Chapter 7: Portable Fire Extinguishers

Types of Fires and Extinguishing Agents

• Class A Fires: Involve ordinary combustibles such as textiles, paper, plastics, rubber, and wood. Easily extinguished with water or water-based agents.
• Class B Fires: Involve flammable liquids and gases (e.g., alcohol, gasoline). Extinguished using carbon dioxide (CO2), dry chemicals, or Class B foam.
• Class C Fires: Involve energized electrical equipment. Must ensure electricity is turned off before treating as Class A or B fire.
• Class D Fires: Involve combustible metals (e.g., lithium, magnesium). Identified by bright white emissions; dry powder extinguishers are recommended.
• Class K Fires: Involve cooking oils (fats and oils). Found primarily in commercial kitchens and extinguished using wet chemical systems.

Extinguishing Methods

• Smothering: Excludes oxygen from the fire.
• Cooling: Reduces burning material temperature to below ignition point.
• Chain Breaking: Interrupts chemical reactions in the fire.
• Saponification: Forms a soapy foam to exclude oxygen.

Properties of Extinguishing Agents

• Water: Primarily cools; secondary method is oxygen depletion.
• Carbon Dioxide: Primarily depletes oxygen; secondary method is cooling.
• Foam: Primarily depletes oxygen; secondary method is vapor suppression.
• Clean Agents: Primarily inhibit chemical chains; secondary method is cooling.
• Dry Chemical: Primarily inhibits chains; secondary is oxygen depletion.
• Wet Chemical: Primarily depletes oxygen; secondary is vapor suppression.
• Dry Powder: Primarily depletes oxygen; secondary involves heat transfer cooling.

Types of Extinguishers

• Manual Pump Extinguisher: Operator uses a pump to create pressure to expel the agent.
• Stored Pressure Extinguisher: Compressed air or inert gas inside the container forces the agent out when the handle is pressed.
• Pressure Cartridge Extinguisher: Uses a separate cartridge containing gas to pressurize the agent for discharge.
• Common types: Pump-Type Water, Stored-Pressure Water, Wet Chemical, AFFF, Clean Agent, CO2, Dry Chemical, Dry Powder extinguishers.

Specific Extinguisher Functions

• Pump-Type Water Extinguishers: Best for ground cover and small Class A fires, used manually.
• Stored-Pressure Water Extinguishers: Effective for small Class A fires; pressurized air forces the water out.
• Wet Chemical Extinguishers: Designed for Class K fires; uses potassium-based agent to form a foam barrier.
• AFFF Extinguishers: Ideal for Class B fires; utilizes foam solution to suppress flammable liquid fires.

Disadvantages and Precautions

• Halon Extinguishers: Effective but harmful to the ozone layer; being replaced by clean agents.
• CO2 Extinguishers: Limited reach due to gas dispersion; do not require freeze protection.
• Dry Chemical Disadvantages: Can obscure visibility and may cause respiratory issues; not all dry chemicals are compatible with foam.

Specific Applications for Extinguishing Agents

• Combustible Metals: Class D fires require specific dry powder agents; no single agent is effective for all metals.
• Dry Chemical Extinguishers: Common for Class A-B-C fires; should not mix agents to avoid dangerous reactions.
• Wheeled Dry Chemical Units: Larger capacity, rated for Class A, B, and C fires; similar operation to handheld units.

Application Techniques

• Dry Powder Application: Must cover the burning area sufficiently to create a smothering effect, often requiring a shovel for certain agents.### Fire Extinguishment Techniques
• Apply extinguishing agents gently to avoid breaking any crust over burning metal.
• Breaking the crust may cause flare-ups and expose more materials to combustion.
• Avoid scattering burning metal; it can complicate extinguishment efforts.
• Cover small amounts of burning metal on combustible surfaces with powder, followed by additional powder layers as needed.
• Develop a 1 to 2 inches (25 mm to 50 mm) deep powder layer for shoveling burning metal onto.
• Leave extinguished materials undisturbed until completely cooled before disposal.

Class D Fire Extinguishers

• Available in both handheld and wheeled models designed for combustible metals.

Class A Fire Extinguishers

• Rated from 1-A to 40-A.
• The rating is based on the amount of extinguishing agent, discharge duration, and range.

Class A Rating Conversion

• A 1-A rating requires 11/4 gallons (5 L) of water; a 2-A rating needs double that amount, 21/2 gallons (10 L).

Class B Fire Extinguishers

• Classified with ratings from 1-B to 640-B.
• Ratings reflect the area of flammable liquid fire a nonexpert can extinguish with one full extinguisher.

Class C Fire Extinguishers

• No specific fire extinguishing capability tests are conducted for Class C ratings.
• Rated because they are essentially for Class A or B fires involving energized electrical equipment.
• They ensure that the extinguishing agent does not conduct electricity.

Class D Fire Ratings

• Established through tests considering metal reactions, agent toxicity, fume toxicity, and extinguishment times.
• Safe and effective agents have application instructions on the extinguisher faceplate, but without a numerical rating.

Class K Fire Extinguishers

• Must saponify vegetable and animal cooking oils.
• Wet chemical agents work by smothering and vapor suppression.

Multiple Markings on Extinguishers

• Common combinations include Class A-B-C, Class A-B, and Class B-C, where each rating operates independently.

Identification of Fire Extinguishers

• Class A: Green triangle
• Class B: Red square
• Class C: Blue circle
• Class D: Yellow star
• Class K: Black hexagon

Considerations in Fire Extinguisher Selection

• Identify the burning fuel classification, extinguisher rating, potential hazards, fire size/intensity, atmospheric conditions, and availability of trained personnel.

Precautions with Computer Equipment

• Avoid dry chemical extinguishers near sensitive computer equipment; residues can damage electronics.
• Clean agents or carbon dioxide extinguishers are preferable in such environments.

Pre-Use Check for Portable Fire Extinguishers

• Evaluate external condition for damage, ensure hose/nozzle is in place, check weight for agent presence, and ensure the pressure gauge is within operable range.

PASS Technique for Fire Extinguishers

• Pull the pin to break the seal.
• Aim the nozzle at the fire base.
• Squeeze the handles to release the agent.
• Sweep the nozzle back and forth to cover the burning area.

Test your knowledge on portable fire extinguishers with these flashcards from Chapter 7. Learn about different classes of fires and the appropriate methods for extinguishing them. Perfect for students and professionals in fire safety training.