One common question we receive is “what is arc rated?” As it applies to flame resistant (FR) garments and personal protective equipment (PPE), arc rated means that the material has been tested for exposure to an electrical arc and assigned a value according to its performance. We’re here to provide background on the term, a clear definition, and explain what it applies to and how it is expressed, according to the standard.
The term “arc rated” comes from NFPA 70E, Standard for Electrical Safety in the Workplace, providing safety-related guidance from workplace electric arc hazards associated with “installation, removal, inspection, operation, maintenance, and demolition of electric conductors, electric equipment, signaling and communications conductors and equipment, and raceways.” (source: NFPA 70E-18, 90.2(A)).
While the term “arc rated” has been in use for several decades, the abbreviation “AR” first entered code in the 2012 edition of NFPA 70E. According to the latest, 2018 version of NFPA 70E, “arc rating” is defined as “the value attributed to materials that describes their performance to exposure to an electrical arc discharge.” For more information, watch our “What is an Arc Rating?” video featuring Tyndale’s Vice President of Technical, Scott Margolin:
Arc ratings apply to shirts, pants, coveralls, jackets, parkas, and rainwear worn by workers who face the risk of momentary electric arc and related thermal hazards as part of their normal work environment (130.7(C)(9) Informational Note), according to the standard. If a garment has an arc rating, it has been tested for exposure to an electrical arc. FR garments that do not have an arc rating have not been tested. This was further clarified in the 2015 version of NFPA 70E which states that all arc-rated clothing is FR but not all FR clothing is arc-rated.
The standard also explains how arc ratings are provided: “The arc rating is expressed in cal/cm2 and is derived from the determined value of the arc thermal performance value (ATPV) or energy of breakopen threshold (EBT) (should a material system exhibit a breakopen response below the ATPV value). Arc rating is reported as either ATPV or EBT, whichever is the lower value.” If you’d like a refresher on the difference between ATPV and EBT, check out our popular blog post: Arc Ratings for FR Clothing: What Is the Difference Between ATPV and Ebt?
Bottom line, if your FR clothing has an arc rating, it is arc-rated. If you face an electric arc hazard, wear FR clothing that has an arc rating.