Question

Describe the process of combustion. How do flammable materials ignite?

Describe the three methods by which heat moves from one object or area to another.

Explain why it is important for an arson investigator to understand these concepts.

Answer 1

Combustion is a chemical process in which a substance reacts rapidly with oxygen and gives off heat. The original substance is called the fuel, and the source of oxygen is called the oxidizer. Flammable substances are those gases, liquids and solids that will ignite if exposed to a source of ignition.

Heat can be transferred by three methods they are (i)conduction in solids, (ii) convection of fluids (liquids or gases), and (iii) radiation through anything that will allow radiation to pass.

(i) Conduction: It is the process of transmission of heat from one part of the body to another due to difference in temperature. Or It is the process of transmission of heat from one place to another place without actual motion of particles.

Example: Heating a metal rod at one end by using a source of heat.

(ii) Convection: It is the process of transmission of heat with actual motion of heated particles. Convection takes place only in fluids There are two types of convections

(a) Natural convection and (b) Forced convection.

Example: Heating up of water taken in a vessel by placing over a gas burner. In human body, the heart acts as pump that circulates hot blood through different parts of the body, transferring heat by forced conversion and maintaining at uniform temperature.

(iii) Radiation: It is the process of transmission of heat without the help of any intervening medium. Example: Heat coming from the sun is in the form of radiation

Heat is a concept that is important to understand in various engineering fields. It is particularly relevant for civil, mechanical and chemical engineers because heat transfer plays a key role in material selection, machinery efficiency, reaction kinetics etc..