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Why there's no doubt that cooler and more comfortable PPE is also the safer option

Compromised firefighter mobility can impact firefighter risk of injury and death


Sponsored by Tencate Protective Fabrics

By Robert Avsec for FireRescue1

Heat stress and its physiological impact on a firefighter while wearing and working in their structural firefighting protective ensemble, PPE, has been garnering more attention in recent years in our efforts to reduce firefighters' risk of injury or death. PPE manufacturers are constantly searching for new ways to keep firefighters safe from the external threats (e.g., thermal, mechanical, liquid) while at the same time lessening the impact of heat stress on the firefighter inside the garment.

Figure 1. When the body is at rest, thermoregulation is relatively balanced as the body’s cooling mechanisms can effectively work. (image by Robert Avsec)
Figure 1. When the body is at rest, thermoregulation is relatively balanced as the body’s cooling mechanisms can effectively work. (image by Robert Avsec)

Heat Stress Can Kill You

On the campus of Skidmore College in Saratoga Springs, New York the folks at the First Responder Health and Safety Laboratory take the subject of heat stress and firefighters very seriously. Denise Smith, Ph.D., is the lab’s director and the Principal Investigator for the Science Medicine and Research & Technology for Emergency Responders (SMARTER) project, a study supported by the DHS/FEMA Grant Directorate for the Assistance to Firefighters Grant Program with a Fire Prevention and Safety Grant.

Smith and her research team published some of the project’s key findings in 2015 with a paper entitled, Effect of Heat Stress and Dehydration on Cardiovascular Function, in which they 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.

Normally, your body regulates its internal body temperature within a narrow range close to 98.6 degrees Fahrenheit, despite wide variations in environmental temperatures. It is important to maintain a temperature within ± 1.5 degrees of 98.6 degrees Fahrenheit because greater changes in body temperature can lead to severe dysfunction, even death.

Figure 2. The amount of both evaporative cooling and radiant cooling is dramatically influenced by clothing. Thick, multilayered clothing with low permeability, such as firefighting turnout gear, can severely limit heat loss. (image by Robert Avsec)
Figure 2. The amount of both evaporative cooling and radiant cooling is dramatically influenced by clothing. Thick, multilayered clothing with low permeability, such as firefighting turnout gear, can severely limit heat loss. (image by Robert Avsec)

Thermoregulation is the process by which your body maintains its temperature and it does so through four processes:

  • Radiation (When the body is hotter than the surrounding air, heat moves to the cooler environment, even when there’s no air movement)
  • Conduction - transfer between objects without contact
  • Convection - exchange with the surrounding air
  • Evaporation - conversion of sweat to vapor

In extreme conditions, such as those you encounter during firefighting, your muscular activity generates a higher heat load and the clothing properties of your PPE severely restrict heat loss. Consequently, your body’s thermal equilibrium is disrupted, and body temperature increases more dramatically.

Smith and the SMARTER team determined that this build-up of heat within the firefighter’s protective ensemble—and the accompanying dehydration if lost body fluids were not replaced--were cause to elevate the risk of cardiovascular strain associated with firefighting to that of a major safety concern (See Figure 3).

Figure 3. Smith and her team found that cardiovascular strain can: (1) lead to a suddencardiac event (SCE) in vulnerable individuals with underlying cardiovascular disease; and (2) lead to fatigue and impaired performance in all firefighters. (figure created by Robert Avsec).
Figure 3. Smith and her team found that cardiovascular strain can: (1) lead to a suddencardiac event (SCE) in vulnerable individuals with underlying cardiovascular disease; and (2) lead to fatigue and impaired performance in all firefighters. (figure created by Robert Avsec).

The Impact of the “Terrible Twins”

Heat stress—that produces the “terrible twins” of hyperthermia and dehydration—can not only be the catalyst for an SCE; it can also have a negative impact on a firefighter’s ability to do their job safely, effectively, and efficiently (See Figure 4).

Factors in Firefighter Heat Stress

The results of the STARTER project showed that there are primarily three factors that contribute to heat stress (see Figure 5).

Figure 4. Hyperthermia and dehydration can severely impact health and job performance. (image by Robert Avsec).
Figure 4. Hyperthermia and dehydration can severely impact health and job performance. (image by Robert Avsec).

As firefighters and officers, there’s not much we can do about ambient temperature and humidity. And there’s only so much we can do about the heavy work that firefighting involves. So, that leaves the personal protective equipment we use, our structural firefighting protective ensemble, as one causative factor where we just might be able to have a positive influence.

The Tencate “Engineered Solution”

Earlier this year, I had the opportunity to speak with Bart McCool, end-use market manager for emergency response for TenCate Protective Fabrics, to learn more about TenCate’s latest fabric innovation, Enforce Technology, that’s been developed by TenCate scientists and engineers.

Figure 5. When these three factors get together the result is hyperthermia and dehydration. (image by Robert Avsec).
Figure 5. When these three factors get together the result is hyperthermia and dehydration. (image by Robert Avsec).

NFPA 1971: Standard on Protective Ensembles for Structural Fire Fighting and Proximity Fire Fighting, addresses the level of performance every PPE manufacturer needs to build into their ensemble elements. Until recently, those performance measures for the outer shell (fabric) have focused on protecting the firefighter inside from flame impingement and mechanical injuries (e.g., cuts or scrapes).

That outer shell (the first layer) was also designed to work in conjunction with the moisture barrier (second layer) and the thermal barrier (third layer) to protect the firefighter from external heat and fluid hazards (e.g., body fluids, hydraulic fluid).

But meeting those requirements has often resulted in PPE that firefighters found to be stiff and hard to move in when new; they also complained of how long it took to “break-in” that new turnout gear. So, with that kind of feedback, TenCate went “back to the drawing board.”

Making Turnout Gear Lighter and Cooler

And that meant TenCate focusing its scientists and design engineers on developing an outer shell fabric that was lighter and that moved better with the firefighter wearing it. The result was Enforce, a yarn used in outer shell fabrics that not only improved comfort for firefighters but also helps reduce work effort by not being a stiff outer shell impeding their movement. And all while still providing thermal and abrasion protection that’s compliant with NFPA 1971 requirements.

According to McCool, having a lighter and more flexible outer shell that moves with you is more than just an advancement in firefighter comfort.

“It also means that the firefighter wearing the garment is not working harder because they’re working against their turnout gear,” said McCool. “Less effort means less exertion and less exertion means less buildup of body heat. And that buildup of body heat is where the effects of heat stress start.”

And TenCate didn’t stop with the outer shell. Its design engineers took that ease of movement for a firefighter to the next level by creating a new thermal liner fabric, Caldura ELITE. Thermal barriers made with this smoother and slicker facecloth (the part of the thermal barrier that’s in contact with a firefighter’s skin) make it easier to get in and out of your PPE coat and pants (Caldura ELITE is manufactured using a proprietary physical process developed by Tencate’s engineers and is not a chemical finish or treatment).

The end result? Turnout gear made using TenCate fabrics for the outer shell and thermal barrier gives you turnout gear that moves with you, not against you. And that means less exertion on your part, less body heat that needs to be dissipated, and a decrease in the risk of you experiencing the effects of heat stress. How cool is that?

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