Three years after the devastating Marshall Fire on December 30, 2021, which destroyed over 1,000 homes in Boulder County, two recent studies shed light on the impacts of urban wildfires on air quality and public health.
Following the destruction of more than 1,000 residences in Boulder County, Colorado, by the Marshall Fire, a new study from CU Boulder revealed that over half of the residents of surviving homes reported experiencing physical symptoms such as headaches, sore throats, or unusual tastes, linking these issues to poor air quality just six months after the fire.
In another related study, researchers discovered that the air quality within one post-fire home mirrored that of downtown Los Angeles on a high pollution day during the 1990s, with harmful gases remaining for weeks after the incident.
“Our findings indicate that individuals returning to homes damaged by smoke or ash might face significant health risks, emphasizing the need for protective measures,” stated Colleen Reid, an associate professor of geography and co-author of the studies.
These studies, published this week in ACS Environmental Science & Technology Air, are pioneering in examining air quality within homes affected by smoke and ash, as well as evaluating the health ramifications for residents. This research is particularly relevant as wildfires in the Wildland-Urban Interface, like those in Paradise, California, in 2018, and Lahaina, Hawaii, in 2023, have become increasingly frequent.
“Most previous research has focused on wildfire smoke from burning vegetation. However, little is known about the emissions from burning homes that contain furniture, electronics, and cars,” explained co-author Joost de Gouw, a professor of chemistry affiliated with the Cooperative Institute for Research in Environmental Sciences (CIRES) at CU Boulder.
A record winter blaze
The Marshall Fire, fueled by 100-mile-per-hour winds and extraordinarily dry conditions, resulted in the burning of 1,084 structures in densely populated regions, led to two fatalities, and prompted the evacuation of 37,000 individuals.
Upon returning home, residents near the fire’s starting point, located just four miles from CU Boulder, began reaching out to scientists for assistance.
“Initially, they felt fortunate, but upon entering their homes, they encountered ash everywhere and noticed an unusual smell—akin to campfire smoke or chemicals,” Reid recounted. “They were concerned and asked what they should do, unsure if it was safe to return.”
With a lack of existing research to provide answers, scientists began their investigation.
Ten days post-fire, de Gouw’s team set up field instruments in an undamaged home that bordered the devastated neighborhood, measuring the presence of 50 different gases continuously over five weeks.
Meanwhile, Reid and her colleagues sent out surveys to residents within the affected area, as well as to a random selection of those living within a two-mile radius.
By six months after the fire, 642 individuals had responded, with 413 responding again a year later.
Approximately 55% of those surveyed attributed their symptoms to the fire after six months. The survey responses heavily depended on the state of their home upon returning.
For example, residents who found ash inside their homes were three times more likely to report headaches than those who did not encounter any ash. Similarly, those who detected unusual smells were four times more likely to report headaches compared to those who didn’t notice any odd odors.
Computer mapping analyses showed that individuals with similar symptoms often lived in close proximity, particularly those near destroyed homes, especially downwind from the fire’s location who were more likely to report experiencing a strange taste.
“These results align with exposure to chemicals, indicating that residents of homes affected by smoke and ash may continue to face air quality and health challenges months after the fire,” said Reid.
Long-term impacts uncertain
The authors could not definitively determine which chemicals caused the reported health issues among survey participants. However, measurements taken in one home revealed elevated levels of volatile organic compounds (VOCs), including benzene, a known carcinogen typically found in gasoline and diesel exhaust.
Dust samples indicated high concentrations of copper, zinc, arsenic, and polycyclic aromatic hydrocarbons (PAHs), which are known to cause eye irritation.
“Even if your home survives, neighboring houses that caught fire can release harmful substances into the air, which may infiltrate your home, settling in your furniture, carpets, and drywall,” Reid explained.
The researchers emphasized that while VOCs are considered carcinogenic only at levels significantly above those measured in their study, people are continuously exposed to low-level pollution.
The research indicated that simple actions, such as opening windows and utilizing inexpensive carbon-activated air filters, can significantly enhance indoor air quality.
A year after the fire, the percentage of residents reporting symptoms had decreased to just 33%, and most expressed increased confidence in the air quality of their homes.
Until further research is conducted, the scientists cannot confirm whether these exposures could lead to long-term health issues.
Nevertheless, Reid advises anyone entering a home damaged by smoke or ash following a wildand-urban interface fire to take precautions, such as wearing KN95 masks and gloves.
The researchers aim for their ongoing studies to contribute to clearer guidelines for policymakers and insurance companies regarding the safety of returning to smoke-affected homes.
“This wasn’t just an ordinary fire. It felt deeply personal,” de Gouw remarked. “Knowing that we are starting to provide answers for our community makes this work incredibly significant.”
