nfpa 70 flame resistant

A Guide to NFPA 70 Flame Resistance Ratings

The National Fire Protection Association (NFPA) is a United States trade association which creates and maintains standards and codes for local governments. Founded in 1896 by a group of insurance firms, its purpose was to standardize fire sprinkler systems. The association’s mascot, Sparky the Fire Dog, promotes fire safety education for children.

Flame Resistant Hazardous Risk Category Levels

The NFPA specifies various FR hazardous risk category levels, which are numbered in order of severity from 1 to 4. Hazard Risk Category is the level of ARC flash protection clothing which must be worn to protect against a minimum level of incident energy measured in calories per centimeter squared. In other words, electrical equipment (depending upon its energy delivering capability) under fault conditions can cause an explosion, or arc fault of a certain level, again measured in calories per centimeter squared. That explosion can deliver a certain amount of heat to a certain distance. Each ARC level, 0-4, is rated at a certain amount of flame resistance, again measured in cal/cm2.

The NFPA guidelines, based on specific job tasks, range from HRC 1 (low risk, allowing for 100% treated cotton), up to HRC 4 (high risk and requires 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.

Hazard Risk Cat 1 – FR Shirt and FR pants or FR coveralls (1 layer) – Minimum ARC rating of 4

Hazard Risk Cat 2 – Cotton underwear plus FR shirt and FR pants (1 or 2 layers) – Minimum ARC rating of 8

Hazard Risk Cat 3 – Cotton underwear plus FR shirt and FR pants plus FR coveralls, or Cotton underwear plus two FR coveralls (2 or 3 layers) – Minimum ARC rating of 25

Hazard Risk Cat 4 – Cotton underwear plus FR shirt and FR pants plus multilayer flash suit (3 or more layers) – Minimum ARC rating of 40

ARC Ratings Explained

The ARC rating is an expression of the amount of the energy needed to pass through any given fabric to cause a 2nd or 3rd degree burn with a probability of at least 50%. The ARC Rating for an article of clothing is determined by a Hazard/Risk Assessment and the resulting HRC. Essentially, the ARC rating determines the protective characteristics of the fabric. The higher the ARC rating value the greater the amount protection provided. When the product is sold to protect workers from arcing faults, clothing manufacturer are required in indicate the ARC rating on the garment.

What is an ARC Flash?

An ARC flash is an explosive release of energy caused by an electrical ARC. ARC flashes result from either a phase to ground or a phase to phase fault caused by such occurrences as accidental contact with electrical systems, a build up of conductive dust, corrosion, dropped tools, and improper work procedures. During an ARC flash, the temperature can reach 35,000° Fahrenheit, and exposure to an arc flash can result in serious burn injury and death. Every year, more than 2,000 people are admitted to burn centers with severe arc-flash burns.


This article is intended to provide a brief introduction to the NFPA and the NFPA/ARC rating system. For more information, please visit the NFPA website at

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