Fire Science And Extinguishers

Question 1

Define the term ‘combustion’

Answer 1

Combustion is a chemical reaction that produces heat and light

Question 2

Describe the triangle of fire

Answer 2

For combustion to occur, three factors are necessary. These factors are known as the triangle of combustion.

Oxygen, heat and fuel. Remove one of the elements (sides of the triangle) and combustion will stop.

Question 3

List and explain the 3 ways heat is transmitted

Answer 3

Conduction - mostly present in solids. Heat energy is passed from molecules vibrating about, colliding into each other. Metals, especially silver and copper are the best conductors of heat. Example is frying an egg.

Convection - occurs only in liquids or gases. When either is heated it expands and becomes less dense. It then rises and is replaced by colder denser gas or liquid. This will continue until either the heat source is removed or a state of equilibrium is achieved. Example is pan of boiling water.

Radiation - heat is transmitted in straight lines by means that is neither conduction or convection. Heat from the sun passes through empty space to warm earth, the same as a heater will make the air around it warm. It does not involve any contact between bodies and is independent of any material in independent space.

Question 4

What are the three methods of extinction

Answer 4

Smothering - removal of oxygen

Cooling - removal of heat

Starvation - remove fuel or combustible material

Question 5

List the six categories of fire

Answer 5

Class A - flammable solids

Class B - flammable liquids

Class C - flammable gas

Class D - flammable metals

Class F - cooking oils

Electrical Fires

Question 6

List the types of extinguisher and their use

Answer 6

Foam - Class A and B

Co2 - electricity and class B

Dry powder - Class A,B, C and electrical. Ideal for running fuel fires.

Water - class A

Water mist - class a, class f and electricity

Wet chemicals - Class F fires

Halon - A,B,C and electrical

Question 7

Label the main parts of a stored pressure cylinder (see diagram in notes)

Answer 7

Operating trigger
Control valve
Discharge tube
Water
Nozzle
Stored pressure area

Question 8

What are the advantages and disadvantages of dry powder extinguishers

Answer 8

Advantages:
Rapid in action
Non-conductor of electricity
Very effective on running fuel fires

Disadvantages:
No cooling effect
Creates visibility problems
Large amount of mess
Health hazard if inhaled

Question 9

List the advantages and disadvantages or co2 extinguishers

Answer 9

Advantages:
No permanent residue
Very good at penetrating closed spaces
Non conductor of electricity

Disadvantages:
Poor performance on class A and B
Has to be sent to manufacturer for recharge
Noisy
Little cooling effect