Rusting of iron or rotting of wood is common examples of slow oxidation.
Fire or combustion is the result of rapid oxidation and energy is given off in the form of heat and light. In order for any substance to oxides, its molecules must be well surrounded by oxygen molecules. Molecules of any solid or liquid are too tightly packed to be surrounded. Thus only vapour can burn.
When a solid or liquid is gradually heated, its molecules move around rapidly and some molecules will break away from its surface and form vapour just above its surface. This vapour will mix with oxygen and start to burn.
The burning vapour produces heat that release and ignites more vapour from the material concerned thus staring a chain reaction.
2.1 THE FIRE TRIANGLE AND THE FIRE TETRAHEDRON
Elements required for a fire to start are:
a. Fuel which will vapourise and burn.
b. Heat to raise temperature of fuel vapour to ignition temperature.
If any element of this fire triangle is missing, a fire cannot start.
If any element of this fire triangle is removed, a burning fire will die out.
If a fourth element “chain reaction” is added to this basic fire triangle, it will result in the formation of fire tetrahedron that represents a continuously burning fire. It illustrates how flaming combustion is supported and sustained through chain reaction.
a. Surrounding air: Refers to the oxygen content of the surrounding air. To support flaming combustion, oxygen volume in the air should be minimum 16%. Smouldering combustion can however continue with oxygen volume in air as less as 3%.
b. Shipboard solid fuels include cordage, canvas, dunnage, wiping rags, furniture, mattresses and a wide variety of solid cargo.
c. Shipboard liquid fuels include oil cargo, bunker fuels, lubricating oils, paints and thinners.
d. Diesel oils and kerosene.
e. Onboard a ship, heat can be obtained from a flame of a matchstick or cigar, sparks caused by ferrous metals striking together, heat generated by friction, lightening, an oxy-acetylene torch cutting or welding metal, electric short circuit, electric arc between conductors or overheating of an electric motor.
f. Also sufficient heat can be produced internally by spontaneous ignition.
