Arcing Before or After Fire

摘要

Did arcing cause or was it caused by the fire? This is a common question but almost neverrnanswered directly by any electrical engineer or fire investigator. Results from surface examination orrncircumstance analysis such as arc mapping usually leave undetermined issues. Results fromrnmetallurgical examinations or chemical analysis may be useful to distinguish if the melting wasrncaused by fire or arcing. Still uncertain is the sequence: did arcing occur before or after the fire?rnThis research examined both damage surface and interior of arced copper wires and beads.rnThe results distinguish which arcs occurred before or after a fire by analyzing cuprous oxide (Cu2O),rnburning soot and gasifying crystal.rnThe higher temperature and longer duration of burning causes more copper surface oxidizingrninto a red cuprous oxide layer instead of a black cupric oxide (CuO) layer. The cuprous oxide showsrnshining red purple under microscopic examination and will melt and flow away as the temperaturernreaches its melting point (1235 °C, 2255 °F). This research found gasifying crystals in arced samples andrnonly those arcing after fire showed the scattered cuprous oxide and/or burning soot in the interior ofrnbolts, beads and gasifying crystals. Results of case studies from Professor Chen’s expert witness inrncourt had successfully proved the procedure’s function.rnThese findings are useful in arcing determination and help fire investigators and electricalrnengineers include or exclude the electrical causes as they establish their fire report conclusions. Also,rnthe new method is very important of manufacturers, their customers, designers and regulators, whornrequire up-to-date information on arc determination issues, including new materials, applications,rnassessment techniques and regulatory requirements or guide of fire investigation.