Unit 2 - Principles Of Fire And Explosion Flashcards
Define an endothermic reaction
Energy is absorbed and cannot occur spontaneously such as a gas canister.
Define exothermic
Energy is released as heat noise and light. Combustion
Normal fire
5 stages of combustion
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
Sources of ignition
8 marks
Electricity Heaters Hot surfaces Fag ends Naked flames Hot works Lighting Arson
Define flash point
Lowest temp when vapours are given off by the liquid and vapours momentarily ignite if ignition applied
Define fire point
Lowest temperature at which there is sustained combustion of the vapours
Define ignition point
Minimum temp at which the substance will burn without additional application of external heat
Define auto ignition
Lowest temp at which the substance will ignite spontaneously without flame or ignition source
Define upper and lower flammable limit
Highest and lowest mixture of fuel and air that will support a flame
5 classifications of fire
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
5 things that Influence the growth rate of a fire
Oxygen availability
Vapour released from substance
Open plan buildings
Stairways and ceiling voids
Materials used in construction
3 ways in which ventilation can help spread fire
Conduction by metal ducting
Convection by smoke travelling
Supply oxygen
Define flashover
Initial fire will radiate heat and may bring other materials to their spontaneous ignition temperature
Define backdraught
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
Define deflagration
Subsonic combustion caused by thermal conductivity where a hit burning material heats up the next material and ignites it
Define detonation
Supersonic combustion shock wave compresses all of the material until it ignites
Define upper and lower explosion limit
Highest and lowest mixture of fuel to air that will support an explosion
6 conditions for an explosion to occur
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
Define bleve
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
3 ways a bleve causes damage
Blast wave
Thermal radiation of fire
Shrapnel
8 ways to prevent a bleve
Atex rates tools No smoking Maintenance Pressure relief valves Suppression Good housekeeping Competent staff Earth equipment
5 things for a dust Explosion
Oxidant Ignition Dispersion of dust Combustible dust Confinement of dust
Define primary and secondary explosions
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
6 ways to reduce the risk of explosion
Good housekeeping Good ventilation Storage and handling of explosive materials Control ignition sources Inert atmosphere Plant controls
Identify 6 protective measures for explosion
Suppression Pressure relief valves Bursting discs Explosion venting panels Containment Cooling