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

The U.S. wildfire response system is currently operating at its highest level of preparedness, known as Preparedness Level 5 (PL5), which has been in effect for weeks during summer 2026. This means firefighting resources are fully committed, and some regions may require emergency staffing to meet demand. In late August 2026, crews were battling over 90 large wildfires, with firefighters in the Southwest and Texas facing daytime temperatures exceeding 100°F (38°C). The extreme heat, combined with physically demanding work such as cutting fire lines and clearing brush, is pushing firefighters to their limits. The National Interagency Fire Center (NIFC) defines Preparedness Level 5 as a situation where firefighting resources are exhausted and additional support is needed to manage ongoing fires.

Wildland firefighters face heat from three primary sources: the environment, the fire itself, and their own bodies. The environment contributes heat through high air temperatures and direct sunlight, while the fire radiates heat toward firefighters. Physical exertion, such as hiking steep terrain with heavy equipment, generates metabolic heat as the body works harder to supply oxygen to muscles. This combination forces the body to circulate more blood toward the skin to release heat, while still supplying oxygen to working muscles. As fluid loss increases, blood volume can drop, causing the heart rate to rise and making firefighting feel more difficult. Studies show that 61% of wildland firefighters in one study reached a core body temperature of at least 100°F (38°C), and half experienced a physiological strain index of 6 or higher on a 0-to-10 scale, which measures how hard the body is working to cope with heat.

Heat strain can lead to immediate health consequences, ranging from fatigue, headaches, and dizziness to more severe conditions like heat exhaustion or heat stroke. Heat stroke is a life-threatening emergency where the body’s core temperature rises above 104°F (40°C), potentially damaging the brain, heart, kidneys, and liver. Another risk is rhabdomyolysis, a breakdown of skeletal muscle that can cause kidney injury. Between 2010 and 2020, the National Institute for Occupational Safety and Health (NIOSH) reported 62 severe cases of rhabdomyolysis among wildland firefighters, though the actual number is likely higher. These conditions highlight the severe physical toll that extreme heat takes on firefighters’ bodies during prolonged wildfire battles.

The demands of fighting wildfires often result in long shifts and inadequate rest. A 2025 study found that wildland firefighters averaged 13.8-hour shifts on fire days while getting only about 6.7 hours of sleep. Poor sleep and extended shifts were linked to reduced cognitive function, which can impair a firefighter’s ability to make quick, critical decisions, such as when to retreat from a dangerous fire. The combination of heat, smoke exposure, and physical exhaustion further compounds fatigue, making it harder for firefighters to recover between shifts. This pattern of sleep deprivation and prolonged exertion can accumulate over days and entire fire seasons, placing additional strain on the body.

The effects of heat, smoke, and exhaustion can extend beyond a single fire incident. A 2019 study estimated that cumulative smoke exposure over a firefighter’s career could increase their risk of dying from lung cancer by 8% to 43% and from cardiovascular disease by 16% to 30%. Another 2025 study of 39 wildland firefighters found temporary decreases in kidney function during a midseason fire incident, raising concerns about potential long-term kidney damage. These findings suggest that the combined impact of heat, dehydration, smoke, and extreme physical exertion may pose ongoing risks to firefighters’ heart, lung, and kidney health over time, even after individual incidents have passed.