Flashcards in Fire Science 2 Deck (31)
What are the two types of flame?
What are the signs of a diffused flame?
Slow, bright, lazy. flickering.
Orange/red in colour
Candles are only _____ efficient, releasing ______ into a room
Candles are only 25% efficient, releasing unburnt fuel into a room
What type of flame will a burning sofa produce?
A diffused flame
What are the characteristics of a pre-mixed flame?
More Violent, blue in colour, cleaner burn, noisier.
What is the difference between a diffused and a pre-mixed flame?
A pre-mixed flame has air mixed with flammable gasses before combustion. This results in a more efficient combustion.
What is the stoichiometric ratio?
The optimum air to fuel ratio for combustion to occur.
What is the upper explosive limit?
The highest possible concentration of a fuel in a mixture for it to ignite.
If the mixture is above the UEL, it is described as too rich to burn.
What is the lower explosive limit?
The lowest possible of a concentration of a fuel in a mixture for it to ignite.
If the mixture is below the LEL, it is described as to lean to burn.
What is the ideal mixture?
Every gas has a particular concentration at which the amount of gas and the amount of oxygen is exactly right for combustion to occur.
At this point, combustion will have the maximum force.
Why is acetylene such a dangerous gas when released into the atmosphere?
Due to its wide range of flammability.
What is a flashover?
The sudden and sustained transition from a fire in a room to a room on fire.
What are the four stages of fire development?
What will cause a fire to decay?
A reduction of the fuel, heat or oxygen available to the fire.
What is the over-pressure?
A mixture of hot fire gasses which have risen from the seat of the fire to the top of the compartment, creating a cloud with a higher than atmospheric pressure.
What is the neutral plane?
The visible divide between the over-pressure and under-pressure.
What is the under-pressure?
The area at the bottom of the compartment at less than atmospheric pressure, caused by air being drawn towards the fire.
What three factors affect fire progression?
An airtight compartment.
How will an airtight compartment affect a fire?
The fire will consume all of the oxygen in the room, causing it to decay.
The heat in the room will cause items to continue to pyrolyse and smoulder.
A higher ceiling will slow a fire's development.
True or false.
A fire in the centre of the room will develop ___ times faster than a fire in the centre of a room.
4 times faster.
If a fire is in the corner of a compartment, the flame height will _______ in height for every _______ of fire development, until the ceiling is reached.
The flame height will DOUBLE in height for every MINUTE of fire development.
What are the signs of a flashover? (List of 8)
A ventilated fire with an oxygen supply.
Visible flames at ceiling height.
The production of fire gasses.
High temperatures and an increasing rate of combustion.
Neutral plane lowering.
Sudden increase in fire development.
Pyrolysis at floor level.
Turbulence in the neutral plane.
What actions should be taken if flashover occurs?
Firefight from outside the compartment.
Communicate to the ECO/IC
Ventilate to remove fire gasses.
Use the TIC to assess the temperature of the over-pressure.
Pulse the over-pressure to cool it.
What is a backdraught?
Sudden deflagration, caused by air being introduced to an oxygen starved compartment where there is a build up of fire gasses.
List 4 signs of a potential backdraught.
A poorly ventilated fire which has been burning for some time.
Fire gasses being pushed through gaps under pressure.
Blackened windows with no signs of flame.
Low neutral plane.
After informing the ECO/IC, what must firefighters do if a backdraught has been indicated?
Ventilate prior to entry (on the orders of the IC)
Use TIC to assess the temperatures inside the compartment.
Use door procedure.
Pulse spray to cool and dilute fire gasses.
Define fire gas ignition
A sudden ignition of fire gasses that have accumulated outside of a compartment.
Name three causes of fire gas ignition
Pyrolysis of material in an adjacent compartment.
Ignited fire gasses leaked from the fire compartment.
The construction of the building causing smouldering of material (e.g. sandwich panels).