Until CSAZ462 was updated in January 2012 (and then again in 2015) the standard often confused people by using the terms hazard and risk interchangeably. A lot of those old misconceptions are still hanging around so I think it’s important that we go through some examples of what is and what is not an arc flash hazard.
An arc flash is a short circuit through air that causes extreme heat and a very strong blast of air pressure. It’s like a grenade going off, you even get the pieces of flying shrapnel. At every place in your electrical distribution system where you could potentially have a phase-to-phase fault, or a phase-to-ground fault you could have an arc flash event occur.
So do I have arc flash hazards all over my site?
Potentially, but not necessarily. An arc flash hazard exists only when a worker is at risk of being exposed to the extreme heat and blast from the arc flash. So you need to have someone present and (this is important) they have to be performing a task which could lead to an arc flash event.
This is where evaluating the risk comes in.
A risk is the combination of the likelihood of occurrence of injury and the severity of the injury that result from a hazard. If you are familiar with safety risk assessment charts, then it’s easy to understand the fundamental problem with evaluating arc flash hazards--they almost always score in the red zone due the fact that the severity will almost always be high. That is why understanding the likelihood of occurrence becomes crucial to evaluating arc flash hazards.
How about an example?
To illustrate this let’s look at falling and the use of fall-arrest PPE for a minute as compared to arc flash and the use of arc flash PPE.
Imagine my friends Gary and Chuck (they are not really my friends, I just made them up for the sake of writing this). Gary is standing on a picnic table and Chuck is standing on the ledge of a ten-story building. Which one should be wearing fall arrest? That’s right, Chuck. This was easy to see because the severity of falling from a ten story building is very high and falling from a picnic table is not so bad.
Now imagine Gary and Chuck are electricians who work in your facility. They are both tasked with working on motor control centers for the afternoon. Gary will be checking the operation of each circuit breaker and Chuck will follow behind and replace any of the breakers that Gary finds deficient.
Who is faced with an arc flash hazard and who needs to wear PPE?
Not as easy this time is it?
They are both working on the same equipment, on the same day, under the same conditions. In this case, the severity never changes. If something does happen they will both be exposed to the same hazard. The time, current and distance principles of the arc flash calculations will always be the same. The key is looking at what they are doing and the likelihood of causing an arc flash.
Gary is checking the operation of breakers. Breakers are designed to operate, this is what they call normal operation (there are other factors to consider for normal operation but we won`t get into them here). As long is Gary follows proper procedures for operating a circuit breaker no arc flash hazard exists.
But Chuck, on the other hand, needs to take extra precaution. Why is that? Well, it’s because the likelihood of causing an electric arc during the course of his task, replacing the breakers, is relatively high. Chuck will be faced with an arc flash hazard and now he needs to take the steps to mitigate that hazard. One of the steps to mitigation will be choosing the proper arc flash PPE and that is what I will be talking about in the next post.