Forensic Support in Fire Investigation

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Forensic Support in Fire Investigation

• Dr. Tom Hannigan
• Forensic Science Laboratory,
• Garda H.Q.,
• Phoenix Park,
• Dublin 8,
• Ireland.

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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

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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

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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.

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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.

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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

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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

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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

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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.

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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

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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

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Fires Gas Chromatography

• Flame ionisation detector
• Temperature ramping
• 30 minute run
• Tenax adsorbant

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CHROMATOGRAPHY
INPUT SYSTEM
SEPARATION SYSTEM
DETECTION SYSTEM
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FLOW
TIME
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Debris from scene
Diesel oil
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Other services (1)

• Cans/continers liquid found near fire
  scenesliquid analysed for accelerantscan sent
  for fingerprinting
• Petrol Bombs (Molotov cocktails)-glass bottle
  petrolwick wick may provide forensic link e.g.
  with torn clothing in suspects house
• Clothing footwear persons suspected of handling
  acclerants-pack in nylon bags-avoid
  contamination-vapour lost rapidly

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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).

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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.