Fact Guide to CO2 Fire Extinguishers
So what’s the best option for tackling electrical based fires? Well the trusty old CO2 fire extinguisher is the only model that is recommended for a fire that involves electrical equipment. This is due to the fact the carbon dioxide gas is non-conductive and that once it has been discharged does not produce or leave any kind of residue as would happen if a powder or foam model was deployed. Another great use of the CO2 extinguisher is on Class B fires that involve flammable liquids, making this quite a versatile product.
It is very easy to recognise a CO2 extinguisher as they are colour coded red with a black panel for fast identification in the event of a fire related emergency. On the smaller 1kg and 2kg models they have a horn instead of a hose, with the larger 5kg extinguishers having a hose with a horn attached at the end.
You can buy much larger CO2 models in the 9kg to 45kg size range for use on industrial premises or at places such as airfields or large computer server rooms. Due to the extreme weight these products tend to come on wheeled bases for easy manoeuvring.
So what can’t a CO2 extinguisher be used on? Well any fire involving Class D materials such as flammable metals ARE A NO GO FOR TWO MAIN REASONS. Firstly The CO2 comes out under high pressure and can blow the metals around causing a fire to spread and secondly, the CO2 gas reacts with several volatile metals as does the extinguishing agents with a few of the other types of fire extinguishers. They are also not suitable for use on Class A fires involving materials such as paper, wood or cloth as again the high pressure jet can spread the burning material around and so spread the fire instead of containing and extinguishing it.
The big advantage of this type of extinguisher is the fact it is perfectly safe to use on electrical equipment and will not damage the items or leave any harmful residue after. If you go to any office or work place where sensitive electrical equipment such as computers are present you will virtually always see a CO2 model. They are often combined with foam, water or water additive extinguishers to offer the maximum level of fire fighting capacity.
Now let’s get down to the technical side of how a CO2 fire extinguisher actually works. Within the body of the extinguisher there is carbon dioxide (CO2) gas stored under pressure which results in it turning into a liquid. As you operate the extinguisher the gas is released under pressure into the horn which as it diffuses and expands turns back into a gas form. This action cools the surrounding air extremely quickly which is why you should not hold the actual horn as you could receive a freeze burn. Some models have frost free horns attached but if in doubt still do not hold the horn.
It is best to stand around 3 feet from the fire and no more than 8 feet for the CO2 gas to be most effective. Any close and you could easily cause the burning materials to be blown around as the pressure is very high when the CO2 is released.
The gas disperses the oxygen from the fire and thus starves the fire and so causes it to go out. This is how all extinguishers work generally. They remove one of the fire elements and as such the fire cannot burn.
The majority of CO2 extinguishers have aluminum bodies to keep the weight down as the body needs to be strong and thick because of the high pressure gas inside. Some marine models have steel bodies as do a lot of foreign imports into the UK.
You may notice that unlike other extinguishers there is not a pressure gauge on the body. This is because the gas is condensed inside the cylinder and so the only way to see if it has leaked or is empty is by weighing it. The gross weight should be stamped on the body of the fire extinguisher so to check if it is full simply remove the swivel horn and weigh the cylinder body. Now compare the two weights and if they match it is full. If not then it is empty or has been used.
It can be expensive to refill a CO2 extinguisher and have a company come out to inspect it so more often than not it is much cheaper to just buy a new one and have your local authority at sites such as waste dumps recycle the old one. Do not just throw them away as this is bad for the environment.