Here is the most basic answer. In the past electricians were just careful not to get a shock. Don’t get zapped! Now, you have to be careful not to get burned or blasted. That’s it…basically. But there is much more. Who started all this? OSHA says “Safety-related work practices shall be employed to prevent electrical shock or other injuries…” Well, we’re into the “other injuries.” Why? Because the number of people injured by electrical burns each year and the extent of the injuries is horrific and no longer considered tolerable.

The cal/cm2 is a measure of the ability of the fabric to withstand heat. It's a heat measurement. An "Arc Flash Analysis" is the engineering calculations performed to determine how much heat an arc may cause at a specific fault location and at a specific distance from the fault. Therefore the combination of all the clothes you are wearing must provide enough protection so that you do not get a "Second Degree Burn" or worse. The heat generated is related to the amount of fault current that can take place at a fault. The concern is "heat" from "fault current" and not voltage. Concern for voltage is concern for "shock hazard" and not "arc flash hazard." Just assuming the higher the voltage, the higher the arc flash hazard, can be a "huge mistake." In the absence of an arc flash analysis, think to yourself. "How much fault current could there be and how long would the fault last?" That last part, "how long would it last," is extremely important. Also, you must be able to justify exposing yourself to energized equipment. Wearing protective equipment doesn't make it safe to work on energized equipment.