Arc flash levels have been talked about and used in electrical safety since the very first days of NFPA70E and CSAz462. They were originally used as a way to simplify people's approach to handling arc flash and jobs that require work where arc flash hazards exist.
Arc flash levels have been misunderstood and misused probably more than anything else in the electrical safety world and in this article we are going set the record straight and help you figure out how to use them.
Arc flash levels: What are they really?
As far as I can tell arc flash levels are completely arbitrary.
Yup... you read that right.
There is nothing that I've ever read or heard that gives me a clear understanding of why certain incident energy levels were chosen to represent each of the levels.
Except for one story that I heard... (and don't get me wrong, it could be totally fabricated, but it makes for a good story) that the equipment manufacturers needed a way to "simplify" arc flash so they could break the clothing into different sections for "easy" selection and sale. Hence, we now have four "categories" or arc flash levels that everyone is bound to.
The four categories are as follows:
- 4 cal/cm2
- 8 cal/cm2
- 25 cal/cm2
- 40 cal/cm2
So where do we go from here?
The first thing we should touch on is how hazardous each of the levels actually is.
And this is the scary part.
They are all hazardous. Very hazardous.
1.2cal/cm2 is the incident energy level that corresponds to the onset of a second-degree burn so we know we don't want to be exposed to that. But what about 4, 8, 25, and 40 cal/cm2... what do they correspond to?
Once again the answer is nothing. 4, 8, 25 and 40 don't seem to have a real-world equivalent to the onset of a second-degree burn. So this adds to the confusion once again.
So what do we do?
My opinion... forget the arc flash levels.
Forget the arc flash levels
I hope you can see by now where I was going with this.
The arc flash levels or categories don't add any value... they just make things more confusing.
If you can calculate the incident energy (and this is a big if) then that's all you really need. Just simply figure out what incident energy you are up against and make sure your body is completely covered in arc flash protective clothing that is greater than the incident energy level.
To make things even easier. In the latest version of the workplace electrical safety standard you are required to wear the arc flash hood for any incident energy over 12 cal/cm2.
So a simplified approach would be to have two types of PPE... your everyday wear being rated 12 cal/cm2 and your "big suit" being rated 40, 65, or 100 (depending on the highest incident energy you typically work with).
Don't have the incident energy calculated?
You still have one option... it's not pretty but it's all you have.
The category method.
This is what remains of the arc flash levels in the latest version of NFPA70E and CSAz462... the trick is though that you need to do a little bit of legwork to make sure you are using it correctly (I won't get into the details... but if you are curious, you need to determine the maximum available fault current and the maximum fault clearing time... not exactly something you have in your back pocket).
They base the PPE required on the type of equipment you are working on.
What's funny is that if you eliminate panelboards rated 240V and below you end up with only 2 arc flash levels. 8 cal/cm2 and 40 cal/cm2.
Very similar to the simplified approach I mentioned above.
So what did we learn?
What you should have got from this is that things have gotten a lot easier... there is no need to spend hours trying to figure these categories out.
Any way you slice it you are going to have two options for PPE. A basic level and a bomb suit.
Hopefully, you don't need to wear the bomb suit all that often.
If you have any questions about this or anything else to do with electrical safety then give me a shout! firstname.lastname@example.org @jonmtravis