary and a random sample of addresses beyond, but within two miles of the boundary. As they were focussing on the impacts of the fire on people whose homes were smoke affected, they removed from the sample those whose homes were completely destroyed.

The survey was sent our in two waves, one six months following the fire, the other around a year afterward.

The survey included the following questions:

• When you returned home after the fire, did it smell differently inside your home than it did before the Marshall Fire? 
• How would you describe the smell inside of your home when you returned after the fire? (Select all that apply)
• How has the smell inside your home changed since you first returned?
• Why do you think the smell inside your home has improved since you first returned? (Select all that apply)
• When you returned to your home, was there ash inside that you could see? yes people who had returned to live in their homes postfire
• Where did you find the ash? (Select all that apply)
• Have you experienced any of the following health symptoms that you think may be related to smoke or air quality impacts of the Marshall Fire? (Select all that apply)

642 people responded to the first survey, 413 to the second.

55% of those who responded on six months reported symptoms that they attributed to the fire. People who had found ash in their home were three times as likely to have suffered from headaches than those who didn’t.

Those who said there was an odd smell in the house were four times as likely to report headaches than those who didn’t.

A localised pattern was identified to the reporting of these symptoms. For example, those living downwind of homes that had been destroyed were much more likely to report a strange taste in their mouth.

The most commonly reported symptoms in the first survey were itchy eyes (33%), headache (30%), dry cough (27%), sneezing (26%), and sore throat (23%).

Six months later (12 months after the fire) these symptoms were still evident but the reporting of them had dropped: itchy eyes (21% down from 33%), headache (13% down from 30%), dry cough (20% down from 27%), sneezing (18% down from 26%), and sore throat (12% down from 23%)

The chemicals causing these health impacts could not be specifically identified but high levels of volatile organic compounds were found, including benzene, a carcinogen found in gasoline and diesel exhaust.

Dust samples also showed high levels of copper, zinc, arsenic and polycyclic aromatic hydrocarbons (PAHs), which are known to cause eye irritation.

Colleen Reid, associate professor of geography and co-author of the studies said: ‘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.

‘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. They asked: What should we do? We don’t know if it’s safe to go back in.

‘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.

‘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.’

The full research can be read here

Photo: Joost de Gouw/CU Boulder