Structural Firefighting

Question 1

Typically, what is the vapour density of refined products? (e.g. LPG)

Answer 1

Greater than 1.

Question 2

What is the vapour density of most flammable gases?

Answer 2

Greater than 1.

Question 3

Typically, what is the specific gravity of refined products? (e.g. petrol)

Answer 3

Less than 1.

Question 4

What is combustion?

Answer 4

Combustion: a chemical reaction that occurs between a fuel (e.g. hydrocarbon) and an oxidising agent (e.g. oxygen) that produces energy, usually in the form of heat and light/glow.

Question 5

What are the stages of combustion?

Answer 5

1. Incipient stage: invisible products of combustion given off. No visible smoke, flame or appreciable hear is present yet.
2. Smoldering stage: combustion products now visible as smoke. Flame or appreciable heat is still not present.
3. Flame stage: Actual fire now exists. Appreciable heat is still not present but follows almost instantaneously.
4. Heat stage: Uncontrolled heat and rapidly expanding air now complete the dangerous combustion. The considerable heat is transferred to the atmosphere and nearby matter.

Question 6

What is fire?

Answer 6

The rapid combination of oxygen with fuel in the presence of heat, typically characterised by flame, a body of incandescent gas that contains and sustains the reaction and emits light and heat.

Question 7

What are the classes of fire?

Answer 7

A: Solids
B: Liquids
C: Gas
D: Metals
E: Electrical
F: Cooking oils

Question 8

What is the flammability range?

Answer 8

A flammable gas will only burn in air if its composition lies between certain limits. If too little or too much fuel is present, combustion will not take place. The mixture is then said to be too lean or too rich.

Question 9

Define the following:
- LEL
- IM
- UEL

Answer 9

LEL: Lower explosive limit.
IM: Ideal mixture.
UEL: Upper explosive limit.

Question 10

What is Pyrolosis?

Answer 10

Pyrolysis: the decomposition of a substance through application of heat.