Unit 2 - Principles Of Fire And Explosion

Question 1

Define an endothermic reaction

Answer 1

Energy is absorbed and cannot occur spontaneously such as a gas canister.

Question 2

Define exothermic

Answer 2

Energy is released as heat noise and light. Combustion

Normal fire

Question 3

5 stages of combustion

Answer 3

Induction - smouldering as it builds up to its ignition point

Ignition phase - sufficient energy for combustion to begin

Growth phase - consumes surrounding fuel and continued until fuel or oxygen runs out

Steady state - massive flames and high temp controlled by the amount of fuel and oxygen available

Decay - fuel has been used and fire dies. Extinguish

Question 4

Sources of ignition

8 marks

Answer 4

Electricity 
Heaters 
Hot surfaces 
Fag ends 
Naked flames 
Hot works 
Lighting 
Arson

Question 5

Define flash point

Answer 5

Lowest temp when vapours are given off by the liquid and vapours momentarily ignite if ignition applied

Question 6

Define fire point

Answer 6

Lowest temperature at which there is sustained combustion of the vapours

Question 7

Define ignition point

Answer 7

Minimum temp at which the substance will burn without additional application of external heat

Question 8

Define auto ignition

Answer 8

Lowest temp at which the substance will ignite spontaneously without flame or ignition source

Question 9

Define upper and lower flammable limit

Answer 9

Highest and lowest mixture of fuel and air that will support a flame

Question 10

5 classifications of fire

Answer 10

A - solids such as paper 
B - liquids such as fat, was or paint 
C - gases such as lpg 
D - metals such as zinc and aluminium 
F - cooking fats and oils

Question 11

5 things that Influence the growth rate of a fire

Answer 11

Oxygen availability

Vapour released from substance

Open plan buildings

Stairways and ceiling voids

Materials used in construction

Question 12

3 ways in which ventilation can help spread fire

Answer 12

Conduction by metal ducting

Convection by smoke travelling

Supply oxygen

Question 13

Define flashover

Answer 13

Initial fire will radiate heat and may bring other materials to their spontaneous ignition temperature

Question 14

Define backdraught

Answer 14

Fire in an enclosed space dies down and smoulders until a door is open and the inrush of oxygen restarts the fire with the fire travelling towards the open door

Question 15

Define deflagration

Answer 15

Subsonic combustion caused by thermal conductivity where a hit burning material heats up the next material and ignites it

Question 16

Define detonation

Answer 16

Supersonic combustion shock wave compresses all of the material until it ignites

Question 17

Define upper and lower explosion limit

Answer 17

Highest and lowest mixture of fuel to air that will support an explosion

Question 18

6 conditions for an explosion to occur

Answer 18

Substance must be combustible
Substance can become airborne
Capable of propagating a flame
Concentration of gas/dust must fall within explosive range
Ignition source in contact with explosive mixture
Sufficient oxygen to sustain combustion

Question 19

Define bleve

Answer 19

Boiling liquid expanding vapour explosion

As liquid evaporates into container the container gets hotter as the liquid does not absorb the heat of the upper section the container cracks and an explosion occurs

Question 20

3 ways a bleve causes damage

Answer 20

Blast wave
Thermal radiation of fire
Shrapnel

Question 21

8 ways to prevent a bleve

Answer 21

Atex rates tools 
No smoking 
Maintenance 
Pressure relief valves 
Suppression 
Good housekeeping 
Competent staff 
Earth equipment

Question 22

5 things for a dust Explosion

Answer 22

Oxidant 
Ignition 
Dispersion of dust 
Combustible dust 
Confinement of dust

Question 23

Define primary and secondary explosions

Answer 23

Initial dust Explosion is the primary, the secondary is caused by the first explosion dislodging more dust which is then ignited by the first explosion or a separate ignition source

Question 24

6 ways to reduce the risk of explosion

Answer 24

Good housekeeping 
Good ventilation 
Storage and handling of explosive materials 
Control ignition sources 
Inert atmosphere 
Plant controls

Question 25

Identify 6 protective measures for explosion

Answer 25

Suppression 
Pressure relief valves 
Bursting discs 
Explosion venting panels 
Containment 
Cooling