Fire Science

Question 1

What is combustion?

Answer 1

An irreversible chemical reaction producing heat and light

Question 2

What is the importance of the relationship between surface area fuel and its volume?

Answer 2

A finely divided material surrounded on all sides by atmosphere will have a large surface area exposed to oxygen relative to its volume and therefore will burn quickly.

Question 3

What is the difference between temperature and energy?

Answer 3

Heat is a form of energy, temperature is a measure of the heat energy present in an object.

Question 4

What is important about an oxidising agent?

Answer 4

An oxidising agent contains oxygen locked up in its make up that will release oxygen during combustion. This makes these substances hard to extinguish

Question 5

Explain pyrolysis

Answer 5

Pyrolysis is the decomposition of a substance by heat into new substances. In wood, carbon dioxide and hydrogen are produced which combust above the surface of the wood producing more heat and making the process self sustaining.

Question 6

Explain Flash point

Answer 6

Flash point is the lowest temperature at which enough vapours are produced to create a momentary flash when an ignition source is introduced.

Question 7

Explain Fire point?

Answer 7

Fire point is the lowest temperature at which enough vapours are produced to ignite and burn for 5 seconds after an ignition source is introduced.

Question 8

Explain what auto-ignition temperature is?

Answer 8

auto-ignition temperature is lowest temperature at which enough vapours are produced to ignite the fuel and burn without any need for an ignition source.

Question 9

Explain surface oxidation?

Answer 9

Surface oxidisation is where a solid fuel is heated in the air till the surface of the fuel reacts with the oxygen in the air to produce sufficient heat to make this process self sustaining e.g. Coal

Question 10

What are the three ways heat and fire can spread?

Answer 10

Conduction
Convection
Radiation

Question 11

Name the different classes of fire and how they can be extinguished?

Answer 11

Class A- Carbonaceous solid- water and foam
Class B- Flammable liquid- carbon dioxide and dry powder
Class C- Flammable gases- isolate the supply
Class D- Metals- sand

Question 12

There are 3 advantages of using water to extinguish fires in terms of dealing with the fuel, what are they?

Answer 12

The rapid expansion of water to steam dilutes the flammable gases
Reduces further production of flammable gases by pyrolysis because of the reduction in heat
The expansion of water to steam drives out some of the existing fire gases.

Question 13

There are 2 advantages of using water to extinguish fires in terms of dealing with the heat, what are they?

Answer 13

Absorb heat from the fire, raising the water’s temperature.

Absorb latent heat when turning water into steam.

Question 14

What is the advantage of using water to extinguish fires in terms of dealing with the oxygen?

Answer 14

The steam limits the amount of oxygen reaching the fire by smothering it.

Question 15

What are the 3 disadvantages of using water to extinguish a fire?

Answer 15

It is a good conductor of electricity
It cannot be using on fires involving flammable liquids since it causes a violent reaction to take place
It can react violently with other substances e.g. Some metals- magnesium

Question 16

Name the 2 different types of flame

Answer 16

Diffused

Premixed

Question 17

What is the name given to the highest concentration of a fuel to oxygen mix that will just support a self propagating flame called?

Answer 17

Upper explosive limit (UEL)

Question 18

Name the four phases of fire progression?

Answer 18

Developing fire
Flashover
Fully developed fire
Decay

Question 19

Explain the 4 2 1 rule.

Answer 19

States flashover occurs at a rapid pace in the corner.
Twice as quick in the corner than against a wall
Four times as quick in a corner than in the middle of the compartment

Question 20

Describe over pressure

Answer 20

The over pressure is the heated fire gases that collect at the top of the compartment. Gases are pressurised above atmospheric pressure and so called over pressure

Question 21

Describe under pressure.

Answer 21

Under pressure is the cooler cleaner air at the bottom of the compartment. Air is drawn in here to feed the fire.

Question 22

Describe the neutral plane.

Answer 22

The neutral plane is the boundary between the over and under pressures. It can be seen as the bottom layer of smoke that with descend and grow thicker as a fire develops.

Question 23

Name the signs of flashover? 8 to name

Answer 23

Ventilated fire
Flames visible in the fire gases.
Combustible material gassing off due to pyrolysis
High temperatures increase rate of combustion
Neutral plane lowering
Sudden increase in Fire development
Pyrolysis at floor level in compartment
Increase turbulence in neutral plane and gas layers.

Question 24

What actions should a fire fighter take at signs of a flashover?

Answer 24

Withdraw from the compartment and fire fight from outside the compartment
Communication hazard to other firefighters
Ventilate to remove gases- IC orders only
Use TIC to assess temperature of compartment
Team should stay low in cool air
Pulse spray into over pressure to reduce radiant heat.

Question 25

Name the three different types of applying water to a fire?

Answer 25

Indirect
Direct
Gas cooling techniques

Question 26

What’s the purpose of indirect spraying?

Answer 26

To suppress a fire by a large quantity of steam and reduce the chance of backdraught

Question 27

What are the 3 parts to the fire triangle?

Answer 27

Heat
Oxygen
Fuel

Question 28

What is the optimum flow rate and pressure the the RB 101 should be used in a fire compartment?

Answer 28

230 litres per minute and at 6 bar