The very first thing after a fire is put out and CSI technicians and fire investigators arrive to look over an arson crime scene is to find out the reason behind the outbreak of fire. They try to find out the clues to determine its origin.
It requires technical and in depth knowledge about fire, if a person wants to know how a fire moves through a structure. Commonly, a fire has the tendency to spread sideways and up from the point of origin, but that pattern is subject to changes mostly due to structural and decorative elements of the particular building. For example- stairwells may force a fire in one direction, and chemicals in manmade carpet may cause abnormal burn patterns. Usually the point of origin is where biggest amount of damage happens. What CSI’s major focus remains throughout the duration of investigation is to look after the possible clues which lead to the determination of the point of origin of the fire. Other facts that can influence or prove to be a hindrance behind the CSI’s effort in determining a point of origin are open windows, stairwells or materials used to build or decorate the building.
CSI can after determining the point of origin, sometimes retrace the fire’s trajectory even when the building has undergone heavy structural damage. Point of origin can be yielded while backtracking the along the fire’s path.
Another way of finding the point of origin of the fire is by searching for a V pattern in burned material. It is the natural tendency of fire to rise and spread so that it burns the wall or a vertical subject in V pattern, where the point of V is located at the origin of fire.
Flammable liquids and fuel containers can hinder the search for true point of origin. An arsonist may have spread various fires in the building or he may have spilled a path of charcoal fluid or any other accelerant throughout the structure, which thus leads to setting up of fire with more than one point of origin.
CSI’s can without any difficulty, by assessing the fire’s effect on structural materials, estimate the gravity of fire on any specific place or subject. Under extremely serious fire situation which gives intense amount of heat, steel beams buckle as well as glass melts around 1500 degrees Fahrenheit. When a place produces heat beyond its optimum temperature, floors and walls crack. Likewise wooden beams, walls and floors may scorch leaving an alligator skin like pattern in the wake.
One of the major problems posed to the arson investigator is liquid and volatile fuels. This is because they spread more quickly and take the shape of their containers. If the perpetrator of the an arson throws the paint thinner on the floor, and the thinner occupies the entire room and also runs down the stairs, then upon igniting the thinner, the fire spreads across the entire room and stairs following the thinner all the way long. Volatile fuels like methane gas diffuse in all directions until they fill their containers.