Extinguishers For Metals

Specialist fire extinguishers are required to tackle Class D flammable metal fires. As you might expect when dealing with such volatile and specialist materials, you need the correct agent for the metal being extinguished.

However, flammable metals are more common than you might imagine, as under certain conditions, even powdered aluminium or swarf can catch fire.

All powder-based specialist fire extinguishers designed for fighting metal fires are categorised as a powder extinguisher, so are coloured red with the familiar blue panel above the operating instructions. The most common Class D fire extinguishers are 9kg M28 models, whereas the most common UK lithium-extinguishing model is the 9kg L2.



How Do Specialist Metal Fire Extinguishers Work?

Specialist fire extinguishers contain a range of fire extinguishing agents designed to tackle certain metal groups. Metals that burn in air also react with other common compounds in potentially dangerous ways. For example, burning magnesium splits water into oxygen and highly explosive hydrogen gas – not what you want in a fire situation!

Specialist fire extinguishers for metal fires work by smothering the fire with a non-reactive agent, which forms a crust and excludes air from contact with the metals.

Specialist Metals and Their Uses

While you may not encounter such metals as pure magnesium potassium or lithium in everyday situations, they are used extensively in industrial processes, engineering, manufacturing and in scientific laboratories. (Volatile metals are no longer used in school science labs, but ask anyone over 40 and they’ll probably have a tale to tell about chemistry experiments with magnesium…!)

Sodium Chloride fire extinguishers are designed for use on Class D fires involving magnesium, sodium, and potassium. They can also be used on fires involving uranium, and waste (swarf) or powdered aluminium. Swarf can be produced by milling or drilling aluminium, so these fires are a more common hazard than you might expect.

When a sodium chloride fire extinguisher is applied to a fire, the heat of the fire makes the sodium chloride cake together and forms an air-excluding crust. And yes, sodium chloride is just plain table salt (NaCl) and it’s the same sort of process as cooking a fish in salt!

Copper powder metal fire extinguishers are designed for use on Class D fires involving lithium. The powdered copper will coat and extinguisher either a static or flowing lithium fire. In addition, the copper powder will stick to any vertical surface, so if the fire is on a wall, you can still extinguish it safely. Most importantly, the low velocity applicator ensures that no burning metal is blown around, causing the fire to spread.

Graphite powder metal fire extinguishers can also be used on lithium fires, although unlike the copper powder, the graphite powder will not stick to a vertical surface. However, graphite powder can be used on metals that burn at very high temperatures, such as zirconium and titanium.

Sodium bicarbonate and sodium carbonate fire extinguishers can both be used on Class D fires. Sodium bicarbonate extinguishers can be used on most metal alkyls, plus liquids that ignite on contact with air. Sodium carbonate fire extinguishers can be used to extinguish fires involving sodium, potassium, or their alloys.

Granulated fire extinguishing powders can be used in place of extinguishers if the fire is on a level surface. Applied with a long scoop or shovel, granulated sodium chloride, copper and graphite can be applied to smother fires involving titanium, magnesium, potassium sodium and aluminium.

Graphite powder can also be applied to burning metal powders, where even the gentle blast from a fire extinguisher could lift up the powder and cause a dust cloud explosion. Graphite powder has the added advantage of drawing heat away from the fire as well as smothering it.

Sand can also be used to extinguish a burning metal fire in the event of an emergency and if no other suitable agent is to hand. However, sand retains moisture, which in the heat of the fire turns rapidly to steam. The resulting steam eruption could then scatter burning metal over a wider area. Sand should always be applied with a long-handled shovel to protect you from flash burns.

Lithium Fires

Lithium fires must be tackled with a specialist lithium extinguisher only, commonly sold as a L2 extinguisher. A sodium chloride extinguisher is not suitable for use on a lithium fire.

Using a Specialist Fire Extinguisher on a Class D Fire

If your work involves a fire risk covered by a D rated extinguisher, you must be provided with specialist training in the proper use of the extinguisher. These specialist fire extinguishers feature a long lance on the end of a hose, so you can safely tackle the fire from a safe distance. The application of the powder is at low pressure to avoid scattering burning materials.

Wet Chemical Extinguishers

Wet chemical fire extinguishers are the new kids on the fire extinguisher scene, developed specifically for use on deep fat cooking fires. The first such extinguisher on the market was the Chubb FryFighter, and its appearance gave rise to a new fire class, Class F and a new British Standard, BS 7937: 2000.

