Mark Goodson PE
\nLee Green PE
\nMichael Shuttlesworth PE
\nGoodson Engineering
\nDenton, Texas USA<\/p>\n
Presented at\u00a0International Symposium on Fire Investigation<\/a>, 2014<\/p>\n ABSTRACT In a fire, it is not uncommon for fire artefacts (wires, as an example) to require cleaning. Historical cleaning\u00a0techniques have relied upon ultrasonic cleaning as a means for debris removal. Ultrasonic cleaning makes use of\u00a0mechanical (sonic) energy to cause debris to dislodge from artefacts. How successful this technique is depends (in\u00a0part) upon the energy imparted, the solvent used, and the interface between the wire and the debris. In the case of\u00a0partially pyrolyzed PVC insulation, there are conditions that occur (depending upon the state or extent of pyrolysis)\u00a0where no amount of mechanical agitation will remove the fire debris.<\/p>\n Oxides can be removed from wires by the use of surfactants or cleaners, some of which can have an etching effect\u00a0on the metal. Treatments such as Alconox\u00a0 or Simple Green\u00a0 sometimes work sufficiently, while a more aggressive\u00a0oxide remover (Branson OR)\u00a0 relies on citric acid to help clean the wires. With more aggressive reagents, the user\u00a0runs the risk of etching the metal and ruining the surface finish.<\/p>\n The writers describe a technique for removing fire debris from metal objects (wire, CSST) for use in removing fire\u00a0debris. The technique is referred to as plasma ashing . In plasma ashing, a vacuum is created around the artefact, and\u00a0a carrier gas is introduced (such as O2). An RF field (13.56 MHz) is applied, and the oxygen takes on a monatomic\u00a0state. Essentially, a plasma i s created, and the monatomic O is free to react with organics associated with the fire\u00a0debris. This process is also referred to as a glow discharge . The end result is that organics are removed from the\u00a0artefact, and the ashing takes place at low temperatures \u2013 sufficiently low such that grain structure of the metal is not\u00a0changed. This technique is essentially what is used in one of the manufacturing steps for making integrated circuits\u00a0(ICs). As such, it imparts sufficiently low energy such that crystalline semiconductor structures are not damaged.<\/p>\n We compare and contrast plasma ashing with other modalities of cleaning. More particularly, we note (through\u00a0visual microscopy) the efficacy of ashing and ultrasonic cleaning, as well as material removal rates. We show that\u00a0despite its relative expensive capital costs, ashing represents a cleaning technique that does what other modalities\u00a0fail to do \u2013 consistent removal of organic debris with no damage to the underlying substrate.<\/p>\n Download the\u00a0complete paper<\/a>\u00a0here<\/p>\n","protected":false},"excerpt":{"rendered":" Mark Goodson PE Lee Green PE Michael Shuttlesworth PE Goodson Engineering Denton, Texas USA Presented at\u00a0International Symposium on Fire Investigation, 2014 ABSTRACT One of the difficulties that has faced engineers who examine electrical or mechanical items and \/ or devices after a\u00a0fire is that of cleaning the item. The key adage in cleaning is essentially … Continue reading Plasma Ashing as a Fire Investigative Tool<\/span>
\nOne of the difficulties that has faced engineers who examine electrical or mechanical items and \/ or devices after a\u00a0fire is that of cleaning the item. The key adage in cleaning is essentially a medical command \u2013 primum non nocere,\u00a0or \u201cdo no harm.\u201d The cleaning technique will preferably cause no damage to the artefact being examined. Successful\u00a0cleaning allows for both microscopic, visual, and SEM \/ EDX analysis.<\/p>\n