Electrical shocks and arc flashes pose a real danger when working on energized electrical equipment. Electric arc flashes have a limited effective distance, and not all arc flashes are equal. In order to establish appropriate safety related work practices, the National Fire Protection Association (NFPA) developed specific safe approach boundaries near energized equipment.
Proper safety procedures help protect employees working on energized electrical equipment. De-energizing the equipment prior to working on it is the preferred method of eliminating the risk of electrical shock and arc flash injuries. Insulation, grounding, Ground Fault Circuit Interrupters, barricades, and implementing other safe work procedures are also essential.
When working on energized electrical equipment and circuit parts, be aware of the various safe approach boundaries established in NFPA 70E. There are two safe approach boundaries related to the electric shock hazard, the Restricted Approach and Limited Approach boundaries. There is also one safe approach boundary associated with the arc flash hazard, the Arc Flash Boundary.
Restricted Approach Boundary
The Restricted Approach boundary is the distance from an exposed live part in which there’s an increased likelihood of electric shock due to electric arc-over combined with inadvertent movement for personnel working in close proximity to the energized electrical conductors and circuit parts. 2. Limited Approach Boundary
The Limited Approach boundary is the distance from the exposed live part where a shock hazards exist. Though the shock hazard exists, proper safety equipment and procedures greatly reduces the associated risk of electric shock injury. Workers should only cross this boundary when necessary.
Note: If there is sufficient energy available in the circuit, there could also exist the potential for injury due to exposure to arc flash while within these boundaries. If this is the case, appropriate arc flash protective PPE must be worn if you are within the arc flash boundary distance. 3. Arc Flash Boundary
The Arc Flash Boundary is the distance from an energized part where an employee could be exposed to a second degree burn should an arc flash occur. The hazards within this boundary include the heat generated which causes burns, high sound levels, intense pressure waves, flying shrapnel and debris, and toxic smoke.
Electric shocks and arc flashes can be a dangerous situation. Proper training and safety equipment can go a long way in preventing accidents and protecting employees. Be sure to always de-energize equipment prior to working on it, and keep the area around a potential hazard clear to maximize employee safety and comply with NFPA 70E requirements.
Special thanks to David Pace for his contributions to this post.