Reproduced from "Firepoint" magazine - Journal of Australian Fire Investigators.
I often read reports where fire investigators forget the purpose of their visit to the fire scene. Their reports are filled with technical waffle describing the building and its contents and the effect of the fire on them, but very little attention is devoted to what they actually think caused the fire and why.
The best point to start an investigation is to collect the circumstantial evidence of the fire. Find out where the eyewitnesses' first saw the fire because it saves a lot of time and conjecture. I have seen fire investigators in court criticize eyewitness reports as being unreliable, particularly when the eyewitness' reports contradict their own conclusions, but in general, most people are able to interpret what they see.
Next talk to the owners or occupiers of the premises and find out what they know and if they have any ideas about the cause of the fire. They generally start thinking and talking about the cause after getting over the initial shock of the fire. Even if they are a suspect for deliberately lighting the fire, they should be given the opportunity to express their views. What they say might be different to what they told the Police and Fire Brigade investigators soon after the fire. It's all evidence which may prove to be valuable further down the track. Take particular note of the first things an insured tells you because it is often the thing which has been mostly on their mind since the fire.
The Fire Brigade investigators are experienced in investigating fires and are always a valuable source of information. They can accurately establish the security of a building and are able to question first hand the building owners or occupiers and the fire fighters. The Fire Brigade in NSW have a sniffer dog which is one of our most important resources in fire investigation. Without a sniffer dog, fire scene excavation is a long and laborious job. The Fire Brigade's efforts over the years have streamlined the fire investigation industry which helps insurers, insured parties, people disadvantaged by the fire, the Police and the legal system.
Be aware of the weather conditions at the time of the fire and when you reach the fire scene, look at the surrounding area for sociological indicators. For example, buildings next to a park are often subject to burglary or vandalism and strange things happen after pubs close.
Once all of the circumstantial evidence outlined above has been established, it is now time to examine the physical evidence. It is often said that fire investigation is the most difficult of all the forensic sciences and this may be true for some fires. Some fires are easy to investigate and some are difficult, if not impossible.
Examining the fire scene is mostly about studying the effect of heat on various materials. Knowing the physical constants such as melt points and ignition temperatures of materials is a basic tenet of fire investigation and understanding the ventilation of a fire is very important. If there is no ventilation then the fire becomes starved of oxygen and self extinguishes. If there is plenty of ventilation then the fire burns rapidly yet the ventilation allows the developing heat to escape and so fires generally reach a limiting temperature of around 600° - 1000°C (colour of red heat). Then the extinguishment of the fire can be like snap freezing a certain stage of the fire because most things found charred black were glowing red during the fire.
The first indicator one should look for to indicate the area of fire origin is the area of most severe fire damage. It is generally a reliable indicator except in severe fires. The other most commonly used and reliable indicator is the lowest level of fire damage however in severe fires, everything can be burnt to floor level. The classic V burn pattern is a very good indicator because fires initially burn upwards. Burn patterns may be consumed by the fire and so non combustible materials such as copper wiring is used to indicate the spread of the fire by identifying arc damage.
Arc damage is a reliable indicator of where a fire first affected a live electrical circuit and so is often found at or near the area of fire origin. Arc damage is produced by a short circuit and is the melting of copper conductors caused by current flowing across a small surface area of contact. If the fault current reaches the rating of the fuse or circuit breaker, then current will stop flowing and no more arc damage can be formed on that circuit.
So what does arc damage look like? Generally it's where the copper has melted into a small globule. If the wiring is still flexible up to the point of the globule, then there is a good chance it is arc damage. If the wiring is stiff up to the point of the globule, then it may not be arc damage but melt damage caused by the fire. Learning to identify arc damage is best done by examining the thicker supply cables. To find arc damage on smaller cables, it helps to remove the cables into sunlight and wash them with water and sometimes the arc damage shines brightly.
Accelerants are normally found on floors and are best preserved in wet, absorbent materials such as rags and carpet. After the water drains from the fire scene, the accelerants start to evaporate as a plume and in still conditions the plume starts to stratify. The sniffer dog detects the stratification and then zeroes in on the plume but us mere humans have to dig out the area of fire origin and smell the absorbent materials as we unearth them. Burnt rubber backed carpets and burnt polystyrene smell very much like petrol simply because they contain many of the chemicals found in petrol.
The constant problem that investigators face is that the most severe fire damage is found at the area of fire origin, which destroys the evidence needed to prove the cause of the fire. For this reason, it is important to check the areas where there is no fire damage for evidence of intruders or a second smaller fire that did not escalate. Burglar alarm computer logs are a valuable aid in investigating fires however caution should be used when interpreting them because the response of detectors to fires is sometimes unpredictable. (More research is needed in this area).
The independence and intelligence of an investigator is important and investigators should study the scene without the constant annoyance of other people being around. It's all about studying the three dimensions of the fire scene so remember to look around, look up, walk the perimeter, get on the roof if possible and concentrate on determining the cause of the fire. Investigators should be willing to get dirty and put up with atrocious conditions at times. Too many fire scenes end up as gabfests and we need thinkers at fire scenes and not personalities.
Investigators should collect important pieces of evidence and photograph the scene extensively. Its best to have at least two photographs to prove each point the investigator is trying to make. I often see investigators take over a hundred photos using digital cameras but only use a handful in their report so to reduce their email transmission time or their own printing costs. If the opinions in a report far exceed the amount of photographs provided, then courts should consider rejecting the report.
Some time well after the fire, you may be called to give evidence in court and this is when you wish you were concentrating at the fire scene and have provided enough photographs to prove your case. It's not about having the best suit or having the winning smile - it's about having the most logical arguments and the proof to back them up. If you fail to effectively communicate your arguments to the barristers, judge or jury, then maybe you're using too much technical jargon. Being a good fire investigator takes years of experience however everybody starts from scratch and I hope this article is of benefit to them.