Scientific fire-related research made practical for use in fire investigations will strengthen the reliability of origin and cause investigations. There have been numerous studies on and reports of laboratory created damage to conductors or cataloging of conductors from full-scale fire tests. Few studies involved metallurgical examination of the damaged area. This research focused on damage to conductors for evidence of persistent internal physical indicators to distinguish arc melting from fire melting. A systematic protocol for the evaluation of damage to conductors is introduced for fire investigators to differentiate mechanical from thermal damage and thermal damage resulting from an arc versus fire melting when external visual indicators are not sufficient or disputed. If required, metallurgical analysis can identify thermal damage resulting from fire melting or from an arc site. The key physical internal indicators of an arc site on both solid and stranded conductors are porosity throughout the bead or notch, irregular or lack of microstructure in the bead or notch and an area or line of demarcation between an arc site and the adjacent conductor. The method and microstructure of arc sites and fire melting damage to conductors prepared in the laboratory and from the field are presented.
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