By Andrew R. Poreda, MD, and Kyle Kelleran, PhD
When temperatures plunge and snow piles up outside the apparatus bay, every firefighter knows the drill: Layer up, rotate fast and warm up in rehab.
Guidance from NFPA 1584 and articles like FireRescue1’s “Cold weather fire operations: Key tips for departments and crews” warn about frostbite, hypothermia and wet-gear exposure, and that advice is valid and important. But our new research at the University at Buffalo shows that cold-weather operations pose a second, less obvious threat: heat stress inside turnout gear, even in freezing air.
| MORE: Braving the cold: Essential EMS strategies for winter emergencies
Inside the study
Our team studied how firefighters’ bodies actually respond while working in the cold. Fourteen certified interior firefighters performed two identical sessions of moderate-intensity work in full turnout gear and SCBA. One session took place in a 68-degree F chamber and the other in a 17-degree chamber. Each session included two 20-minute work intervals separated by a brief rest period and followed by 20 minutes of rehab. Throughout the protocol, we measured core body temperature, mean skin temperature, hand and finger temperatures, heart rate, respiratory rate, perceived exertion and thermal comfort.
Despite the icy environment, firefighters’ core body temperatures still increased during exertion. The cold slowed the rise slightly, but heat accumulation was still significant. Turnout gear, designed to protect from flame and radiant heat, also traps metabolic heat extremely effectively. Even at 17 degrees, the body generated enough heat to raise core temperature and increase heart rate during work. Projections from our study suggest core hypothermia during active fireground activities may not be a major risk until significantly below 0 degrees, depending on wind conditions and wetness exposure. Future research would be needed to verify this claim and account for other variables because this projection does not account for frostbite or other thermal risks to the face and extremities.
What made this more complex was how firefighters felt in the cold. Physiologically, they were still generating and retaining heat. But perceptually, they felt comfortable, cooler and more capable. Heart rates and breathing rates were lower in the cold condition, and recovery was faster. But internal core temperature was still elevated. This created a mismatch between comfort and physiology. A firefighter may feel fully recovered long before they actually are.
This phenomenon matters because firefighters often rely on their own perception to determine whether they’re ready to go back to work. NFPA 1584: Standard on the Rehabilitation Process for Members During Emergency Operations and Training Exercises emphasizes the use of objective criteria, such as vital signs and temperature normalization, before a crew member is cleared to return. Our study strongly supports that standard. Comfort is not an accurate indicator of physiological safety in cold-weather operations.
The physiology behind the paradox
The physiology is straightforward. Turnout gear is very good at preventing heat transfer to the environment. In cold weather, the skin and superficial tissues may feel cool, especially in spots where gear is compressed or exposed to wind or in the extremities that are farther from the core. But deeper inside the gear, metabolic heat is accumulating. The body’s internal thermal load rises even as external temperature gives the illusion of safety. In addition, temperatures in gloved hands and fingers dropped in our study, showing that modern insulated firefighting gloves may not provide adequate protection in extremely cold ambient conditions.
This results in a weird and counterintuitive scenario: Winter firefighting presents the dual hazards of frostbite and heat stress. A firefighter may be building heat internally while their extremities are at risk of frostbite. Cold weather also reduces thirst sensation, meaning firefighters may become dehydrated without realizing it. All these risks must be monitored simultaneously, not one at the expense of the other.
Traditional cold-weather rehab often focuses on warming up quickly. Heated tents, blankets, warm fluids and heavy coats are staples of winter incident response. But if firefighters exit a structure overheated and sweating, a common scenario, immediate exposure to high heat in the rehab area can actually delay recovery. Our findings suggest that a neutral-temperature rehab area, protected from wind and moisture but not overheated, may allow for faster true physiological recovery. Because sweating and fluid loss still occur under turnout gear, hydration should remain a priority even in the cold. Finally, warming stations could be necessary for extremities.
Operationally, the reduced physiological strain observed in cold conditions raises the possibility of longer safe work intervals or shorter rehab times. However, this must be approached with caution. Heat stress risk remains real, and frostbite risk increases with prolonged cold exposure. Any extension of rotation times would require strict monitoring and validation through vital signs, heart-rate recovery and possibly, in the future, wearable sensors.
NFPA 1584 and key takeaways
NFPA 1584 already provides a strong framework for evidence-based rehab: rest, hydration, medical monitoring and documentation. Our study adds nuance to how this plays out in cold weather. Firefighters may not need aggressive external warming in all circumstances. Instead, they may benefit more from removing gear, cooling naturally to baseline, rehydrating and adding warming layers only if cold stress is present. Additionally, monitoring for signs and symptoms of frostbite may be necessary.
Key takeaways for officers include the following:
- Do not rely on comfort or self-assessment as a marker of readiness. Objective data must guide return-to-work decisions.
- Balance frostbite and heat stress prevention; both hazards can coexist in winter operations.
- Maintain hydration protocols even when firefighters do not feel thirsty.
- Build rehab areas that are dry and sheltered but not excessively warm.
- Ensure that firefighters fully recover before redeployment, regardless of how they feel.
Final thoughts
Looking ahead, future research should explore how wind, snow, moisture and contact with cold tools affect firefighter safety in winter operations because these variables were not tested in our study. Wearable physiological monitors may eventually give Incident Commanders real-time data on thermal strain. For now, the message is simple: Firefighters don’t stop generating heat when it’s cold outside. The cold can mask heat stress but does not eliminate it.
The next time snow is falling at a fire scene, remember that comfort can be deceptive. A firefighter who feels fine may still be running hot. The safest rehab is not the warmest one; it’s the one that restores the body to true physiological balance.
| WATCH: Cold weather response tips for EMS
ABOUT THE AUTHORS
Dr. Andrew Poreda has over 25 years of experience in prehospital care, beginning as a volunteer firefighter and EMT before training as an emergency medicine physician. He is nationally certified as a Firefighter II and holds multiple special operations certifications, maintaining strong involvement in fire and EMS throughout his career. After completing medical school and residency at SUNY Upstate, Dr. Poreda returned to Buffalo, where he now serves as dual-boarded faculty in emergency medicine and EMS at UBMD. Dr. Poreda lectures regionally and nationally and serves as medical director for multiple fire and EMS agencies, overseeing more than 210 providers and 11,000 annual calls. He is also active in fire and EMS research and education.
Dr. Kyle Kelleran is a researcher specializing in emergency medicine, with a background that bridges academia and frontline service. Holding a PhD in applied kinesiology, Dr. Kelleran serves as an assistant professor in the Department of Emergency Medicine at the University at Buffalo. A firefighter and EMT with over 15 years of experience, Kelleran remains actively involved as a volunteer with his local fire company. He has authored numerous peer-reviewed scientific manuscripts, contributing significant advancements to the field of emergency medicine.
