When a fire breaks out, instinct might tell you to grab the nearest fire extinguisher and start spraying. But using the wrong type of extinguisher can quickly turn a manageable situation into a dangerous one.
Fire extinguishers are colour-coded and classified for good reason; each is designed to deal with specific types of fires. In the UK, guidance is governed by BS 5306-8, which sets out the correct extinguisher use for various fire classes.
This article explores the real-world consequences of using the wrong extinguisher, including risks to life, property, and legal compliance, and how to ensure your extinguishers are correctly matched to your environment.
Fire Classes at a Glance
Understanding the basics helps make sense of extinguisher choices:
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Class A: Solid combustibles (wood, paper, textiles)
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Class B: Flammable liquids (petrol, paint, solvents)
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Class C: Flammable gases (butane, propane)
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Class D: Combustible metals (magnesium, aluminium)
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Class F: Cooking oils and fats (deep fat fryers)
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Electrical: Not a class, but a risk factor in live electrical fires
Common Fire Extinguisher Mistakes and Their Consequences
Here’s what can happen when an extinguisher is used incorrectly:
1. Water on an Electrical Fire
Why it’s dangerous:
Water conducts electricity. Spraying it onto a live electrical fire can cause a serious electric shock to the user and potentially spread the fire further.
Real-world risk:
Attempting to extinguish a sparking electrical socket or server cabinet with a water extinguisher could result in electrocution and system failure.
What to use instead:
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CO₂ extinguisher (black label): Non-conductive and leaves no residue
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Dry powder (blue label): Suitable but messier — only in well-ventilated areas
2. Powder Extinguisher in a Confined Space
Why it’s dangerous:
While effective on multiple fire types, dry powder displaces oxygen and creates dust clouds, which can impair visibility and breathing.
Real-world risk:
In a small office or plant room, deploying a powder extinguisher could cause respiratory issues for staff, obscure escape routes, and even result in inhalation-related injuries.
What to use instead:
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CO₂ extinguisher for electrical
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Foam or water mist for Class A and B fires in small areas
3. Foam on Flammable Metals
Why it’s dangerous:
Foam or water can react violently with metals like magnesium or aluminium, intensifying the fire or causing explosive reactions.
Real-world risk:
In manufacturing or engineering workshops, this mistake could lead to sudden flare-ups or shrapnel from rapid metal reactions.
What to use instead:
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Class D dry powder extinguisher designed specifically for metal fires
4. CO₂ in Kitchens with Deep Fat Fryers
Why it’s dangerous:
CO₂ can disturb the surface of hot oil, causing splashing and flare-ups. It’s also ineffective at cooling oil to prevent re-ignition.
Real-world risk:
In commercial kitchens, using CO₂ on a pan fire can spread burning oil and cause burns.
What to use instead:
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Wet chemical extinguisher (yellow label): The only safe option for Class F fires
5. No Extinguisher at All, or the Wrong Type Nearby
Why it’s dangerous:
Even with training, the wrong extinguisher on hand is useless when seconds count.
Real-world risk:
If the nearest extinguisher in a warehouse is water, but the fire is electrical, staff might freeze, misuse it, or delay response.
Solution:
Conduct a proper fire risk assessment and ensure correct placement and signage for all extinguishers.
How to Avoid Extinguisher Misuse
1. Know your fire classes
Every business should train staff in the types of fire risks present and which extinguishers are appropriate.
2. Use clear labelling and signage
UK extinguishers are colour-coded and should have signage indicating what they’re for and not for.
3. Don’t over-rely on multi-purpose extinguishers
While some are rated for multiple fire classes (like ABC powder), they’re not always suitable in every location.
4. Carry out regular fire risk assessments
This ensures your fire protection matches the current layout, usage, and hazards of the premises.
5. Provide hands-on fire extinguisher training
Knowing how to use a fire extinguisher is just as important as knowing which one to pick up.
A Quick Extinguisher Match Guide
| Fire Type | Use This Extinguisher |
|---|---|
| Electrical | CO₂ (black) or Dry Powder (blue) |
| Office/Combustibles | Water (red) or Foam (cream) |
| Flammable liquids | Foam or Powder |
| Cooking oils/fats | Wet Chemical (yellow) |
| Combustible metals | Specialist Dry Powder |
Final Thoughts
Using the wrong fire extinguisher can put lives at risk, worsen the fire, and even cause serious legal consequences if your fire safety measures are found to be non-compliant.
The right choice depends on your environment, and that means conducting regular fire risk assessments, stocking the correct types of extinguishers, and ensuring staff know how and when to use them.
For expert advice on fire protection and prevention measures, contact Martyn Young Fireproofing Consultancy on 07585 896648