Wildfire smoke lingers in homes long after the fire is over

New research from Colorado State University (CSU) suggests that the aftermath of wildfires may be more dangerous than previously thought, with smoke potentially lingering in homes even after the fire is doused or the winds have shifted. This could extend residents’ exposure and increase the risk of health problems.

Lingering threats

The study, which was recently published in the journal Science Advances, highlights that wildfire smoke has a tendency to cling onto surfaces inside homes such as carpets, drapes, and countertops. 

This means that even after an initial round of cleaning with air purifiers, residues can remain. 

Professor Delphine Farmer of CSU, who played an integral role in the study, noted that simple surface cleaning – like vacuuming, dusting or mopping – can reduce exposure risk.

Increasing number of wildfires 

Farmer points to the increasing number of wildfires in the Western U.S. over the past decade as a potential long-term health concern.

“This research shows that events like the Marshall Fire in Colorado, the wildfires in Canada and the recent fires in Hawaii present serious exposure potential – not just when they occur but well after,” said Farmer. 

“This paper is a key initial step towards providing actionable and practical information on how to protect yourself and clean your home.”

How the research was conducted 

In a quest to understand how smoke penetrates and remains in buildings, the researchers used the National Institute of Standards and Technology (NIST)’s net zero energy residential testing facility in Maryland. 

At this facility, pine wood chips were burned to simulate wildfire smoke, allowing the team to study the behavior of the smoke in real-time.

Dustin Poppendieck, an environmental researcher at NIST, praised the capabilities of the facility. 

“The NIST Net Zero House allowed the researchers to track the movement and transformation of chemicals in the air and onto surfaces in real time using instruments in ways that don’t interfere with the behavior of the smoke,” said Poppendieck.   

Changes in the home

Various measurements were taken post-smoke exposure, including the air quality and surface conditions after cleaning and the utilization of the home’s built-in air cleaning systems.

A key observation from the CSU team centered on the gas-phase compounds emerging from the smoke. Comparisons were drawn between different states to determine the actual changes in the home post-burn.

Indoor smoke

Farmer mentioned previous studies on indoor cigarette smoke. She said that while nicotine reacts on surfaces to produce harmful nitrosamines, wildfire smoke releases a diverse range of organic compounds that adhere to surfaces, gradually emitting over time.

“Nicotine reacts on surfaces to create a particularly nasty set of compounds called nitrosamines, which is where the real concern from thirdhand smoke that is left behind comes from,” said Farmer. 

“Whereas with wildfire smoke, we found there was a huge diversity of organic compounds that stick to surfaces, which then slowly bleed off.”

Study implications 

Understanding the composition and behavior of these compounds is vital for recommending effective cleaning strategies. 

Farmer explained that the amount of smoke residue on surfaces was proportional to the surface area cleaned. This insight underscores the importance of thorough cleaning, particularly in overlooked areas like cabinets and HVAC systems.

“As we continue this research, we would like to know just how effective different cleaning approaches are and when residents should move from relatively simple steps like using commercial cleaning supplies for mopping to more drastic steps like replacing the drywall altogether,” said Farmer.

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