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Forensic Support in Fire Investigation

Forensic Support in Fire Investigation. Dr. Tom Hannigan Forensic Science Laboratory, Garda H.Q., Phoenix Park, Dublin 8, Ireland. Forensic Science Laboratory. Agency of Dept of Justice, Equality & law Reform Approximately 70 staff (all civil servants)

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Forensic Support in Fire Investigation

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  1. Forensic Support in Fire Investigation Dr. Tom Hannigan Forensic Science Laboratory, Garda H.Q., Phoenix Park, Dublin 8, Ireland.

  2. Forensic Science Laboratory • Agency of Dept of Justice, Equality & law Reform • Approximately 70 staff (all civil servants) • 4 sections; Biology, Chemistry, DNA, Drugs • Fires dealt with in Chemistry Section • Housed in Garda Technical Bureau with whom we work closely

  3. Services to criminal investigation • Identification of substances e.g. controlled drugs, explosives, accelerants in fire debris • Linking individuals and/or scenes to one another through • Biological • Impression or • Trace Evidence

  4. How forensic science may link individuals/scenes • Biological – biological fluid e.g. blood or cigarette butt at scene – DNA profile extracted– compared with profile of suspect. • Impression – fingerprints, footwear impressions, tyretracks, toolmarks. • Trace Evidence – anything that can be transferred e.g. fibres, paint , glass, firearm residue etc.

  5. Example • Man wearing woolly jumper breaks into home of elderly person. • Breaks window, having first attempted to force open window with tool. • During violent assault, victim suffocates and dies. • Attempts to light fire but fire fails to take hold.

  6. Examination of crime scene • Window frame checked for fingerprints & fibres • Control samples paint & glass taken • Cast made of toolmark • Clothing of victim taken at post-mortem. • Suspect arrested – clothing taken for examination for glass & fibres • Tool in his possession examined for paint • Marks made with tool compared with scene marks

  7. Scene Preservation • Trace evidence lost with passage of time • Forensic evidence usually delicate – avoid disturbing • Importance of preserving scene & limiting access • Fire suspected to be malicious is a potential crime scene • DNA & Fingerprints can sometimes survive extreme heat

  8. Role of FSL in fire investigation • Mainly to assist in determining whether or not fire malicious • Done by analysing debris samples for hydrocarbon fire accelerants • Sanples must be taken from seat of fire • Finding of accelerants, when unaccounted for, an indicator of arson • Must be interpreted in conjunction with other indicators • Many other ways in which a malicious fire can be started

  9. Hydrocarbon Fire Accelerants Main Classes: Petrol White Spirit Paraffin Oil Diesel Oil All complex mixtures of hydrocarbons Flammable & Volatile If used to start fire, good chance that some of the heavier hydrocarbons will survive fire, perhaps by seeping into carpet & floorboards.

  10. Packaging of debris samples • Proper packaging essential • Debris samples should never be packed in paper or plastic bags/containers (contamination) • We recommend nylon bags for packaging debris samples. • Knotted or sealed & appropriately labelled • Garda Scenes of Crime examiners have supplies nylon bags

  11. Analysis of hydrocarbon fire accelerants • Analysed using Gas Chromatography (GC) • A technique for separating chemical mixtures • Debris sample is heated at 110C for 40 mins to drive any accelerant residue into the vapour phase • Sample of vapour from the bag drawn through a glass tube containing Tenax, a polymer which adsorbs hydrocarbons • Tube placed in injection port of GC (325C) – hrdrocarbons driven off onto column and separated into individual components • Printout is a pattern of peaks characteristic of mixture

  12. Fires: Gas Chromatography • Flame ionisation detector • Temperature ramping • 30 minute run • Tenax adsorbant

  13. CHROMATOGRAPHY INPUT SYSTEM SEPARATION SYSTEM DETECTION SYSTEM

  14. FLOW TIME

  15. Debris from scene Diesel oil

  16. Other services (1) • Cans/continers liquid found near fire scenes–liquid analysed for accelerants–can sent for fingerprinting • Petrol Bombs (Molotov cocktails)-glass bottle petrol+wick; wick may provide forensic link e.g. with torn clothing in suspect’s house • Clothing & footwear persons suspected of handling acclerants-pack in nylon bags-avoid contamination-vapour lost rapidly

  17. Other Services (2) • Unburnt or partially burnt materials-basic flammability tests to determine whether or not material burns, how rapidly it burns • Electrical items – difficult to judge without visit to scene or access to comprehensive record of scene incl. photos. Can comment on signs of electrical activity in cable (arcing, fuse blown) or if device plugged in when fire started (smake pattern on plug).

  18. Conclusion • Fire investigation is a multi-disciplinary exercise. • I hope this presentation has been helpful in clarifying the contribution of the Forensic Science Laboratory to the process. • Thank you for your attention.

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