Forensic Investigation and Determining the Cause of a Fire

In his book, Invisible Evidence, Bill O'Brien writes about the processes involved in investigating a fire. He says that analyzing a fire is difficult as much of the evidence is burnt and destroyed. By using theories and working backwards, investigators are normally able to determine what is abnormal and prove if the fire was accidental or deliberate. A fire scene will be treated like a crime scene while facts are gathered.

Forensically Analyzing the Pattern of a Fire

Through training and experience it is possible to examine a fire scene and work out where it started, how it spread and whether accelerants were used. Factors to consider include how different materials burn, the progression of burning, the products of combustion and how fire affects glass, aluminum, copper and concrete.

Forensic investigators work out the fuel loading of a room by analyzing what it contained before the fire. Everything from curtains to carpets to furnishings are considered. Based on this, it is possible to work out if the fire behaved in a pattern consistent with the fuel available.

Fuel loading refers to the combustible material in a room. Many products such as plastics and polymers are petroleum based and an average lounge may contain the equivalent of 50 to 100 liters of petrol.

Testing for Accelerants at a Fire Scene

Forensic investigators test for accelerants by using hydrocarbon analysis. This is done by taking samples of wood, ash and soil from the scene and suspending charcoal strips over them. Any volatile organic material such as petrol will be absorbed into the strip. It is then extracted by using a solvent and analyzed by a gas chromatograph.

Accelerants normally cause a fire to be more fierce and destructive than an accidental fire and this can be seen by the amount of damage caused.

Determining the Starting Point of a Fire

Bill O'Brien states that there are three factors required for a fire to start: heat, fuel and oxygen. An investigator will analyze the following when trying to determine how and where a fired started:

• Smoke lines, degree of charring and direction of burning
• Presence of electrical outlets
• Mechanical, electrical, static or chemical reactions
• Ventilation
• Position of the item that started the fire
• Patterns of convection, conduction and radiation

Fire investigation is a difficult area to work in as much of the evidence is destroyed. By testing for accelerants and conducting a thorough search of the scene, scientists are generally able to conclude what started the fire and where it began. Their work is invaluable in homicide cases and insurance claims.

Reference:

O'Brien, Bill, Invisible Evidence, David Bateman Ltd, 2007