FIRE
The most familiar combustion reactions are fires or explosions. Whether a fuel burns or explodes has to do with the nature of the fuel and how close the oxygen and the fuel are to each other during the reaction. Everyone is familiar with fire, the various types of fires, and many ways that fires can start. From the forensic science standpoint, it is necessary to know the cause of a fire because, in many cases, fires are deliberately set with criminal intent. These fires are classified as arson. Deliberately setting fires constitutes criminal acts and the perpetrators must be punished. A chemical explosion results from the same type of chemical reaction as a fire. Fires take place by a slow or ordinary combustion wherein the fuel and the oxygen are physically and chemically separated; the oxygen being obtained from the air that surrounds the fuel. The oxygen in air is supplied in a molecular form, O2.
∆+O2→O+O
Part of activation energy In order for the fire to take place, the oxygen molecules must be broken up into atoms and they must get close to the fuel molecules. This takes energy and time, so this type of combustion is relatively slow. The energy needed to sever the oxygen molecules is part of the activation energy for the fire. Other types of activation energy include that which is needed to vaporize the fuel or the source of oxygen. The study of fires for forensic purposes involves determining the characteristics and damage caused by the fire as well as the point of origin and cause. In this chapter, we will deal with the following questions. The answers will provide a pretty complete picture of the investigation of fires, especially those of suspicious origin.
• What are the necessary conditions for a fire?
• What are the types of fires?
• How are ire scenes investigated?
• What are ire residues and how do they arise?
• What is the role of the forensic science laboratory in ire scene investigation?
