F80 Fire Behavior and Combustion Principles 2 — Questions and Answers
Question 1: What is the lower explosive limit (LEL) of a fuel vapor?
- The flash point temperature of the fuel
- The minimum concentration of fuel vapor in air required to sustain ignition (Correct answer)
- The highest temperature a fire can achieve
- The maximum oxygen level needed for combustion
Correct answer: The minimum concentration of fuel vapor in air required to sustain ignition
The lower explosive limit (LEL) is the minimum fuel vapor concentration in air below which the mixture is too lean to ignite.
Question 2: What is autoignition temperature?
- The temperature at which a sprinkler head activates
- The lowest temperature at which a material ignites spontaneously without an external ignition source (Correct answer)
- The temperature of a fully developed room fire
- The boiling point of a flammable liquid
Correct answer: The lowest temperature at which a material ignites spontaneously without an external ignition source
Autoignition temperature is the minimum temperature at which a material will self-ignite without any spark or open flame present.
Question 3: Which phase of fire development follows the incipient (early growth) stage?
- Decay stage
- Flashover
- Free-burning stage (Correct answer)
- Spontaneous combustion
Correct answer: Free-burning stage
After the incipient stage, the fire enters the free-burning (growth) stage where it grows rapidly and consumes available fuel.
Question 4: What does pyrolysis refer to in fire science?
- Chemical decomposition of materials due to heat, producing combustible gases (Correct answer)
- Suppression of fire using foam agents
- The spread of fire through structural walls
- Temperature measurement within a burning compartment
Correct answer: Chemical decomposition of materials due to heat, producing combustible gases
Pyrolysis is the thermal decomposition of solid or liquid fuels by heat, generating flammable gases that feed and sustain combustion.
Question 5: How does fire primarily spread within a structure via convection?
- Through direct flame contact with adjacent surfaces
- Through rising hot gases and smoke carrying heat to upper levels and adjoining compartments (Correct answer)
- Through electromagnetic radiation transmitted across open spaces
- Through heat conduction along structural steel members
Correct answer: Through rising hot gases and smoke carrying heat to upper levels and adjoining compartments
Convective heat transfer occurs as buoyant hot gases and smoke rise and travel horizontally, spreading fire to upper floors and adjacent spaces.
Question 6: What is the upper explosive limit (UEL)?
- The maximum temperature a fire can sustain
- The highest fuel vapor concentration in air above which the mixture is too rich to ignite (Correct answer)
- The maximum pressure rating of a suppression system
- The highest flash point value of a combustible liquid
Correct answer: The highest fuel vapor concentration in air above which the mixture is too rich to ignite
The upper explosive limit (UEL) is the maximum fuel vapor concentration above which there is insufficient oxygen to support ignition.
F80 Fire Behavior and Combustion Principles 2
What is the lower explosive limit (LEL) of a fuel vapor?