Q & A: How Airborne Health Risks Follow Wildfire

January 27, 2025

Authored by:

Ruth Steinhardt

A series of wildfires devastated Southern California in first weeks of 2025, claiming at least 28 lives and billions of dollars in property damage. In communities ravaged by the Eaton, Hughes and Palisades fires, residents whose neighborhoods were leveled may no longer be in danger of active fire-because there are so few buildings left to burn-but they still face serious secondary health risks as they struggle to return and rebuild. One major hazard is air pollution, which is spread by California's powerful winds even to areas outside active burn zones. GW Today spoke to Kelvin Fong, assistant professor of environmental and occupational health in the George Washington University Milken Institute School of Public Health, about what's in wildfire smoke, why it's so dangerous and how to stay safe.

Q: What makes wildfire smoke so dangerous? What kind of health problems can it cause?

A: Wildfire smoke contains a very high level of fine particulate matter, tiny solids in the air, notably the general class of pollutant particles smaller than two and a half micrometers (PM_2.5). These extra fine particles are harmful because they get into the deepest parts of our lungs. Even at relatively low levels, they are known to cause health effects-increased risk of stroke, cardiovascular effects and cognitive problems. Pregnant women who are breathing in PM_2.5have an increased risk of pre-term birth. The EPA has designated around nine micrograms per cubic meter as a safe annual exposure level and 35 micrograms as a dangerous daily level. And in fire areas, concentrations reach as high as 500 micrograms per cubic meter.

The materials in that smoke are also dangerous. A lot of these fine particles come from vegetation, but an urban fire is also consuming plastics, industrial waste, and building materials. Some of those materials are highly toxic and even carcinogenic. So that's not good. Besides particles, there are also volatile gases, which have health risks of their own. But the fine particulates are the air pollutants with the most well-established health risk.

Q: How can people protect themselves from fine particulate matter?

A: The number one thing is a high-efficiency particulate air (HEPA) filter. If you're spending time outside, it's also recommended to wear an N95 respirator. It's important to note that these are not the conventional surgical masks that we got used to during COVID; those will not be as protective against tiny particles that can get so deeply into our lungs. The respirators look a little like something out of a science fiction movie, but they work.

(Adobe Stock)

If you live anywhere near a wildfire zone, it's becoming more common for weather apps to monitor air quality, including PM_2.5levels. So people can adjust their behavior and whether they wear a respirator based on that.

If you are in an area with low outdoor air quality, be careful about bringing those particles inside. So if you live near a fire, or in an area that's recovering, and you're walking on ash, take your shoes off when you come in.

You also want to check to make sure you have HEPA-rated vacuum bags. Otherwise, you may think you're cleaning up but you're actually just re-suspending those particles in the air when you vacuum.

Elderly people and children are particularly vulnerable, so protecting them should be a priority.

Q: These fires have been particularly destructive for a number of reasons, including extreme, see-sawing weather: the California drought of the second half of 2024 followed a wet year, so there was more vegetable material to dry out and burn. As the climate continues changing, are we likely to see more events like this?

A: Oh, yes. These fires are what we call a "compound event" in climate and health research, where you have multiple climate risks happening at once or in quick succession: the increased vegetation growth, the drought, the Santa Ana winds. And we can observe these extreme weather events becoming more common everywhere. Not to veer off track, but right now we have record snowfall in New Orleans, which hasn't seen that kind of snow in 130 years. So we as a society have to anticipate this kind of extreme weather and prepare for the health dangers it can cause.