User:HSE Trainer Saad Abdul Wahab/sandbox

Saad Abdul Wahab
Simple equation

Fire Chain Reaction (Reduction-Oxidation – Redox Reaction - Exothermic) '''Initiator	      +	Oxidizer	       +	Reducing Agent	  →	Combustion Chain '''(Ignition Source)	       (Oxygen Source)	                (Fuel Source)		(Gaseous Products Fire, CO2, CO, Heat H2O (v), Ash)

Making any of the above three (03) reactants as Limiting Reactant may control fire;

All fires occur when three type of elements come into contact simultaneously, which are Ignition sources, Oxygen and Fuel. Ignition source includes all those sources which can provide threshold energy (minimum amount of energy required to ignite a fuel) like, heat, spark, ultra violet rays, friction, electrostatic charges, etc. Second component is oxygen or any other source that can give oxygen, such as all chemicals which are labelled as oxidizing agents, and the third component is fuel or reducing agent which includes all combustible and flammable materials regardless of their physical state as solid, liquid or gas. Encounter of all these components in right proportions causes fire. To extinguish a fire we need to disconnect any of the three components. Practically we cannot remove oxygen from open atmosphere as air contains 21% oxygen whose deficiency may cause suffocation. For open fires we can use cooling and starving methods. Cooling decreases the temperature of fire to reduce the heat below fire point of fuels. Other method is starving which is the removal of residual unignited fuels from fire scene. For indoor fires we use another technique “Smothering” to remove oxygen which acts as a supporter of combustion by means of purging with some non-flammable gas mostly Carbon Dioxide.

It is quite relevant to discuss here that all fires possess same chain reaction which is known as oxidation-reduction (Redox) reaction. A lot of extinguishing agents are available cheaply in market which can extinguish fires by direct attack on redox reaction. The most common extinguisher with commercial name Dry Chemical Powder (DCP) is cheaply available in market to extinguish all classes of fire. As fires are generally classified in six different groups based on the physicochemical properties of fuels or burning materials. Class A fires include ordinary solid combustibles like paper, wood, cloth, rubber, plastic, etc. Class B fires include flammable and combustible liquids like organic solvents, diesel, kerosene, gasoline, lubricating oils, base oils. Class C fires include flammable gas fires like hydrogen, methane, CNG, LPG, LNG etc. Class D fires are metal fires which includes all pyrophoric metals like sodium. Class E fires are electrical fires where electricity act as ignition source, when we de-energize the supplies the burning material can be extinguished on the basis of its nature or chemistry of construction. Class F fires are kitchen based fires which involve edible Oil & Fat, Ghee etc. for all these classes of fires we have different type of extinguishers like Water, Foam, Dry Chemical Powder, Carbon Dioxide and Wet Chemical respectively.