Arc hazard risk categories, also known as HRCs, are National Fire Protection Agency (NFPA) classifications that rate the risk of arc flash-related injuries based on actors like arc voltage, and a worker’s proximity to an arc fault source. Because potential arc flash situations can vary greatly in terms of the physical risks involved, the NFPA has created four arc hazard categories.
Each hazard risk category requires a different level of protection, which is specified by a minimum Arc Thermal Performance Value, or ATPV. An ATPV is a rating that denotes how many calories of heat per square centimeter (cm²) a particular piece of arc flash PPE can tolerate and protect against. The categories are also set apart by the amount of PPE required for each. As their numbers climb from 1 to 4, arc hazard categories require higher ATPVs, as well as additional articles of Flame Retardant (FR) arc flash clothing and PPE.
CATEGORY 1
FR Garments and PPE Required: Safety glasses, hard hat, FR shirt and pants (or FR coveralls), leather protective gloves and leather shoes
Calories per cm²: 5
Minimum ATPV: 4
CATEGORY 2
FR Garments and PPE Required: Safety glasses or goggles, hearing protection, hard hat, cotton underwear, FR shirt and pants (or FR coveralls), arc rated face shield (or arc flash hood), leather gloves and leather shoes
Calories per cm²: 8
Minimum ATPV: 8
* Please note that a variation on this level, Category 2*, has the same PPE requirements, with the exception that an arc flash hood must always be worn, with no option to use a face shield instead.
CATEGORY 3
FR Garments and PPE Required: Safety glasses or goggles, hearing protection, hard hat, cotton underwear, FR shirt and pants, FR coveralls (in addition to FR shirt and pants), arc flash hood, leather gloves and leather shoes.
Calories per cm²: 25
Minimum ATPV: 25
CATEGORY 4
FR Garments and PPE Required: Safety glasses or goggles, hearing protection, hard hat, cotton underwear, FR shirt and pants, FR coveralls (in addition to FR shirt and pants), full flash suit with hood, leather gloves, and leather shoes.
Calories per cm²: 40
Minimum ATPV: 40
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