The wildfire danger we’re only just beginning to understand

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Wildfires are popularly considered wild — restricted to the remote wilderness or the edge of forests, and to most, a problem for the dry and hot states of the Western US. But over the past few years, and now across the country, these fires are getting less wild and far more urban.

Urban construction is rapidly expanding into the wilderness, putting more communities closer to wildfires.

Fires in urban areas expose us to burning metals and other substances that release numerous toxic chemicals.

The long-term effects of those chemicals — including higher cancer risk and cardiovascular or respiratory illnesses — make wildfires more dangerous.

This summer, fires in Spokane, Washington, demolished over 800 homes in a suburban neighborhood, and earlier in the season, the northeast coast was engulfed in smog from fires in Ontario. The Hawk Fire in Nevada razed more than 15,000 acres near Reno, destroying 47 homes before it was extinguished. The Los Angeles fires of last year remain some of the most devastating in recent memory, with over 37,000 acres burned — much of it densely built residential neighborhoods — and displacing 205,000 people from their homes. In Boulder, Colorado, the 2021 Marshall Fire destroyed nearly 1,000 homes.

This changing geography of fires is affecting the health risks they present, too.

When vegetation burns, it releases particulate matter, or PM 2.5, and with over 46 million homes in the continental US — this is approximately one-third of all homes — on the edge of fire-prone wildland, many more of us are being exposed to air filled with that soot. This alone is a major health risk. According to the World Health Organization, PM 2.5, is associated with premature death, severe damage to respiratory health, and cognitive impairment. It is especially dangerous for aging populations: a study published in February found that accumulated exposure to wildland smoke was associated w

But the urban landscape has also changed the very composition of the smoke that increasingly hangs over all of us. As human structures and vehicles burn, the fires expose us not just to particulate matter but also to the chemical toxins of urbanization itself, from plastic to metal oxides and vehicle fuel. The changing nature of this smoke, in fire zones but also in surrounding regions as it drifts outward, exposes us to a new class of health risks.

While researchers are still learning what exactly those risks might entail, early research suggests long-term dangers that are deeply troubling, especially as exposed populations age.

In 2020, the worst California fire year on record ate up 4.2 million acres of land, most of it wild, spewing huge amounts of PM 2.5 into the air as the blazes raged. Emergency rooms, already short-staffed by the ongoing pandemic, buckled under the burden immediately. Northern California’s Stanford Health Care system saw a 12 percent jump in hospital admissions over the weeks following the fires, and a 43 percent increase in cardiovascular conditions. In Oregon that same year, 10 percent of emergency room visits were due to asthma-like conditions induced by smoke as fires migrated north.