CFI CFI Fire Dynamics & Behavior 2 — Questions and Answers
Question 1: What is the stoichiometric ratio in fire chemistry?
- The ratio of oxygen to nitrogen in air
- The ideal fuel-to-air mixture ratio for complete combustion (Correct answer)
- The proportion of carbon to hydrogen in a hydrocarbon fuel
- The ratio of heat released to heat absorbed during burning
Correct answer: The ideal fuel-to-air mixture ratio for complete combustion
The stoichiometric ratio is the theoretically perfect fuel-to-air mixture that allows complete combustion with neither excess fuel nor excess oxygen.
Question 2: Which fire behavior phenomenon describes the movement of flames along the underside of a ceiling or overhead accumulation of hot gases before flashover?
- Flashover
- Rollover (Correct answer)
- Plume extension
- Flame spread
Correct answer: Rollover
Rollover (also called flameover) occurs when unburned gases that have collected at the ceiling level ignite and flames roll along the ceiling surface.
Question 3: The 'lower flammable limit' (LFL) of a gas refers to:
- The lowest temperature at which the gas will auto-ignite
- The minimum concentration of gas in air that can sustain combustion (Correct answer)
- The pressure at which gas becomes liquefied
- The lowest point in a room where flammable gas accumulates
Correct answer: The minimum concentration of gas in air that can sustain combustion
The LFL is the minimum concentration (percentage by volume in air) of a flammable gas below which the mixture is too lean to ignite or propagate flame.
Question 4: In NFPA 921, what does the term 'fire pattern' specifically refer to?
- The shape of flame visible during active burning
- Visible or measurable physical changes or identifiable shapes caused by a fire effect (Correct answer)
- The behavior of fire based on mathematical models
- The sequence of events leading to ignition
Correct answer: Visible or measurable physical changes or identifiable shapes caused by a fire effect
Per NFPA 921, a fire pattern is a visible or measurable physical change or an identifiable shape caused by a fire effect such as char, smoke deposition, or heat damage.
Question 5: What is pyrolysis in the context of fire investigation?
- The burning of pyrotechnic materials
- The chemical decomposition of a material by heat without combustion (Correct answer)
- The study of fire patterns using infrared cameras
- The process of oxygen combining with fuel vapors
Correct answer: The chemical decomposition of a material by heat without combustion
Pyrolysis is the thermal decomposition of a solid or liquid material into simpler chemical compounds through the application of heat without direct combustion.
Question 6: Which factor most significantly affects the angle of a fire's V-pattern on a wall surface?
- The type of fuel involved in the fire
- The rate of heat release and intensity of the fire (Correct answer)
- The color of the wall surface
- The time of day the fire occurred
Correct answer: The rate of heat release and intensity of the fire
Higher heat release rates produce wider, shallower V-patterns, while slow, low-intensity fires produce narrower, more pointed V-patterns on wall surfaces.
CFI CFI Fire Dynamics & Behavior 2
What is the stoichiometric ratio in fire chemistry?