Protective clothing guidelines for electric arc exposure

Abstract

Since 1982 when Ralph Lee wrote about "The Other Electrical Hazard: Electric Arc Blast Burns" [l], industrial and utility engineers have been attempting to better quantify the degree of risk to personnel associated with electric arc exposure and the appropriate protactive clothing to wear to mitigate serious injury. Recent activity by OSHA, NFPA 70E and ASTM F-18 has further emphasized the need to protect workers from arc flash burn injuries. This paper discusses the results of recent multiphase arc testing which has enhanced knowledge about: 1) potential arc energy as a function of prospective fault current, and 2) arc protective clothing designs that are suitable for different levels of incident arc energy. Incident energy levels are correlated with second degree burn criteria for unprotected human skin. Protective clothing systems consisting of flame resistant outer layers in singlelayer and multiple-layer construction, as well as combination systems of jlame resistant outer layers with natural and man-made fiber inner layers are discussed Protection recommendations for the face, head, hands and feet are also includedRegulations in OSHA 1910 Subpart R require that employees wear appropriate clothing when they may be exposed to an electric arc hazard. To meet these regulations, employees must not wear clothing that could increase the extent of injury that would be sustained by the employee in the event of electric arc exposure. Clothing made from acetate, nylon, polyester or rayon, either alone or in blends, is prohibited by OSHA 1910.269 unless the employer can demonstrate that the fabric has been treated to withstand the conditions that may be encountered, or that the clothing is worn in a manner that eliminates the hazard. OSHA has issued supplementary guidance for untreated cotton and wool, c l m n g the need for employers to determine that these materials would not ignite in potential arc exposure situations.The most recent edition of NFPA 70E, "Standard for Electrical Safety Requirements for Employee Workplaces,"[5] was completed at the request of OSHA and was issued by NFPA on February 7, 1995. Part 11, Chapter 3 covers personal protective equipment and requires for body ISBN: 0-7803-3587-2 96-CH35988-6/96/0000-028 1 $05.00 @ 1996 IEEE

Improved method for arc flash hazard analysis

“…There was also a box effect; K must be multiplied by 0.797 for tests in a box. The waveshapes are similar to published data [5,16]. The current stabilizes quite quickly because of the damping effect of the fault arc resistance.…”

“…current over the last cycle before the circuit opened, and iteratively adjusting V ARC to obtain agreement. Then X and Y were determined by a multiple regression fit to equation (5). (304 test shots were used in the analysis -the tests with series current-limiting fuses being excluded).…”

“…There are several different methods in use at present to calculate the flash boundary distance and incident energy upon a worker [2,[4][5][6][7], and the IEEE standard 1584 contains formulae based on a statistical fit to test data obtained in several high-power test laboratories in North America [8].…”

Electrical Safety, Electrical Hazards, and the 2018 NFPA 70E: Time to Update Annex K?

“…Although The "safe" threshold for incident heat on bare skin has generally been accepted at 1.2 cal/cm 2 [35], based on Stoll's onset of a 2 nd degree burn, which involves the formation of a blister [36]. Fabric testing on blue cotton, twill shirt material, 5.2 ounces per square yard, demonstrated a 90% chance of ignition when exposed to incident heat levels of 6.9 cal/cm 2 [37].…”

Investigation of Arc Flash in Single-Phase Vertical Conductors in a Box

“…The arc flash is initiated with a fuse wire. System voltages used in early work were 600 V and 2400 V, with available arc currents up to 45 kA [13].…”