Questions and Answers
What is the fire tetrahedron and how can it be used in fire extinguishment and fire prevention?
The fire tetrahedron consists of fuel, heat, oxygen, and a chain chemical reaction. If any can be taken away, the fire will be extinguished.
Identify the products of complete combustion and the products of incomplete combustion.
Complete combustion = H2O and CO2; Incomplete combustion = H2O, CO, and H2.
What happens during the Incipient stage of a fire?
Where the fire initially ignites either piloted or nonpiloted. The fire begins to grow into a fire plume.
Describe the Free-Burning stage of a fire.
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What occurs during the Smoldering stage of a fire?
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Air normally contains what percentage of oxygen?
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What are the four methods of fire extinguishment?
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What does Class A fuel refer to?
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What does Class B fuel refer to?
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What does Class C fuel refer to?
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What does Class D fuel refer to?
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What does Class K fuel refer to?
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What factors are important characteristics when dealing with Class A fires?
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What is the difference between vapor density and specific gravity?
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What does it mean to be 'too lean to burn'?
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What is the Lower Explosive Limit (LEL)?
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What does the flammable range/flame limit refer to?
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What is the Upper Explosive Limit (UEL)?
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What does it mean to be 'too rich to burn'?
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On what types of fires are dry chemicals effective?
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On what type of fires are dry powder extinguishers used?
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What is a flash point?
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What is a fire point?
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What is boiling point?
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How do flash point and fire point differ?
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Define ignition temperature.
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What is the extinguisher rating for a 2½ gallon pressurized water portable fire extinguisher?
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Which classes of fires have numerical ratings on fire extinguishers?
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On which class of fire is a wet chemical fire extinguisher intended to be used?
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How do ordinary base and multipurpose base dry chemical extinguishing agents differ?
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What problems can flammable liquids present in a spill incident based on specific gravity, vapor density, and flammable limits?
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What is the correlation between a liquid's flash point and its lower explosive limit?
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Why would a hazardous material classified as a flammable gas (such as methane) have an ignition temperature, but no flash point?
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Study Notes
Fire Tetrahedron
- Comprises fuel, heat, oxygen, and a chain reaction; removing any one component can extinguish fire.
Combustion Products
- Complete combustion yields water (H2O) and carbon dioxide (CO2).
- Incomplete combustion can produce water (H2O), carbon monoxide (CO), and hydrogen (H2).
Fire Stages
- Incipient Stage: Fire begins igniting, fuel plume develops; oxygen concentration is 20-21% and temperature reaches 1,112°F.
- Free-Burning Stage: Transition to fully developed fire; flashover occurs when all fuels ignite; oxygen level drops to 16%, temperatures range from 1,300°F to 2,000°F.
- Smoldering Stage: Fire starts to extinguish; superheated smoke fills area; oxygen levels fall below 15%.
Air Composition
- Normal air contains approximately 21% oxygen.
Fire Extinguishment Methods
- Fire can be extinguished by reducing temperature, removing fuel, excluding oxygen, or inhibiting the chain reaction.
Classes of Fuel
- Class A: Ordinary combustibles (wood, paper).
- Class B: Flammable liquids and gases.
- Class C: Energized electrical equipment.
- Class D: Combustible metals.
- Class K: Cooking oils and greases.
Class A Fire Characteristics
- Factors like surface area, moisture content, and flame spread are crucial in Class A fires.
Vapor Density vs. Specific Gravity
- Vapor Density: Indicates if a vapor will rise or sink in air.
- Specific Gravity: Determines if a substance will float or sink in water.
Ignition Dynamics
- Too Lean to Burn: Insufficient vapor-to-oxygen ratio for ignition.
- Lower Explosive Limit (LEL): Minimum vapor concentration required for ignition in presence of an external source.
- Flammable Range/Limit: Concentration range where gases can ignite.
- Upper Explosive Limit (UEL): Maximum concentration of vapor/gas that can cause ignition.
- Too Rich to Burn: High vapor concentration with insufficient oxygen for ignition.
Dry Chemical Effectiveness
- Effective on Class B (flammable liquids) and Class C (energized electrical) fires.
Dry Powder Extinguishers
- Specifically used for Class D fires (combustible metals).
Flash Point vs. Fire Point
- Flash Point: Minimum liquid temperature to emit enough vapor to ignite, does not sustain combustion.
- Fire Point: Temperature at which a liquid can sustain combustion.
Ignition Temperature
- Minimum temperature a substance must reach for ignition.
Extinguisher Ratings
- A 2½ gallon pressurized water extinguisher has a rating of 2A (equivalent to 1.25 gallons of water).
- Only Classes A and B fires have numerical ratings on extinguishers.
- Class K extinguishers are specifically designed for cooking oils/greases.
Base Dry Chemical Agents
- Ordinary base agents are limited, while multipurpose base agents can be utilized on various metal types.
Liquid Spill Hazards
- Liquid spills pose risks due to specific gravity; they may float on water and release flammable vapors that can ignite based on their vapor density.
Connection of Flash Point and LEL
- When a liquid reaches its flash point, it can produce enough vapor to reach its lower explosive limit.
Flammable Gases and Ignition
- Flammable gases (like methane) have an ignition temperature but no flash point, as they are already capable of combustion without requiring a vapor-producing phase.
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Description
Test your knowledge on the fundamentals of fire science, including the fire tetrahedron, combustion products, and the stages of fire development. This quiz covers essential concepts related to fire extinguishment methods and the composition of air. Perfect for students and professionals in fire safety and prevention.