CFM Fire Behavior & Combustion Principles 2 — Questions and Answers
Question 1: What does the term 'fuel load' refer to in fire science?
- The weight of combustible materials per unit area in a given space (Correct answer)
- The amount of fuel used by firefighting equipment
- The rate at which a fire consumes oxygen
- The number of ignition sources present in a building
Correct answer: The weight of combustible materials per unit area in a given space
Fuel load refers to the total quantity of combustible materials per unit area in a given space, typically expressed in BTUs or pounds per square foot.
Question 2: Which mechanism of fire spread involves the movement of hot gases and smoke carrying heat to unburned areas?
- Conduction
- Radiation
- Convection (Correct answer)
- Direct flame contact
Correct answer: Convection
Convection spreads fire through the movement of hot gases and smoke, which rise and carry heat energy to adjacent unburned areas above and around the fire.
Question 3: Backdraft occurs when a fire in an oxygen-limited environment suddenly:
- Runs out of fuel and self-extinguishes
- Receives a sudden influx of oxygen (Correct answer)
- Reaches its auto-ignition temperature
- Produces excessive amounts of carbon monoxide
Correct answer: Receives a sudden influx of oxygen
Backdraft occurs when a smoldering, oxygen-starved fire receives a sudden fresh supply of oxygen — such as when a door is opened — causing rapid, explosive combustion.
Question 4: The rate of heat release (HRR) from a burning material is most commonly expressed in:
- Pounds per square foot per minute
- BTUs per hour or kilowatts (kW) (Correct answer)
- Degrees Fahrenheit per second
- Parts per million of combustion gases
Correct answer: BTUs per hour or kilowatts (kW)
Heat release rate (HRR) measures the power output of a fire and is expressed in BTUs per hour or kilowatts (kW), indicating how quickly energy is being released.
Question 5: Smoldering combustion is best characterized by which of the following?
- Rapid flame spread and very high temperatures
- Burning at the fuel surface without producing a visible flame (Correct answer)
- Complete and efficient oxidation of all combustible materials
- Simultaneous ignition of all combustible contents in a room
Correct answer: Burning at the fuel surface without producing a visible flame
Smoldering (glowing) combustion occurs when a material burns without producing a visible flame, typically at the fuel surface, and can persist for extended periods.
Question 6: What is pyrolysis in the context of fire behavior?
- The chemical process of rapid oxidation producing heat and light
- The thermal decomposition of materials producing combustible gases (Correct answer)
- The spread of fire through radiant heat energy transfer
- The process of extinguishing fire using chemical suppression agents
Correct answer: The thermal decomposition of materials producing combustible gases
Pyrolysis is the thermal decomposition of solid or liquid materials when exposed to heat, producing combustible gases that can then mix with air and ignite.
Question 7: The upper explosive limit (UEL) of a flammable gas or vapor refers to:
- The highest temperature at which combustion can occur
- The maximum concentration above which the mixture is too fuel-rich to ignite (Correct answer)
- The highest pressure at which ignition can take place
- The temperature at which a fire reaches flashover conditions
Correct answer: The maximum concentration above which the mixture is too fuel-rich to ignite
The upper explosive limit (UEL) is the maximum concentration of flammable vapor in air above which the mixture contains too much fuel and insufficient oxygen to sustain combustion.
CFM Fire Behavior & Combustion Principles 2
What does the term 'fuel load' refer to in fire science?