Fire extinguisher types and colours: which one goes on which fire

Ask the internet what a Class C fire is and a good share of the UK results will tell you it means electrical. That is the American answer, taken from NFPA 10 and OSHA, where Class C is defined as “a fire involving energized electrical equipment”. Under BS EN 2, the standard that classifies fires in Britain, Class C means gases. Methane, propane, butane.

Electrical fires are not a class at all here. The classes describe what is burning, and electricity is not a fuel. ISO 3941, the international parent of the British standard, says so in its introduction: it defines classes according to the material undergoing combustion and “in consequence, it does not define a particular class of fire involving an electrical risk.”

The distance between those two readings is the distance between isolating a gas supply and pointing a CO2 extinguisher at a socket. So it is worth getting the letters right before anything else.

The quick answer

Every one of those is a red cylinder. The colour is a band, panel or circle on the body, not the body itself.

The five fire classes in the UK

BS EN 2, “Classification of fires”, was published on 15 December 1992 and as first written it classified fires “in four categories”. Class F arrived later, by amendment in 2004/2005, once the industry accepted that cooking oil behaved differently enough to need its own category. That leaves five:

Class A is solid materials, usually organic, which burn with glowing embers. Class B is liquids and liquefiable solids. Class C is gases. Class D is metals. Class F is cooking oils and fats in cooking appliances.

There is no Class E. It is a genuine ghost: the European system did once carry one for electrical hazards, and Australia and New Zealand still designate energised equipment as Class E under AS/NZS 1850, so the letter keeps resurfacing in material copied from older or overseas sources. Class K has the same problem in reverse. It is the American designation for cooking media, created by NFPA in 1998, and it has no standing in the UK. Anything sold here as a “Class K” unit is either American labelling or marketing.

What about a fire in live equipment, then? Once the supply is isolated, it is a fire of whatever is actually burning, which in an office is usually Class A plastics and cable insulation. Suitability for use near live electrics is a property of the extinguisher rather than a class of fire, and it is earned by passing a test rather than by carrying a letter.

That test is worth knowing about. Under BS EN 3-7, an extinguisher is discharged from at least a metre at a one-metre-square metal plate charged to 35,000 volts, with the leakage current measured back at the handle. Passing it means the discharge stream will not conduct a dangerous current back to whoever is holding the thing. It does not mean the extinguisher will put an electrical fire out.

What the colours actually mean

Two documents are doing two different jobs here, and almost every guide on the subject conflates them.

BS EN 3-7:2004+A1:2007 is the product standard, covering characteristics, performance requirements and test methods, and it gives you the predominantly red body. What it does not do is say which colour means which medium.

That belongs to BS 5306-10:2019, a UK code of practice whose scope reads: “This part of BS 5306 gives recommendations for the colour coding used to identify the extinguishing medium used in portable fire extinguishers, and for the size and location of the colour indication.” It replaced BS 7863:2009 on 16 October 2019, the same day BS 7863 was withdrawn.

One colour has moved recently. Specialist powder for metal fires, Class D, changed from blue to signal violet, so a site with older stock can have two different powders wearing the same blue band.

Are old colour-coded extinguishers illegal?

No, and the standard says so directly. Before the change, whole bodies were painted in the colour of the contents: a solid cream cylinder was foam, a solid black one was CO2. BS 5306-10:2019 carries a note in its scope covering exactly this point: “The requirements of BS EN 3 and the recommendations of this British Standard concerning colour coding apply only to new extinguishers. Extinguishers conforming to withdrawn standard BS 7863 might still be found in service and are still acceptable.”

HM Government’s own fire risk assessment guide for offices and shops agrees, saying older extinguishers “remain acceptable until they are no longer serviceable”, and adds only that it is good practice not to mix old and new styles on the same floor. Old units almost always get replaced eventually, but the reason is condition or spares, not legality. The exception is the green halon extinguisher, which is banned by substance rather than colour under Regulation (EC) No 1005/2009 outside a short list of critical uses.

Which extinguisher for an electrical fire?

CO2 is the usual answer for live equipment. Dry powder is rated for it too, with a caution attached.

