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Forensic Arson Investigation – How Did a Fire in an Arson Crime Scene Start?

When CSI or fire investigators arrive at an arson crime scene and determine the location where the fire started, the next question on their mind is how the fire started and what materials were used to start a fire.

In this article, we will elaborate on how a perpetrator starts a fire and what common methods he/she uses to start a blazing inferno.

After having determined the point of origin of a fire at an arson crime scene, fire investigators then focus on the potential causes of the fire. They look at the conditions and factors that allowed the fire to start and spread. At the top of the list of potential causes of a fire are human factors, whether accidental or willful, for arson investigators.

Fire investigators conduct a thorough search of the area around the point of origin for accelerants and igniters. Electrical wiring, candles, fireplaces, complex electrical timers, oil lamps, cigarettes, and spontaneous combustion make potential ignition sources.

Spontaneous combustion, an internal chemical reaction that starts a fire, is a rarity but can happen when flammable materials are contained in an enclosed area such as keeping oil-soaked towels in a small, closed pantry. In an enclosed space, heat is produced when the oils slowly undergo the process of oxidation. Since the heat is confined to a closed area, the heat has nowhere to go and may cause an increase in temperature in that area such that the oil or the towels will ignite.

Analyzing these possibilities helps arson investigators in categorizing fires as natural, accidental, or willful.

 

  • A natural fire is the result from events such as a lightning strike.
  • Accidental fires are the result of a smoldering cigarette or faulty electrical wiring.
  • Presence of an electrical or combustible timing device is indicative of a willful act of arson.

 

In the case against Ryan-Neely Otts of Austin, Texas in the dual arson case back in 2005, these apartment complex fires were determined to be willful based on the same accelerants found at both crime scenes. A jury later convicted him of first degree arson and sentence him to 10 years in prison.

What do perpetrators use to start a blaze?

Low-tech tools

Tools for starting a fire vary from simple to complex. A match is perhaps the most common ignition tool. Arson perpetrators many times light fires and toss the matches aside, thinking that the fire will completely destroy them. Even a tiny match can leave behind trace evidence for CSI investigators to find.

The heads of matches contain a material called diatoms, which are unicellular organisms found in silica based earth and are used in the production of matches. The shells within these small organisms contain silica, a strong material that has the capability to survive fires. Interestingly enough, match manufacturers use different materials, so that distinct diatom species are found in their matches. Since individual species of diatom has a unique shell structure, identifying these shell remains many times identifies the brand of matches used by the arsonist.

Another effective, low-tech ignition tool can be made by putting a candle on a pile of paper. When the flame consumes the candle, the flame ignites the paper, and the fire spreads. An arson perpetrator may even put a lit cigar across an open book of matches under flammable curtains.

High-tech tools

On the high-tech end, an electrical timing device can serve as an ignition tool. Either commercial grade timers or a modified clock can be used to time when a circuit closes and turns on an initiator. There is no limit to the imagination of an arsonist when building one of these devices.

If a detailed search of the crime scene unveils candle residue, a cigar or cigarette butt, or the remnants of an electrical device, CSI investigators have discovered a possible igniting device.

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