Chemical Insights
Today, wildfires are becoming larger and more destructive as they burn in the wildland urban interface (WUI) – where human development meets or intermixes with undeveloped wildland fuel. Wildfires are increasing in both frequency and severity due to climate change, the expansion of interface communities, and historical land management practices.
The economic, environmental, and human health impacts of these fires are substantial. Today, close to one-third of the U.S. population, residing in nearly 50 million homes located in the WUI, is directly at risk of experiencing a wildfire. Even more of the population may be indirectly affected by poor air quality issues as the result of wildfire smoke.
WUI fires can be more catastrophic because they involve urban materials (or fuels) such as homes, cars, and other human-made structures. Compared to the vegetative biomass that combusts in a wildland fire, combustible materials found in the WUI have different elemental compositions and densities, and are present in different quantities and arrangements. For example, chemical elements and materials of concern, such as halogens, plastics, and metals, exist in much higher concentrations in the WUI, resulting in different emissions, exposure outcomes, and health effects. Additionally, materials unique to urban areas, such as polyvinyl chloride or polyurethane, often contain much larger amounts of chlorine or nitrogen, which are known to impact combustion chemistry.
While all wildfires produce smoke and a large mix of pollutants, including volatile and semi-volatile organic compounds (VOCs and SVOCs respectively) and particulate matter (PM), when a wildfire spreads to include the urban fuels in the WUI, an entirely different mix of pollutants are released. Environmental pollutants come in many forms, including:
As a wildfire burns, it generates a giant mass of emissions, including particles and chemicals, called a plume. Once these emissions are put into the environment, the plume evolves over time through a process called atmospheric transformation. Initially, gas-based compounds condense onto other particles in the atmosphere. Then, some compounds react with atmospheric compounds to create new compounds as other compounds photochemically react in the sunlight. The process continues as the plume mixes with other urban pollutants in the air, such as vehicular or industrial emissions. As the plume moves further downwind, the process slows and ultimately particles begin to fall from the sky, leaving residents in proximity to the plume vulnerable to different types of exposure. While larger particles may be visible as ash, smaller particulate matter (PM2.5) may be harder to detect and can take longer to settle as dust.
Wildfire plumes can travel great distances, even spanning across entire continents. While there is much to learn about the health effects from an atmospherically transformed plume at regional and continental scales, more is known about the health effects closer to the initial source.
Certain members of the population may be more vulnerable to exposure than others, such as children, older adults and pregnant women. Additional examples include people who have:
Since WUI fires cannot be left to naturally burn out, nearby workers, such as firefighters, emergency response teams, and clean-up recovery crews are increasingly exposed to emissions, smoldering and resulting residues, and dust. Additionally, outdoor workers in surrounding areas, such as farmers and landscapers, may be at a greater risk.
While wildfire emissions contain a wide array of dangerous pollutants, particulate matter is a primary concern.
While wildfire emissions contain a wide array of hazardous pollutants, PM2.5 (particulate matter that is 2.5 microns or less in diameter) is a primary concern. When PM2.5 is inhaled, it can penetrate deep into the lungs, and may even infiltrate into the bloodstream. Studies have directly linked wildfire PM2.5 to health issues such as exacerbation of asthma, chronic obstructive pulmonary disease, premature death, and circulatory effects, such as heart attacks and stroke.
How small is 2.5 micrometers? The average human hair is about 70 micrometers in diameter – making it 30 times larger than the largest fine particle.
There are several ways to reduce or avoid exposure to wildfire emissions, including PM2.5, with varying levels of feasibility. Air filtration (or “air cleaning”) is one of the most practical and effective ways to safeguard indoor air quality during and after a wildfire. Air filters are designed to capture pollutants and remove them from the indoor environment. Since PM2.5 is so small, specialty or high-quality air filters are needed to capture it.
Applying higher performance filtration on supply ventilation in homes can reduce outdoor particles by up to 97%, and portable air cleaners can reduce indoor PM exposure by 48% – 78%.
Many people are using DIY air cleaners to remove particles from wildfire smoke. However, since consumers are retrofitting box fans not intended or evaluated for this purpose by the manufacturer, there have been some concerns about their safety during use. In 2021, CIRI, with support from the Fire Safety Research Institute, partnered with the U.S. Environmental Protection Agency’s (EPA’s) Office of Research and Development to provide scientific information to help people stay safe during wildfire events. In July 2021, CIRI published a report that presented findings on the evaluation of potential safety risks while operating a DIY air cleaner.
How to Make a DIY Air Cleaner
We demonstrate how to make and use a DIY air cleaner to protect your indoor air quality during a wildfire smoke event.
Educational Handouts |
Nov 10, 2023
Application Notes |
Aug 13, 2022
Technical Reports |
Jul 01, 2021
While people may primarily associate air and water contamination with the combustion products of a wildfire, there is an often-overlooked hazard of residual dust. During and after a wildfire, even after the sky clears, a hazardous mixture of particulate matter (PM), dust, and ash can infiltrate homes and other buildings for several days or weeks. If not properly removed, this dust can settle on surfaces, contaminate textiles like carpet and upholstered furniture, and even resuspend in the air, presenting a continued exposure risk for residents. The majority of household dust comes from the outside through windows, doors, vents, and on the soles of shoes. Therefore, in the aftermath of a wildfire, it is particularly important to take additional steps to remove settled dust.
The negative health effects from exposure to settled dust may include eye, nose, and throat irritation, exacerbation of asthma, eczema, chronic obstructive pulmonary disease, and cardiovascular disease, such as heart attacks and strokes. Dust is also an important route of exposure to toxins. Since settled dust is hard to clean up and can remain in environments for an extended period, it presents a long-term (chronic) exposure risk for people, beyond the short-term (acute) risk posed in the immediate aftermath of a wildfire.
CIRI partners with the Insurance Institute for Business and Home Safety (IBHS), the National Fire Protection Association (NFPA), the U.S. Environmental Protection Agency (EPA), and other organizations to communicate the effects of WUI wildfires on both human health and the built environment.
Mitigation strategies for the built environment involve:
