Definition - What does Arc Rating mean?
Arc ratings are ratings of the protective characteristics of a piece of fabric or other wearable material used for protecting a worker against electrical hazards.
A fabric’s arc rating is a measure of the amount of energy that it can absorb before the energy penetrates or moves through it with enough force to carry a 50% probability of causing a second- or third-degree burn. The value of an arc rating is measured in units of calories/cm2.
Safeopedia explains Arc Rating
Arc ratings are defined by the National Fire Protection Association (NFPA) standard 70E, which was developed at the request of OSHA to help workers avoid workplace injury or fatality due to electrical hazards.
As of a 2014 OSHA Final Rule, the use of arc-rated clothing in areas containing arc flash hazards has become a mandatory workplace requirement, giving NFPA Standard 70E a legal weight. The use of arc-rated equipment is required to meet OSHA regulations 29 CFR 1910 and 29 CFR 1926.
The NFPA’s arc rating system is used to classify protective clothing into one of four categories, ranging from Personal Protective Equipment (PPE) Category 1 to PPE Category 4. For instance, PPE Category 1 equipment must be arc-rated for 4 calories/cm2, and it includes equipment such as face protectors. Work in a PPE Category 4 environment requires equipment to be arc-rated for at least 40 calories/cm2, and it includes PPE such as full flash suit hoods.
Arc rating a material involves testing its arc thermal performance value (APTV) and energy break open threshold (EBT). The APTV measures the amount of energy (calories/cm2) that can be applied to material before it heats up to a degree that will cause burns, while the EBT measures the amount of energy that can be applied to material before it breaks open. The lowest of these two values becomes the material’s arc rating.