The arc flash hazard should be an integral part of any electrical safety training program. NFPA 70E, IEEE 1584 and several other standards address this hazard in terms of incident energy with the severity normally quantified in terms of calories per square centimeter (cal/cm2). The phrase “the onset of a second degree burn” and incident energy of 1.2 cal/cm2 also are frequently used, as shown in the following examples.
The definition of “arc flash boundary” from NFPA 70E contains an informational note that references “the onset of a second degree burn on unprotected skin is likely to occur at an exposure of 1.2 cal/cm2.”
Informational Note 3 of the definition of “arc rating” includes, “The onset of a second-degree skin burn injury based on the Stoll curve.”
NFPA 70E 130.7(C)(6) states, “Employees shall wear arc-rated clothing wherever there is a possible exposure to an electric arc flash above the threshold incident energy level for a second-degree burn (1.2 cal/cm2).” There are a few other locations, such as Table 130.5(G), where this value is referenced.
Even IEEE 1584 contains “An incident energy of 1.2 cal/cm2 is likely to cause the onset of a second-degree burn” in Annex B2.
To better understand the severity of burn injury, the National Institutes of Health provides the following definitions: First-degree burns damage the outer layer (epidermis) of the skin. Second-degree burns damage the outer layer and the layer beneath it (dermis). Third-degree burns damage or completely destroy both layers of skin, including hair follicles and sweat glands, and damage underlying tissues.
Since the onset of a second-degree burn is the transition from first- to second-degree, what do these burns look (and feel) like? Here are two personal examples.
Case No. 1: sauce
My wife is quite a chef and sometimes gets into one of her maniacal cooking moods—that’s when I know it is time to run and hide. On one occasion years ago, I heard a metal pan hitting the tile floor accompanied by loud shrieks and screams. I ran into the kitchen and looked past the sauce covering every surface. She was bent over holding her hand, still screaming.
She had reached into the oven and grabbed a metal skillet by the handle—bare handed. This resulted in first-degree burns at the base of her fingers and a small blister. Being the nice guy that I keep reminding her I am, I took her to the kitchen sink and ran cool water on the injury while trying to calm her down. I cued up the camera on my phone while continuing the calming effort.
“There, there. Let me take a look at your hand.” SNAP! I got the picture. Of course, this did not go over well, but it does make a good illustration.
The pain began to subside the next day, and about a week later, except for a small blister (Figure 1), her hand had healed. Keep in mind arc-flash protection is intended to minimize the burn injury, but the onset of the second degree burn still hurts!
Case No. 2: chili
Two years ago, my wife took burn injury to the next level. For years, she has participated in a local chili cookoff as part of a Halloween event. But, this time, her competitive cooking streak kicked in—she was in it to win—and I ran and hid!
While manically cooking her potentially award-winning chili, there was a familiar shriek. Once again, I ran into the kitchen, but this time, it was more serious. She had rested a plastic microwave splatter screen on the electric stove top, and somehow, the burner had come on. It began to smoke and melt, so she used a spatula to scoop it up and toss it into the sink. However, the molten plastic dripped down onto her fingers. The result—full blown second-degree burn injury and uncontrollable screaming.
This injury required a trip to the urgent care. The pain took many days to subside, and the blisters lasted for quite some time. While changing her bandages after the incident, she held up her fingers and said, “I suppose you want a picture of this?” SNAP! Yes! (Figure 2).
Two years later, she says the feeling in her finger tips still has not returned to normal.
Although these were not electrical burns, you get the idea. Burns happen without notice. Some can be very painful, and others can be quite deadly. Wear your PPE, even in the kitchen.
By the way, she won the chili cookoff.