(This article was published in INTREPID Forensics Newsletter Issue 3 on 05 October 2015)
The INTREPID Forensics group has the chance to participate in numerous special practical sessions. The live fire demonstration was just one of these. It is true that basics in physics and chemistry allow inferences about the cause of a fire and its origin; but nothing is like the captivating sight of real flames as they grow from their activation energy point up until they vanish back into the ground.
On May the 11th 2015, we gathered around an open air parking lot near campus to witness a live fire inside a heavily neglected type of indoor domestic environment staged especially for our experiment. Fire investigators John Caulton and Julie Sykes from JCFire, along with Jack, their trained accelerants’ sniffing dog, designed and carried out a state of the art experiment.
John managed to create a ‘room’ by equipping the inside of a mobile trailer accordingly. The sidewalls and the floor were covered respectively with wallpaper and a carpet, while a couple of electric sockets were installed into the wall under a furnished suspended lamp. There were also a couch, a bed and a bedside cabinet at the back of the ‘room’, in front of which was a large chest of drawers on which sat a computer screen. The place was intentionally untidy so as to reflect carelessness in lifestyle. A hair straightener, a radio, a syringe and a bunch of other items were randomly scattered around.
As soon as unleaded petrol was poured and before we could notice the cause and location of the first spark, small flames had already emerged from the carpet and kept on evolving. Factors like the continuous access to oxygen and the presence of fast and slow combustibles created a resistant fire that engulfed most of the space for about seven minutes. It was then extinguished by closing the backdoor of the trailer, hence limiting the airflow, then by water spraying the resisting flames. It was difficult to see any details once we reopened the door, as opaque dark clouds obstructed the view.
The investigation of a fire event does not start before ensuring the safety of everyone inside or about to enter the scene; including the scene of crime officers. It was therefore necessary to wait for a clearer vision, less toxic smokes and the premises to cool down. This was the perfect time for Julie and her arson dog Jack to demonstrate their skills at detecting the use of accelerants. Dogs have hundreds of millions times more scent receptors than humans do and they use their olfactory senses to process most information around them. The dogs’ sniffing capabilities combined with a special human-dog bond that is created during a competent training makes the pair today’s most effective trace evidence detection system. Police dogs are usually classified within their specialty area and build different reactions when the wanted substance is identified. A cadaver dog that digs in the ground indiscriminately at the presence of a decomposing body for example cannot be used to detect buried explosives. Explosive sniffing dogs are usually taught to emit a passive reaction such as sitting down at a positive detection. Jack had a very unusual reaction which consisted of constantly lifting his limbs as if running in place, each time he could sniff ignitable liquid residues.
This live fire demonstration was also an opportunity to conduct a real life experiment that contributes to my INTREPID forensics PhD project. As I am working towards developing a new method for recovering DNA from surfaces subjected to extreme conditions, I seized this live fire demonstration to degrade then collect and analyse biological traces from known individuals. A number of colleagues made this experiment possible by each drinking a soft drink from a can in a relatively controlled fashion before handing it back to me; I then placed the aluminium soft drink cans, which contained traces of my colleagues saliva and epithelial cells, around the fire epicentre before ignition.
Once safe again, we investigated the burned scene under John and Julie’s mentorship. They listened carefully to what we had to say while guiding us through a consistent train of thought that helped us to determine the origin and progression of the fire. A melted red candle was located within what remained of the couch’s seating zone. From there the flames could have reached the carpet by the possible fall of blazing combustibles. We were also able to eliminate the electrical cause even though electrical hazards represent one of today’s most common indoor fire threats. Both fire by negligence explained by the burning candle left on the couch, and arson using a liquid accelerant that was detected by Jack were combined in one exercise to give us an idea about the comprehensive processes of inquiry a fire investigator must take to reconstruct the event.