CO2 works by displacing the oxygen around the fire. It does not work by cooling, despite how often that is written, and the Scottish Government’s practical fire safety guidance states the consequence plainly: “Since CO2 does not cool a fire appreciably, the fire may re-ignite.” That is why you stay and watch the area afterwards. The discharge is intensely cold, which is a hazard to the user rather than a mechanism: Hampshire and Isle of Wight Fire and Rescue Service warns “Never hold the horn while using the extinguisher. It can get extremely cold and may burn or freeze your skin”, and advises using CO2 only in well ventilated spaces, since the gas that smothers a fire does the same to a room.

Dry powder is the reason so many buildings have blue extinguishers and so many fire officers wish they did not. It is rated across A, B and C and passes the electrical test, but it destroys visibility in seconds indoors, which is a serious problem when the room you can no longer see is the one you are escaping through. Hampshire and Isle of Wight advise against powder in enclosed spaces for that reason.

Commercial kitchens, and why four of the five make things worse

Cooking oil is the hazard that broke the old classification, and one number explains why. As the Fire Industry Association’s Class F fact file puts it, cooking oils and fats have “auto ignition temperatures in excess of 340C and are very difficult to extinguish using conventional extinguishers with a Class B capability.”

That temperature is the whole problem. Put the flames out without cooling the oil, and the oil is still above the temperature at which it ignites by itself. It relights.

Water is worse than useless. It sinks below the oil, flashes to steam, expands roughly seventeen hundred times, and blasts the burning oil out of the pan as an ignited spray. That is the fireball in every fire service demonstration you have seen.

CO2 and dry powder fail differently. Neither cools the oil, and BS EN 3-7 goes further than advice here: powder and CO2 extinguishers are excluded from Class F conformance altogether, so they cannot legitimately carry a Class F rating at all.

Wet chemical is the one that works, and it works chemically rather than by smothering. The media are alkaline potassium salts, typically citrate, acetate, lactate or carbonate. The potassium knocks the flame down while the salt reacts with the hot oil to form a soap layer across the surface, sealing it and cooling it below its auto-ignition point. It is also the only extinguisher applied slowly and deliberately, through a lance held above the surface, because blasting it in would do exactly what CO2 does.

Class F ratings tell you how much oil the unit was actually tested against. The four benchmark tests use 5, 15, 25 and 75 litres of sunflower oil, giving the 5F, 15F, 25F and 75F ratings you see on the label. A 25F unit behind a large multi-basket fryer is undersized, and the label is the only place that tells you.

One more detail that surprises people: because kitchens are full of electrical appliances, BS EN 3 requires every Class F extinguisher to pass the 35 kV dielectric test.

How many, and how far away

Nothing in law sets a number. Article 13 of the Regulatory Reform (Fire Safety) Order 2005 requires only that premises are “to the extent that it is appropriate, equipped with appropriate fire-fighting equipment”, and that any non-automatic equipment is “easily accessible, simple to use and indicated by signs”. Appropriate is judged on the dimensions and use of the premises, the equipment in them, the substances likely to be present and the number of people there. No figures attach to any of it.

The numbers everyone quotes come from BS 5306-8:2023, the code of practice for selecting and positioning extinguishers, published on 30 November 2023 to replace the 2012 edition. It is guidance, not law, and HM Government’s guides say as much about the standards they cite.

Its travel distances are where the widely repeated “30 metres” falls apart, because they are not the same for every class:

• Class A: 30 m
• Class B: 10 m
• Class F: 10 m
• Class C: case-by-case specialist assessment, changed from 30 m in the 2023 revision

Distance is measured as walked rather than straight-line, and reduced by 5 m for every door the user has to open on the way. So a wet chemical extinguisher sited 30 metres from the fryer it exists to serve is three times further away than the code contemplates. Government guidance makes the same point in words: extinguishers for a located risk, a fryer or a flammable liquid store or switchgear, belong near that hazard, and the 30 m figure is written as “ideally no one should have to travel more than 30m”, covering risks not confined to one spot.

On quantity, the recommendation is at least two Class A extinguishers per storey with a minimum combined rating of 26A, relaxed by the 2023 revision to a single 26A unit on storeys under 50 m². Government guidance frames it as roughly one water-based extinguisher per 200 m² of floor space, reducible to one in premises under 90 m².

Using one, and when not to

There is a real gap between what the public is told and what workplace guidance says, and both are right for their setting.

For a domestic fire, UK fire services are close to unanimous: do not. Kent Fire and Rescue Service says “Never attempt tackling a fire”, the reason being how fast smoke builds, with a few seconds of exposure enough to render someone unconscious. London Fire Brigade’s pan fire advice is the same: “Don’t tackle the fire yourself and don’t try to move the pan.”

