Fire extinguisher classes

Extinguishers should be regularly inspected to ensure they are in good working order. Guidelines state that extinguishers are to be tested and inspected by a competent technician at least once every 12 months.

There are five common types of fire extinguishers, each of which will put out specific classes of fire. They use a labelling system with pictures to show the type of fire for which they may be used. Class A, B, and F fire extinguishers also have a numerical rating related to tests conducted using Australian Standards test criteria reference AS/NZS 1850 by third party test authorities. The rating indicatted the extinguishing potential for each size and type of extinguisher.

Class A Extinguishers

Class A extinguishers will put out fires in ordinary combustibles like wood, paper, cardboard and most plastics. The rating indicated the amount of water contained in the extinguisher and the amount of fire it will extinguish.

Class B Extinguishers

Class B extinguishers are appropriate for fires involving flammable liquids such as kerosene, grease, petrol, oil etc. The rating for this class of extinguisher indicated the approximate number of square meters of burning flammable liquid a non-expert can expect to extinguish.

Class C Extinguishers

Class C extinguishers are suitable for fires arising from gas pressure vessels such as LPG cylinders and gas stoves. This class of extinguisher doesn’t usually have a numerical rating but the presence of the letter ‘C’ indicated the extinguishing medium is suitable for use on Class C gas risks.

Class D Extinguishers

Class D extinguishers are commonly found in chemical laboratories, automotive and aircraft industry workshop environments. They are designed to be used for flammable metal fires e.g. magnesium, titanium, potassium and sodium – and they are often specific for a given type of metal. This type of extinguisher has no picture designator and no rating number. They are not given a multi-purpose rating for use on other types of fires as they are designed for Class D fires only.

Class E Extinguishers

Class E extinguishers are rated for use with energized electrical equipment such as industrial switchgear and high voltage machinery. Often extinguishers with a Class E rating will also be rated for other classified risks, i.e. A, B, and E for Dry Powder Extinguishers and B and E for CO2 extinguishers.

Class F Extinguishers

Class F extinguishers are specifically designed and rated for use with deep fryer oils. These oils are often difficult to contain due to the potential of fire spread on discharge. The rating number gives specific reference to the deep fryer size it should be used on i.e. 3F and 4F ratings are the common industry standard requirements. Fire blankets can also be used on smaller oil fires encountered in domestic home environments and commercial kitchens.

Types of fire extinguishers

It’s always important to know what type of fire extinguisher you are using and what type of fire it can safely be used for. Using the wrong type of extinguisher to fight a fire can be dangerous and even life-threatening.

Dry Chemical

Dry chemical extinguishers come in a variety of types and are usually rated for A, B and E Class use. They contain a dry chemical extinguishing agent (powder) with a compressed non-flammable gas (nitrogen) as propellant. The key advantage of the dry chemical type of extinguisher is that it leaves a coating of non-flammable substance on the extinguished material, reducing the likelihood of re-ignition. BE is the regular type of dry chemical extinguisher. It is filled with sodium bicarbonate or potassium bicarbonate, which leaves a mildly corrosive residue. This must be cleaned up immediately after use to prevent damage. ABE is the multipurpose type of dry chemical extinguisher. It is filled with monoammonium phosphate, a yellow powder that leaves a sticky residue that may be damaging to electrical appliances such as computers or analytical instruments, so this factor should be taken into consideration when selecting appropriate fire extinguishers for the workplace.

Water

Air Pressurised Water (APW) extinguishers contain water and compressed gas (pressurized air or gas). They are suitable only for Class A (ordinary combustibles) fires. NEVER use a water extinguisher on grease fires, electrical fires or Class D fires – it will make the flames spread and the fire will end up bigger! Only use a water extinguisher if you are certain the fire contains only ordinary combustible materials (i.e. paper, cardboard, plastics).

Carbon Dioxide

Carbon dioxide (CO2) extinguishers are most effective on Class B and E fires (burning liquids and electrical fires). The carbon dioxide is stored as a highly pressurized compressed liquid in the extinguisher. The gas disperses quickly, so these extinguishers are only effective from about one to two metres. As the compressed liquid CO2 expands, it cools the surrounding air, often causing dry ice to shoot out of the nozzle and form around the dispensing nozzle. CO2 extinguishers are best for use on sensitive electronic equipment. Unlike dry powder extinguishers they do not leave any damaging residue. CO2 extinguishers don’t work well on Class A fires because they may not displace enough oxygen to put out the fire completely and the fire can re-ignite. To avoid the fire re-igniting, continue to apply the CO2 extinguisher even after the fire appears to be out.

Foam

Foam extinguishers are most effective on A and B Class fires. These extinguishers combine compressed air with Aqueous Film Forming Foam (AFFF) to create a sealing foam blanket over B Class risks such as fuels, spirits and oils. A competent operator often achieves total containment as the foam blanket has a high burn-back resistance, effectively sealing off the vapour from the ignition source. Also able to be used on A Class ordinary combustibles, this type of unit is most commonly used around Dangerous Goods type locations with volatile hydrocarbons and oils, i.e. service station forecourts and industrial storage sites.

Wet Chemical

Wet Chemical extinguishers are designed for use on commercial deep fat fryers found in the fast food and hospitality industries. With a competent operator the wet chemical agent discharges at a controlled rate removing the risk of a violent reaction. Forming a blanket of agent it smothers the fuel source from oxygen and starves the fire.

Selecting and using the right fire extingusiher

To ensure the right type of fire extinguisher is available, determine what flammable materials are in use in a given area and what type of extinguisher is required for each. For example, in an office where paper is the main fire hazard a Class A (water) fire extinguisher may be appropriate. But if there are various types of combustible materials, it may be preferable to select an ABE rated extinguisher to cover the range. Always read the manufacturer’s instructions for each type of fire extinguisher and become familiar with its parts and workings in advance. A typical fire extinguisher only has about 10 seconds of extinguishing power, so it is important to know what to do before you set out to use it. In addition, a partially discharged fire extinguisher will have reduced capacity, so it is important to check extinguishers regularly and maintain them at their full capacity. Fire prevention experts recommend hands-on training before operating a fire extinguisher. Fire extinguisher service companies or trade training companies may provide this service.

Extinguisher location

Extinguishers should always be located in an easily accessible location that is not likely to be blocked in the case of an emergency. NZ Standards state that they should be mounted on a wall bracket between 100mm and 1200mm above the ground. If particular fire hazards exist, extinguishers should be located nearby, but not so close that in the event of a fire they would not be safely accessible.

Vehicle extinguisher requirements

It is recommended that all motor vehicles carry fire extinguishers. The standard model required for an average size car would be a 1kg ABE extinguisher. For larger vehicles a 1.5kg or 2.3kg ABE extinguisher should be used. Different types and sizes of extinguisher may be necessary if hazardous material is being carried on board. Refer to the extinguisher type chart on page 322 of the NZ Safety catalogue to identify the type of extinguisher required for different hazardous materials. Vehicle extinguishers should always be securely mounted on a bracket. An unsecured extinguisher could become a dangerous projectile in the event of the vehicle stopping suddenly.