Wet chemical fire extinguishers are red with a yellow panel above the operating instructions.


How Wet Chemical Fire Extinguishers Work

Normal fire extinguishers are worse than useless in a deep fat fire, since they cannot cool the oil and cause hot oil to splash up on contact with the extinguisher’s agent. Fat can burn at 340 degrees, and an average fat fryer holds up to 75 litres of oil.


Unfortunately, until the invention of the wet chemical extinguisher, many commercial kitchens were supplied with foam or powder units with the occupants falsely thinking these could be used on the fat fryers. The cost can also be high compared to other extinguishers but the risks are much higher in the kitchen and, if bought online at a discounted, the costs are not high these days.

The active ingredient in a wet chemical fire extinguisher is potassium acetate, often with added potassium citrate or potassium bicarbonate. When operated, a wet chemical extinguisher creates a fine mist, which cools the flames and prevents splashing.

The potassium salts then have a saponification effect on the oil’s surface, creating a thick, slippery foam layer that smothers the fat and prevents re-ignition. The chemical foam will also cool the fat over a prolonged period of time.

Unlike other extinguishers, the idea is to completely empty the contents into the fat fryer to enable the cooling process to begin.

A point to note is that the contents can be corrosive so the quality extinguishers are made from stainless steel. Beware of the cheap Middle-Eastern imports made from mild steel as the lifespan will not be as good and the linings could be affected.

Saponification: Here’s the Science

Saponification is the same process used to create soap from fats and oils as a result of a reaction with a metallic alkali, or base. The base acts on the oil to convert it into hydrolyzed acid and alcohol. Essentially, a wet chemical fire extinguisher converts the surface of the cooking oil or fat into a non-combustable soap.

An added benefit is that the soap-creation process is endothermic, meaning it absorbs heat energy from the oil, cooling the oil down in the process.

Using a Wet Chemical Fire Extinguisher

Like other specialist fire extinguishers, the wet chemical fire extinguisher has a long lance, allowing the user to stand well back from the fire and to spray the agent gently and evenly over the fire’s surface. As with all specialist extinguishers, full training should be given in the proper and effective use of this extinguisher, a common sight in commercial kitchens and food manufacturing environments.

Just Fats, Please

Wet chemical fire extinguishers only work with animal fats and vegetable oils, so they cannot be used on Class B fires involving flammable liquids such as petrol or diesel.

They have usually been tested to a 13A Class A rating but should not be specified for anything other than a kitchen.

Wet Chemical Fire Extinguishers and Electricity

Wet chemical fire extinguishers are not designed for use on electrical equipment, but in the modern kitchen environment, it is hard to avoid electricity cables. Hence, the lance of a standard wet chemical fire extinguisher is non-conductive, and passes the BSi 35kv conductivity test.

Other Fire Extinguishers in the Commercial Kitchen

Wet chemical fire extinguishers have a very specific function, and are not suitable for other fire types except Class A fires if no other extinguisher is available.

Most Fire Risk Assessments would recommend that wet chemical extinguishers are kept in proximity with other fire safety items such as a CO2 extinguisher for electrical items, and a substantial fire blanket such as a 1.8m x 1.2m size. Fire blankets should be used to smother small pan fires, not to deal with commercial fryer fires.

A small fire blanket is a useful fire safety device for any kitchen, commercial or domestic. Simple to use, yet effective, it should be used to smother a fire and then LEFT ALONE for a considerable length of time to ensure the fire is completely extinguished. If in doubt, smother, get out, stay out and call the Fire Brigade.

Foam Fire Extinguishers

Foam fire extinguishers have come a long way in 30 years. The original foam was thick, gloopy and smelled appalling, due to its high animal protein content. (Not good for vegetarians, then!)

Modern Aqueous Film Forming Foam (AFFF) fire extinguishers are another breed altogether, one of the best all-round units available. Foam extinguishers are red with a cream panel above the operating instructions.

How Aqueous Film Forming Foam (AFFF) Fire Extinguishers Work

When sprayed onto a fire, AFFF foam (pronounced A-triple-F) extinguishes and smothers the flames, then seals in any harmful vapours under the outer film of foam.


The foam also penetrates absorbent materials, and cools the fire as the water in the foam evaporates.

Foam is extremely effective on Class A fires, involving paper, wood, etc, so they are a good choice for a general office fire extinguisher are particularly great on man-made furnishings, where the fibres in the fabrics might otherwise liquify in the heat of the fire.

