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A carbon dioxide fire extinguisher is a specific type of extinguisher used for live electrical apparatus fires and fires involving flammable liquids such as paint, petrol and diesel, which are commonly referred to as Class B fires. They are not be used for fires occurring from cooking which would occur from oil and grease as this type of extinguisher could push the flames around.

The carbon dioxide fire extinguisher is commonly identified with a black label, black long horn and an ID sign stating, ‘CO2 extinguisher’.

The extinguisher works by diluting the oxygen within the atmosphere around the fire with the carbon dioxide gas to the point where the fire is unable to continue to burn. The extinguisher is often paired with foam extinguishers for internal environments as they together cover the majority of fire risks that could occur.

The benefits of carbon dioxide fire extinguishers are that they are very effective for putting out electrical fires and do not leave behind any residue. However, the disadvantages are the risk of burning hands if the horn is not frost-free and that the extinguishers are not as environmentally friendly in comparison to other types of extinguishers. In addition to this, the device poses the risk of asphyxiation if used in an indoor/confined space.



History
The Walter Kidde Company invented the first carbon dioxide fire extinguisher in 1924 as there was a need for a device to extinguish fires in telephone switchboards without conducting further heat. The original carbon dioxide fire extinguisher held 3.4kg of carbon dioxide within a tall metal cylinder. The first model has a wheel valve and a woven brass hose covered in cotton along with a funnel-like horn as a nozzle. It still had a prominent red coloured base with black features.

When to use
Carbon dioxide fire extinguishers were designed to be used for flammable liquid fires involving electrical equipment as it leaves no residue behind and is non-corrosive. It should be used for Class B and Class C fires.

They are not recommended to be used outdoors as they work by displacing the oxygen around the fire and thus would not be of use around fresh air. It also should not be used for chip pan fires as this would blast the flames around the area. Carbon dioxide fire extinguishers are ineffective at putting out fires formed by flammable solids, as they do not put out fires by cooling. They displace the oxygen in the air and replace it with carbon dioxide and thus cannot be used in confined spaces.

The carbon dioxide fire extinguisher is inoffensive to electrical equipment and thus are optimal for areas such as; offices, shops, hospitals, schools, workshops and any premises that holds the risk of a live electrical fire.

How it works
The carbon dioxide fire extinguisher works to put out fires by neutralising the oxygen that the fire is feeding on. This dilutes the oxygen with the carbon dioxide gas until the fire no longer has any air to burn, disabling the ability to spread.

This occurs within the device as carbon dioxide is a self-expelling agent, which means it naturally ejects at a strong force. It is stored in a liquid form at room temperature and ejects in a mixed state of part gas and part vapor droplets through the horn.

Once it has expelled and meets the atmosphere it almost instantly transforms into a gas, hence providing a very short effective range. The carbon dioxide fire extinguisher is effective at putting out fires and preventing reoccurrence due to the extremely cold temperature of the carbon dioxide that is emitted from the fire extinguisher and the lack of oxygen that remains in the atmosphere.

How to use
Carbon dioxide fire extinguishers are available in an array of sizes and they vary slightly in how they are properly used to extinguish a fire. Sizes range from 0.9 to 2.3kg/2 to 5lb to around 9.1kg/20lb. There are also wheeled carbon dioxide fire extinguishers which range from 22.7 to 45.5kg/50 to 100lb, having larger capacities. TThe main difference is where the horn is placed. Smaller models, designed to be used with one hand, have the horn attached directly to the discharge valve on the top of the extinguisher by a hinged mental tube. However, larger twohanded models have the horn attached at the end of the hose, which is shorter. Older models may have metal horns which can be dangerous around fires concerning energized electrical equipment. For this reason, metal horns are no longer made for carbon dioxide fire extinguishers however due to the expensive costs of replacing this device, many older models are still in service. Any carbon dioxide fire extinguishers which still hold the mental horn do not have a “C rating”. Another safety hazard is the need for frost-free horns.

Not all carbon dioxide fire extinguishers have frost-free horns and thus cannot be held from the horn as it will becomes extremely cold which can lead to severe frost burns. Frost free horns are manufactured to withstand the freezing carbon dioxide gas and thus can be held by the user. Furthermore, carbon dioxide fire extinguishers should be used differently depending on the nature of the fire they are extinguishing.

Prior to using a fire extinguisher, the user must ensure that it is safe to use by checking that the locking pin is undamaged and that the tamper seal is intact. The extinguisher should be examined for apparent physical damage such as corrosion, leakage or a clogged nozzle. Furthermore, the pressure gauge or indicator must be examined to ensure it is in the operable range or position. The operator of the extinguisher should also ensure the device is full.

Steps to use a carbon dioxide fire extinguisher;

1.	Stay a safe distance from the fire and remove the safety pin, breaking the tamper seal

2.	Check if the horn is a frost-free horn. If it is the extinguisher can be held from the horn. If not do not hold the horn.

