Understanding High Heat & Fire

Fires are inherently hazardous and exhibit rapid, unpredictable temperature increases, reaching up to 2000 Degrees F in mere seconds. This overview delves into the diverse heat conditions within a fire and their impact on protective clothing.

Types of Heat Transfer

Three primary types of heat transfer in a fire pose burn risks: conduction, convection, and thermal radiation.


Wet or compressed protective clothing heightens the risk of conductive heat burns. Water, a poor insulator, can facilitate conductive bonds, displacing insulating air and increasing heat transfer. Serious burns can result from compressed clothing surfaces, as seen in injuries from contact with hot surfaces or objects. Example: blistering on knees during crawls on hot surfaces or compression injuries from extended forearms toward heat sources.


Convective heat, transmitted through the air, can elevate protective clothing temperatures, especially if clothing is wet. Immediate fire presence is not required for convective heat, making it a latent threat. Elevated temperatures may lead to conductive heat burns.

Thermal Radiation:

Heat transfer in the form of light energy directly from flames or reflected from hot objects. Factors affecting radiant heat transfer include temperature difference, distance, and surface reflectiveness. Radiant heat transforms into stored energy, intensifying and transferring inward, causing injuries even at temperatures as low as 180 degrees F.

Firefighters encounter all three heat transfer types during firefighting operations. It’s crucial to be aware of these dynamics to ensure the effectiveness of protective gear and minimize the risk of burn injuries.

What Is An Arc Flash?

An arc flash is a sudden release of electrical energy that occurs when current jumps across a gap between two conductors or from a conductor to a ground. The arc flash generates an intense burst of heat and light that can cause serious injuries, damage to equipment, and fires.

Arc flashes can occur in a wide range of electrical systems and equipment, including switchgear, transformers, motors, and other high-voltage components. They can be caused by a variety of factors, including equipment failure, human error, or a short circuit.

The intense heat generated by an arc flash can cause severe burns, as well as ignite clothing and other materials in the surrounding area, leading to secondary fires. The bright light from the arc flash can also cause temporary or permanent vision damage.

To prevent arc flash incidents, it’s important to follow proper electrical safety procedures, including wearing appropriate personal protective equipment (PPE), de-energizing equipment before working on it, and maintaining a safe distance from energized equipment.

Understanding Arc Ratings and Calories

Now that you understand FR clothing is tested and given an arc rating, you know that the arc rating measures the amount of heat the flame resistant fabric blocks when exposed to electric arc. The arc rating is the number of calories that the garment is expected to “absorb” if exposed to an electric arc. Arc rating is, in essence, the level of protection provided to you, the wearer.

Calorie is the unit of measure of the heat energy of an arc flash and the protective level of FR clothing. The bigger the calorie number, the greater the heat energy level of arc flash and the greater the protective level of the clothing. You will be protected from an electric arc if your clothing has a higher calorie arc rating than the calories of heat generated by the arc.

While it does not matter if the fabric has an Ebt,  ATPV and or ELIM value, it is important to pay attention to the calorie level the fabric can support* (as expressed in cal/cm2)