The more training I do and the more people I talk to about electrical safety the more I'm amazed at the amount of misinformation there is about arc flash. Chances are if you are an electrician you might be making these very same assumptions that I see all too often and if you don't correct them right away you could be in for a big surprise.
Make sure you remember these 3 things and share them with everyone you know who works in the trade. These aren't mistakes that can be taken lightly.
Lower voltage means lower arc flash
I did a science experiment the other day with my 8-year-old.
We placed two ice cubes on a saucer and covered one with salt. We checked back in about 5-minutes later to see what had happened and what most of you probably had guessed, the ice cube covered in salt had melted faster.
The next part of the experiment was placing two ice cubes in separate cups of hot water, one with fresh water and one with salt water. Now guess which ice cube melted faster? Think about it... ok, ready. The one in the fresh water melted faster.
What? Yeah try it out for yourself if you like but what happens is the cold water which melts off the ice cube actually floats on top of the salt water, thus insulating the ice cube from the hot water momentarily.
This is what you would call counter-intuitive. The same thing applies to arc flash levels and how they relate to voltage. The results of the incident energy analysis are often not what you would expect.
Go into any industrial facility and take a look at what the electricians are wearing while working on the 13.8kV switchgear line-up. Probably at least a 40 cal/cm2 suit. Now check the arc flash label on the equipment... hmm.. that's odd... 6.2cal/cm2.
Now go down the hall and see what's going on in the MCC room. Routine maintenance on a 30A 600V disconnect... and what is the electrician wearing for PPE? You'd be lucky to find them wearing an AR shirt and pants but that's only if it's standard issue... and just for good measure we will check the arc flash label on this equipment... hmm... strange... 22.3cal/cm2.
The thing is that these numbers are not strange, they are quite typical. Lower voltage means higher current, and higher current means higher incident energy. So next time do not be fooled by the system voltage into thinking the arc flash is probably low... check the label.
1.2 cal/cm2 is nothing to worry about
I've gone over this before but it still catches people off guard in every training session I've done. 1.2cal/cm2 is the onset of a 2nd-degree burn.
In almost all other sectors of safety, the goal is to prevent injury, reduce recordable frequencies, and eliminate loss-time injuries and fatalities. While second degree burns are not likely to cause fatalities they are nothing to sneeze at.
Just read this information on second-degree burns from www.healthline.com.
"Second-degree burns are more serious (than first-degree burns) because the damage extends beyond the top layer of skin. This type burn causes the skin to blister and become extremely red and sore.
Some blisters pop open, giving the burn a wet or weeping appearance. Over time, thick, soft, scab-like tissue called fibrinous exudate may develop over the wound.
Due to the delicate nature of these wounds, keeping the area clean and bandaging it properly is required to prevent infection. This also helps the burn heal quicker.
Some second-degree burns take longer than three weeks to heal, but most heal within two to three weeks without scarring, but often with pigment changes to the skin.
The worse the blisters are, the longer the burn will take to heal. In some severe cases, skin grafting is required to fix the damage. Skin grafting takes healthy skin from another area of the body and moves it to the site of the burned skin."
That sounds pretty serious to me and something that we want to protect against. You need to treat 1.2cal/cm2 as a hazardous level and protect yourself accordingly.
Working distance is how far you have to travel from your house to work
While this is a good guess, those of you who thought that the working distance was the sum of the distance between the worker and the equipment; and from the front of the equipment to the potential arc source inside the equipment would have been given the golden star sticker on a test.
So what's the big deal anyway?
Well, most people do not pay any attention to the working distance. And for the most part, this really isn't a problem. As long as the engineer followed these typical working distances used for incident energy calculations:
- low-voltage (600 V and below) MCC and panelboards: 460 mm (18 in);
- low-voltage (600 V and below) switchgear: 610 mm (24 in); and
- medium-voltage (above 600 V) switchgear: 900 mm (36 in).
And all you have on site is typical equipment, and you are a typical electrician with robotic arms then the working distance is negligible. But there may be cases when parts of your body need to cross this imaginary boundary. There are times when the equipment you are working on is not typical, and those numbers really don't apply. There are also times (unfortunately I've come across this more than once) when the working distance used in the calculations is not the correct working distance!
These can all lead to potentially higher arc flash incident energy exposures and inadequately rated PPE.
Always make sure to check the working distance on the arc flash label before starting the work. If it doesn't match your actual working distance then either adjust your plan so work outside the imaginary boundary or determine the new arc flash levels at the closer working distance.
These are three things that every electrician has to understand. Please take the time to make sure you review these topics with your team and make sure you are not making the same mistakes.
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For more information with regards to on-site training and electrical safety consulting services, you can contact me directly.