Everyday hundreds of fires happen worldwide. But how can an investigator distinguish whether it was accidental or intentional? Some fires are caused accidentally, some are the doings of nature, many are for economic reasons, quite a few are just reckless acts of arson, and some are concealing murder or vital evidence. There are ways to tell.

When a fire happens it takes time for it to be investigated usually, as, if it was a building on fire, specialists would have to be called in to make sure the building was safe to enter. Of course by this time some vital evidence may be gone. However there are some clues to be noticed before the fire has even been put out. The fire and smoke itself can give strong clues as to just what type of fire is being dealt with. For example, the colour of the fire changes if different accelerants are being used, and the smoke may also be a lighter or darker colour depending on what kind of material the fire is burning.

The first step in fire investigation, after the fire has been put out of course, is to establish the origin of the fire. The lowest, darkest point of burning tends to be the starting point of a fire, as the flames move up. Of course this can be affected if there are draughts or winds present, as they may direct the fire to spread another way. There are many other clues around the scene that can help reconstruct the events which took place. Blackening at the top of doors indicate the door was open during the fire, or else the entire door would be black. Thin lines of severe burning on the ground suggests the use of accelerants.

Arson can be distinguished from other types of fire quite easily. The use of accelerants is a definite sign of deliberate fire-starting. Also, forced entry, valuables missing from the scene, broken window glass lying on the inside. All of this points towards arson.

Accelerants are flammable liquids such as petrol. These are spread around the scene and set alight. Most arsonists believe that accelerants can not be detected after a fire has burned, but they are wrong. Before being set alight small traces of the liquid soak into carpet, floorboards, plaster and just about any other material it comes into contact with. "Sniffing" devices such as the Hydrocarbon Detector are used to determine whether objects contain accelerants.