Health hazards from wildfire smoke can linger for long periods in homes that have avoided burning

Three years ago, December 30, 2021, a fire caused by wind raced through two communities just outside Boulder, Colorado. In about eight hours, over 1000 houses and businesses burned down.

The fire left entire blocks in ash, but among them fragments of houses survivedseemingly untouched. The owners of these homes may have felt relief at first. However, fire damage can be misleading, as many soon discovered.

When fires like the Marshall Fire reach the wildland-urban interface, they burn both vegetation and man-made materials. Vehicles and buildings burn along with everything in them – electronics, paint, plastics, furniture.

Studies show that burning such man-made materials causes the chemicals released are different from what is emitted when the vegetation itself burns. Smoke and ash can billow under the doors and around windows of nearby homes, introducing chemicals that stick to walls and other indoor surfaces and off-gas for weeks or months, especially at higher temperatures.

In new studyMy colleagues and I looked at the health effects people experienced when they returned to their still-standing homes after the Marshall Fire. We also created the so-called a checklist for use by people following urban fires in the future to assist them protect their health and reduce the risks they face when returning to smoke-damaged homes.

Tests conducted in homes showed increased metal and VOC content

In the days after the Marshall fire, residents quickly contacted nearby scientists who are studying fire smoke and health risks at the University of Colorado at Boulder and area labs. People wanted to know what was hidden in the ash and what was causing the unpleasant smell in their homes.

My colleagues discovered that in homes we could test increased levels of metals and PAHs – polycyclic aromatic hydrocarbons – in the ash. We also found increased concentrations of VOCs – volatile organic compounds – in airborne samples. Some VOCs, e.g dioxins, benzene, formaldehyde AND PAHsmay be toxic to humans. Benzene is known carcinogen.

People wanted to know whether the chemicals that entered their homes that day could harm their health.

At that time, we found no information about the physical health consequences of people who returned to smoke-damaged homes after the fire. To look for patterns, we surveyed residents affected by the fire six months, one year and two years later.

Symptoms 6 months after the fire

We found it even six months after the fire many people reported symptoms which are consistent with the health risks associated with smoke and ash from wildfires.

More than half (55%) of people who responded to our survey said they experienced at least one symptom six months after the fire they attributed to the Marshall Fire. The most frequently reported symptoms were itchy or watery eyes (33%), headache (30%), parched cough (27%), sneezing (26%), and sore throat (23%).

All of these symptoms, as well as a strange taste in the mouth, were associated with people reporting that their home smelled different when they returned a week after the fire.

Many survey respondents said odors fade over time. Most attributed the improved odor to the passage of time, cleaning surfaces and air ducts, replacing furnace filters, and removing carpets, textiles, and furniture from the home. Despite this, many people still had symptoms.

We found that living near a vast number of burned buildings was associated with these health symptoms. For every 10 additional buildings destroyed within 250 meters of a person’s home, there was a 21% escalate in headaches and a 26% escalate in a strange taste in the mouth.

These symptoms are consistent with what can be expected from exposure to chemicals we found in the ash and measured in the air in several smoke-damaged homes that we were able to examine in depth.

Persistent symptoms and questions

There are still many unanswered questions about the health risks of homes damaged by smoke and ash.

For example, we don’t yet know what the long-term health consequences might be for people living with home gases caused by fire smoke and ash.

We found significant decrease in the number of people reporting symptoms one year after the fire. However, 33% of people whose homes were affected by the fire still reported at least one symptom that they attributed to the fire. About the same percentage also reported at least one symptom two years after the fire.

We also could not measure the levels of VOCs or metals to which each person was exposed. However, we believe that reports of a change in odor in an individual’s home one week after the fire indicate the likely presence of VOCs in the home. This has health consequences for people whose homes are exposed to smoke or ash from the fire.

Tips to protect yourself after future wildfires

There are fires houses and other structures burning more and more often as more people move to the intersection of wild and urban areas, temperatures are rising and the fire season is getting longer.

Knowing what to do if your home has survived a nearby fire can be confusing. To assist, my colleagues and I created a website with steps to take if smoke or ash from a fire ever enters your home.

Here are some of these steps:

• When you’re ready to neat your house, start by protecting yourself. Wear at least an N95 (or KN95) mask and gloves, glasses, and clothing that covers your skin.

• Vacuum floors, curtains and furniture. However, avoid harsh chemical cleaning products because they may react with the chemicals in the ash.

• Pristine the HVAC filter and ducts to avoid further spread of ash. Portable air purifiers with carbon filters can assist remove VOCs.

A recent scientific study documents how cleaning all surfaces in your home can reduce VOC build-up and lower VOC concentrations in indoor air.

Given that we don’t yet know much about the harm of smoke- and ash-damaged homes, it’s critical to pay attention to how you neat to best protect your health.