Glossary of key NFPA® 70E terms

Arc Flash:

An explosive release of energy caused by an electrical arc. An arc flash results from either a phase to ground or a phase to phase fault caused by such occurrences as accidental contact with electrical systems, 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. Back to Top

Arc Rating:

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. Back to Top

Calorie:

The energy required to raise one gram of water one degree Celsius at one atmosphere pressure. Second-degree burns occur at 1.2 calories per centimeter squared per second (cal/cm²). Back to Top

Electronically Safe Work Condition:

When the conductor or circuit part to be worked on has been disconnected from energized parts, locked/tagged in accordance with established standards, tested to ensure the absence of voltage, and grounded if determined necessary. Back to Top

Flash Hazard:

A dangerous condition caused by the release of energy from an electric arc. Back to Top

Flash Hazard Analysis:

A study investigating the potential exposure to arc-flash energy that a worker faces while performing a specific job task. The data collected in a Flash Hazard Analysis is used for the purpose of injury prevention and the determination of safe work practices and the appropriated levels of FR clothing and PPE. Back to Top

Flash Protection Boundary:

The distance from an exposed live part within which a person could receive a second-degree burn if an electrical arc were to occur. Back to Top

FR (Flame Resistant):

FR refers to the ability of a material to self-extinguish upon the removal of an ignition source.. Back to Top

HRC (Hazard/Risk Category):

The five Hazard/Risk categories are specified by the chart listed in NFPA® 70E. The chart, based on specific job tasks, ranges from HRC 0 (which is low risk and allows for 100% untreated cotton), up to HRC 4 (which is 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. Back to Top

Limited Approach Boundary:

The distance from an exposed live part within which a shock hazard exists. Back to Top

NFPA® 70E:

A work standard published by the National Fire Protection Association (NFPA®) that covers aspects of electrical safety in the workplace. It includes the recommendation that those who work with, on or around energized equipment use adequate protection, including FR clothing. Back to Top

Prohibited Approach Boundary:

The distance from an exposed live part within which work is considered the same as making contact with the live part. Back to Top

Qualified Person:

One who has the skills and knowledge related to the construction and operation of the electrical equipment and installations and has received safety training on the hazards involved. Back to Top

Restricted Approach Boundary:

The area near an exposed live part that may be crossed only by qualified persons using appropriate shock prevention techniques and proper FR clothing and PPE. Back to Top