Arc Week Season 3, Ep. 2: Return to the Danger Zone – Determining Arc Flash Energy Part 2

In today’s episode, we’re diving right in to the three remaining variables that determine arc incident energy level. Watch the video above, featuring your Arc Week host, Scott Margolin as he explains what fighter jets, shark teeth, and shark feeding zones have in common with cycle time, arc gap, and distance.

In Episode 1, we learned about the first two variables that determine arc incident energy level, voltage and amperage. Like amperage, cycle time is directly related to the arc incident energy level. Arc gap and distance of the worker from the arc gap are also key factors that determine the potential power of an arc flash.

• Cycle time: The cycle time of an arc flash is the duration of the arc flash, and one cycle is equivalent to 1/60 of a second. Cycle time is a critical variable because it’s directly proportional to arc incident energy, the longer the cycle time of an arc, the more energetic the arc flash. For example, if we were to go from a five-cycle arc to a ten-cycle arc, the energy of the arc has doubled, requiring that much more protection, and the same applies if the arc went from a 20-cycle arc to a ten-cycle arc, the arc incident energy level would be cut in half, requiring PPE with a lower arc rating. Electrical breakers aren’t often exercised properly, causing the breaker to “stick” which can be particularly dangerous. If a breaker is supposed to trip in ten cycles, but it “sticks” and trips in 15 cycles, that’s 50% more energy than expected, increasing the severity of the arc flash and your risk of injury if you’re not outfitted in the higher level PPE.
• Arc gap: Three phase industrial electrical gear typically includes three conductors, and the arc gap is defined as the distance between two conductors. This is important because the further apart the conductors are, the larger the potential arc. Depending on the size of the industrial gear, conductors are typically spaced between 1.5” - 2.5” apart.
• Distance of worker from the arc gap: We saved the most important variable for last, pay close attention! This variable is crucial because the individual worker is in control of it. The distance variable is measured by how far the worker (typically their torso) is from the arc gap, and the closer the worker is to the arc gap, the higher the energy level. For example, the difference of standing just three inches closer could mean an increased energy rating of four calories! This completely changes the calorie rating requirement for your PPE, and if you’re not prepared, you risk suffering from burn injuries because the arc incident energy is greater than the arc rating of your PPE. Workers must be especially conscious of this since our arms are only so long. So, remember, distance is your friend.

In addition to the five variables that determine arc incident energy, explained in episodes 1 and 2, there are a few other factors specific to industrial electrical arcs or “arc in a box” that workers should be conscious of while on the job. That is, the size, shape, and depth of the “box.” Arc incident energy levels increase as the enclosure size of the source of the potential arc gets smaller or shallower. Finally, the orientation of the electrodes within the industrial equipment affects the hazard, and vertical electrodes tend to be more hazardous.

Please join us tomorrow to catch Episode 3: Great Balls of Fire – Live at the Arc Ratings Lab. In this episode, we travel to North America's only arc rating lab to take you on a behind-the-scenes look at arc flash testing from the bottom up. Scott Margolin, Chair of ASTM F1959 the Standard Test Method for Determining Arc Thermal Performance Value of Textile Materials for Clothing by Electric Arc and Related Thermal Hazards is joined by industry expert Brian Shiels, Service Line Manager at Arcwear and Director of the ASTM Board of Directors, to conduct testing and determine an arc rating from beginning to end. Swim along as we explore the science behind the safety.

Do you have a flash fire – rather than an arc flash – hazard? The hazards may differ, but the valuable lessons in this series are relevant to workers in oil and gas and other industries that use PPE to protect workers from thermal hazards. Tune in!