Often times you hear about the cause of a fire being a cigarette for example. However, isn’t the cigarette already long gone after the house/forrest/etc. has burnt down? How is it still possible find out what started the fire?
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One thing investigators do is interview witnesses and first responders to see how large the fire was when they arrived. The south corner, first floor had flames or it started in the top of the pasture and jumped the road.
Fire behaves in certain ways and they can make educated guesses as to where it likely started
Unless it’s human spontaneous combustion. Now that is weird the human and seat could be completely burnt but everything else can be fine. It’s very weird
>However, isn’t the cigarette already long gone after the house/forrest/etc. has burnt down?
Interviews help. Talk to their friends and family members. “Yeah, Joe would get shitfaced every Saturday night and fall asleep with a cigarette in his mouth. Once he lit my couch on fire but I put it out.”
Combine with any evidence left or other interviews and you can often build a picture of things.
Also in most urban and suburban areas fire departments tend to be fairly close so if they get called to a fire the places rarely fully burn down and some evidence is preserved.
23 years in the fire department here.
We can’t always determine the exact cause especially with extensive damage.
It’s science mixed with art for a lack of better words.
With the cigarette example you used, let’s say someone’s house burned. Patterns indicate it started in their living room and the worst damage was in the area of the remnants of a chair. We’d dig that area out and look for sources of ignition such as electronics. If none are found we’d assume it was a different source. We would interview the residents and if they said a certain person always sat in that chair we’d ask more questions. Let’s just say they say he sat there and smoked a lot and was even sitting there an hour before the fire started.
So what we couldn’t say for certain is that the fire started in that chair and was for sure caused by the resident smoking. What we can say is the fire started at or near the chair, that no ignition sources such as electronics were in that area, and the fire was most likely caused by another ignition source. We can take samples to be tested for accelerants as well but if those aren’t present what’s the most likely cause? Most likely the resident who was known to smoke in the chair accidentally discarded smoking materials. They continued to smolder until the chair caught fire. The fire then spread to items nearby then the structure itself.
I heard a park service ranger talk about how they trace the origin of wildfires.
Grasses when burning tend to bend over in the direction the flames come from. So the residue points towards where the fire originated. Just follow the direction the grass points and you’ll find the origin, and then look for evidence of a source – a cigarette butt, a campfire ring, residue from chainsawing, or shell casings that indicate maybe someone fired a round that created a spark. Lightning strikes leave their own mark.
Hmm that sounds a lot like something an arsonist would ask, doesn’t it?
Step one is finding where exactly the fire started. This is determined using a handful of methods, including eyewitness accounts, how much of the location was burned, etc. This kind of shapes the rest of the investigation, as fires starting in various locations are usually do to specific things. Like fires in the kitchen are either cooking mishaps if cooking was in progress at the time, or maybe electrical due to the large number of appliances, or gas leaks if the house used gas.
Then, we need to find out if the fire burned organically or if there were other factors. How charred things are is a rough indicator of how long it was in the fire or how hot it got. Usually, the seat of the fire gets the hottest, and things burn less and less as they get farther away. But if there are multiple really burned or charred areas, it *could* mean there were multiple ignition points, and therefore it could be arson. Note that this isn’t always the case, if a fire burns a house down and it looks like there was ignition in the kitchen and the garage, it could just be that the fire started in the kitchen and ignited a gas can that was already in the garage, but it is something that would be investigated.
We can also look for chemical residue, which is left by a number of things. If it was arson, and someone used an accelerant to start it, then maybe some of the original accelerant is left (possible if the fire doesn’t have time to really take hold or the arsonist applies it in a dumb manner) or it burns and leaves behind a chemical that wouldn’t normally be found. It doesn’t have to be extra chemical residue though, information about stuff that burned that was already there could be very important. Some stuff only burns at a certain temperature, so if we find that stuff burned we know the fire got at least that hot. Maybe that temperature would be impossible to achieve without an accelerant, which would be a strong sign towards arson, even if we didn’t find any evidence of the accelerant itself.
And lastly just common detective work. Sometimes we never really know, we just make educated guesses. It reminds me of Willem Dafoe in Boondock Saints sometimes, there is a decent chunk of science involved but at the end of the day it’s just finding the most likely cause and making sure that it is reasonable. Of course it’s way more complicated and there are countless other things that could be studied, but that’s a relatively short overview.
I have no idea but I feel like they just walk around until they see a melted electrical wire and then say, ‘AHA! Electrical fault’.
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Great question, adding another one, I’m a writer and want my character to burn down a car (with a person in it) and make it look like an accident, how should I go about it using the principles discussed in this topic?
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