When a wildfire threatens a community, most people don’t think to ask whether the firefighters coming to help slept enough the night before, recovered from the previous day’s shift or have enough energy left for another day on the fire line. They simply expect firefighters to show up.

But that workforce is increasingly being stretched to its limits.

The U.S. national fire preparedness level has been at 5 for weeks in summer 2026, its highest level, suggesting firefighting resources are fully committed and some regions may need emergency staffing measures to meet the demand. Crews were battling more than 90 large fires in late August, and firefighters in the Southwest and Texas faced daytime temperatures over 100 degrees Fahrenheit (38 degrees Celius) at times.

In conditions like this, the unrelenting heat, stress and smoke take a toll on firefighters’ bodies.

Training, fitness and protective equipment allow firefighters to work in these extraordinary environments. But as a nurse practitioner, firefighter and founder of Purdue University’s FIRE Lab, I know too well that none of that makes the human body’s capabilities limitless.

Heat hits firefighters from 3 directions

Wildland firefighters face heat from the environment, the fire and their own bodies.

Hiking steep terrain with heavy equipment, clearing brush and cutting fire line to stop fires from spreading creates internal metabolic heat. Sun and high air temperatures add environmental heat, while flames and smoldering fuels contribute radiant heat.

The body responds by sending more blood toward the skin to release that heat while........

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