Fire Science Overview

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.

The transition between growth and fully developed. Flashover occurs where all fuels reach their ignition temperature and ignite. Signup and view all the answers

What occurs during the Smoldering stage of a fire?

The fire begins to die out with superheated smoke and gases present above ignition temperature, and oxygen levels are below 15%. Signup and view all the answers

Air normally contains what percentage of oxygen?

21% Signup and view all the answers

What are the four methods of fire extinguishment?

Reduction of temperature, removal of fuel, exclusion of oxygen, and inhibition of chain reaction. Signup and view all the answers

What does Class A fuel refer to?

Ordinary combustibles. Signup and view all the answers

What does Class B fuel refer to?

Liquids and gases. Signup and view all the answers

What does Class C fuel refer to?

Energized electrical equipment. Signup and view all the answers

What does Class D fuel refer to?

Metals. Signup and view all the answers

What does Class K fuel refer to?

Cooking oils/greases. Signup and view all the answers

What factors are important characteristics when dealing with Class A fires?

Surface area, moisture content, and flame spread. Signup and view all the answers

What is the difference between vapor density and specific gravity?

Vapor density determines if a vapor or gas will sink/rise in air; Specific gravity determines if a substance will float or sink in water. Signup and view all the answers

What does it mean to be 'too lean to burn'?

Not enough vapor to oxygen ratio to ignite. Signup and view all the answers

What is the Lower Explosive Limit (LEL)?

Lowest concentration of vapor/gas to oxygen that is capable of producing a flash of fire in presence of an external ignition source. Signup and view all the answers

What does the flammable range/flame limit refer to?

Range of gas/vapor concentration to oxygen where it can ignite. Signup and view all the answers

What is the Upper Explosive Limit (UEL)?

Maximum concentration of vapor/gas to oxygen where it can ignite. Signup and view all the answers

What does it mean to be 'too rich to burn'?

Vapor/gas is too concentrated, not enough oxygen for it to ignite. Signup and view all the answers

On what types of fires are dry chemicals effective?

Class B and Class C. Signup and view all the answers

On what type of fires are dry powder extinguishers used?

Class D. Signup and view all the answers

What is a flash point?

Minimum temperature of a liquid at which it gives off vapors sufficient enough to ignite, but does not sustain combustion. Signup and view all the answers

What is a fire point?

Temperature at which a liquid gives sufficient vapors to ignite and support combustion. Signup and view all the answers

What is boiling point?

The temperature where a liquid rapidly becomes a vapor. The rate of evaporation exceeds the rate of condensation. Signup and view all the answers

How do flash point and fire point differ?

Flash point cannot sustain combustion. Signup and view all the answers

Define ignition temperature.

Minimum temperature to which a substance must be raised before it will ignite. Signup and view all the answers

What is the extinguisher rating for a 2½ gallon pressurized water portable fire extinguisher?

2A (A = equivalent to 1.25 gallons of water). Signup and view all the answers

Which classes of fires have numerical ratings on fire extinguishers?

Class A and B. Signup and view all the answers

On which class of fire is a wet chemical fire extinguisher intended to be used?

Class K. Signup and view all the answers

How do ordinary base and multipurpose base dry chemical extinguishing agents differ?

Multipurpose can be used on different types of metal. Signup and view all the answers

What problems can flammable liquids present in a spill incident based on specific gravity, vapor density, and flammable limits?

A liquid spill can cause several problems. Depending on specific gravity, it can float on water. Flammable vapors can either rise or sink in the air according to its vapor density. If the vapor is within its flammable range, it can ignite. Signup and view all the answers

What is the correlation between a liquid's flash point and its lower explosive limit?

Once it reaches its flash point, it will produce enough vapors to reach its lower explosive limit. Signup and view all the answers

Why would a hazardous material classified as a flammable gas (such as methane) have an ignition temperature, but no flash point?

Flash point is defined as the temperature a liquid needs to be heated to release enough vapors to ignite. A flammable gas is already primed for combustion. Signup and view all the answers

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.