How hot does a firefighter get?

Firefighters engage in intense physical labour while being exposed to extreme heat. We now know more about what happens to their body temperature during smoke dives.

Three firefighters walking down some stairs.

A simulated smoke dive revealed high physiological strain on the firefighters.

(Photo: Trøndelag Fire and Rescue Service)

Kathrine Nitter Communications Adviser

Presented by: SINTEF

Published 11 March 2025 - 00:01

The heat hits you like a tonne of bricks. Maybe flames do too. Smoke is everywhere, and it's hard to see anything. But you have to go in. You will likely have to lift, drag, or carry heavy objects.

High-intensity work in extreme heat puts high demands on a firefighter. The body is subjected to significant strain.

Heavy protective clothing and equipment can contribute to high cardiovascular stress. Overheating is also a risk.

Physical and mental impact

An increased body temperature affects the ability to think clearly. Physical reaction time decreases. The risk of heat strain and heatstroke increases.

A recent study conducted at FRIC, Norway’s fire research and innovation centre, examines how heat affects firefighters.

“We have investigated the physiological response to a simulated smoke dive in extremely hot environments. We also looked at the subsequent recovery phase,” says SINTEF researcher Mariann Sandsund.

19 male firefighters performed a 15-minute simulated smoke dive inside a two-story heat chamber with temperatures ranging from 110 to 272 degrees Celsius. This was followed by five minutes of stair climbing outside the heat chamber.

Heart rate, core body temperature, and skin temperature were recorded continuously during the experiment.

Increasingly higher body temperature // Continuously rising body temperature

“Measured exposure temperatures of well over 250°C showed the extreme temperatures that firefighters can be exposed to,” says Edvard Aamodt.

He is a researcher at RISE Fire Research in Trondheim.

“We also know from studies in other countries that the temperature can be much higher for short periods when working on a live fire event. This is important to be aware of,” he says.

A sensor for measuring temperature is attached to the outside of the jacket.

Heat stress tests have now been introduced as annual mandatory exercises for firefighters. However, such tests vary between countries and even within them.

More knowledge is essential to ensuring good health and safety in this profession.

“Physiological data from actual firefighting activity or realistic training has been in short supply,” says Sandsund.

Knowledge can contribute to increased safety

During a smoke dive, firefighters use compressed air cylinders that provide about 20 minutes of air. Firefighting activity may be repeated several times after short recovery breaks to cool down, hydrate, and change air cylinders.

The highest recorded core temperature among all firefighters was 39.6°C, with one reaching 40.2°C. It takes a long time for such high temperatures to return to normal.

When heat production exceeds cooling, the body enters a state where temperature continues to rise.

This means firefighters risk returning to activity with a higher body temperature for each successive smoke dive. This can lead to dangerously high temperatures. Short 20-minute breaks are therefore not always enough for body temperature to return to normal.

The study provides a better understanding of how the body reacts, the effects of protective clothing, and the strain on firefighters.

“The results can contribute to promoting health measures and improving safety by adjusting the work routines, such as cooling strategies, hydration, and rest schedules,” says Sandsund.

The researchers also believe that increases in body temperature and heart rate should be considered during real fires when repeated smoke dives are necessary.

Research collaboration

The smoke dive work has been carried out in collaboration with Trøndelag Fire and Rescue Service, which is one of the partners in FRIC (Fire Research & Innovation Centre). FRIC is funded by all the partners, as well as the Research Council of Norway (Fire Safety programme, project number 294649), including a significant gift donated by the Gjensidige Foundation. FRIC is led by RISE Fire Research in Trondheim, with NTNU and SINTEF as research partners.

Reference:

Sandsund et al. 'Heat strain in professional firefighters: physiological responses to a simulated smoke dive in extremely hot environments and the subsequent recovery phase', Industrial Health, vol. 62, 2024. DOI: 10.2486/indhealth.2023-0151 (Abstract)