Sudden cardiac events (e.g., heart attacks or stroke) are the leading direct cause of firefighter line of duty deaths in the U.S. In 2016, sudden cardiac events (SCE) caused 39 percent of firefighter LODDs; over the past 10 years, SCEs were responsible for 42 percent of firefighter LODDs.
Heat stress has been identified as a major factor in firefighter SCEs. This article explores strategies to protect firefighter cardiac health by avoiding extreme temperature changes, utilizing cooling technology and using structural firefighting protective gear that can protect from thermal injury and exposure, while at the same time reducing trapped moisture and heat inside the protective ensemble.
Effects of heat stress on the cardiovascular system
In a study done by the Illinois Fire Service Institute’s Firefighter Life Safety Research Center, researchers found that:
- Eighteen minutes of simulated firefighting activity caused significant physiological disruption, including an increase of heart rate (75 bpm) and an increase of core temperature (1.2 degrees).
- The simulated firefighting activities caused a significant increase in platelet numbers and a significant increase of platelet activation, resulting in faster clot formation.
- Firefighting activity resulted in an increased level of coagulation (increased factor VIII activity and PF1.2) and significant changes in clot breakdown (fibrinolysis).
Simply put, heat stress causes physiological changes in the body. Figure 1 depicts how the resultant heat stress from firefighting tasks affects the human body.
The most profound of these effects are those to the cardiovascular system, especially when there is already cardiovascular disease present.
Strategies for protecting your cardiovascular system from heat stress
Here are three strategies to protect your cardiovascular system from heat stress on the fireground.
1. Limit PPE time
Limit the amount of time that you are in your PPE to the shortest amount of time necessary to complete your assigned tasks.
When you’re doing strenuous work in a hot environment, it raises your body’s core temperature, which triggers profuse sweating as the body attempts to lower its temperature through evaporative cooling. However, the encapsulating properties of your structural firefighting protective ensemble creates a warm, moist, stagnant microclimate around the skin, severely limiting the evaporation of sweat, and hence, the effect of evaporative cooling.
2. Use adaptable PPE
Adopt structural PPE that can protect from thermal injury and exposure without trapping extraordinary amounts of moisture and heat inside. NFPA 1971: Standard on Protective Ensembles for Structural Fire Fighting and Proximity Fire Fighting requires that the composite garment that makes up the coat and pants of your PPE (outer shell, moisture barrier and thermal barrier) have a Thermal Heat Loss (THL) of not less than 205 W/m2.
THL is the test in the NFPA standard used to determine the capability for a turnout composite to lose heat. This is a static test performed on a "skin model" that simulates heat transfer through the skin. It tests how much heat is lost from the combined effects of wet (evaporative) and dry (conductive) conditions.
The higher the THL, the better it will move moisture from your skin’s surface outward to the garment’s thermal layer and thus cool the skin. This wicking action works to offset the lack of evaporation that’s taking place when you’re wearing your PPE.
3. Use cooling technology
While most people focus on structural firefighting PPE and its role in reducing heat stress, there have been great strides in what goes under the PPE.
Fire-resistant undergarments and station wear, manufactured using provide active moisture wicking and improved breathability.
Perspiration is wicked away from your skin’s surface by your underwear, to your uniform, and finally transferred to your PPE’s thermal barrier, allowing you to dissipate more heat more quickly.