Portable Fire Extinguisher Training (OSHA-Compliant Online Courses)

Helpful Information About How Different Types of Fire Extinguishers Work

Portable fire extinguishers put out fires by removing one or more elements of the fire triangle: heat, fuel, or oxygen. Here’s how the main types work:

1. Water (Class A) Extinguishers

   • How it Works: Cools the burning material by absorbing heat and reducing the temperature below the combustion point.

   • Effective On: Ordinary combustibles like wood, paper, cloth (Class A fires).

   • Not for: Electrical or flammable liquid fires, as water conducts electricity and can spread burning fuel.

2. Carbon Dioxide (CO₂) Extinguishers

   • How it Works: Replaces oxygen around the fire with CO₂, smothering the flames. Also cools the fire due to CO₂ expanding rapidly when released.

   • Effective On: Flammable liquids (Class B) and electrical fires (Class C).

   • Not for: Ordinary combustibles (Class A), as fire can reignite once the CO₂ dissipates.

3. Dry Chemical Extinguishers (ABC or BC)

   • How it Works: Releases a fine powder (usually monoammonium phosphate or sodium bicarbonate) that coats the fuel, interrupts the chemical reaction, and smothers flames.

   • Types:

     • ABC Dry Chemical – Works on Class A, B, and C fires.

     • BC Dry Chemical – Works on Class B and C fires only (not effective on Class A materials).

   • Not for: Confined spaces, as the powder can impair breathing and visibility.

4. Class D (Metal Fire) Extinguishers

   • How it Works: Uses dry powder (like sodium chloride or graphite) that smothers the burning metal by forming a crust over it, blocking oxygen.

   • Effective On: Burning metals like magnesium, titanium, or sodium.

   • Not for: Any other fire types, as the powder is designed specifically for metals.

5. Wet Chemical (Class K) Extinguishers

   • How it Works: Releases a potassium-based solution that cools the fire and reacts with burning cooking oils or fats to create a soapy layer that smothers flames.

   • Effective On: Kitchen fires involving grease (Class K).

   • Not for: Electrical or flammable liquid fires.

Helpful Information to Help You Understand Fire Extinguisher Numbers and Ratings

Fire extinguisher size and effectiveness are identified by numbers in their designation (e.g., 5A:10B:C or 20B:C). Here’s what they mean:

1. Class A Ratings (2A, 5A, 10A, etc.)

• The number represents the equivalent amount of water the extinguisher holds.

• 1A = Equivalent to 1.25 gallons of water.

• 2A = 2.5 gallons of water, 5A = 6.25 gallons, and so on.

• A higher A rating means more cooling and soaking power for Class A fires.

2. Class B Ratings (10B, 20B, 40B, etc.)

• The number represents the square footage of flammable liquid the extinguisher can handle.

• 10B = Can cover 10 square feet of flammable liquid fire.

• 40B = Can cover 40 square feet, and so on.

3. Class C Rating (Electrical Fires)

• The C rating means the extinguisher is non-conductive and safe for use on electrical fires.

• Class C does not have a numerical rating; it simply means the extinguishing agent won’t cause electrical shock.

4. Class D and K Ratings

• Class D (metal fires) and Class K (kitchen fires) don’t use numbers because their effectiveness depends on the specific type of metal or cooking oil involved.

• The manufacturer provides testing data for specific fire types.

Examples of Portable Extinguisher Ratings and What They Mean

1. 5A:10B:C – Can fight Class A fires equivalent to 6.25 gallons of water, handle a 10-square-foot flammable liquid fire, and is safe for electrical fires.

2. 10A:60B:C – More powerful, can fight Class A fires with 12.5 gallons of water equivalence, cover a 60-square-foot flammable liquid fire, and is safe for electrical use.

3. 200B:C – Large extinguisher designed for 200 square feet of flammable liquid fire and electrical hazards.

4. Class K Extinguisher – No numbers, but designed specifically for kitchen grease fires.