Forensic Support in Fire Forensic Support in Fire Investigation Investigation Dr. Tom Hannigan Forensic Science Laboratory, Garda H.Q., Phoenix Park, Dublin 8, Ireland.
Jan 10, 2016
Forensic Support in Fire Forensic Support in Fire InvestigationInvestigation
Dr. Tom HanniganForensic Science Laboratory,
Garda H.Q.,
Phoenix Park,
Dublin 8,
Ireland.
Forensic Science LaboratoryForensic Science Laboratory
Agency of Dept of Justice, Equality & law Reform
Approximately 70 staff (all civil servants)4 sections; Biology, Chemistry, DNA,
DrugsFires dealt with in Chemistry SectionHoused in Garda Technical Bureau with
whom we work closely
Services to criminal Services to criminal investigationinvestigation
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
How forensic science may link How forensic science may link individuals/scenesindividuals/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.
ExampleExample
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.
Examination of crime sceneExamination 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
Scene PreservationScene 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
Role of FSL in fire Role of FSL in fire investigationinvestigation
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
Hydrocarbon Fire AccelerantsHydrocarbon 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.
Packaging of debris samplesPackaging 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
Analysis of hydrocarbon fire accelerantsAnalysis 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
Fires: Gas ChromatographyFires: Gas Chromatography
• Flame ionisation detector
• Temperature ramping
• 30 minute run
• Tenax adsorbant
INPUTSYSTEM
SEPARATION SYSTEMDETECTION
SYSTEM
CHROMATOGRAPHY
FLOW
TIME
Diesel oil
Debris from scene
Other services (1)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
Other Services (2)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).
ConclusionConclusion
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.