Fire Safety Fire Behavior and Combustion Science 5 — Questions and Answers
Question 1: What is the name of the phenomenon where fire spreads rapidly along the ceiling in a layer of unburned gases ahead of the flame front?
- Flashover
- Rollover (Correct answer)
- Backdraft
- Flameover
Correct answer: Rollover
Rollover (also called flameover) occurs when unburned gases at the ceiling ignite and flames roll across the top of the compartment ahead of the main fire.
Question 2: Which factor does NOT directly affect the rate of heat release (RHR) of a burning fuel?
- Surface area of the fuel
- Moisture content of the fuel
- Color of the fuel (Correct answer)
- Density of the fuel
Correct answer: Color of the fuel
Color has no significant effect on rate of heat release; surface area, moisture content, and density all directly influence how quickly a fuel burns.
Question 3: Pyrolysis is best described as:
- The ignition of a fuel by an external spark
- The chemical decomposition of a solid fuel by heat into combustible vapors (Correct answer)
- The smothering of a fire by removing oxygen
- The cooling of a fire below its ignition temperature
Correct answer: The chemical decomposition of a solid fuel by heat into combustible vapors
Pyrolysis is a thermochemical decomposition process where solid fuels break down under heat, releasing combustible vapors that can then ignite.
Question 4: In fire behavior, what is the 'upper flammable limit' (UFL)?
- The concentration of fuel vapor below which ignition cannot occur
- The maximum temperature a fuel can reach before vaporizing
- The concentration of fuel vapor above which the mixture is too rich to ignite (Correct answer)
- The highest altitude at which a fuel will burn
Correct answer: The concentration of fuel vapor above which the mixture is too rich to ignite
The UFL (upper flammable limit) is the highest fuel-vapor concentration in air above which there is insufficient oxygen to sustain combustion.
Question 5: A fire investigator notes a low burn pattern and 'V' pattern on a wall. What does a narrow, sharply defined 'V' pattern typically indicate?
- A slow, smoldering fire origin
- A fast, intense fire with a well-defined point of origin (Correct answer)
- Fire spread from an external source through a window
- Poor ventilation conditions during the fire
Correct answer: A fast, intense fire with a well-defined point of origin
A narrow, sharp 'V' pattern indicates a fast, intense fire with a localized point of origin, while a wide 'V' suggests slower fire development.
Question 6: What effect does high humidity have on the ignition and spread of wildfires?
- It lowers the moisture content of fine fuels, promoting ignition
- It raises the moisture content of fine fuels, making them harder to ignite (Correct answer)
- It increases wind speeds, accelerating fire spread
- It has no measurable effect on fire behavior
Correct answer: It raises the moisture content of fine fuels, making them harder to ignite
High relative humidity causes fine fuels to absorb atmospheric moisture, increasing their moisture content and making them more resistant to ignition and spread.
Question 7: Which of the following best explains why a fire in a well-insulated, tightly sealed room reaches flashover faster than one in a drafty room?
- More oxygen is available in the sealed room
- Heat accumulates faster because less energy escapes through gaps or ventilation (Correct answer)
- The sealed room has lower humidity, drying out fuels more quickly
- Radiation cannot escape the room, increasing fuel surface temperatures only
Correct answer: Heat accumulates faster because less energy escapes through gaps or ventilation
In a tightly sealed, well-insulated compartment, heat energy cannot escape, so the upper gas layer and ceiling temperature rise more rapidly, accelerating flashover.
Fire Safety Fire Behavior and Combustion Science 5
What is the name of the phenomenon where fire spreads rapidly along the ceiling in a layer of unburned gases ahead of the flame front?