Extreme heat is taking a toll on firefighters as wildfires stretch crews to the limit

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 continuing to supply oxygen to working muscles. The heart works harder to support both jobs.

As fluid losses increase, the volume of blood circulating through the body can fall, the heart rate rises, and the work of fighting fires feels harder.

Field studies show how this strain can become severe. In one study of 221 wildland firefighters on the job, 61% reached a core temperature of at least 100 F (38 C). About 50% reached a physiological strain index of 6 or greater on a 0-to-10 scale that combines heart rate and core temperature to measure how hard the body is working to cope with heat. Among those whose body temperatures crossed 100 F, the majority remained above that temperature for more than 30 minutes.

A core temperature of 100 F does not by itself mean heat stroke, but it signals substantial physiological strain. Staying hydrated helps the body sweat and keep blood circulating, but even a fully hydrated firefighter can overheat when the body gains and produces heat faster than it can release it.

Immediate consequences can develop quickly

Heat strain may begin with fatigue, headache, dizziness, weakness or nausea and progress to heat exhaustion or heat stroke. Severe hyperthermia can affect the brain, heart, kidneys and liver.

Wildland firefighters can also face rhabdomyolysis, a breakdown of skeletal muscle that can contribute to kidney injury. The National Institute for Occupational Safety and Health reported 62 severe cases among wildland firefighters from 2010 to 2020 and cautioned that the true number was probably higher.

Heat adds to fatigue when firefighters must anticipate fire behavior and make rapid decisions.

A 2025 field study found that wildland firefighters averaged 13.8-hour shifts on days when they were fighting fires and got around 6.7 hours of sleep. Poorer sleep and longer shifts were associated with reduced cognitive function, which can affect a firefighter’s ability to make split-second calls, such as when to retreat from an escalating fire.

Effects stay with bodies beyond one shift

The effects of heat and exhaustion can also add up. A firefighter can finish a shift hot, smoke-exposed and physically depleted, sleep in a warm camp and return to the line before fully recovering. Repeating that pattern across days and fire seasons may place ongoing strain on the heart, lungs and kidneys.

Smoke adds another health risk. Wildland firefighters commonly work in smoke without the kind of protection that firefighters use when fighting blazes inside buildings.

A 2019 exposure-modeling study estimated that, depending on the number of fire days worked over a career, cumulative smoke exposure could increase a wildland firefighter’s risk of dying from lung cancer by 8% to 43% and dying from cardiovascular disease by 16% to 30%. These are estimates, but they show why career-long exposure deserves attention.

Kidney health is another emerging concern. A 2025 study of 39 wildland firefighters found temporary decreases in kidney function and changes in kidney-injury biomarkers during one midseason fire incident. More research is needed to determine whether firefighting over seasons and years can lead to persistent kidney damage.

These findings raise an important occupational health question: What happens when heat, dehydration, smoke, sleep disruption and extreme physical exertion accumulate not only across one incident but across an entire career?

How to lower the risk

The heat isn’t going away, but there are ways wildfire management agencies can reduce the risk to firefighters.

First, firefighter health should be an important part of national wildfire readiness policies. Having adequate staffing so firefighters aren’t overworked and have meaningful enough recovery time to rehydrate, cool down and sleep between shifts are important. So are conditions that allow real sleep between shifts.

Monitoring firefighters’ health can also help catch early warning signs, such as kidney stress or burnout.

The public can also help by reducing the likelihood of high-stress fire situations.

The National Interagency Fire Center estimates that about 85% of U.S. wildfires are caused by human activities. Some of those can be avoided by fully extinguishing campfires, checking local fire restrictions, avoiding spark-producing activities on dry, windy days when fire risk is high, and maintaining vehicles and trailers so metal does not drag and ignite vegetation.

If you live in wildfire-prone country, creating defensible space and reducing combustible material around your home can reduce the fuel for fires. Evacuating promptly in an emergency also reduces the likelihood firefighters will have to put themselves in high-stress situations to rescue you.

We all expect firefighters to be there when the worst happens. Making sure they can do their jobs and stay healthy will allow them to continue to show up.