How do firefighters figure out what started a fire and where it started?

23 January 2012

Above: Image © MateuszF93, Wikimedia Commons

Solve this mystery — a new homeowner calls the gas utility for their gas meter to be turned on. The serviceman does this but smells gas in the kitchen, so he turns off the gas stove. An explosion later occurs. What happened and how do we figure it out?

It's pretty clear that the explosion was caused by gas, and since turning off the stove didn't stop the problem it was probably a problem with the gas line. In a scenario like this, determining the cause of the fire requires deduction and scientific knowledge, and has implications for insurance companies and the people who might be held liable.

The destructive nature of fire was pretty obvious last week when old buildings caught on fire in downtown Toronto. It was uncontrollable for hours, even with a city-full of firemen (and women) to put it out. Before we can find out what started a fire, the first priority is for firemen to put it out. Afterwards, there's an investigation by the fire investigators that will be of interest to anyone who is left with the consequences.

Did you know? fire investigators usually try to find out the place of origin of the fire before they determine its cause.

Looking into what starts a fire, or fire investigation, is very tricky, as fire consumes evidence. Fire Investigators must be very knowledgeable about the appliances they are investigating. This means knowledge on the relationships between physics, chemistry, fire protection methodology, and forensic engineering (the study of materials that fail to function properly). Fire investigators are not only required to have a significant scientific understanding of fire, they also use deductive skills to question witnesses and look for suspicious activities.

Did you know? Typically, fire investigators will consult a specialist, like an electrical engineer to pinpoint the problem, just as doctors would consult a specialist to determine what is the exact cause of a person's illness.

The general causes of fires could be:

Electrical - If an electrical wire is damaged, it is possible for heat to build up at a certain location which has friction and ionized gas present (meaning it has an electric charge) to ignite a fire. Heat or fire could spread if other components of the electrical system are not functioning. Investigators analyze circuitry and look at the environment for things that conduct heat to visualize the progression of fire.

Did you know? the presence of a 'beaded' wire means arcing has occurred (extreme heat was localized), but doesn't necessarily mean the fire had an electrical.

Chemical - Certain chemicals inside or outside your house can cause an exothermic (heat releasing) chemical reaction to occur. The chemical can function as a fuel or an accelerant. An accelerated fire has a large heat release rate, meaning it burns more quickly. More intense fires are also fueled by their own end-products (i.e. oxygen feeding a fire even more). Investigators analyze the chemicals present and try to work backwards in terms of the possible chemical reactions that could have taken place.

Arson - This means someone has caused a fire deliberately. Investigators must judge if this is the case following guidelines in the National Fire Protection Association that is made for investigating fires and explosions (NFPA 921). The fact is that proving arson can be difficult for investigators since the evidence is in ashes.

Finally, accidents happen, and sometimes fires do too. Even if you caused the fire, investigations are always beneficial (if not only to your insurance company), because learning about a certain appliance's malfunctions encourages engineers to make better designs and improve everyone's safety in the end.

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About Me:

My name is Magdalena Bugno and I am doing a specialist in Comparative Animal Physiology at the University of Toronto, St. George Campus & a minor in French Second Language. A cool fact about me? I will just say that I am trying to live life to the fullest.


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