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. The necessary Arc Rating for an article of clothing is determined by a Hazard/Risk Assessment and the resulting HRC. Usually measured in terms of ATPV or EBT. Simple put the ARC rating determines the protective characteristics of the fabric. The higher the ARC rating value the greater the protection. When the product is sold to protect workers from arcing faults, clothing manufacturer are required in indicate the ARC rating. Click here to find more info on NFPA 70E and Hazard Risk Categories.