An extinguisher rating is a standardized classification system that indicates the type of fire a fire extinguisher can combat and its extinguishing potential. This rating is crucial for ensuring the correct fire extinguisher is used for a specific fire, maximizing safety and effectiveness.
Every fire extinguisher carries a rating, typically found on its label, composed of a letter and often a number. The letter corresponds to the class or type of fire the extinguisher is designed to put out, while the number, if present, correlates to the extinguishing potential or size of fire it can handle.
Understanding the Fire Classes (Letters)
The letter on an extinguisher rating indicates the specific category of combustible material it is effective against. Using the wrong type of extinguisher can be ineffective or even dangerous.
Here are the primary fire classes:
| Fire Class | Type of Combustible Material | Examples | Extinguisher Symbol |
|---|---|---|---|
| Class A | Ordinary combustible materials that leave an ash. | Wood, paper, cloth, rubber, many plastics, trash | Triangle (Green) |
| Class B | Flammable liquids and gases. | Gasoline, oil, paint, propane, natural gas, solvents | Square (Red) |
| Class C | Energized electrical equipment. | Appliances, wiring, circuit breakers, motors | Circle (Blue) |
| Class D | Combustible metals. | Magnesium, titanium, potassium, sodium, lithium | Star (Yellow) |
| Class K | Cooking oils and fats (specifically in commercial kitchens). | Vegetable oils, animal fats (e.g., deep fat fryers) | Hexagon (Black) |
Deciphering Extinguishing Potential (Numbers)
The number preceding the "A" or "B" in an extinguisher rating indicates its capacity to extinguish a fire of a specific size under test conditions.
- For Class A Fires (e.g., 2A, 4A): The number represents the equivalent amount of water the extinguisher holds or its extinguishing capacity compared to a standard 1.25-gallon water extinguisher. For example, a "2A" rating means it has the equivalent extinguishing capability of 2.5 gallons of water (2 x 1.25 gallons). A higher number indicates a larger extinguishing capacity for ordinary combustibles.
- For Class B Fires (e.g., 10B, 20B): The number indicates the approximate square footage of a flammable liquid fire that the extinguisher can put out. For instance, a "10B" rating means the extinguisher can extinguish a 10 square foot Class B fire. A larger number signifies a greater capacity to suppress flammable liquid fires.
- For Class C, D, and K Fires: These ratings typically do not have a preceding number. This is because the effectiveness of extinguishers for these classes is not measured by size or volume but by their ability to interrupt the specific chemical reaction (Class C for electrical, D for metals, K for cooking oils). The "C" rating simply means it is safe and effective on electrical fires; the "D" means it's suitable for combustible metals; and "K" indicates its specific use for cooking media.
Examples of Extinguisher Ratings
Many fire extinguishers are multi-purpose, meaning they are rated for more than one class of fire. Here are some common examples:
- 2A:10B:C: This is a very common multi-purpose dry chemical extinguisher.
- "2A" means it can handle Class A fires equivalent to 2.5 gallons of water.
- "10B" means it can extinguish a Class B fire up to 10 square feet.
- "C" means it is safe and effective to use on energized electrical equipment.
- 10B:C: This might be a CO2 or Halotron extinguisher, effective on flammable liquids and electrical fires, but not ordinary combustibles.
- K: A dedicated wet chemical extinguisher specifically for commercial kitchen fires involving cooking oils and fats.
Importance of Proper Extinguisher Selection
Choosing the correct fire extinguisher based on its rating is paramount for effective fire suppression and safety. Using an inappropriate extinguisher can:
- Be ineffective: A water extinguisher on a grease fire (Class B) could spread the fire.
- Be dangerous: Using a conductive extinguisher (like water) on an electrical fire (Class C) can lead to electrocution.
- Cause damage: Certain extinguishing agents can damage sensitive equipment.
Knowing the fire risks in a specific environment—whether it's a home, office, workshop, or commercial kitchen—is the first step in selecting the correctly rated fire extinguishers. Regular maintenance and proper training on how to use them are also vital components of fire safety.
