By David Stymiest, PE, FASHE, CHFM, GBE
NFPA 70E® defines a series of boundaries related to electrical safety near energized equipment. These boundaries can be based on the voltage; the available short-circuit current and the predicted fault duration. The definitions are not repeated here, but the following considerations are useful to gain an overview of the issues involved.
• Flash Protection Boundary – an imaginary boundary within which there is the potential for a second-degree burn injury. Fire resistive protection (also called PPE) is required. This is the first item that must be determined by an arc flash hazard analysis.
• Limited Approach Boundary – previously described as “working near” but terminology was changed to reflect that non-work activities can be equally dangerous when carried out within this boundary. Some incidents have shown that arcs occurred even with equipment doors closed, an arc flash can cause equipment doors to bulge or become missiles, and hot gases can escape through equipment ventilation louvers.
• Restricted Approach Boundary – this is a shock protection boundary unrelated to arc flash or incident energy, rather it invokes where special considerations and constant supervision by qualified workers are required for unqualified workers. (A qualified worker must possess the necessary skills and knowledge, must have received relevant safety training, and according to OSHA 1910.399 must have also demonstrated these skills and knowledge.)
• Prohibited Approach Boundary – this is also a shock protection boundary unrelated to arc flash or incident energy. It must not be crossed without full-voltage PPE and possession of an authorized (signed) energized work permit. The worker must also comply with all other restrictions and controls of the electrical safety program.
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