Something that seems to be confused in the arc flash and electrical safety world is how to use arc flash PPE categories. People just seem to have it mixed up. From reverse engineering incident energy levels to not wearing face shields and gloves in times that they should be I've seen enough issues to warrant a bit of discussion on the matter.
What is an arc flash PPE category?
Historically, the arc flash PPE category was referred to as the hazard/risk category and in my opinion this is where most of the confusion began. Because risk played such a large role in the overall level you really couldn't get a good sense of what the hazard (or protection level) really was.
This is also where the reverse engineering started. Engineers would calculate the incident energy and then put an arc flash category on the sticker... why would you do that? Your incident energy level was a better number.
The second thing that happened is people started to believe that at category 1 you did not require your arc flash face shield or rubber insulated gloves. Category 1 still burns so why would anyone want a burnt face and hands? Doesn't make sense.
Today, things are actually a lot clearer. The arc flash PPE category is just that. It's a category which offers a certain protection level from the heat energy produced in an arc flash explosion. Categories 1, 2, 3, and 4 offer protection against incident energy levels up to 4, 8, 25 & 40 cal/cm2 respectively. Forget about risk, that's left up to another table.
So how do we use this?
As you might have already figured out the use of these categories is a two part process. Determine risk, then determine the hazard.
The first step is to determine whether or not the task you are performing is in fact risky enough to need any arc flash PPE at all. To do this you'll need a copy of CSAZ462, turn to Table 4A and find the task you are completing... if there is a yes under the PPE required column then move to the next step.
The second thing you'll need to do is determine the category level required. Using Table 4B in CSAZ462 you simply find the equipment you are working on with correlating maximum available short-circuit current and fault clearing time to determine the category. If you're lucky enough to work in a static environment this is something you could figure out beforehand for each piece of equipment in your facility.
Certain equipment will always have the same hazard category (depending on maximum available short-circuit current and fault clearing time). Once you know what these categories are then just cover your entire body in PPE that is higher than the corresponding rating of that category.
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