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Understanding what the thermal heat loss of your PPE means for you

Your gear can protect you from flames but what about heat stress?


Sponsored by Tencate Protective Fabrics

By Robert Avsec for FireRescue1 BrandFocus

Fire suppression operations are hot, exhausting, and dangerous. And that’s just inside the building where the firefight is happening. Add in high ambient temperatures and elevated humidity levels outside and it gets very uncomfortable very fast. But heat stress is not just uncomfortable, it can kill you.

Heat stress puts an extraordinary insult on a firefighter’s cardiovascular system and is among the biggest threats for firefighters. (image/Getty)
Heat stress puts an extraordinary insult on a firefighter’s cardiovascular system and is among the biggest threats for firefighters. (image/Getty)

Current research, like that from the Science Medicine and Research & Technology for Emergency Responders (SMARTER) project, indicates that heat stress also puts an extraordinary insult on a firefighter’s cardiovascular system, the worst outcome being a sudden cardiac event (SCE) like a stroke or heart attack.

Dr. Denise Smith is the principal investigator for the SMARTER Project and director for the First Responder Health and Safety Laboratory on the campus of Skidmore College in Saratoga Springs, New York.

In “Effect of Heat Stress and Dehydration on Cardiovascular Function,” Smith and her colleagues wrote:

Firefighters are exposed to numerous life-threatening dangers, including high temperatures, flames, smoke, hazardous chemicals, and unstable structures. Despite these dangers, the physiological strain, specifically cardiovascular strain, associated with firefighting poses the greatest threat to the life and health of a firefighter.

Smith and her associates determined that three distinct elements of a firefighter’s work contribute to firefighter heat stress (See Figure 1 below).

Figure 1. Smith, D. (2015). Effect of Heat Stress and Dehydration on Cardiovascular Function. SMARTER Project. First Responder Health and Safety Laboratory. Skidmore College. Saratoga Springs, New York. Original graphic by Robert Avsec
Figure 1. Smith, D. (2015). Effect of Heat Stress and Dehydration on Cardiovascular Function. SMARTER Project. First Responder Health and Safety Laboratory. Skidmore College. Saratoga Springs, New York. Original graphic by Robert Avsec

Their research has demonstrated that hyperthermia and dehydration—if fluids lost during sweating are not replaced—are the two acute factors (the “terrible twins”)—that can lead to cardiovascular strain (Vulnerable individuals with underlying cardiovascular disease being the major chronic factor).

The SMARTER team also found that the presence of the “terrible twins” led to a wide variety of unwanted consequences in all firefighters studied (See Figure 2 below).

Firefighter PPE: Friend and Foe

As we’ve seen in Figure 1 above, the structural firefighting protective ensemble (PPE) is a major contributor to a firefighter developing hyperthermia and dehydration.

Why? Because a firefighter’s PPE is tasked with meeting two very difficult objectives: (1) Protect the firefighter from external heat (from the fire); and (2) protect them from their own heat building up inside their PPE.

NFPA 1971: Standard on Protective Ensembles for Structural Fire Fighting and Proximity Fire Fighting, provides the specifications and performance requirements that manufacturers must meet for all elements of the protective ensemble. There are more than 70 performance tests specified in NFPA 1971 for those components, but we’ll look at two of the most relevant ones: TPP and THL.

The thermal protective performance (TPP) test measures a garment’s thermal performance (protecting the firefighter during emergency firefighting conditions where there are high thermal exposures (e.g., during flashover or backdraft); the THL test measures that same garment’s breathability (its capability to release the heat generated by the firefighter inside the PPE).

Keeping Firefighters Cooler, Drier, and Safer

The fabric designers and engineers at Tencate Protective Fabrics work diligently to provide PPE components that work better at dissipating the heat generated by the working firefighter inside the PPE (THL) while still protecting them from the external heat threat (TPP).

And the component of a firefighter’s turnout gear that has the most impact on the garment’s THL is the thermal liner/moisture barrier. TenCate’s lineup of thermal liner uses a combination of Kevlar and Nomex fibers that give fire departments the capability to protect their personnel with a thermal liner that more effectively and efficiently wicks (moves) perspiration away from the body.

That helps keep the firefighter inside drier and more comfortable (The company’s DEFENDER M Thermal Barrier is designed with the same fiber and technology that’s been used to protect U.S. Army ground forces in Iraq and Afghanistan since 2007).

And safer, because moisture (sweat) that stays in the thermal barrier of your turnout coat and pants can significantly affect performance, potentially causing serious drops in thermal protection. Dry gear provides better protection than wet gear particularly with the layer that’s closest to the firefighter, the thermal/moisture barrier.

Working easier

Reducing firefighter heat stress also involves making turnout gear that’s easier to get on and off, and easier to work in once it’s on. TenCate’s leading thermal liner fabric, Caldura ELITE, is a leader in thermal liner fabrics because its smooth, slick face cloth allows the firefighter using the turnout gear to don and doff their coat and pants easier.

How? Because the facecloth (the part of the thermal barrier that’s in contact with a firefighter’s skin) has been put through a process to make it slicker, softer and easier to wear (this is a proprietary physical process developed at Tencate and is not a chemical finish or treatment).

“We focus very hard on engineering thermal liners that provide moisture management,” said Stuart Perry, brand communications manager at TenCate Protective Fabrics. “Reducing heat stress is our goal and our inherently wicking face cloths really set us apart in the industry.”

It’s also easier work for firefighter wearing PPE with a Tencate thermal liner. Because when their turnout gear is stiff or bulky (or both) it means their gear is working against them, not with them, and that means they’re generating more body heat that needs to be dissipated.

So, when looking for turnout coat and pants as part of the structural firefighting protective ensemble to protect your department’s firefighters, consider the TenCate difference. Because the heat from within can be just as dangerous to a firefighter’s health and wellbeing as the fire they’re working to extinguish.

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