Fire extinguishers can contain different types of chemical agents to fight particular fires and we all need to know what types for what fire.
Whilst you don’t need to know the chemical formulas of what each extinguisher contains, it is important to know the differences in extinguishants so that you pick the right one for the right fire.
It is unlikely you will have all types in your home or office, and so here is a brief guide to the different fire extinguisher agents available today.
Fire Extinguisher Types
Multi-Purpose Powder Fire Extinguishers
Multi-purpose fire extinguisher agents are ones that can be used for a variety of fire types, with some being able to be used for A, B and C type fires.
One of the most common is mono ammonium phosphate, which is a dry powder chemical and is known as ABC powder or Multi-purpose powder.
It is non-conductive and so fine for fires involving electrical equipment. These can be used in homes, workshops and anywhere that a large, fast-growing fire could occur.
However, there are disadvantages to using these. Firstly, is that the power can massively reduce visibility and impact breathing, and are therefore no longer recommended for use inside in enclosed spaces. Secondly, the powder residue can cause corrosion which means you need to scrub the extinguished area afterwards to avoid rust.
Although hard to find in the UK, Halotron is another multi-purpose extinguishing agent, but this one is a vaporising liquid and requires no clean-up (this is a modern replacement for halon 1211). This is particularly good for rooms where sensitive equipment is stored like offices or computer rooms.
Dry Chemical Fire Extinguishers
Dry chemical extinguishers are also fairly multi-purpose, and can be used for B and C type fires. The agent is sodium bicarbonate, is non-toxic and non-conductive so can be used for fires involving electrical equipment.
Foam Fire Extinguishers
Foam is a very common extinguishant these days known as AFFF (Aqueous Film Forming Foam) and foam spray. Its popularity is due to the foam content being added to a water base that makes the water “wetter”. That is, it removes the surface tension and allows the water to spread better.
A 6 litre foam fire extinguisher has the same fire rating as a 9 litre water and the obvious weight reduction makes it popular for offices.
As AFFF forms a film and cuts out oxygen, it is particularly effective for class B flammable liquids and running fuel fires.
Water Fire Extinguishers
Water will never go out of fashion and, contrary to myth, is plain old H2O from a tap with nothing more. Water can only be used for type A or paper/wood based fires as it is dangerous near electrical equipment or near flammable liquids.
Water Additive Fire Extinguishers
Nowadays, you may see “water and additive” (with names like Hydrospray, AquaPlus, Elite, Water+ amongst others). This has a similar effect to the AFFF additives by making plain water more effective and easier to pick up.
CO2 (Carbon Dioxide) Fire Extinguishers
For class B fires and fires involving electrical equipment, CO2 will almost always accompany another extinguisher as it cannot be used on class A wood, paper, material fires.
They differ by having a horn which acts as a diffuser to reduce the pressure down from around 55 bar! It’s important to make sure this horn is on as trying to use one without it could break your arm. Also, due to the temperature, the short horn should never be held as your hand may suffer freeze burns.
Wet Chemical Fire Extinguishers
Class F is relatively new and covers fires involving cooking oils and fats and that’s all. It was brought out to combat fires in commercial kitchen deep fat fryers.
The wet chemical has a saponification effect and the special lance on the end of the hose diffuses the pressure so that the chemical falls gently on the fat to stop splashing it around. The entire extinguisher must be emptied and this coats a thick soapy layer to cut out oxygen and cool the fire.
Water Mist Fire Extinguishers
The ultimate clean extinguisher, water mist vaporises the water making it non-conductive (but don’t stand in the water run-off) and also enhancing its cooling and soaking characteristics.
Unfortunately, water mist is not found often in the UK at the moment.
Specialist Metal Powder Fire Extinguishers
These are purely for class D metal fires such as magnesium and involve a special applicating lance like the wet chemical to diffuse the powder and let it settle gently on the fire without spreading it. Laboratories are a common place for these.
Which Type Of Extinguishing Agent?
Knowing which type of extinguishing agent to use is important, both in terms of how effective it will be for a particular fire and how convenient it will be to clean up and use.
In general, homes benefit from having multi-purpose powder fire extinguishers as the variety of fires that are possible covers the full spectrum.
Agents like CO2 require virtually no cleanup afterwards and so are great for extinguishing fires whilst keeping the surrounding objects undamaged. However, CO2 completely ineffective against type A fires, and so it is advisable to have a water extinguisher or foam extinguisher as well.
Foam is probably the best option, because it can be used for more than just type A fires and so will provide good cover in other areas along with a CO2. But, if you have more specific needs just as industrial premises or a laboratory, it is a good idea to consult a Fire Safety Specialist or speak to a Fire Officer about your specific needs.
Whilst all fire extinguishers might appear the same at first, by knowing about the different types of fire extinguisher agents you are in a better position to choose the right ones for your needs.
You never know, this knowledge of fire extinguishants may save your life one day.