Fire Safety Fire Behavior and Combustion Science 4 — Questions and Answers
Question 1: What term describes the minimum temperature at which a liquid produces enough vapor to ignite momentarily when exposed to an ignition source?
- Fire point
- Flash point (Correct answer)
- Auto-ignition temperature
- Boiling point
Correct answer: Flash point
The flash point is the lowest temperature at which a liquid generates sufficient vapor to briefly ignite with an external ignition source.
Question 2: In a backdraft event, what atmospheric condition inside a compartment triggers the explosive ignition?
- Excess oxygen entering a fuel-rich, oxygen-deficient environment (Correct answer)
- A sudden drop in temperature causing rapid condensation
- Excess fuel vapor escaping through roof vents
- Water vapor from suppression systems contacting hot surfaces
Correct answer: Excess oxygen entering a fuel-rich, oxygen-deficient environment
Backdraft occurs when oxygen rushes into a superheated, fuel-rich, oxygen-depleted space, causing instantaneous ignition of accumulated unburned gases.
Question 3: Which type of heat transfer is primarily responsible for fire spread across a room before direct flame contact occurs?
- Conduction
- Convection
- Radiation (Correct answer)
- Advection
Correct answer: Radiation
Radiant heat travels in straight lines through space and can ignite materials across a room before flames physically reach them.
Question 4: What is the primary combustion product responsible for the majority of fire-related deaths in structure fires?
- Carbon dioxide
- Carbon monoxide (Correct answer)
- Hydrogen cyanide
- Nitrogen dioxide
Correct answer: Carbon monoxide
Carbon monoxide (CO) is colorless, odorless, and bonds with hemoglobin far more readily than oxygen, making it the leading cause of fire fatality.
Question 5: A fire in a compartment transitions from the growth stage to flashover when ceiling gas temperatures reach approximately:
- 200°F (93°C)
- 400°F (204°C)
- 1,100°F (593°C) (Correct answer)
- 1,700°F (927°C)
Correct answer: 1,100°F (593°C)
Flashover typically occurs when upper-layer gas temperatures reach approximately 1,100°F (593°C), causing all exposed combustibles to ignite simultaneously.
Question 6: What does the 'stoichiometric' mixture of fuel and air refer to in combustion science?
- The mixture that produces the most smoke
- The theoretically perfect ratio where all fuel and oxygen are consumed (Correct answer)
- The mixture at the lower explosive limit
- The mixture that burns at the lowest temperature
Correct answer: The theoretically perfect ratio where all fuel and oxygen are consumed
A stoichiometric mixture contains exactly the right proportions of fuel and oxidizer so that complete combustion occurs with no excess of either.
Question 7: Which class of fire involves combustible metals such as magnesium, titanium, and sodium?
- Class B
- Class C
- Class D (Correct answer)
- Class K
Correct answer: Class D
Class D fires involve combustible metals and require specialized dry powder extinguishing agents; water can intensify these fires.
Fire Safety Fire Behavior and Combustion Science 4
What term describes the minimum temperature at which a liquid produces enough vapor to ignite momentarily when exposed to an ignition source?