When used on flammable liquid fires (Class B), the foam forms a film that prevents re-ignition of the flammable liquids by sealing the liquids away from oxygen in the air.

Light in Weight but Not Lightweight

AFFF extinguishers are lighter than ordinary water ones because the 6 litre foam has the same 13A fire rating as the heavier 9kg water only equivalent.

Foam Fire Extinguishers and Electricity

The foam spray nozzle that sprays the foam evenly, allowing you to coat the fire area quickly. Since the foam fire nozzle is non-conductive, you can use an AFFF fire extinguisher near (but not directly on) live electrical equipment. The quality models will have been tested to the BS EN3 35,000V dielectric test as defined by BSEN3-7:2004.

Foam Fire Extinguishers Containing PFOS

Perflourooctane Sulphonate (or PFOS) was used for many years in foam extinguishant. However, it has been proved to be toxic and a potential risk to aquatic wildlife, in addition to having a known carcinogenic content. Major manufacturers UK of extinguishers such as Chubb and Thomas Glover have not used PFOS in their foam fire extinguishers since 2001.

3m’s Lightwater was the world’s most popular fire fighting foam but production was stopped long ago.

Chrome Aqueous Film Forming Foam Fire Extinguishers

AFFF fire extinguishers are also available in chrome, for when “red will so clash with the decor, darling!” Chrome finish fire extinguishers of any type are not BS EN3 certificated, as they are not painted red.

However, from the quality manufacturers such as Chubb Fire, Thomas Glover and Amerex, they still feature all the required safety instructions, and CE mark and use the same components as their red versions.

Dry Powder Extinguishers

Dry powder fire extinguishers are excellent all-round fire extinguishers, often recommended for use on vehicles and in the home. All powder fire extinguishers are red with a blue panel, are either ABC or BC rated and are safe to be used on fires involving electrical equipment. (Remember to look for the electrical safety pictogram.)

Dry powder extinguishers are not suitable for use in enclosed spaces such as offices, hotels, schools, etc, as the fire-fighting agent creates a cloud that can obscure vision. The contents may also create breathing problems.

How Dry Powder Fire Extinguishers Work

Dry powder fire extinguishers contain an extinguishing agent, which is propelled out of the extinguisher body by a compressed, non-flammable gas. The agent forms a ‘blanket’ over the fire, smothering it and preventing re-ignition. All used powder residue must be cleaned away and properly disposed of once the fire is extinguished.

Sodium bicarbonate is an effective fire extinguishing agent as it decomposes at 158 degrees F, releasing CO2 which starves the fire of oxygen.

There Are Three Main Types Of Dry Powder Extinguishers

  1. ABC rated or multi-purpose powder, which contain ammonium phosphate
  2. BC rated extinguishers, containing potassium bicarbonate or sodium bicarbonate (otherwise known as bicarbonate of soda or baking soda!) Some BC rated powder fire extinguishers contain Monnex. The pressurising gas is usually nitrogen
  3. A and D rated graphite powder fire extinguishers are usually used only in Class D fires

Both types of non-graphite dry powder extinguisher are potentially corrosive to soft metal such as aluminium, and can also be abrasive when sprayed.

Dry Powder Extinguishers and Water

Unfortunately, the additional benefit of ABC rated dry powder fire extinguishers being able to tackle flammable gas fires also has a major drawback. Ammonium phosphate can react with any water present to form phosphoric acid, which is corrosive and can seep into even the slightest cracks in equipment.

For this reason, dry chemical ABC rated fire extinguishers should not be used on sensitive electrical equipment such as computers, switch installations, scientific instruments or aircraft, if other fire extinguishing options are available.

Left in place, powder will draw moisture from the air and a common example of corrosion will be the chrome on tools being replaced with rust.

In the event of an emergency when only a dry powder fire extinguisher is available, however, always remember that electrical equipment can be replaced, a human life cannot. If in doubt, get out, stay out and call the fire brigade immediately.

Monnex Dry Powder Fire Extinguishers

Invented by ICI, Monnex powder is the most effective dry powder you can get. A 9kg Monnex fire extinguisher is ideal for situations where flames must be extinguished as quickly as possible.

You’ll find Monnex dry powder fire extinguishers at airports, fuel depots, on oils rigs, in flammable liquid stores, at motor racing tracks and at other high-octane fuelled locations. Proper training is recommended for effective use of this type of powder fire extinguisher.

