Classes of Fire Explained Simply
What puts out one fire can make another explode. Understanding the classes of fire is the simplest way to make sure you reach for the right extinguisher — and avoid a dangerous one.
Why fires are sorted into classes
Not all fires are the same, and what puts one out can make another far worse. To keep things clear and safe, fires are grouped into classes based on the type of fuel that is burning. Knowing the class tells you which extinguisher is suitable and which to avoid — knowledge that can prevent a small incident turning into a serious injury.
This classification follows the joint standard AS/NZS 1850 and underpins the colour coding on portable extinguishers used across New Zealand. Helping staff understand fire classes supports the wider fire safety duties set out in the Health and Safety at Work Act 2015, enforced by WorkSafe New Zealand.
The class of fire is decided by one question: what is actually burning? Get that right and choosing the correct response becomes much simpler.
The classes of fire
Class A — ordinary combustibles
Fires involving solid materials such as wood, paper, cardboard, textiles and most plastics. These are the most common workplace fires and are typically tackled with water or foam extinguishers.
Class B — flammable liquids
Fires involving liquids such as petrol, diesel, oils, paints and solvents. Foam, CO2 or dry powder extinguishers are generally suitable. Water must not be used, as it can spread the burning liquid.
Class C — flammable gases
Fires involving gases such as propane, butane or natural gas. The safest action is usually to isolate the gas supply if it is safe to do so. Dry powder extinguishers may be appropriate, but a gas fire should be treated with great caution.
Class D — combustible metals
Fires involving metals such as magnesium, aluminium swarf or sodium. These need specialist dry powder extinguishers designed for metals; ordinary extinguishers can react violently.
Class F — cooking oils and fats
Fires involving cooking oils and fats, most often in kitchens. These require wet chemical extinguishers. Never use water, which can cause a dangerous explosion of burning fat.
Electrical fires
Fires involving energised electrical equipment — power boards, computers and other powered equipment — are commonly classed as Class E in New Zealand. They need a CO₂ or dry powder extinguisher; water and foam conduct electricity and must not be used until the power is isolated.
Key takeaways
- Fires are classed by fuel: A solids, B liquids, C gases, D metals, F cooking oils.
- Class E (energised electrical equipment) fires need CO₂ or dry powder, never water or foam.
- Water on liquid, oil or live electrical fires can be extremely dangerous.
- Extinguisher colour codes map directly to these classes.
- Knowing the class is the first step to choosing a safe response.
Putting it into practice
Understanding fire classes is not an academic exercise — it directly affects how your workplace is equipped. Your fire risk assessment should identify which classes are realistically possible in each area, so the right extinguishers are provided where they are needed. A kitchen needs wet chemical units; a server room needs CO2; a general office is mostly Class A.
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From knowledge to safe action
Once staff know the classes, the next step is being able to act safely. That means recognising which extinguisher to reach for, using it correctly, and — crucially — knowing when a fire is too large to fight and it is time to evacuate. Training brings these together so people are not making life-or-death choices for the first time during a real emergency.
Why colour coding helps
To make the right choice quick and obvious, extinguishers in New Zealand follow AS/NZS 1850 and share a common red body with a coloured band or label that identifies their contents: blue for foam, black for CO₂, white for dry powder and oatmeal for wet chemical. Learning to read these colours at a glance means staff can grab the correct unit even under pressure.
It is worth walking your team around the building so they know which extinguishers are where and which classes of fire each area is most likely to face. Pairing that local knowledge with an understanding of the fire classes turns abstract theory into fast, confident action.
