CPS Fire Behavior and Combustion 2 — Questions and Answers
Question 1: What is the fourth element added to expand the fire triangle into the fire tetrahedron?
- Carbon dioxide
- Uninhibited chain reaction (Correct answer)
- Pressure
- Ignition source
Correct answer: Uninhibited chain reaction
The fire tetrahedron adds the uninhibited chemical chain reaction as a fourth element, recognizing combustion as a self-sustaining chemical process.
Question 2: What is pyrolysis?
- The process of extinguishing fire with water
- The chemical decomposition of a material by heat, producing flammable gases (Correct answer)
- The spread of fire through radiation alone
- A method of controlled burning used in firefighting
Correct answer: The chemical decomposition of a material by heat, producing flammable gases
Pyrolysis is the thermal decomposition of solid or liquid fuels by heat, releasing flammable vapors that then mix with oxygen and ignite.
Question 3: What is rollover (flameover) in a structure fire?
- When a fire doubles in size within 60 seconds
- When flames roll across the ceiling through accumulated unburned gases ahead of the main fire (Correct answer)
- When fire spreads from one floor to the next
- When hose lines are overwhelmed by fire intensity
Correct answer: When flames roll across the ceiling through accumulated unburned gases ahead of the main fire
Rollover occurs when unburned flammable gases accumulate at the ceiling level and ignite, creating flames that roll across the ceiling in advance of the main fire.
Question 4: Which fire class involves fires in flammable and combustible liquids and gases?
- Class A
- Class C
- Class D
- Class B (Correct answer)
Correct answer: Class B
Class B fires involve flammable liquids (gasoline, oil) and flammable gases, which require foam, CO2, or dry chemical agents for suppression.
Question 5: What does the lower flammable limit (LFL) of a gas indicate?
- The minimum temperature at which a gas will self-ignite
- The minimum concentration of gas in air required to sustain combustion (Correct answer)
- The pressure at which a gas becomes explosive
- The maximum safe storage temperature for flammable gas
Correct answer: The minimum concentration of gas in air required to sustain combustion
The lower flammable limit is the minimum concentration of a fuel gas mixed with air below which the mixture is too lean to ignite and sustain combustion.
Question 6: How does convection transfer heat in a fire environment?
- Through direct molecular contact between solids
- Through electromagnetic waves requiring no medium
- Through the movement of heated gases and liquids carrying thermal energy (Correct answer)
- Through chemical reactions releasing energy
Correct answer: Through the movement of heated gases and liquids carrying thermal energy
Convection transfers heat through the physical movement of heated air and gases, which is why hot gases and smoke rise and spread fire to upper floors.
Question 7: What is thermal layering (thermal balance) in a burning structure?
- Equal heat distribution throughout a room
- The stratification of hot gases near the ceiling and cooler air near the floor (Correct answer)
- The process of heat sinking into concrete floors
- A firefighting technique using water fog
Correct answer: The stratification of hot gases near the ceiling and cooler air near the floor
Thermal layering refers to the stratification of smoke and gases by temperature, with hottest gases at ceiling level and relatively cooler air near the floor.
CPS Fire Behavior and Combustion 2
What is the fourth element added to expand the fire triangle into the fire tetrahedron?