Workplace guidance is narrower rather than contradictory. The Home Office fire risk assessment guides put it precisely, in identical wording across the offices and shops, sleeping accommodation and residential care versions: “People with no training should not be expected to attempt to extinguish a fire. However, all staff should be familiar with the location and basic operating procedures for the equipment provided, in case they need to use it. If your fire strategy means that certain people, e.g. fire marshals, will be expected to take a more active role, then they should be provided with more comprehensive training.”

Care homes get a further rule of their own, and it is the clearest statement of priority in any of the guides: “In residential care homes the emphasis must be towards the safety of residents rather than fighting the fire; extinguishers should primarily be used to protect life and facilitate safe escape.”

London Fire Brigade sites extinguishers “in conspicuous positions on escape routes, preferably near exit doors”, which tells you the intended posture: you are between the fire and the way out. The Fire Protection Association adds four limits, one of which matters given what Class C actually is: never use an extinguisher on escaping gases, only tackle a fire in its very early stages, stay a metre back, and do not use more than one extinguisher. If the first has not worked, you are leaving.

Does the law require extinguisher training?

Not in the way the training industry often implies. Article 21 of the Fire Safety Order requires “adequate safety training” when someone is first employed and when they face new or increased risks, repeated “periodically where appropriate”. It sets no interval, and it never mentions extinguishers, firefighting equipment or practical drills at all. GOV.UK’s wording on equipment is conditional: train your staff to use them “if necessary”.

The targeted duty sits elsewhere. Article 13(3)(b) requires the responsible person to nominate competent persons to carry out firefighting measures and to ensure their number, training and equipment are adequate for the size and hazards of the premises. Competence is defined by outcome, as “sufficient training and experience or knowledge and other qualities”, with no course or awarding body named anywhere in the Order. Practical extinguisher training for nominated people is a sensible call where the risk assessment supports it. It is not a statutory duty owed to everyone on the payroll.

Scotland and Northern Ireland carry materially the same duties, under regulation 12 and regulation 20 of the Fire Safety (Scotland) Regulations 2006 and regulation 20 of the Fire Safety Regulations (Northern Ireland) 2010, and are equally silent on hands-on practice.

Frequently asked questions

What are the five types of fire extinguisher in the UK?

Water, foam, dry powder, CO2 and wet chemical, identified by a coloured band on a red body: red for water, cream for foam, blue for powder, black for CO2, canary yellow for wet chemical. Specialist powder for metal fires carries a signal violet band.

What fire extinguisher should be used on an electrical fire?

CO2 is the usual choice for live equipment because it leaves no residue and does not conduct. Dry powder is rated for it too but ruins visibility indoors. Electrical is not a fire class in the UK: once the supply is isolated, the fire is classed by whatever is burning.

Is Class C electrical or gas?

In the UK, Class C is gases. Class C means electrical only under the American system, NFPA 10 and OSHA. The UK classes are A for solids, B for liquids, C for gases, D for metals and F for cooking oils.

What colour is a fire extinguisher for a deep fat fryer?

Canary yellow, identifying a wet chemical extinguisher rated for Class F. Water, foam, CO2 and dry powder should not be used on cooking oil, and BS EN 3-7 excludes powder and CO2 from carrying a Class F rating at all.

Do fire extinguishers have an expiry date?

No expiry date is set in law. BS 5306-3 recommends a basic service annually, an extended service at five years for water, foam and powder, and an overhaul at ten years for CO2. Article 17 of the Fire Safety Order requires only that equipment is kept in efficient working order.

Are old colour-coded fire extinguishers still legal?

Yes. BS 5306-10:2019 says its colour coding recommendations “apply only to new extinguishers”, and that older units built to the withdrawn BS 7863 “might still be found in service and are still acceptable”.

Where this actually bites

The letters and colours are easy to look up. What they are for is the ten seconds in which somebody decides whether the thing on the wall is the right thing to pick up, and whether to pick anything up at all.

That decision is mostly made long before the fire, in the risk assessment that put a canary yellow cylinder within ten metres of the fryer and a black one near the switchgear, and in whether the nearest person has been told which is which. Our fire warden duties guide covers the nominated role, and the UK fire safety training requirements guide sets out the wider duties on the responsible person. For the underlying awareness across a team, Fire Safety covers it in about an hour, and Health and Safety in the Workplace picks up the rest.