“Arc Flash” Hazards, Incident Energy, PPE Ratings, and Thermal Burn Injury—A Deeper Look

Tremendous resources are being invested in arc flash studies and personal protective equipment (PPE) to protect workers from “arc flash” hazards. In the flurry to comply with OSHA regulations and NFPA 70 and 70E standards, the real understanding of the arc hazard and incident energy may be lagging behind. The term “arc flash” does not adequately convey the range of potential arc hazards-light, pressure, and heat transmission, as well as others. The term “arc flash” also fails to emphasize that arc flash injuries primarily arise from thermal burns and that the risk of a potentially severe or fatal arc burn is often present when performing electrical work. Worker risk assessment and the appropriate PPE are represented as definitive quantities in “cal/cm ²;” however, the quantitative potential heat exposure and heat protection afforded by PPE are usually less precise than what concrete numerical values imply. Basic concepts of incident energy, PPE ratings, and burn injury are also explored in this paper to help identify factors influencing the burn hazards posed by arcing faults in electrical power systems.

I. Introduction

While industry is rushing to conform to OSHA and NFPA 70 and 70E requirements on labeling equipment and protecting workers from “arc flash” hazards, those charged with the responsibility may not have paused to reflect on the wide range of human hazards created by arcing faults in power systems. The push toward scientific accuracy may obfuscate the real imprecision associated with quantifying the impact of thermal arc energy on those in the vicinity of the arc. Section II of this paper discusses the range of arc hazards. Section III addresses incident energy concepts and rating personal protective equipment (PPE). Section IV covers basic physiology and the effects of burn injury so that the nature of burns is better understood by those not familiar with thermal injury. Finally, Section V briefly introduces some foundational burn research and burn modeling. Fig. 1.

Enclosure testing. Light generated by arc (recorded at 10 ft), roughly 5.83 ms after light was first visible (1200 fps video). (a) Vertical electrodes, , and calorimeters at 33.” (b) Vertical electrodes, , and calorimeters at 42.” (c) Horizontal electrodes, , and calorimeters at 24.” (d) Vertical-barrier electrodes, , and calorimeters at 42.”