Key Cooling Strategies to Mitigate Firefighter Heat Stress

Being a firefighter means leading a life dedicated to serving others in a most honorable manner. It means saving lives at the cost of losing your own.

Firefighters are constantly exposed to burns, smoke inhalation and crush injuries from collapsing structures. They are also exposed to heat stress, on a daily basis, which leads to severe job-related illnesses, from heat stress disorders such as heat stroke, heat exhaustion, heat stress rash, to sudden cardiac deaths.

2,475 thermal stress injuries were reported among firefighters in 2016, according to a National Fire Protection Association (NFPA) report.

Find out the most important methods and strategies that support heat stress prevention and heat stress control within the fire service, securing the health of those who protect their communities every day.

Heat stress prevention before work

Resistance to heat stress can be improved through fitness and heat acclimatization.

Fitness workout is essential for firefighters, as it develops a healthy circulatory system and an increased blood volume that supports body temperature regulation through sweat. Fit firefighters also have a lower heart rate and body temperature. They adjust to heat stress twice as fast as unfit workers, losing acclimatization more slowly and gaining it more quickly, according to a study conducted at the University of Montana Human Performance Laboratory.

Acclimatization is a complex process of changes that occur in the body as a response to heat stress-induced in a controlled environment over 5 to 10 days. It is achieved by gradually increasing work time in the heat, replacing fluids and taking rest as needed. The adaptations that occur are beneficial to exercise in the heat, as afterward, firefighters will better cope with heat stress.

 Acclimatization favors:

·         Sweating at a lower temperature

·         Sweat production increase

·         Blood circulation improvement

·         Heart rate and body temperature decrease

Heat stress prevention on the job

When on duty in hot environments, firefighters should take several heat stress control measures: pace themselves, avoid working close to heat sources as much as possible, change tools or tasks to minimize fatigue.

Most importantly, firefighters should hydrate themselves to replace lost fluids and avoid heat stress dehydration.

According to studies published by the US Forest Service, during fire suppression activities, a firefighter needs to evaporate about 1 liter of sweat for each hour of work. Therefore, replacing lost fluids is crucial for preventing heat stress dehydration by drinking water before, during and after work. Thirst does not estimate correctly the fluid needs; therefore, firefighters should drink more water than they feel they need, avoiding excess caffeine as it hastens fluid loss.

When we sweat, we lose water and electrolytes – salts such as sodium, chloride, potassium. Therefore, a balance of different electrolytes is vital for the healthy function of the body. On the contrary, electrolyte imbalance is prone to happen. Symptoms can include twitching, weakness and even seizures and heart rhythm disturbances. Therefore, carbohydrate or electrolyte beverages are recommended, as they support fluid retention and rehydration, also maintaining energy levels. 

The role of protective clothing

A major component of heat stress control is the proper selection of Personal Protective Equipment (PPE), according to the type of incident call involved.

The U.S. Occupational Safety and Health Administration (OSHA), Canadian General Standard Board (CGSB), and state and provincial entities enforce regulations to assure safe working conditions in North America, to reduce the risk of injury due to fire, falls, chemical exposure and other physical hazards.

For firefighters in North America, PPE should meet NFPA 1971: Standard on Protective Ensembles for Structural Fire Fighting and Proximity Fire. This standard requires fire departments to provide each member with protective clothing and equipment for hazards likely to be faced in the line of duty.

In Europe, PPE should conform with CE and ISO standards that demonstrate compliance with the Personal Protective Equipment Regulation and European Standards.

Regulation (EU) 2016/425 on personal protective equipment (the PPE regulation) defines legal obligations to ensure that PPE on the EU internal market provides the highest level of protection against risks. The CE marking provides evidence the product complies with the applicable EU legislation.

The European Committee for Standardization (CEN) is producing harmonized standards in the EU to meet the health and safety requirements of the regulation for PPE.

NFPA 1971

NFPA 1971, that governs structural fire PPE in the US, requires proper garment protection to be used by firefighters. The standard specifies two required measures for adequate firefighting protection. The thermal protection performance (TPP), should achieve a minimum of 35 rating to meet the NFPA 1971 standard. The total heat loss (THL) must be at least 205 w/m2 for structural fire use.

The performance of a garment is mostly recognized after the TPP, which is a marker of resistance to thermal exposure. This garment key standard is high, due to thicker, heavy fabric material. In contrast, a high THL rating means a garment’s good ability to dissipate heat, which requires a thinner and lighter fabric material. Therefore, the requirements for TPP come in contradiction with those for a high THL.

What is turnout gear made of?

