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By Sheila Kennedy, contributing editor
Every day, electrical arc flash accidents injure or kill, but wearing proper personal protective equipment (PPE) minimizes accident frequency and severity. PPE alone, however, is no substitute for thorough safety training, consistently following lockout/tagout procedures, keeping electrical equipment well-maintained, and applying engineering controls. Burns aren’t the only risk. A high-amperage arc produces an explosive pressure wave blast that can cause severe fall-related injuries.
Four-step hazard calculations: First, establish the job’s hazard risk category. Second, determine what clothing and equipment the hazard risk category requires. Third, identify what arc thermal performance value (ATPV) rating is necessary. Finally, select personal protective equipment that meets or exceeds the designated ATPV rating.
OSHA bases its safety mandates on NFPA 70E. The current standard includes a table of job task hazard categories that are heavily footnoted as valid only under specific ranges of conditions. “Deciphering risk categories and PPE needs for your individual employees isn’t a do-it-yourself job,” says Joe Weigel, arc flash product manager at Square D. “It requires a qualified, licensed electrical engineer.”
The calculations in the NFPA table and IEEE 1584-2002 Guide for Performing Arc-Flash Hazard Calculations assume that circuit breakers and fuses are in like-new condition. Most of the free online arc-flash calculators and worksheets are based on this assumption. However, according to Weigel, arc flash analysis studies often uncover existing equipment that is old, not well maintained, and questionable as to whether it will quickly detect and clear a fault. Engineers also might discover code violations and overloaded equipment.
Square D’s service personnel leverage the NFPA table, the IEEE standard and professional expertise to sort through unique requirements. SKM Power Tools for Windows software helps the technicians perform the detailed calculations. Your updated short-circuit analysis and coordination study is fed into the arc flash hazard analysis, which computes the working distance, incident energy exposure, flash protection boundary and level of PPE gear required.
Personal protective gear: More companies are manufacturing PPE gear using innovative fabric and material technologies, and the quality and comfort level is growing. Oberon Company uses permanently flame-resistant custom fabrics instead of cotton fabric treated with a flame-retardant, which risks losing flame resistance in the wash. Oberon’s garments have half the fabric weight of treated cotton systems for greater comfort with extended use.
Nasco’s Sentinal outerwear provides its highest level of protection against an electric arc flash. The durable, flexible material doesn’t melt, drip, ignite or break open. The MP3 product is a lightweight, breathable DuPont Nomex system suitable for any weather conditions. It protects against electric arcs while reducing worker heat stress. For rugged and abrasive environments, Nasco’s ArcTuff series uses a blend of Nomex and Kevlar that resists punctures and tears.
The better hoods have sizeable, distortion-free transparent viewing windows that provide impact strength and resistance to scratches and fogging. Oberon’s optional FreshAir Hood Ventilation System blows a steady stream of air into the hood to improve comfort and reduce perspiration.
Body-cooling vests and packs can provide about an hour’s worth of added comfort. Look for nonflammable hypoallergenic brands. Oberon’s cooling packs are recharged by placing them in ice water. Keeping a spare set in a cooler allows rotation for continuous use.
Educational resources: Numerous companies provide arc flash training or consulting services. Mastery Technologies provides an introduction to the topic in its online course, Electrical Safety: NFPA 70E Arc Flash Training. These audio lessons prompt the learner to ensure understanding. When a wrong answer is entered, the material can be reviewed until the learner enters the correct answer. A follow-up review provides time-delayed reinforcement of the material.
E-mail Contributing Editor Sheila Kennedy, managing director of Additive Communications, at Sheila@addcomm.com.
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