FPE FPE Fire Dynamics & Combustion Science 2 — Questions and Answers
Question 1: Which SFPE Handbook equation is used to estimate the plume centerline temperature rise above ambient in a buoyant fire plume?
- Heskestad plume correlation (Correct answer)
- McCaffrey plume correlation
- Zukoski plume correlation
- Thomas plume correlation
Correct answer: Heskestad plume correlation
The Heskestad plume correlation is the most widely used SFPE-referenced equation for predicting centerline temperatures and velocities in axisymmetric fire plumes.
Question 2: In fire dynamics, the term 'heat release rate' (HRR) is most commonly expressed in which unit?
- BTU
- Watts (W) or kilowatts (kW) (Correct answer)
- Calories per second
- Joules per kilogram
Correct answer: Watts (W) or kilowatts (kW)
HRR is expressed in watts or kilowatts and represents the thermal power output of a fire, the fundamental quantity driving fire engineering calculations.
Question 3: What is the lower flammability limit (LFL) used to determine in fire and explosion protection design?
- The minimum oxygen concentration for ignition
- The minimum fuel-vapor concentration in air required to sustain combustion (Correct answer)
- The maximum heat release rate before suppression is required
- The lowest ambient temperature at which a gas ignites
Correct answer: The minimum fuel-vapor concentration in air required to sustain combustion
The LFL is the minimum fuel-vapor concentration (% by volume) in air below which a flame cannot propagate, guiding ventilation and hazardous area classification.
Question 4: Which compartment fire stage is characterized by oxygen-limited burning and potential backdraft conditions?
- Incipient stage
- Growth stage
- Fully developed stage (Correct answer)
- Decay stage
Correct answer: Fully developed stage
During the fully developed (steady-state) stage, fuel-rich burning consumes available oxygen, creating conditions that can lead to backdraft if fresh air suddenly enters.
Question 5: The 'effective heat of combustion' of a material differs from its theoretical heat of combustion primarily because of:
- Pressure differences at altitude
- Incomplete combustion and soot production (Correct answer)
- Moisture content in the air
- Sprinkler water interference
Correct answer: Incomplete combustion and soot production
Incomplete combustion and the formation of carbon monoxide and soot reduce the actual energy released compared to the theoretical complete-combustion value.
Question 6: Which parameter describes the ratio of actual mass of fuel burned to the theoretical maximum in fire dynamics?
- Oxygen depletion factor
- Combustion efficiency (Correct answer)
- Stoichiometric ratio
- Flame spread index
Correct answer: Combustion efficiency
Combustion efficiency (χ) is the fraction of fuel energy actually released as heat, typically 0.7–0.9 for most ordinary combustibles.
FPE FPE Fire Dynamics & Combustion Science 2
Which SFPE Handbook equation is used to estimate the plume centerline temperature rise above ambient in a buoyant fire plume?