How to determine the likelihood of arc flash and shock

In my opinion being able to determine the likelihood of an electrical incident happening is the most important element of your approach to electrical safety. That’s because without this you’ll never quite know for sure if you should be applying any protective measures or not. Which leads to either being exposed to hazards you are not protected from or wearing protection when you are not exposed to hazards! Both outcomes are not desirable.

You'll need to pair this knowledge with what you know about the severity of the hazard to truly understand the level of risk involved with the task and to round out your approach to electrical safety.

Shock hazard

Let’s start by looking at shock hazard.

With shock hazard, there is one key element that determines whether or not you are likely to get a shock, and that is if the energized conductors or circuit parts, the actual pieces of copper that have the electricity flowing through them, are considered to be exposed.

When I say exposed I am not using the word in the context of wiring methods, such as the exposed overhead power lines, I am using the word as it applies to electrical safety. You have to think while I’m doing this specific task is it possible for me to inadvertently touch these energized conductors?. So if you were flying a kite around those overhead lines the answer would be yes those are considered exposed. If you were going for a jog, then the answer is no they are not exposed.

The bottom line is you need to think about the specific task you are doing and determine if the energized conductors are exposed or not. Are they in an enclosure or is the enclosure door open? Does the cable have a protective jacket or are they bare conductors? Are there vents on the side of the equipment large enough for a tool to slide through? Are you cutting or drilling into something that could expose the energized conductors or come in contact with them? These are the questions you need to consider.

Once you’ve determined if you are working on or near exposed energized conductors then you simply assume the likelihood of coming in contact with these is great enough to warrant some protective measures, such as rubber insulated gloves.

Arc flash hazard

Now we will discuss how to determine the likelihood of an arc flash event occurring.

There are a number of variables we need to consider but we’ve already covered the first one. As long you’ve determined that the equipment you are working on is capable of producing an arc flash and the energized conductors are exposed then you can assume it’s likely to cause an arc flash if you inadvertently touched the exposed conductors (either with your hand or a tool).

The other consideration you need to take into account is the interaction with electrical equipment and more specifically whether that interaction is a normal operation of the equipment and under normal operating conditions.

An operation of the equipment that is considered normal is doing anything that the manufacturer has designed that equipment to do. Operating a disconnect switch as part of a proper lockout sequence would be considered normal. It’s what the switch is designed to do. On the other hand, racking a circuit breaker on a live bus is not a normal operation. The manufacturers typically recommend that the bus is de-energized before you rack the breaker.

To decided if you are performing the operation under normal conditions you need to ask yourself the following questions. Is the equipment properly installed? Has the equipment been properly maintained? Are all equipment doors closed and secured? Are all equipment covers in place and secured? And there is no evidence of impending failure which would be loud crackling or buzzing sounds, strong smells of burning insulation, or smoke coming from the equipment.

Conclusion

Once you’ve determined either that the energized conductors are exposed or the interaction you are performing is not considered normal then you will need to take introduce some protective measures during the task.

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