To protect operators, OSHA and NFPA 70E standards require a "flash protection boundary." OSHA has adopted the National Fire Protection Association's "70E Standards for Electric Safety in the Workplace" as an acceptable means of compliance to meet this requirement.
The Occupational Safety and Health Administration (OSHA) maintains that electrical work should only take place on de-energized equipment. Access to potentially energized equipment capable of generating an arc flash must be limited to qualified personnel with extensive protective clothing and equipment, including fire-resistant suits and hoods along with non-conductive wands.
The National Electric Code requires that electrical control panels that might generate arc flash carry a permanent label applied by the panel builder.
Incident energy, defined by NFPA as "the amount of energy impressed on a surface, a certain distance from a source, generated during an electrical arc event," is a key term in understanding arc-flash hazards. Incident energy is a measure of the heat created by the electrical arc and is expressed in calories per centimeter-squared.
The two most important numbers to remember are 1.2 and 40. Incident energy levels greater than 1.2 calories per centimeter-squared can produce second-degree burns. The NFPA 70E requires that workers wear personal protective equipment (PPE) when working with 50 volts or more. Arc flash levels above 40 calories per centimeter-squared can be fatal, usually resulting in a massive pressurized blast with sound pressure waves and projectiles. The PPE is available for exposures up to 100 calories per centimeter-squared; however, the force from the pressurized blast can be fatal regardless of the PPE.
Refer to the NFPA website, nfpa.org, for complete information.
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