Arc flash, according to OSHA and the West Virginia State University’s presentation on the subject, are produced by arcing faults that discharge electrical currents and radiation. It comes in the form of a ball of fire or spark, but imagine it a thousand times more lethal.
To put the hazard level of arc flashes in perspective, let’s take data from the said presentation into account: The sun’s surface temperature measures 9,000 degrees Fahrenheit; the temperature of arc terminals measure 35,000 degrees Fahrenheit. Treatable burns are burns that subjected the skin at a temperature of 176 degrees Fahrenheit. Metal melts from arcing at a temperature of 1,832 degrees Fahrenheit.
Many workers die as a result of arc flashes. Some do not die, but face terrible injuries such as third degree burns and lacerations from debris, fire and electrical currents; eye and facial injuries, hearing loss and respiratory damage. An arc blast can send projectiles flying up to ten feet or more. Unfortunately, working on energized equipment is inevitable in both construction and general industry.
Thanks to the National Fire Protection Agency’s NFPA 70E, preventive measures against arc flash-related injuries has improved throughout the years. The agency, in tandem with OSHA, has released guidelines to limit workers’ exposure to arc flashes, which include standards for labeling requirements and hazard analysis.
Personal protective equipment or protective clothing shields workers from the deadly effects of arc flashes. In choosing the right PPE, workers have to understand the concept of incident energy as it is the main basis for selecting PPE.
Incident energy is a thermal energy that results from an arc flash. Its measurement value is cal/cm2. 1.2 cal/cm2 is enough to cause a second degree burn.
The following arc ratings determine the selection of PPE, according to the NFPA. The higher the class means the more flame retardant the PPE should be.
Class 0 – 1.2 cal/cm2
Class 1 – 4 cal/cm2
Class 2 – 8 cal/cm2
Class 3 – 25 cal/cm2
Class 4 – 40 cal/cm2
However, take note that protective clothing materials also have to meet ASTM F1506, according to the Electrical Construction and Maintenance (EC&M) website. The standard requires companies to make use of materials that “do not melt.” EC&M notes that just because some fabric companies claim the fabric is “flame resistant” or “will not sustain flames under high heat conditions”, doesn’t mean they will not melt due to arc flashes.
Calculating for the highest incident energy to determine the PPE is a bit technical, but to get your fill of the formula, you can check out Professional Power System PLLC’s white paper Understanding Arc Flash Requirements. The Journal of Industrial Technology also published a paper that enumerates methods on computing arc flash which you can access here.
Workers have to note that PPE may provide them initial protection, but may not completely protect them from the dangers, specifically, the impact of arc flashes.
For more ways on how to protect yourself from arc flashes, visit the Workplace Safety Awareness Council’s online primer on arc flash, or enroll in our OSHA 10 Construction or OSHA 10 General Industries course.