Basics Of Fire Behavior

Combustion:

Combustible material and oxidizing agent produce heat and energy and other products.

Fire Tetrahedron

Model of the four elements/conditions required to have a fire. The four sides of the tetrahedron represent fuel, heat, oxygen, and chemical chain reaction. Must have all four elements to be self sustaining.

What are the four types of fire?

1. Diffusion flame: flame we see when we light a match, camp fire, structure fire. Most natural flame fires. Combustible gas emitted by burning material mixed with oxygen. 2. Smoldering: glow of charcoal is a good example. No flame but heat. When enough air flows over product and enough heat is present it will erupt into flames. May also be the final phase of a fire. 3. Spontaneous combustion/self-heating: material undergoes oxidation where the heat cannot be dissipated. Temperature increases and promotes reaction. Material smolders or flames if enough heat is present. 4. Premixed flame: requires gas fuel and air mix to ignite. Gas fuel must be within flammable limits. Gasoline engine is an example of this - air and fuel enters the the cylinder and the piston compresses it to ignition point.

Define the terms fire and combustion and explain the difference.

Combustion is a chemical reaction in which a combustible material and an oxidizing agent (typically oxygen in the air) produce heat or energy that promote a self-sustaining process. Fire is a chemical reaction that produces energy in the form of heat, light, and flame that is self-sustaining. In the combustion process, the released energy stays in the reaction to continue the reaction. Fire is a form of combustion that emits and dissipates energy as heat and light.

What is the four methods of extinguishing fire?

1. cooling: 1 gallon of water can cool 8,000 BTU's 2. oxygen reduction: foam is commonly used; carbon dioxide is heavier than air and displaces oxygen 3. removing fuel supply: setting a fire ahead of a wildfire removes that fuel source. Foams prevent liberation of vapors. Water from sprinklers prewet materials making it harder for them to catch fire. 4. interrupting chain reaction: dry chemical, halon and other clean agents disrupt the chemical chain reaction.

Class K Fire:

Cooking oils and cooking fat. Class K agents extinguish fire by saponification. Fatty acids in cooking agent combine with extinguishing agent and convert to foam.

Compare and contrast the fire triangle and fire tetrahedron.

Fire triangle is the 3 basic elements needed for a fire heat, fuel, and oxygen. The fire tetrahedron adds the element of chemical chain reaction. Eliminate any of the 3 elements needed for fire or disrupt the chemical chain reaction and the fire will go out.

Class B Fire:

Flammable and combustible liquids. Class B agents smother or blanket the fire. Typical agents: foams, carbon dioxide, dry chemical agents, halon. Reduce oxygen.

Class D Fire:

Flammable metals. Magnesium, titanium. Class D agents are dry powder.

What components make the fire triangle?

Fuel, air, and heat.

Class A Fire:

Ordinary combustibles suchs as cloth, paper, and wood. Class A materials release approximately 8,000 BTU per pound. Water is the most effective suppression agent. Reduces heat.

Each year, wildland fires destroy hundreds of homes. Using the modes of heat transfer for guidance, develop a list of strategies to reduce the amount of damage.

You can preburn areas to remove the fuel before the wildfire gets to the area. You can also wet the area to cool and prewet possible fuel.

Class C Fire:

Energized electrical equipment. Shutting off electricity is critical. Only fires involving electricity is class C, when electricity is removed the fire is reclassified.

Fire produces?

Energy in the form of heat, light , and flame.

What are the factors that contribute to the flashover stage of a fire?

The amount of available air within confined spaces or compartments and the amount of available fuel in the case of outside fires regulate this stage.

What is the stages of fire?

1. pre-ignition: requires some form of energy transfer, usually in the form of heat. 2. ignition: need heat, fuel and oxygen. Ignition occurs when more is generated than dissipated. 3. growth: adequate oxygen must be available. 4. fully developed: combustible contents are fully inflamed. Flashover is the transition from the growth stage and the fully developed stage. Stage is regulated by the amount of oxygen and fuel. 5. decay or smoldering: fuel is exhausted or oxygen level drops below 16%.

Explain the term oxidation.

The process of combining a substance or material with oxygen.