Wildfires have increased in frequency and severity over the past few decades. More fires are burning at the wildland-urban interface (WUI), where homes and other buildings meet the natural landscape — but our understanding of emissions from structure fires is still growing.
New research led by the University of Colorado Boulder's Cooperative Institute for Research in Environmental Sciences (CIRES) shows that common synthetic materials used in homes, like plastics and insulation, can release harmful compounds into the air when they burn.
But synthetic materials make up only a small fraction of a home. Timber and wood panels make up the majority of the materials used, and the burning emissions from those are not so different from a vegetation fire. The work, published in ACS Environmental Science & Technology, identifies compounds that are enhanced in smoke from a house fire.
"Urban fires are becoming more prevalent," said William Dresser, a CIRES research scientist and lead author of the paper. "We've seen some pretty notable examples, such as the Marshall Fire, the Lahaina Fires, and the LA Fires, so there are emerging questions from an air quality standpoint of how these types of fires change exposures."
Dresser partnered with CIRES Fellow Joost de Gouw and a team from Colorado State University (CSU) to explore how different building materials impact fire emissions.
"There's a need to better understand what these emissions look like for structures that contain a complex mixture of different synthetic materials that have unique emission profiles," Dresser said.
CSU scientists led a series of laboratory experiments, burning 18 different building materials in a fume hood to capture emissions. During and after each burn, CIRES researchers sampled the smoke to measure volatile organic compounds (VOCs), a broad group of carbon-based compounds that can impact air quality and human health.
The team found elevated levels of VOCs, including benzene and styrene — compounds that can cause cancer — and other hazardous air pollutants when synthetic materials like plastics or insulation were burned. Their results also reveal that many of the synthetic materials have unique, less well-understood emissions, like molecular fragments derived from nylon polymers, that future work will need to explore.
But when the team considered emissions from a whole-house fire, the picture is more complicated. Synthetic materials exhibit higher VOC emissions, but they only represent a small fraction of the mass of a home.
"We wanted to know — If you make an inventory of materials that mimics a house with all these materials and look at that overall emission, what still stands out?" Dresser said.
Dresser and the team used estimates for the materials composition of a typical home to calculate emissions for a whole house fire. They then compared the house fire emissions to other fire emission scenarios: a structural wood fire, which is representative of the kind of wood used to build homes, and a natural Douglas Fir forest fire, which includes all parts of the tree.
Their results indicate that while the house fire exhibited higher levels of some potentially harmful VOCs, such as benzene and styrene, other VOC emissions did not stand out as clearly from structural wood and forest fires.
"Since synthetic materials are a pretty small part of a home, we found their impact can be muted," Dresser said. "But it was in part surprising to see the nuanced picture."
The team's work highlights the complexity of fire emission research — and is one step of many needed to better understand emissions from structure fires at the WUI.
"Our research shows clearly that some toxic compounds are higher when a home burns, relative to a wildfire," said de Gouw. "Future work is focused on the compounds that end up in ash or can be leached from ash into waterways."