Water Additive Extinguishers

Chemical additives can radically increase the effectiveness of a water fire extinguisher by up to 300%, as well as reducing the size of extinguisher required. Water additive fire extinguishers, often referred to by Chubb Fire’s brand name of Hydrospray, are smaller and lighter than standard water fire extinguishers.

A 3 litre Hydrospray Elite extinguisher matches the 13A rating of an ordinary 9 litre water extinguisher and, if you have ever picked up a 9 litre extinguisher, you’ll understand the benefit. A 6 litre water additive will normally have a 21A rating. As premises need a minimum of 13A, these have become extremely popular.

Water additive extinguishers are still solid red in colour, and bear the usual rating and safety marks.


How Water Additive Fire Extinguishers Work

The additives work by removing water’s natural surface tension, making the water ‘wetter’ or ‘stickier’, so it adheres to and soaks into the burning materials more effectively. Can you remember school chemistry experiments with water tension and then adding detergent to break the tension down?

The additive extinguishers also has a special spray nozzle attached that atomizes water and spreads it in a more effective arc than a conventional nozzle. In addition, the nozzle enables safe use in the vicinty of (but not directly on) electrical equipment. They will have passed the BSi 35,000V dielectric test to BSEN3-7:2004, just in case.

What’s Special About a Hydrospray Fire Extinguisher?

Since ‘Hydrospray’ fire extinguishers operate at a higher pressure than standard water fire extinguishers (15bars), they are available in smaller, high grade steel cylinders of 3 litre and 6 litre capacity.

This makes them much easier to handle and lighter to lift, and with a modern external coating of epoxy polyester, they are also scuff and dirt resistant. Inside, the cylinder is lined with polyethylene to prevent the inside of the fire extinguisher corroding.

The 3 litre version weighs just 5.5kgs, yet easily equals its 9 litre water-only equivalent’s 13A rating. The 6 litre weighs 10kg and earns a 21A fire rating, thanks to its increased efficiency. A standard 9 litre version tops the scales at 15kg.

Water and Electricity

Water conducts electricity, so non-additive water should never be used near exposed live electricity cables. High quality water additive nozzles have passed the 35kv conductivity test, so can be used with minimal risk near (but never directly on) electrical equipment.

For the best protection in an office or retail environment, water additive extinguishers are usually provided alongside a CO2 fire extinguisher to make the best combination.

Water Additive on non-Class A Fires

These modern marvels should only be used on Class A fires, although unlike the simple water extinguishers, they have a safety nozzle. Both types of water fire extinguisher, however, are actually more dangerous if used on other classes of fires.

The jet of water will, for example, simply spread a Class B fire of flammable liquids over a larger area, whilst the same action will scatter the burning metals of a Class D fires, causing more fires to erupt. Equally, never use any extinguisher other than wet chemical on a Class F fire, as this is extremely dangerous.

What’s In a Name?

Once Chubb Fire has devised and effectively marketed their Hydrospray and Hydrospray Elite, other manufacturers came out with similar models so you may find a TurboSpray, AquaPlus, WaterPlus, Ecojet and other wacky names.

Water Extinguishers

Water remains one of the most effective fire-extinguishing agents we have, from the humble fire bucket to today’s more sophisticated water fire extinguishers.

Water extinguishers should only be used where they work best, on Class A fires, sometimes called ordinary combustible fires. Paper, wood, fabrics, furniture, indeed most things you’ll have stored in your home or office, will provide the fuel for a Class A fire.

A water fire extinguisher is solid red in colour, unless your premises have invested in designer stainless steel extinguishers for a better look. (These are just as effective as their bright red counterparts, but are not BS EN3 certificated, simply because they are not painted red.) Water untis have a hose and nozzle attached, so you can direct a jet of water at the base of the fire.

How Water Fire Extinguishers Work

Water works in two ways, by both extinguishing the flames and soaking the materials in the fire, cooling them down and preventing them from burning any further. (As any Boy Scout will tell you, wet wood won’t burn!)

Most water fire extinguishers are 13A rated (with 21A being better), as they have a limited fire fighting capacity. They also are heavy to handle, as the standard size contains 9 litres of water and weighs 15kgs.

Why Use Water Extinguishers?

Water extinguishers are simple to use, and their contents are neither harmful to people or damaging to the environment. If one is set off accidentally, all you get is a large puddle of water, so you will often see these in schools (usually secured by anti-tamper seals or covers to keep away prying fingers…).

