Safety Knights

We're actually working on overhauling our electrical safety program so I have quite a bit of exposure to all this stuff at this point. We define crossing into the "Restricted approach boundary" as the delineation of energized electrical work.

1. 115 in is where your flash is going to have at minimum 1.2cal/cm2. Think second degree burns. I would personally use this as my limited approach.

2. It is telling you at 18in the energy would be 19cal/cm^2. More than second degree. I would use this as your restricted.

3. Level 4 protection is required within those 18 inches at 19cal/cm^2.

I have never actually seen an Arc Flash event in person. But I have seen the results after a few seconds. The first was 40 years ago. I will never forget a few things I observed. I was the first person on the scene a few seconds after the event. #1 As I approached he was flat on his back, his right leg was broke above the knee half way to his hip. His right foot was under his back and the upper femur was poking through is pant legs like a spear. He had been blown off the top of a substation. #2 His head was charred and the size of a basketball! I could not recognize him (turned out I knew him very well). #3 There was a perfect 16"X2" rectangle between his breasts down through a couple layers of skin. Form the side I could see the blue of his work shirt, then the white of his t-shirt, his upper black layer of skin, and then lighter layers of skin. #4 The smell is still literally burned in my memory! Smelled like charred chicken and ozone! #5 He was unconscious and when I felt for a pulse in his neck, it was irregular. Took 10 minutes for the ambulance so I kept taking it, prepared to do CPR if needed. It was way before I ever heard of AEDs.
What is the most vivid is going to the U of Michigan Burn unit in Ann Arbor to see him a couple months later. He was covered in bandages with room for breathing holes and his one eye (his other had been blown out). He also lost an ear and hearing on that one side. I asked him about his family and things like that. Then I said, "Bobby, you are lucky to be alive, I was really worried you would not make it!" What he replied is burned in my memory forever, "Yeah Fitz you are mostly right on! But every morning for an hour they take me down to the Lye Bath, and for that hour I always wish I was dead as the pain is unbearable!" I did not know what to say, as anything I thought of was inadequate! I fought back the tears till I got to the car, and then cried like a baby for half an hour, before I could drive home!

John nailed the answer, but I just want to add that the flash hazard boundary isn't a safe place to be. It's the distance at which you're likely to survive and not suffer permanent disability. 2nd degree burns to your face are no joke, temperature will be over 400 degrees, still a chance for shrapnel.

Ironically, I'm teaching an NFPA 70E Qualified Person training today, so this is right up my alley.

1. At 115", that is where you have an incident energy level of 1.2 cal/cm2. At this level, you would experience 2nd degree burns when exposed to this incident energy for 1 second without PPE.

2. At 18" working distance from the equipment (measured from the equipment to your face and chest), there will be an incident energy level of 19 cal/cm2. Based on this level of incident energy, you would need to wear PPE in accordance with PPE Category 4 (which is actually more than what they show on there). As you move closer to the conductors, your incident energy level increases. On the opposite side, as you move further away, your incident energy level decreases. Keep in mind that this is only PPE addressing the arc flash hazard, not the shock hazard - that is where the Class 00 rubber insulating gloves with leather protectors comes into play.

3. Limited and restricted approach boundaries deal with shock hazards. A shock hazard assessment and corresponding boundaries are completely independent of your arc flash assessment and boundary. 208 VAC is the nominal voltage you're exposed to, which requires the Class 00 rubber insulating gloves (rated for 500 VAC). At your limited approach boundary, that's where a shock hazard begins to exist. At your restricted approach boundary, that's where you have an increased likelihood of a shock hazard and only qualified persons are allowed to work within this boundary.

In addition, NFPA 70E requires that incident energy analyses be reviewed every 5 years and updated as necessary. Since the label says this was done in April 2017, it should have been reviewed for accuracy in April 2022.