Wouldn't it be nice if the definitions for all FR terminology we use were in one spot? Here they are!

All-season -

used to define an FR garment that can be worn year-round.

Arc flash -

a type of electric explosion from a voltage breakdown of the resistance of air. More on this subject here.

ARC rating -

values that indicate the ARC performance of the material. The number is stated in cal/cm².

ARC-rated protective clothing -

PPE that protects from arc flashes and electric arc hazards. ARC-rated garments are measured in cal/cm². More on this subject here.

Aramid -

a chemical family of FR fibers like Nomex® (meta-aramid) and Kevlar® (para-aramid).

ATPV (Arc Thermal Protective Value) -

is what ARC-rated protection in fabrics measures. It creates the maximum performance capability for a specific FR garment or fabric and is shown in cal/cm².

Base layer -

FR clothing worn beneath primary FR clothing for added safety.

Breakopen -

the formation of holes in the fabric during ARC rating testing. This is the point of failure of FR protective garments as those holes allow heat or flames to pass through. This deterioration of a flame-resistant fabric, caused by breakopen, is measured as cal/cm² and is expressed as EBT rather than ATPV.

Char length -

a measurement used for FR clothing performance founded on the amount of damaged fabric when ASTDM 6413 is performed. Hook and loop - a broad term for what is commonly referred to as VELCRO® brand fasteners. These hook fabrics adhere to the loops to create a strong bond.

Energy Breakopen Threshold (EBT) -

a substitute measure to ATPV. Energy Breakopen Threshold (EBT) is reported when ATPV cannot be measured due to FR fabric breakopen.

Flame-resistant -

a fabric or material that burns slowly or self-extinguishes. Unlike synthetic polyester materials, FR materials don't fuel a flash fire.


flame-resistant clothing.

Heat stress -

OSHA states that heat stress can cause illness and death. The most serious heat illness is heat stroke, followed by heat exhaustion. Lightweight, breathable fabrics can help reduce heat stress. Summit Breeze® technology provides ultimate breathability with vented heat stress management.

HRC (Hazard Risk Category) -

defined by NFPA 70E and based on the risk associated with electrical and arc flash hazards. It governs the appropriate ATPV of flame-resistant clothing. In 2015, the terminology was changed from HRC levels to PPE levels.

HRC 2 -

have an ARC rating between 8 cal/cm² and 25 cal/cm².

HRC 3 -

have an ARC rating between 25 cal/cm² and 40 cal/cm².

HRC 4 -

have an ARC rating equal to or greater than 40 cal/cm². High ARC ratings are achieved with multiple FR layers and liners, such as those found in insulated outerwear.

Inherent -

FR fabric made of FR fibers that do not require additional chemical treatment to achieve flame resistance. More found on this definition here.


National Fire Protection Association. More on this organization here.

Manikin Test -

a simulated flash fire test using an instrumented manikin to gauge the assessed percentage of second- and third-degree body burns after three seconds of contact.

Moisture-wicking -

fabrics that transfer sweat away from the body and allows it to dry quickly. This keeps a wearer cooler, drier, and more comfortable.


National Electrical Safety Code.

Primary protection -

FR clothing designed for wear during activities where a worker is constantly exposed to flame, radiant heat, or molten metal splash.

Secondary protection -

FR clothing designed for intermittent hazards.


total body surface area (%TBSA) that is affected by a burn.

Thermal Protective Performance (TPP) -

a fabric's TPP is determined by the amount of heat it takes to pass through the fabric and cause a second-degree burn.

Treated FR -

fabrics where chemicals are added to the fabric to achieve flame resistance. More found on this definition here.

Vertical Flame Test -

this is a standard test method for measuring the flame, also commonly referred to as ASTM D6413.

Everything you need to know about FR gear

For those who require a little bit more technical FR information, such as FR fabrics and FR standards, you’ll notice below links to our FR Knowledge Center. You can directly navigate to the resource page for that specific topic from here.

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Click one of the links below to learn more about that topic.

Online FR Clothing Catalog