FST 50 Midterm (CH.4)
Identify and describe the four stages of fire.
1.Incipient Stage- The fire has ignited and reaches a point where it no longer needs input heat from outside sources to continue burning. In this stage, oxygen in the surrounding air is 21 percent, heat is starting to be produced, and the combustion reaction begins to accelerate. Free- Burning stage- The fire releases heat, bringing more fuel to its ignition temperature. The fire begin to spread and gain intensity. 3.Flashover Stage- When the contents in the room (which may include PPE) are brought to their ignition temperature and sufficient oxygen is present, flashover can occur. 4.Smoldering/Decay stage- The decay stage occurs when the fire has run out of available fuel or oxygen.
Discuss five classifications of fire.
Common Combustibles (Class A)- wood, paper cloth etc Flammable liquids & gases (classB)- gasoline, propane & solvents Live electrical equipment (class C)t- computers, fax machines Combustible metals (class D)- magnesium, lithium, and titanium Cooking media(class K) - cooking oil and fats
Identify and describe and four methods of heat transfer.
Conduction: Transfer of heat without visible motion Ex: pan over a stove Convection: Circulating medium such as liquids and gases Ex: Hot smoke rises over a fire Radiation: Transferred through wavelengths Ex: Solar radiation causing a sunburn Direct Contact: Transfer of heat through immediate vicinity Ex: Touching a hot stove
Discuss the chemistry of fire in terms of oxidizers and fuels.
Fuel, can exist in three states of matter, solid liquid, and gas. Oxidizers are substances that evolve or generate oxygen when exposed to ambient temperatures or heat.
Differentiate heat and temperature.
Heat is the total energy of all molecular motion inside an object. Temperature on the other hand is a measure of the average heat or thermal energy of the molecules in a substance
Discuss the differences between the fire triangle and the fire tetrahedron?
In the fire tetrahedron there is a chemical chain reaction. This occurs when fuel is broken down by heat, producing free-radicals which combine with oxidizers. This reaction releases more heat and chemical reactants, causing the fuel to keep burning.
Discuss the physics of fire in terms of the three states of matter.
The state of fire is Plasma which resembles a gas. Fire doesnt have a definite shape or volume and doesn't expand.