Fire

Question 1

Describe the combustion process?

Answer 1

Fire is basically an exothermic reaction involving the combination of substances with oxygen. In order for a fire to occur there must be 3 elements present:

1) Fuel
2) Heat
3) Oxygen

Question 2

Describe what is meant by ignition?

Answer 2

If sufficient heat is applied to a substance, there will be a release of vapour if a liquid and a volitile substance in the case of a solid through a process known as pyrolysis. Combustion of the resulting combination of fuel and gaseous/vapour phase with oxygen can be done by applying a pilot flame or spark with sufficient heat. If sufficient heat is already present then auto-ignition could occur.

Liquid fuels tend to have a flashpoint. This is the temperature at which a liquid will ignite from a pilot flame.

The firepoint or ignition temperature is also important as this is the temperature that not only will the fire start but will also be maintained.

For autoignition temperatures are likely to be much higher.

Question 3

What is heat release?

Answer 3

The property of combustion for any material is known as heat of combustion it is the total energy released per unit mass by complete combustion. The maximum heat available. In reality complete combustion doesn’t always occur because there is a restriction of oxygen and other fuels etc.

Question 4

What is fire load?

Answer 4

Fire load is the sum of all materials in mass multiplied by the heat of combustion figure divided by the space in m2. It is needed to determine and size certain materials.

Question 5

What is radiation intensity?

Answer 5

Radiation intensity is the rate at which radiation will occur from hot smoke on the skin.

Determined by I = εσT4
T= Absolute temperature of the smoke
ε= emissivity of the smoke
σ= Stefan-Boltzman constant