3.	Aiming the extinguisher

a.	At flammable liquids; The horn should be aimed to the base of the fire and moved carefully along the area. Take care to not splash the burning liquid with the extreme thrust of the carbon dioxide fire extinguisher.

b.	At electrical equipment; if it is safe to switch off the power of the source, do so, then aim the hose directly onto the fire

4.	To begin discharging the fire extinguisher, slowly squeeze the lever. As the fire begins to weaken move closer to it as the carbon dioxide fire extinguisher has a very short discharge time.

5.	Take care to ensure that the fire has been completely extinguished.

Installation and signs
Carbon dioxide fire extinguishers have been designed to be distinguishable by their main body being a true red colour and having a large black banner across the top front of the fire extinguisher with write writing stating, “Carbon Dioxide”. Older models may have an entire black body.

Installation of all fire extinguishers is commonly done by professional and must follow strict guidelines, in Australia AS 2444-2001. Carbon dioxide fire extinguishers must be installed in a location between 2m to 20m from the fire hazard, meaning electrical equipment. It must be installed at a height so that it is no less than 100mm from the floor level and that the top of the carbon dioxide fire extinguisher handle is no more than 1200mm from floor level. Most fire extinguishers when purchased come with a wall bracket so that it can be attached to a wall. Other mounting methods include double sided tape. This is convenient as it is fast, affordable and easy however the wall used must be appropriate, referring to issues such as no paint flaking off the wall. Another method is glue/silicon sealant. This is also affordable and easy and stays on walls through harsh conditions such as outdoor walls. Screw fixings, although rarely used, are a possible method of installation.

Many considerations must be taken into account when installing a carbon dioxide fire extinguisher. Before installing, ensure that it is the correct type of device for the location, that it provides sufficient square meter coverage for the location, that the wall is suitable to have a fire extinguisher attached to it, such as being able to withstand the weight and that there are no interfering cables or pipework behind the installation wall. Furthermore, the amount of pedestrian traffic surrounding the installation location should be taken into account as issues such as accidental demounting, damage and misuse could occur. If the surrounding environment is not completely free of obstruction a cabinet or cover may be required.

Following the AS2444 standards all signs must be at least 2000mm from floor level or installed at a height in which the average heighted person has visibility to the sign as well as the carbon dioxide fire extinguisher device itself. When the fire extinguisher is located in a corridor/nook a double-sided angle sign may be required. The signs must be located directly above the carbon dioxide fire extinguisher. The considerations concerning where to mount the device are also applicable to mounting the signage.

The signage is a white square background with a red circle on top. It has black text reading ‘THIS EXTINGUISHER’ curved along the top and boarded by a black line following the circumference of the circle. Directly underneath in a larger font reads ‘CO2’, then in slightly smaller font ‘TO BE USED FOR PAINT, OIL, ELECTRICAL AND OTHER LIQUID FIRES’.

Maintenance
All types of fire extinguishers require monthly visual inspection and an annual basic service. The carbon dioxide fire extinguisher requires an extended service every 10 years.

A visual inspection includes aspects such as; checking the location of the extinguisher, ensuring that it is positioned so that it is easily visible, that the instructions are facing outwards and are legible. The condition of the device is also examined to see if it has been used, checking for any apparent damage or missing parts. The extinguisher pressure is inspected to ensure it is within safe operation limits and the tamper seals and indicators are checked to ensure they haven’t been broken. If there are any damages the basic service may need to occur more than annually.

The extended serving includes a hydrostatic pressure test to meet the standards of pressure vessel legislation and fitting the carbon dioxide fire extinguisher with a new valve. This is an expensive and difficult process, so as a result majority of fire extinguisher servicing engineers will simply supply a new carbon dioxide fire extinguisher.

Dangers
Dangers and misconceptions occur with all types of fire extinguishers. The risks involved with the carbon dioxide fire extinguishers include the possibility of reignition. It is a common myth that all fire extinguishers stop the fuel of the fire, however this is not the case with this device. Since the extinguisher simply removes the surrounding oxygen, the source of the fire can still pose a risk. It is important that the person putting out the fire observes carefully that there is no "spark" or any chance of reignition since there will still be some remaining oxygen, fuel and hot surfaces present.

Carbon dioxide fire extinguishers are not considered environmentally friendly as they expel carbon dioxide into the atmosphere. They have been found to having a damaging effect on the ozone layer. Scientist are working on developing the invention as to be more environmentally friendly using carbon dioxide hydrate crystals which release far less carbon dioxide into the atmosphere.

A further danger of carbon dioxide fire extinguishers is due the the device displacing the oxygen in the atmosphere, asphyxiation is a threat when used in confined spaces. The way to combat this risk is by not using the extinguisher in confined spaces and keeping young children away.