Classification of Fire – Understanding Different Types of Fire (Based on International Standards)
Introduction
Fire is a rapid chemical reaction that releases heat, light, smoke, and gases. It occurs when fuel, oxygen, and heat combine in the right proportions — commonly known as the fire triangle.
To control and prevent fire effectively, we must first understand what type of fire we are dealing with. That’s why international bodies like NFPA (USA), EN (Europe), and ISO have developed fire classification systems.
Correctly identifying fire classes is essential because using the wrong extinguisher can worsen the fire and even endanger lives.
This guide explains:
- 🔹 The fire triangle and fire tetrahedron
- 🔹 International fire classification systems (NFPA, EN, ISO, AS)
- 🔹 Detailed breakdown of fire classes A, B, C, D, K/F
- 🔹 The right extinguishing agents for each class
- 🔹 Fire safety tips and regulatory standards
The Fire Triangle & Fire Tetrahedron
1. Fire Triangle (3 Elements)
- Fuel – Wood, paper, gas, oil, metals, etc.
- Oxygen – At least 16% in the air is needed for fire.
- Heat – Ignition temperature varies by fuel.
Remove any of these, and the fire will go out.
2. Fire Tetrahedron (4 Elements)
Modern science adds a fourth element — the chemical chain reaction.
- Fire can self-sustain unless this chain reaction is broken.
- Dry chemical powders work by disrupting this reaction.
👉 This concept helps explain why some extinguishers are more effective than others.
International Standards for Fire Classification
| Region | Standard | Fire Classes Used | Notes |
|---|---|---|---|
| USA | NFPA 10 | A, B, C, D, K | Class K = Kitchen fires |
| Europe | EN 2 | A, B, C, D, F | Class F = Kitchen fires |
| Australia | AS 1841.5 | Similar to EN | Recognizes Class F |
| Global (ISO) | ISO 3941 | Solid, liquid, gas-based | Broader system |
👉 Key Difference:
- USA → “K” for kitchen fires
- Europe → “F” for kitchen fires
Fire Classes Explained
1. Class A Fires – Ordinary Combustibles
Characteristics:
- Fuel: Wood, cloth, paper, plastics, rubber
- Leaves ash and embers after burning
- Most common in homes and offices
Extinguishing Agents:
- ✅ Water – Removes heat
- ✅ Foam – Smothers flames
- ✅ ABC Dry Powder – Interrupts chain reaction
Examples:
- House fire involving furniture
- Forest fire spreading through dry grass
2. Class B Fires – Flammable Liquids and Gases
Characteristics:
- Fuel: Gasoline, diesel, alcohol, paints, propane, butane
- Spread rapidly, producing black smoke
- Explosive risk indoors
Extinguishing Agents:
- ✅ Foam – Prevents oxygen contact
- ✅ CO₂ – Displaces oxygen, cools surface
- ✅ Dry Powder (BC/ABC) – Breaks chain reaction
Examples:
- Petrol station fire
- Chemical plant solvent fire
👉 Related: Types of Fire Extinguishers and Their Uses
3. Class C Fires – Electrical Fires
Characteristics:
- Involve energized electrical equipment (wires, appliances, panels)
- High shock hazard if water is used
Extinguishing Agents:
- ✅ CO₂ – Non-conductive, leaves no residue
- ✅ Dry Powder – Safe for live equipment
- ❌ Never use water
Examples:
- Short circuit in a distribution panel
- Fire from overheated computers or machinery
4. Class D Fires – Combustible Metals
Characteristics:
- Involve reactive metals: Magnesium, titanium, sodium, potassium
- Burn at extreme temperatures
- Water = violent explosion
Extinguishing Agents:
- ✅ Class D Dry Powder (sodium chloride, graphite)
- ✅ Sand in small lab fires
- ❌ Water & foam are dangerous
Examples:
- Magnesium wheel rim fire in automotive plants
- Sodium spill in a laboratory
5. Class K (USA) / Class F (Europe) – Cooking Oils & Fats
Characteristics:
- Involve high-temp oils and grease (deep fryers, commercial kitchens)
- Can reignite if not cooled properly
- Leading cause of restaurant fires
Extinguishing Agents:
- ✅ Wet Chemical (potassium acetate) – Forms a soapy layer
- ✅ Fire Blanket – For pan fires
- ❌ Water – Causes oil to splash and spread fire
Examples:
- Grease fire on a stove
- Deep fryer fire in fast food outlets
6. Electrical Fires – Sometimes Separate
- Some standards classify under Class C, others treat separately.
- Rule: Always disconnect power supply first.
- Use only non-conductive extinguishers.
Fire Extinguishers & Fire Classes
| Extinguisher Type | Works On | Do Not Use On |
|---|---|---|
| Water | Class A | B, C, D, K/F |
| Foam | A, B | C, D |
| CO₂ | B, C | A (ineffective), K/F |
| Dry Powder (ABC) | A, B, C | D (special powder needed), K/F |
| Wet Chemical | K/F | Other classes |
| Class D Powder | D | All others |
👉 OSHA (29 CFR 1910.157) requires workplaces to have appropriate extinguishers based on hazards.
Fire Prevention & Safety Tips
- Install smoke alarms in homes & offices
- Train staff in fire extinguisher use (PASS method)
- Store fuels & chemicals properly
- Maintain electrical wiring regularly
- Conduct monthly fire drills at home/workplace
- Ensure kitchen safety training for staff
Conclusion
Understanding fire classification is not just theory — it saves lives.
- 🔹 Class A → solids
- 🔹 Class B → liquids/gases
- 🔹 Class C → electrical
- 🔹 Class D → metals
- 🔹 Class K/F → cooking oils
By applying the correct extinguishing method for each fire type, accidents can be controlled quickly and safely.
👉 Whether at home, in a commercial kitchen, or in an industrial plant — knowing fire classes = being prepared.
External Link: OSHA Fire Extinguisher Standard 1910.157
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Electrical Safety Toolbox Talk – Preventing Shocks, Fires, and Accidents
FAQs
Q1: Which standard is followed in the EU vs USA?
- EU → EN 2 (A, B, C, D, F)
- USA → NFPA 10 (A, B, C, D, K)
Q2: Can an ABC extinguisher put out all fires?
No — it doesn’t work for metal fires (D) or cooking oil fires (K/F).
Q3: Why shouldn’t water be used on grease or electrical fires?
Because it either spreads oil or conducts electricity, worsening the hazard.
Q4: Is Class K the same as Class F?
Yes — K (USA) and F (Europe) both refer to cooking oil/fat fires.
Q5: What’s the OSHA requirement for extinguishers?
OSHA requires accessible, properly rated extinguishers in workplaces, based on fire risks.
