How do firefighters (or investigators idk) find the cause of a fire? Isn’t that super hard if everything is just ash and dust?
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This is UK based where police investigate and the fire investigator gives their expert opinion on how the fire started and developed.
It’s fairly common for them to say they don’t know, but that there’s no obvious accidental cause. If your fire started in a building with no electric hookup and no residents it’s unlikely to be an accident, even if its just ash. “Don’t know” or “not sure” is fairly frequent as a response, closely followed by “probably”.
However, often a fire won’t entirely destroy a premises. Sometimes there’s spots of burnt carpet indicating dripping accelerant, burnt out fuel bottles, or multiple patches of intense burning in different rooms.
This is out of my expertise but often they will look at, say, a cooker [stove] which is wired in wrong, and based on witness accounts say it probably started there. Usually in a part burned building it really stands out as a completely destroyed unit with loads of damage all around it.
You often have footage or witnesses described masked individuals running to or from the scene, sometimes lobbing ignition devices at the target which is a fairly good indicator lol
Sorry for the essay, I find fire investigation really interesting.
From the little I have learned it’s that every material, burning at varying degress, creates a bit of a “signature” with accelerants (gas, kerosene, etc) being some of the most recognizable signatures. Couple this with patterning (let’s say a can of kerosene tipped over accidentally and hit a flame source – you have one big “glob” of kerosene accelerant signature – but, if someone *really* wanted to “make sure” the place burned down, you would be more likely to find a trail or unnatural spreading of the kerosene signature where they doused multiple parts of the structure.)
There’s an upper limit where everything gets hot enough to burn away many of these traces, but thankfully people underestimate just how much it takes to get to that point, fires are pretty noticeable, so typically most arson fires (or fires in general) don’t get to that point.
In an even less complete burn, there can be (relatively) minimal damage to a structure and you can determine that there was no faulty wiring, no smokers in the house with lit cigs falling onto furniture, no outdoor fire situations, stove isn’t on, etc and come to the conclusion that the usual natural fire suspects weren’t at play.
One method is the level of deflection in steel framework. They measure how far the steel has moved from straight, it gives them clues as to the source
You are probably more interested in structure fires, but for wildland fires, it can be relatively easy to find the origin. For example, grass will bend and fall pointing at where the fire came from. Trees will often get limb freeze when a fire is really raging, where needles and limbs will point away from the origin. You can take a few sample points where the vegetation is intact enough to leave these clues and start working back to the fire origin. When well practiced, you can get to the origin pretty fast and because the origin of a wildfire is usually the coolest part of the burn, any evidence of the ignition source is usually intact.
We also usually know within a relatively small area where the fire started, so it’s not like we have to trace it back for miles. Even massive conflagrations that get to kicking ass from the get go, we can get to within a 1/4 mile of the origin to start tracing things out.
Most of the time, it’s a guess. Unless the actual trained fire investigators are called, the fire officers just make an assumption. It’s almost always “electrical”.
We had a car fire across the street. Fire chief declared that it was the fault of the driver for parking it on dry leaves. He was so sure of it until we reviewed our security cameras and it caught some asshole stuffing a flaming rag into the filler neck of the gas tank, closing the door, and running away.
“Dry leaves, huh Chief?”
Like any investigation it will be a combination of things and will result in varying levels of success.
There is a lot of science now behind determining the origin of the fire such as burn patterns, depth of char, evidence of flow path and temperature, etc that has been fairly well covered in most of these comments but also the interview of first responders, residents, witnesses, and such.
Often there are people who can give lots of valuable info such as where and when they saw fire, color of smoke or fire, noises, smells, seeing someone where they shouldn’t have been, progression of the fire (what was it like when the chief first arrived vs. 20 minutes later?) and much else. Once all the available info is collected and looked at as a whole investigators can put together what happened and why.
There is an entire education and career path for fire investigators. While it is ultimately the fire chiefs responsibility to determine cause and origin of a fire that task will often be delegated to an investigation team with specialized training.
I actually did some lab work relating to flammable compounds found in arson cases, and from just the vapor found in the air, I could pick out different hydrocarbons and trace them back to a few sources with alarming accuracy.
The eli5 of it is: anything that burns very rarely burns completely. With sensitive enough equipment, I could find the “fingerprint” of different chemicals that can be used to start fires. Based on some concentrations and other fun factors, you can narrow down location. It’s really neat stuff.
Looks like arsonists better start investing in better vacuum cleaners to clean up their tracks!
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