FPE Fire Dynamics & Combustion Science Flashcards

What does the 'critical heat flux' value represent in surface flame spread analysis?

Answer: Minimum radiant flux needed to sustain flame spread on a material surface

Critical heat flux is the minimum irradiance below which a material surface cannot sustain flame spread, used in material flammability testing and engineering models.

In zone modeling of compartment fires, how many control volumes typically represent a single room?

Answer: Two

Two-zone models divide each room into an upper hot gas layer and a lower cool layer, tracking mass and energy exchanges between them.

Which dimensionless number governs the transition between laminar and turbulent flow in fire plumes?

Answer: Reynolds number

The Reynolds number compares inertial to viscous forces; high Reynolds numbers in large fire plumes indicate turbulent flow dominating mixing and combustion.

What is the primary purpose of conducting a fire dynamics analysis using FDS (Fire Dynamics Simulator)?

Answer: To perform CFD-based numerical simulation of fire-driven fluid flow and heat transfer

FDS, developed by NIST, uses large-eddy simulation (LES) to model combustion, smoke transport, and heat transfer for performance-based fire engineering.

Which smoke layer height criterion is commonly used in performance-based egress analysis to ensure tenable conditions for occupants?

Answer: Smoke layer must remain above 1.8 m (6 ft) from the floor

A smoke layer maintained at or above 1.8 m (6 ft) is the standard tenability threshold to protect standing occupants during egress.

The 'thermal inertia' (kρc) of a material determines which fire behavior characteristic?

Answer: How quickly a material surface temperature rises when exposed to a heat flux

Thermal inertia (product of conductivity k, density ρ, and specific heat c) controls the rate of surface temperature rise; low kρc materials ignite faster.