NFPA 70E - Standard for Electrical Safety in the Workplace 

NFPA 70E helps companies and employees avoid workplace injuries and fatalities due to shock, electrocution, arc flash, and arc blast. Employees’ equipment contains flame-resistant clothing, which meets the requirements of ASTM F1506.

The NFPA 70E standard provides tables of common electrical tasks, which are assigned one of five Hazard Risk Categories (HRC 0, 1, 2, 3 or 4). Each HRC category has a minimum arc rating for protective clothing measured in cal/cm² plus other PPE requirements.

Arc Thermal Performance Value (ATPV), a value of the energy necessary to pass through any given fabric to cause with 50% probability a second- or third- degree burn. This value is measured in calories/cm². ATPV indicates the level of protection provided by flame-resistant clothing as measured in cal/cm²: the higher the ARC rating, the greater the protection.

Hazard Risk Category (HRC) is the level of arc flash protection clothing you must wear to protect against a minimum level of incident energy measured in calories per centimetre squared.

HRC 1 (low risk), up to HRC 4 (high risk, requiring FR clothing with a minimum arc rating of 40). The HRC is used to determine the necessary arc rating of a garment worn during a given job task. Wearing multiple layers of clothing may be required to obtain the necessary rating for your work.