Oxidizers Study Guide for McGraw-Hill's Firefighter Exams (page 2)

Oxidizer

Oxygen gas is the most common oxidizer that firefighters deal with during fire operations. The atmosphere consists of 21 percent oxygen, 78 percent nitrogen, and 1 percent other elements. An oxygen-enriched atmosphere (greater than 21 percent) will enhance the rate and intensity of burning. Conversely, an oxygen-deprived atmosphere (less than 15 percent) will not be able to sustain combustion.

Chemical Chain Reaction

The chemical chain reaction process that occurs during flaming combustion is the fourth component that was added to the fire triangle model to form the fire tetrahedron model. It depicts self-sustaining combustion with an ample amount of fuel and oxygen chemically interacting. As fuel burns it generates radiant heat traveling in all directions. Heat directed back onto the burning substance (radiated feedback) helps to raise more fuel to its ignition temperature and generate more vapors to mix with air and form a combustible mixture. Additional oxygen is then drawn (entrainment) into the zone of chemical reaction. This addition of oxygen also increases the heat of burning. The chemical reaction between the components of the fuel vapors and oxygen is called an oxidation reaction. The chemical reaction we know as fire continues until all the fuel is consumed, the oxygen in a confined area is diminished, or heat dissipates beyond the zone of the chemical reaction, causing the temperature of the fuel to drop below its ignition temperature.