- Early in my career as a forensic engineer I investigated one arc flash case where a maintenance worker on a golf course was troubleshooting a 480 volt alternating current (VAC), three-phase pump control panel using an inexpensive meter. The worker overrode the safety latch on the disconnect switch so the power remained on. The worker attempted to make a continuity test across a fuse that was blown, and since the circuit was still energized, fault current passed directly through the meter. The meter blew up as he was holding it causing second degree burns to his face and hands.
- I investigated another case where an electrician was troubleshooting a fused distribution panel and took another person’s word that the power was shut off. The electrician used a pair of pliers in an attempt to remove a fuse and initiated an arc flash that burned his arms and face. The electrician’s helper was standing close by and was also burned.
- A third case involved an untrained worker in a feed mixing and repackaging plant trying to determine if a fuse was blown by using a light-indicating continuity device. The device blew up in his face, causing second degree burns to his face and arms. Obviously, the power was not disconnected.
- A fourth case was an incident that only arced and melted a large screwdriver with no insulation on the shaft; luckily, the screwdriver was the victim and not the electrician. This took place in a grocery store where the night shift was restocking. An electrical crew was tasked with changing out some power distribution breakers (bolt-in type) for lighting. Because the store was essentially in operation, the manager would not allow power to be shut down so the electricians could safely perform their work. An electrician was inserting an attachment screw of the circuit breaker into the power bus and touched the side of the screwdriver shaft to a grounded metal component. The result was an arc flash that melted the tip of the screwdriver and arced out a “divot” in the side of the screwdriver shaft. NFPA 70E requires the contractor to have an Energized Electrical Work Permit to be filled out by the requester (store owner in this case) and a detailed description of the work to be performed by the electrically-qualified person including the safe work practices that will be employed.
The National Fire Protection Association (NFPA) has released a 2015 edition of NFPA 70E: Standard for Electrical Safety in the Workplace. It covers and assists in complying with the Occupational Safety and Health Association’s requirements, including changes to requirements since the last edition. For personal safety in forensic studies it is important to stay informed of these updates. NFPA 70E covers arc flash risk assessment, establishment of arc flash boundaries, requirements of Personal Protective Equipment (PPE), use of PPE within the arc flash boundary, and equipment labeling requirements regarding arc flash hazards. The following examples illustrate the importance of staying abreast of the latest standards.