The turnout gear required by NFPA 1971 to be used by firefighters in structural fire situations includes three layers of protection, each performing a critical function: the outer shell, the moisture barrier, and the thermal liner. They are all made up of flame-resistant fibers and have attributes such as break-open resistance, flexibility, weight, strength, abrasion resistance, and durability.

The outer shell’s main purpose is to protect the firefighter from direct flame. It also has abrasion, cut-protection and strength features.

The moisture barrier layer protects the firefighter from water, chlorine, battery acid, aqueous film-forming foam, gasoline, hydraulic fluid, and antifreeze fluid, which NFPA calls “common liquids”. This layer also has a breathability role, allowing perspiration to move away from the skin.

The thermal liner is responsible for the thermal protection of most of all layers. Therefore, the thickness of the thermal liner indicates the level of heat the firefighter will feel.

Together, the three layers protect firefighters against thermal, physical, environmental and bloodborne pathogen hazards of a firefighting event. 

Turnout gear & heat stress risks

Although NFPA 1971 standards are created to prevent heat stress in firefighters, the necessary protection intensifies the risk of heat stress. While protecting firefighters from lots of hazards, the turnout gear determines microclimate formation between the body and the gear. It appears when the temperature of the skin differs from the temperature outside the turnout gear.

Although helpful in keeping core temperature lower when fighting structural fires, microclimates reduce the body’s natural cooling capacity as the thermal heat loss is reduced, meaning that sweat, the body’s natural cooling mechanism, is blocked inside the gear to different degrees, thus occurring the risk of heat stress or heart illnesses.

When a firefighter leaves a fire, the resulting humid microclimate with a higher temperature than the environment offers proper conditions for a heat stress episode. Also, during non-fire events, even if the weather is cold, the turnout gear may trap heat within the suit, reducing the body’s own cooling process. Therefore, alternative PPE is very important.

Four cooling strategies for firefighters

Keeping cardiovascular and thermoregulatory strain within safe levels is very important for firefighters wearing PPE. Several practices for heat stress mitigation include:

•  active cooling
• passive cooling
• conductive cooling
• convective cooling
• evaporative cooling.  

During active cooling, firefighters reduce elevated core temperatures by using external methods and devices such as hand and forearm immersion in buckets or coolers full of ice water, misting fans and ice vests. According to the NFPA 1584: Standard on the Rehabilitation Process for Members During Emergency Operations and Training, active cooling should become a standard operating procedure.

Passive cooling techniques, such as the opening of the PPC and sitting in a shaded area also help reduce body temperature. However, passive cooling is 50–60% less effective than active cooling, according to a study conducted by the Orange County Fire Authority (OCFA). After a simulated live-fire interior attack with simulated victim rescue and fire-ground support activities, firefighters performed active and passive cooling remedies. After 20 minutes of cooling techniques, the average drop in core temperatures was 0.75 °F in the case of passive cooling; 0.88 °F when using the misting fan; 1.18 when using cold/wet towels; and 1.22 °F, when performing the forearm immersion.

There are also heat stress mitigation methods based on the ways heat is exchanged with the environment – conduction, convection, radiation, and evaporation.

·         Conductive cooling refers to heat loss through direct contact with a cooler object.

·         Convective cooling is the dissipation of heat when cool air passes over exposed skin.

·         Radiative cooling is the release of heat from the body directly into the environment.

Evaporation through perspiration is the body’s most effective method of cooling under most circumstances, dissipating up to 600 kcal per hour in optimal conditions, according to a study written by M.D. James L. Glazer for the American Family Physician. In evaporative cooling, a mist of cool water (59°F) is sprayed on the skin, while warm air (113°F) is fanned over the body. With this technique, cooling rates have been measured at (0.56°F) per minute, the same author reports.

Honeywell PPE to mitigate heat stress

Honeywell has been thinking solutions for firefighter’s heat stress mitigation for decades.

Honeywell’s Morning Pride® Gear Shield was created to significantly prevent dangerous smoke particles with the associated fire gases from getting onto firefighter’s skin while maintaining breathability and encouraging air circulation throughout the gear to combat heat stress. Its integrated particulate-shielding design addresses the key interface areas – helmet to hood to air mask, coat to pant, glove to coat sleeve, and boot to pant cuff.

The Morning Pride Heat Release Liner is the latest exclusive self-regulating feature designed to help combat heat stress. It provides vents that allow warm/moist air normally trapped inside the liner to rise and escape at the chest and shoulder blades through vents. As the warm air rises out of the coat and liner when the collar and top of coat closure are opened, cooler and drier air enters through the bottom of the coat, where four liner vents are also provided.