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Lead Author: Sydney Lyon
Fire is dangerous. It spreads and destroys evidence, but it also creates its own evidence. A fire can be a tragic accident, but it can also be an act of arson. When fire investigators arrive at the fire scene, their main goal is to determine if that fire was deliberately set. How do they do this though? Through decades of fire investigations, two main arson indicators have been identified: multiple points of origin and traces of accelerant.
Arson is defined as the deliberate setting of a fire with criminal intent
Arson is defined as the deliberate setting of a fire with criminal intent
How do you find a point of origin, let alone multiple points of origin? There are a few visual indicators that can show where a fire started. The most commonly cited indicator is the V pattern. This looks just like what it sounds like: a charred V burnt into a wall or siding. When a fire starts, the hot gases expand rapidly upwards, often charring whatever they touch. Caution should be used with this indicator though. When a fire spreads throughout a room, the objects in that room will each light up on their own. When this happens, a V pattern could be created even though it isn’t where the fire originated.
A more reliable visual characteristic is the location with the deepest charring and burning. The origin is where the fire will have burned the longest, so the location with the most fire damage will most likely be the origin.
Ok, so now we can find the origin (or origins) of a fire. How do we know if it was deliberately set though? Well, the biggest and best indicator of an arson fire is multiple points of origin. This shows that someone went around setting many things on fire just to make sure the place went up in flames.
V Pattern at fire scene
Arson can’t be ruled out if there is only one origin though. Another great indicator of arson is the presence of accelerants. When someone wants a place to go up in flames, they will usually make sure the fire will spread hot and fast by using some kind of ignitable liquid. This type of accelerated fire can create patterns. These patterns, or indicators, include alligatoring, lines of demarcation, and spalling, among others.
Alligatoring
Alligatoring
Lines of demarcation
Lines of demarcation
spalling
spalling
The emphasis here is that these are indicators.
The emphasis here is that these are indicators.
Due to the dedicated work of arson investigators like John Lentini, these patterns have been proven to appear in non-accelerated fires, making them unreliable at best (The Mythology of Arson Investigation). Therefore, they should only be used and an initial indicator of whether an accelerated fire was set. Further analytical testing is needed for a confident arson determination.
Accelerant fluorescing under UV light; courtesy of Ljungkvist and Thomsen
How would you do this testing, though? The first step is to collect your samples. They could be collected from those locations we identified before, but there are more secure methods. Arson dogs, UV light, and electrochemical sensors can all reveal where traces of accelerant are present. After the sample is collected, it must be extracted. Now that you finally have your sample in a testable form, all that is left to do is run analytical tests to determine if an accelerant is present. If accelerant is present, then you’ve got an arson case!
analytical Testing
analytical Testing
Extraction Methods
Extraction Methods
In order to test your sample, you first have to extract it from the collected debris. Explanations of some common methods are linked below.
Analytical Methods
Analytical Methods
Once you have your sample in a testable form, all that is left to do is analyze it. The most common method is gas chromatography mass spectrometry. However, there are variations on this method that are useful.
Enjoy the famous Billy Joel song that inspired this article :)
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