I really enjoy the destructive force of fire, something about near complete annihilation really piques my interest. But fire is also full of life, and can almost be classified as a living thing and that in itself is also interesting. It consumes oxygen and leaves carbon dioxide behind (breathes), requires physical input materials (eats), leaves ash (excretion), grows and shrinks in size with age, but lacks an intelligence and doesn’t perspire.
They all have a few things in common like origin points, oxygen, fuel, ignition source, and heat; and fires are largely classified to be either natural, accidental or purposeful. A fire triangle in forensics are a reminder of the necessary components for a successful fire. You need oxygen, fuel, and heat. And the pentagon adds in a chain reaction (the reaction can cause self ignition once the initial ignition begins) and an initial ignition source.
Fuels-
Common gaseous fuels include: hydrogen, natural gas, propane, etc.
Common liquid fuels include: gasoline, kerosene, ethanol, most solvents are liquid fuels, etc.
Common solid fuels include: charcoal, paper, sugar, wood, etc.
Complete reactions form carbon dioxide, incomplete reactions forms carbon monoxide and usually require input energy for the initial reaction. Combustion reactions also require activation energy, which is also the ignition source. In most combustion reactions vapors are required and are produced from solid or liquid sources. When the vapors are made, depending on the fuel, have different names.
A flash point is the lowest temperature in which a liquid will turn into a vapor, and since combustion reactions produce heat, is usually the point in which ignition would occur.
A fire point, is the lowest point in which a fire will sustain itself, even in absence of an ignition source.
Another important note for vapors is the flammable range, the range in which the most air can mix with a fuel to create a sustaining flame or ignition. Pyrolysis is the process, in which, a solid will decompose by heat to sustain combustion.
Origin Points: Fairly easy to spot when pointed out to you and are usually the darkest points in the fire since they burn the hottest. Pyrolysis travels outwards and upwards, so look for a ‘v-shape’ and where the 2 lines intersect is the point of origin. Usually this is where an ignitable liquid will be found, IF the fire happened to be started with one. Like if someone were to splash gas onto the laundromat to just ‘send a message’ and light it on fire, the gas if the liquid accelerant. Hydrocarbon sniffers can be used to detect if accelerants were used, since hydrocarbons make up most common accelerants and only need to be near the point of origin to pick up vaporized accelerant.
Fire debris samples collected are vaporized and analyzed with gas chromatography.
There are several ways to vaporize samples taken, heating the headspace above the taken sample, distilling the sample with ethylene glycol and vaporizing it that way, carbon strip and solvent washing, or otherwise solvent washing. You’ll do this to test which accelerant(s) w[ere/as] used.