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Howitt, D.G. The Chemical Composition of Copper Arc Beads: A Red Herring for the Fire Investigator. Fire and Arson Investigator. Vol. 48. No. 3 (March 1998). p 34-39.

Abstract: The chemical composition of arc beads, determined by Auger analysis, has been cited as a method for determining whether the arcing was the cause or result of a fire. The hypothesis is based on the idea that atmospheric gases are preferentially trapped in the liquid metal during the formation of an arc bead so that the gas concentrations are indicative of the atmospheric conditions at the moment of arcing. The published literature on the solubility of gases in copper clearly indicates that not only are atmospheric gases actually less likely to be trapped in liquid copper than in the solid copper, but that all the solubilities are so low anyway that none of them could possibly be detected by Auger analysis. An analysis of the composition variations amongst the various types of arc beads, using scanning electron microscopy, indicates that the composition variations are related to local oxidation and contamination on the surface. In addition, the variations which are found on a single bead readily account for the different measurements that have been erroneously claimed to be significant between arc beads formed under entirely different circumstances.

For more information, contact:
International Association of Arson Investigators (IAAI)
300 Broadway Suite 100
St. Louis, MO 63102-2808
Phone: 314-621-1966

 
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