Water and Electricity

Water conducts electricity, so water fire extinguishers should never be used in a situation where there are exposed live electricity cables, or a danger of wiring becoming exposed during a fire. They are best paired with another that is suitable for use on electrical equipment fires, such as a CO2.

Water Extinguishers and Other Classes of Fires

Water is only suitable for Class A fires, as they can do more harm than good on other classes of fires. For example, in a Class B fire involving flammable liquids, the water will simply spread the burning liquid over a larger area rather than extinguish it. On a Class D fire, the spray action will simply blow the burning metal into a wider area, and probably cause it to spark more in the process.

Water additives

The efficiency and effectiveness of a humble water fire extinguisher can be radically improved with additives. See our page on water additive fire extinguishers for more details.

CO2 Fire Extinguishers

CO2 fire extinguishers (carbon dioxide) are the only fire extinguisher recommended for fires involving electrical equipment. CO2 is safe to use on and around electrical equipment, as the gas itself is non-conductive, and once used, there is no sticky foam or messy powder left behind. They are also effective on Class B fires (flammable liquids).

Carbon dioxide fire extinguishers are painted bright red with a black panel above the operating instructions. They have a distinctive horn-shaped nozzle at the side on the smaller models with 5kgs and above having a hose and horn.

Extinguishers of 9kgs or higher are available but tend to come mounted onto a wheeled trolley as they will be far too heavy to be carried safely. It is possible to find 45kg twin cylinder wheeled units for offshore or airport use.

How Carbon Dioxide Fire Extinguishers Work

CO2 extinguishers stores carbon dioxide gas under great pressure (55 bar or 825psi), where the gas becomes a liquid. When you operate the fire extinguisher levers, the pressure is released, the CO2 pressure is reduced by the diffuser (horn) and expands back into a gas, rapidly cooling the surrounding air.

This process is so fast, it can cause ice to form on the horn, so never hold a CO2 fire extinguisher by the horn to avoid freezing your skin. To be most effective, a carbon dioxide fire extinguisher should be used no closer than 3 feet and no further than 8 feet from the fire itself.

For the UK, they are commonly made in two sizes, 2kg and 5kg. The compressed gas required an extremely thick cylinder so many buyers prefer super-strong aluminium rather than heavier steel models, so that their staff can lift and use the CO2 extinguishers more easily. Steel is normally used for marine extinguishers although many of the cheap imports are made from steel.

The 2kg models tend to have a swivel horn, which must not be held during operation to avoid freezing your hands. The 5kg models usually feature a hose with the horn attached with the horn normally having a handle.

CO2 Fire Extinguishers and Electricity

CO2 fire extinguishers are safe to use on fires in, on or around electrical equipment and live cables. CO2 gas is dry, inert in air, and leaves behind no residue that will affect electrical equipment’s future operation. So, you will often find a CO2 fire extinguisher next to precious electrical equipment, from switchgear to mobile discos.

In most office, workplace, factory or warehouse situations, the best combination is to have a water additive or foam unit alongside your CO2 extinguisher, for maximum fire fighting ability.

Carbon Dioxide Fire Extinguishers and Other Fire Classes

CO2 fire extinguishers should not be used on Class D fires, involving flammable metals. The CO2 gas reacts with many volatile metals, and as with other non-D rated extinguishers, can also blow burning metal over a wide area, making the situation worse. And it is not affective on Class A fires such as paper, wood or cloth.

Carbon Dioxide Fire Extinguisher Pressure Gauges

CO2 fire extinguishers do not have pressure gauges, as the gas is condensed in the cylinder. The only way to assess if a CO2 fire extinguisher is empty is to weigh it. The gross weight (G W) is stamped into the meatl of the cylinder shoulder with other information. To assess how full your CO2 fire extinguisher is, weigh it (without the swivel horn) and compare this to the stamped gross weight.

However, rather than take the risk of a part-used fire extinguisher, or have the expense of a call-out visit and factory refilling or service exchange, it is often more cost effective to replace a used CO2 fire extinguisher with a new one. Expert firms or your local Civic Amenity Centre (the local dump) will be happy to recycle your old CO2 fire extinguisher.

Chrome CO2 Fire Extinguishers

CO2 fire extinguishers are also available in a smart “chrome” finish – highly polished aluminium, in fact. The combination of jet-black printing and shiny metal gives a CO2 chrome fire extinguisher a true designer look, without compromising your fire safety in any way.

Chrome fire extinguishers are not BS EN3 certificated, as they are not painted red, but will still have the required usage instructions, coloured panel, quality marks, etc.