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A Better Understanding of NFPA 70E: Your Risk Tolerance

NFPA 70E®, Standard for Electrical Safety in the Workplace® changed from an arc-flash hazard analysis to an arc-flash risk assessment several editions ago. Users are still having issues with the change. The most common complaint is that risk should not be a consideration when considering the electrical hazards an employee might be exposed to. Many want the standard to provide an absolute solution to what the employer should do to protect their employees. They don’t want to have to decide what to do, they want to be told what to do. They can apply the current that way if they wish. Others want guidance which is what the current edition provides. It allows for more leeway in determining the course of action to be taken for a given task on a piece of specific equipment.

The hazard analysis determined the flash boundary, the incident energy at the working distance, and the personal protective equipment (PPE) necessary. The risk assessment first determines if an arc-flash hazard exists. If the hazard exists, the risk assessment then determines appropriate safety-related work practices, arc flash boundary and PPE to be used. Both methods require that the worst-case condition be labeled on the equipment to provide appropriate warning of the hazard lurking inside regardless of the assigned task. There is not much of a difference between the two except for determining if an arc flash hazard exists for a specific task. Imagine a battery system in a room with two terminals of the dc system in another room. If the conductors from the battery system are shorted together there is a potential for an arc-flash with an incident energy of 42 cal/cm2. However, that energy level only exists if the two conductors are shorted together. The positive conductors are brought into the terminal room on the left side and the negative conductors are brought in on the right. Those two covered terminals are separated by 12 feet. The first component after the terminals is an overcurrent device which lowers the incident energy to 14 cal/cm2. The entry to room is correctly labeled to require a 42 cal/cm2 arc-rated suit as the worst-case condition regardless of the task to be performed.

Under the old system, at least a 42 cal/cm2 suit would have to be worn every time someone enters the room. Under the current method, when does the 42 cal/cm2 arc-flash hazard exist? The full amount of incident energy is always present in the room. The arc-flash hazard might exist if there is way to connect the two conductors. A task that involves pulling conductors around the room, using tools with a long span, or having conductive fluid present may exposure a worker to the full incident energy. Employee error while in the room may warrant concern. Under a risk assessment for the assigned task, you might determine that it is not possible for a worker to connect ahead of both overcurrent device terminals based on the assigned task. Would you let an employee enter that room wearing 14 cal/cm2 rated gear to perform the assigned task?

If you believe that a risk assessment should not be part of the standard, you are not required to accept any risk. The risk assessment method allows you to decide that the worst-case incident energy always presents an arc-flash hazard regardless of the task performed on the equipment. If you can accept that a twelve-foot span cannot be bridged by the employee based on all possible factors, you might permit something different for the task. There are many things that might affect your acceptance of some risk instead of having a zero-risk tolerance. Regardless of your risk-tolerance, remember that it is the employee’s well-being that is wagered on your decision.

NFPA 70E is available on NFPA LiNK™, the association’s information delivery platform with NFPA codes and standards, supplementary content, and visual aids for building, electrical, and life safety professionals and practitioners. Learn more at nfpa.org/LiNK.

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Christopher Coache
Senior Electrical Engineer

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