NFPA 70E Clothing
The National Fire Protection Association 70E (NFPA 70E) requires workers to be outfitted in Flame Resistant Clothing that meets the requirements of ASTM F1506 when there is a possible exposure to Electrical Arc Flash. The short duration and intense energy of an arc flash explosion presents a great safety hazard. Employers must assess the potential hazard and determine the flash protection boundary distance, so as to determine the Hazard-Risk Category and the minimum Arc Thermal Protection Value (ATPV) rating.
It has been confirmed by OSHA that NFPA 70E Clothing meets the requirements of ASTM F1506 are in compliance with OSHA 29 CFR 1910.269.
Calories per Centimeter Squared (cal/cm2) is the calculation number identifying the amount of energy that can be delivered to a point at a particular distance from an arc flash. Once this value is known, the ATPV rating of the NFPA 70E Clothing required for work at that distance from the potential flash hazard is also known.
The basic category table for determining NFPA 70E Clothing is as follows:
| Risk/Hazard Category |
Incident Energy (cal/cm2) |
Examples of PPE Required* |
| 0 | 2 or lower | Non-melting clothing |
| 1 | 2-4 | FR shirt and pants |
| 2 | 4-8 | FR shirt and pants, cotton underwear |
| 3 | 8-25 | FR shirt and pants, FR coveralls, cotton underwear |
| 4 | 25-40 and higher** | FR shirt and pants, full-coverage arc flash suit, cotton underwear |
An arc flash happens when a circuit shorts out through the air, and the NFPA 70E specifies boundaries to protect employees from arc flashes. The minimum required distance is three feet at fewer than 750 volts. Voltages of 15 to 36 kilovolts require a distance of 19 feet.
The Heat Attenuation Factor (HAF) is also an important component of NFPA 70E Clothing, describing the amount of heat blocked by the fabric. Even though a fabric may be 100 per cent flame resistant, it doesn’t mean it will block all of the heat. An HAF of 85 per cent means that it will block 85 per cent of the heat the PPE encounters.
It is important to note that voltages over this level must be calculated individually.
NFPA 70E Clothing can be as basic as simple 100 per cent cotton (as it burns off without melting into the skin, like plastic nylon or elastic rubber). To enhance the flame resistant (FR) level, a special chemical process is applied to the clothing to reduce the heat that reaches the skin.
Electrical workers must wear NFPA 70E Clothing that is rated according to the amount of energy that would cause second-degree burns and the amount of protection the clothing provides against an arc flash. The clothing must maintain its rating through its life, even after repeated cleanings.
Certain pieces of protective equipment are required if an employee must go within an arc flash boundary. A face shield or pair of safety glasses must be worn, as well as gloves with a leather cover over a rubber interior. Leather boots are required when the arc flash energy level is high.
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For more information, see:
Electrical Safety OSHA
Electrical Safety Workplace
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