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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If it’s truly burned completely to ash you don’t have much to go on. But that’s not usually what happens…firefighters are relatively good at what they do, some stuff usually survives. There’s pretty good techniques, if there’s something left, that can tell you how hot it got, what direction the fire came from, possibly how it ignited.
So you generally start looking at wreckage and figure out what direction it was lit from, then work backwards from there until you find the “center” of the ignition. Then you use common sense. If the ignition point is a plug or junction box, likely electrical…maybe check the fuse/breaker on that circuit if it survived. If it’s a candle or remains of a cigarette filter or something like that…there you go. If it’s random, maybe do chemical analysis of the residue to see if you can find an accelerant or something similar.
Not always. First of all, fires need lots of oxygen and as they spread they suck more and more, which typically means the place a fire *starts* gets quickly surrounded by new fire which suffocates and puts out the original fire. Meaning if you go to a room that that’s all burned up and you see a random spot in the corner that looks surprisingly *less burned* that’s probably where the first started.
Similarly you can often see how fire’s spread, how hot they burned, but looking at the char and burn patterns. If you see areas that are overly burned, meaning they burned hotter than they should have, or paths of fire travel that don’t appear to be the most obvious, that’s probably due to an accelerant. For example, someone poured a stream of gasoline down a hallway to spread the fire, you’d be able to see that gasoline path in the char.
But yeah, if you’re talking about complete burning down to ash and dust, you can’t tell super much. It’s the middle ground fires that can tell you a story.
17 year veteran arson investigator (now retired) here –
If I were to explain my job to a true 5-year-old, I would say “I had *tons* of training that showed me how to interpret the damage fire leaves behind when it burns. If the fire completely burns up everything, leaving nothing behind, I would have to find other evidence. If I can’t find anything, I have an ethical and moral obligation to say ‘I don’t know’.”
There is so much that goes into a fire investigation, it would be impossible to give all of the details here (nor would I want to give potential arsonists a guide on how to effectively set a fire). Most of the answers you’ll hear are only generalities and “rules of thumb”; the investigation has to address all of the fuels’ locations and materials, building openings and ventilation paths, as well as all potential ignition sources in the area of fire origin once the origin itself has been determined.
Additionally, there are non-physical pieces of evidence to consider; witness statements, electronic evidence, and financial documents. Whether or not the fire investigator assigned to the case can conduct a criminal investigation varies by jurisdiction.
Does that help? I know it’s vague, but fire scenes should be treated as undetermined until proof is found that supports a cause determination.
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Fire investigation is kinda fake. Or like, there is a lot of real actual stuff mixed in with a lot of nonsense. Like there is real actual science used for some stuff but as it gets into criminal investigation stuff a lot of the techniques are verifiably wrong and not write and things that tend to be true are treated as always true and it’s a mess the same way a lot of police investigation stuff is.
First, different materials burn at different rates and temperatures, which can be measured and known beforehand. Second, the longer something burns, the more it is damaged. Thus, experts can analyze the burn pattern, noting where the fire did the most damage and where it was more or less intense, particularly relative to the materials involved, to draw conclusions about where the fire started and whether an accelerant was involved. If they can determine where the fire started, that will also provide clues about what started it. This analysis can be supplemented by chemical and other tests.
Well they used to use fire patterns and other forensic techniques, now days they prioritize saving computers.
It goes by priority level
1. Humans
2. Animals
3. Computers.
Often the computer records include “how to burn my house down”
And then it’s a matter for the District Attorney/Insurance Adjustor.
Fire/Life Safety Inspector here with a degree in fire science, years of my life given to reading NFPA, attending classes and fighting fires.
The simplest way to explain it is looking at factors of fuel sources, heat, chemical reactions (fuel interacting with fuel) and how much/ when oxygen comes into play. The fire tetrahedron, if you will. Time too plays a factor. Besides those you’re looking at construction type, human influence, the class of materials involved in the building/area. Though fire is a simple concept the thing that makes it ever changing is us. Having a prevailing consensus for how arson investigation is performed is short sighted and needs to be challenged consistently. If you’re ever interested NFPA provides a good starting point in the 921 standard.
Electrical fires have tell tale signs. The live conductor will start arcing- little zaps of electricity- to something grounded. This is so hot that it melts the copper leaving splashes of copper and little craters. Pure copper melts at over 1000 deg C, so regular fires aren’t melting copper.
As electricity is a common way of accidentally fires to start, it’s a good place to start looking.
They often can’t. They can make some educated or likely guesses but in many cases the cause is undetermined.
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