Incident Prevention Magazine

Hugh Hoagland and Zarheer Jooma, BSEE, M.S.

Using Arc Protective Blankets as an Engineering Control Method

Web-Capture-Ejected-Arc

While engineering controls are preferred over personal protective equipment for worker protection, many engineering controls, such as arc-resistant switchgear, require the purchase of new electrical equipment in order to fully implement them. When replacing equipment, this type of installation makes total sense, but it rarely can be the only company policy to mitigate arc flash in all facilities.

OSHA always prefers that organizations use the highest option possible on the hierarchy of controls. This is clear in the preamble to 29 CFR 1910.269, in which OSHA states the following: “NFPA 70E-2004 warned that ‘[d]ue to the explosive effect of some arc events, physical trauma injuries could occur’ … OSHA expects that the hazard analysis required by paragraph (g)(1) in the final rule will identify nonthermal hazards, including physical trauma hazards posed by flying debris, associated with employee exposure to electric arcs. … [OSHA requires] employers to address [these hazards] … [and] provide shields and barriers necessary to protect employees from physical trauma hazards. However, as noted by NFPA 70E, not all arc events pose physical trauma hazards from flying debris; therefore, this protection will not always be necessary …”

The 2018 NFPA 70E standard rightly took out the reference to 40-cal/cm² exposures posing a hazard from arc blast, since arc blast is more a function of containment and current than calories. In fact, our recent research surveyed the literature on arc blast pressure waves and found that many of the formulas did not come close to predicting our lab data from 4,000A to 12,000A (E. H. Hoagland, C. Maurice, A. Haines and A. Maurice, "Arc Flash Pressure Measurement by the Physical Method, Effect of Metal Vapor on Arc Blast," in “IEEE Transactions on Industry Applications,” vol. 53, no. 2, pp. 1576-1582, March-April 2017). New work continues to expand this knowledge and will be presented to the IEEE Electrical Safety Workshop this March in Fort Worth, Texas.

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