Urban Fires Emit More Toxic Poisons than Wildfires
This sounds logical–homes are not trees. The furnishings in our homes and cars in our garages are not trees or grasses. Therefore, when buildings and cars burn, they emit poisons that are different from burning trees or grasses. What does this mean for those living near huge urban fires? I think we’re just beginning to find out.
The Marshall Fire in 2021 damaged or destroyed about 1,200 homes and businesses. (Boulder County releases updated list of structures damaged and destroyed in the Marshall Fire) Because of the location and involvement of University of Colorado staff and students’ homes, the environmental impact of this fire was an unprecedented focus of study. We wrote an article about the toxins encountered in dust found in homes that were otherwise undamaged. Elevated concentrations of potentially harmful materials like polycyclic aromatic hydrocarbons (PAHs) were detected in the dust samples. PAHs can be found in urban fires and true wildfires.
The Los Angeles fires in 2025 caused more than 16,000 homes and businesses to be damaged or destroyed. Because an air quality monitoring station happened to be downwind of one of the fire, the Eaton Fire, researchers are getting a rare insight into exactly what chemicals were being released, and in what quantities. Lead and chlorine are known as trace elements in the air because they are supposed to stay in the nanograms-per-cubic-meter range. In the days after the fire, they reached levels of micrograms per cubic meter. When at their maximum that on January 11, chlorine levels reached about 40 times the normal amount, and lead peaked at more than 100 times the usual level. (Aerosol monitoring site collects data in aftermath of urban firestorm) Lead in any quantity is poisonous to humans, especially children, and inhalation of lead fumes is a route of poisoning that is not uncommon during paint removal/renovation (see our article on lead poisoning).
A 2023 study by researchers at the Environmental Protection Agency found that emission factors for some toxic compounds were more than 1,000 times higher in urban wildfires than in fires that burned in woodland areas. Paints, sealants, insulations, metals, and more can release many kinds of volatile organic compounds, gaseous pollutants and particulate matter. Toxicity also depends on the temperature of the fire, and how far and how long the smoke travelled, because the chemical aspects of the smoke can change as it’s exposed to sunlight. Here’s the specifics on what is more toxic (What Makes Urban Wildfire Smoke So Dangerous?):
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PAH emission factors were three orders of magnitude higher in urban emissions than those from woodland fires. (PAHs are also found in cigarette smoke and have been linked to blood and liver disorders.)
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Levels of other types of dangerous chemicals such as dioxins and furans, meanwhile, were five to six orders of magnitude higher in urban fire smoke than in vegetation-fuelled conflagrations. These substances have previously been shown to disrupt hormone regulation, inhibit fertility, and contribute to cancer.
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Research has also found elevated concentrations of the toxic organic compounds benzene, toluene, ethylbenzene, and xylenes – collectively known as BTEX – in the smoke released by city-based fires. Also present in vehicle emissions and cigarette smoke, these nasty chemicals have been linked to cancer and autoimmune disorders. The benzene can easily be produced in plastic water pipes that are heated, but don’t burn, which after resuming service, leach benzene into the water. Benzene was found at a level 8,000 times the federal drinking water limit and 200 times the level that causes immediate health effects after the 2017 Tubbs Fire and 2018 Camp Fire (California fires). (Plastic pipes are polluting drinking water systems after wildfires – it’s a risk in urban fires, too)
How can a person safely avoid smoke from urban wildfires while sheltering in place? It’s not easy, but if you live in a place where wildfires can quickly mushroom into urban fires, it’s best to do extensive preparation beforehand.
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The easiest way of sealing up your home is to let an experienced energy auditor show you where the bigger gaps in your home envelope are. They will do a “blower door test” to find them and make recommendations (or actually do the work to seal them). Check with your electric power company to see if they have recommendations for the service or will even do it for free!
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Sometimes gaps are not obvious because they’re not at eye-level. Here are some articles on finding and sealing these gaps yourself.
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Implement the other filter and HVAC recommendations we have in our article here.
- Make sure to have a good supply of food and bottled water, since community water systems may be contaminated with toxins from damaged pipes.
- Make sure you check out how to drive through polluted areas by reading this article, and get it ready with a new Cabin Air Filter, especially one with activated carbon.
