All flammable liquids will need to be secured in an area where no sources of ignition can be located. It is also helpful to understand the terms which will be used to describe their chemical properties. When stored all information about the flammable liquids needs to be noted these would include the flash point, flammable range, Ignition Temperature and Vapour Density. A flash point is the temperature at which the liquid would give off a vapour which could ignite. The Flammable Range refers to the percentage of the liquid whist in a gaseous state which could mix with the air to create an explosion. The ignition temperature is the temperature which is needed for the liquid to continue to let off vapours which will cause combustion.
Chemistry of Combustion and Extinction
Combustion is a chemical reaction which will give the fire more heat which will eventually let it continue and grow. Combustion can also be defined as:
as any reaction evolving heat. Oxygen is the sole supporter of combustion, and a combustible (fuel) may therefore be defined as a substance capable of combining with oxygen to produce heat.
There are four stages to combustion which are as follows:
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Incipient Stage- In this stage decomposition is starting to occur at the surface of the fuel due to heat yet combustion is still not visible.
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Smouldering Stage- In this stage up to 10% of the decomposition products are visible.
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Flaming Stage- This stage involves the vapours igniting and the flames are beginning to grow.
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Heat Stage- The burning has progressed to there the fire is still small but generating heat to warm the air which would send warm products of combustion upwards using convection.
The speed of combustion depends on the amount of oxygen needed to combine with the fuel but it can also depend on the conditions surrounding the fire.
Extinction
The chemistry of fire extinction involves the removal of one of the elements which will cause a fire; these are illustrated of the Fire Tetrahedron.
Completing one of the following principles can stop the fire as it will remove one of the elements.
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Smothering- By removing the oxygen surrounding the fire the fir can be extinguished. This method can be achieved by using a flame proof fabric to cover the fire.
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Starvation- This can achieved by removing the fuel which is being used in the fire. If the fuel is gaseous substance the valves in which are giving this substance out can be turned off.
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Cooling- This is the most common method used as it is simple, this can be achieved by soaking the fire with water or any other substance which will cool the fuel down and stop the fire.
A method of stopping the chain reaction can also be used this method will need to use more than one of the principles.
All staff building is also issued with fire extinguishers for any certain fire which could take place in that building for example electrical fires or paper fires. There are many types of fire extinguisher these being those listed below:
- Water Extinguishers- This type of extinguisher would be able to tackle paper or wood fires as the water would be able to cool down the paper and wood.
- Foam Extinguishers- This type of extinguisher would again be able to tackle paper and wood fires yet it has an added bonus, it can fight against flammable gas fires as the foam would cover the fire and smother the fire not letting the gas into the mix.
- Dry Powder Extinguishers- This extinguisher can also fight against paper and wood yet it can fight against electrical based fires.
- Carbon Dioxide Extinguishers- These extinguishers can fight against paper, wood and electrical fire yet it can not fight against gaseous type fires.
Structural Effects of Fire Behaviour and Occupancy of Behaviour
All buildings being constructed or be checked need to be fire safe, in order to show that this is right a certificate will be issued from the fire station stating that this building has been checked and is in order with the regulations. All buildings need to be designed and constructed that there can be early warning signs of a fire such as fire alarms, appropriate means of escape with a safe place to escape to also need to be in place.
When constructing a house the builders need to be sure they follow rules such as:
- All walls and ceiling are made of a reasonable material which will resist the spread of flames over that surface and if ignited can have a reasonable rate of heat release.
Buildings must be constructed so in case of fire:
- Stability will be able to last for a certain period of time.
- Walls joining on to more buildings will resist the spread of fire so other buildings will not catch fire.
- Fire spread will be stopped with fire resisting walls and floors.
- Concealed areas will be sub-divided to restrict unseen spread of flames.
Yet there is still old buildings in our towns which are made of old features such as wood which could be the support for the ceiling and walls, if any of this kind of building were to set alight then this would consume the whole building. This is why more modern buildings contain steel girders which will not ignite or crumple under the pressure.
