Exercise 6. Read the text A Combustion Process

Burning, also called combustion, is a simple chemical reaction. It is described as a “rapid, persistent chemical reaction that releases heat and light and is accompanied by flame especially the exothermic oxidation of a combustible substance”.

When fighting a foe, one of the best weapons one can have is knowledge and understanding of the enemy. Firefighters need to know about the behaviour of fire as one of the elements in understanding the enemy.

Combustion is often confused with the term “fire”. It is important to know that there is a difference on a chemical level. Fire is a chemical reaction that is a self-sustaining process that emits light and heat as a by-product of that reaction.

In combustion, the released heat energy is reinvested in the process, causing the continued reaction to occur repeatedly. Unchecked, with involvement of greater access to fuel, oxygen, and heat, the growth will accelerate. The products of combustion can be hazardous and deadly to firefighters.

The combustion process was once depicted as a triangle with three sides. Each side represented an essential ingredient for fire. Heat, fuel and oxygen were thought to be the essential elements.

As our scientific study of fire progressed, it became evident that a fourth ingredient was necessary. That fourth element was the actual chemical reaction that permitted flame propagation. A new four-sided figure was created to represent the essential ingredients for fire, fire tetrahedron. The fire tetrahedron is a pyramid shape describing the heat, fuel, oxygen, and chemical reaction necessary for combustion.

The fuel segment is any solid, liquid, or gas that can combine with oxygen in the chemical reaction as oxidation. A fuel with a sufficiently high temperature will ignite if an oxidizing agent is being liberated. Combustion will continue as long as enough energy or heat is present. Under most conditions, the oxidizing agent will be the oxygen in air. However, some materials, such as sodium nitrate and potassium chlorate release their own oxygen during combustion and can cause fuels to burn in an oxygen-free atmosphere. While scientists only partially understand what happens in the combustion chemical chain reaction, they do know that heating a fuel can produce vapors that contain substances that will recombine with oxygen and burn. These substances must continue to be produced for combustion to continue.