Arc Flash Pressure and Door Ejection Measurement

The effects of arc blast pressures have been theorized for about years, but the direct effect on workers has been less studied. A search of the literature gives no satisfactory quantification for hazard assessment [1] . Most articles to date with any worker focus have measured or predicted noise levels for auditory damage, but there is still no consensus standard or unified method to predict the pressure or thermoacoustic blast created by an arc. In a 2016 article, on the effect of copper and steel vapor, the authors also looked at the speed of an ejected door; however, that article did not address additional buildup of pressure should the door be affixed, as real doors are [1] . This article presents the results of affixing the door with both light and heavy gauge hardware as suggested in Crawford–Clark–Doughty [2] . These represent two different levels of shear strength to assess the effect of allowing pressure to build on the face of the door. Additionally, an impact plate and a load cell are used to measure the actual force from the ejected door to estimate the effect on a human worker. More work will need to be done to develop an arc blast assessment model, but the measurements obtained by these experiments may lead toward a productive means to develop one. Although the authors know of only one fatality [2] and a few injuries from arc blast, it is important to understand if, and when, severe injuries could occur. And with the removal of the 40 cal/cm ² limit to arc flash exposure in the 2018 NFPA 70E—since the committee correctly understood that incident energy has no correlation to arc blast [3] —it is also important to determine where a limit might be needed for worker safety, and what fault current and containment size could be dangerous until most equipment is arc resistant.