The first thing the CSI technicians or fire investigators will look for once the fire at an arson crime scene is put out is clues that determine the fire’s origin.
To determine where the fire started, prior knowledge of how fire moves through a structure is required. Usually, fire spreads up and sidewards from the point of origin; however, due to the building’s decorative and structural components, that pattern is variable. Any chemicals in human-made carpets can cause an abnormal fire pattern, or the stairs may push the fire in a particular direction. However, the point of origin is normally the most damaged. The CSI’s look for clues such as any accelerants or igniters that may determine the point of origin. However, certain factors that may hinder or influence these efforts to determine the origin are stairwells, open windows, or materials used to build or decorate the building.
The fire’s trajectory can be traced even if the building has undergone severe structural damage once the point of origin is determined. Backtracking on the fire’s path where possible too can yield the point of origin.
Another way of finding the point of origin is searching for a V pattern in burned material. Going by the tendency of fire, it is likely that it may burn a wall or other vertical surface in a V pattern where the point of origin is the V.
Fuel containers and other flammable liquids, being accelerants themselves, often hinder the search for true point of origin and arson-related accelerants’ location. It could also have been a fire with multiple origin points, with the arsonist setting various fires in the building or spilling an accelerant or charcoal fluid throughout the structure.
CSI’s can estimate the fire’s intensity at a particular place by assessing the effect on structural materials. While glass melts at 1500 degrees Fahrenheit, extremely intense heat also causes steel beams to buckle. Another indication of high heat is the crackling or flaking off walls and floors, while wooden beams, floors, or walls may leave behind an alligator skin-like pattern after being scorched. The hottest point of the fire is where the smallest scales are.
CSI’s can also ascertain the fire path and locate the point of origin based on the time at which fire alarms set off if the building is fixed with smoke detectors.
Arson investigators may be left challenged if liquid or volatile fluids were used since they spread easily. For example, if the arson perpetrator spreads paint thinner on the floor, it is likely to spread throughout, flowing down any slopes or stairs. Thus, on the occasion of a fire, the point of origin is majorly spread out. Methane gas, too, is a volatile fluid that will diffuse in all directions till the container is filled, and on being set on fire, they may explode, making it impossible to locate the point of origin.