Fire Science Flashcards
What is the definition of combustion? Give an example
An irreversible chemical reaction producing heat and light
Burning wood will produce ash, but ash cannot be transformed back into it original state wood.
What three components form the triangle of fire?
Heat
Oxygen
Fuel
What is the difference between vapour and permanent gas?
Vapour has the potential to change back to liquid with a change of pressure
Heat is a form of what?
Energy
What is an ignition source?
Name some examples of an ignition source
The heat energy required for combustion to occur. Naked flames Electrical arcs or sparks Frictional heat or sparks Chemical reaction Pressurisation of gas Spontaneous heating
Heat energy is measured in what?
Joules
Joules per kilogram
Temperature is measured in what?
Celsius
How much oxygen is in the air and how much is needed for combustion?
21% in the air
16% needed for combustion
What is an oxidising agent?
A substance that releases oxygen when heated, that can lead to combustion
What are passive agents or
Passive?
Name some examples
Substances that take no part in the chemical reaction of combustion, but can have an effect on the fire’s behaviour by absorbing heat
Non flammable gases
Weather, temperature and humidity
Nitrogen in the air
Walls and ceilings, furniture
The amount of oxygen available for combustion will determine what three things?
How quickly and efficiently a substance will burn
The type of fire gases that are released
The amount of smoke produced
What is pyrolysis?
What is the process of pyrolysis?
The self-sustaining decomposition of a substance by heat
Heat from the flame radiates onto the surface of the fuel, causing it to pyrolyse, producing flammable gases to feed the flames
What is the flash Point?
The lowest temperature at which vapours are being produced for a momentary flash to occur when an ignition source is introduced.
Does not continue to burn once the ignition source is removed
What is a Fire point?
The lowest temperature at which sufficient vapours are being produced for the fuel to ignite and continue to burn once the ignition source is removed
Temperatures are only very slightly above the flash point
What is the auto-ignition temperature (A/T)?
The lowest temperature at which fuel will spontaneously ignite and continue to burn without the need of an ignition source to be introduced
Often referred to as the spontaneous ignition temperature (SIT)
What is surface oxidisation?
Give an example
A reaction in which the substances making up the surface of the solid react with oxygen, generating sufficient heat to be a self-sustaining process
What are the three methods in which heat spreads, and what are the meanings
Convection - movement of warmer gases through cooler surroundings
Conducting - the passage of heat through a material
Radiation - the transfer of heat energy as electromagnetic waves
In order to extinguish a fire, it is necessary to break the triangle of fire by removing one or more of the components. What three methods achieve this?
Cooling - removing the heat
Starving - removing the fuel
Smothering -removing the oxygen
Name six examples of extinguishing media?
Water Foam Dry powder Carbon dioxide Sand Fire blanket
What are the advantages of using water on a fire?
Five examples
The rapid expansion of steam dilutes flammable gases
Reduces further production of flammable gases by pyrolysis
Absorbs heat from the fire
Absorbs latent heat when turning to steam
Limits the amount of oxygen reaching the fire
What are the four classes of Fire?
Class A - carbonaceous solids
Class B - liquids and liquefiable solids
Class C - gases and liquefiable gases
Class D - metals
What is the best extinguishing media for class A fires?
Water
What is the best extinguishing media for class B fires What other extinguishing media can be used?
Foam
Fire blanket
Dry power
Carbon dioxide
NOT WATER
What should be done when trying to extinguish class C fires?
Try and isolate the gas supply
What is the best extinguishing media for class D fires?
Sand
Specialist dry powder (TEC powder)
What is the best extinguishing media for electrical fires?
What shouldn’t be used?
Carbon dioxide can be used
Water Definitely should NOT be used
