ARC Flash Pressure Door Ejection Measurement

Abstract

The effects of arc blasts pressures have been looked at theoretically for several years but the direct effect to workers, is harder to quantify. A search of the literature does not give any satisfactory quantification for worker danger [1]. Most of the published work focuses on the theory and how to contain or shunt the thermal energy using arc resistant equipment, which is to be applauded. However, most of the equipment in industry is not arc resistant so research on the true extent of the hazard is critical. Most papers, 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. The authors explored the effect of copper and steel vapor on arc flash in a 2016 paper [1] which also looked at the speed of an ejected door. That paper evaluated several quantified methods of promising prediction and chose the Crawford-Clark-Doughty [2] paper which correlated well with the paper's test measurements [1]. Crawford-Clark-Doughty predicted that the shear strength of a door's hinge or bolts could be used to predict the force on the door and subsequently on the worker if the door is blown off by the pressure from the arc event. The previous paper [1] had the weakness of not addressing additional build up of pressure should the door be affixed, as real doors are, so this paper chooses two means to affix the door with a light gauge mounting hardware and a heavy gauge mounting hardware. These represent two different levels of shear strength to assess the effect of allowing pressure to build on the force of the door. Additionally, an impact plate and a load cell is 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 a model but these measurements may lead toward a productive means to develop a model. Note that the literature and anecdotal evidence does not indicate many arc blast injuries and the authors know of no fatalities. It is important to understand if, and, when severe injuries could occur. With the removal of the 40 cal/cm2 limit to arc flash exposure in the new 2018 NFPA 70E [3], there is a need to understand where a limit could be needed for worker safety and what fault current and containment size could be dangerous until most equipment is arc resistant.