Compartment Fire Stage 3:Fully-DevelopedFully-developedorPost-flashoverfireisventilationcontrolledHRRiscontrolledthebyincomingair-Heavysmoke:unburnt (brown)orpartial-burnt (black)fuelgasKawagoe'sLaw(1958)formaximuminletairflow ratema=0.5ApH,2[kg/s]Ventilationfactor:ApH,zFire power or heat release rate (HRR)is controlled by incoming airand estimatedby heat ofoxidation (13.1 MJ/kg)HRR = mo2AHox ~ Yo2maAHox = 1.5ApH,2 MWAllareempiricalcorrelationswithalargeuncertainty16Fire ScienceDrXinyan Huang
Fire Science 16 Dr Xinyan Huang Compartment Fire Stage 3: Fully-Developed Fully-developed or Post-flashover fire is ventilation controlled ▪ HRR is controlled the by incoming air ▪ Heavy smoke: unburnt (brown) or partial-burnt (black) fuel gas Fully-developed Kawagoe’s Law (1958) for maximum inlet airflow rate 𝒎ሶ 𝒂 = 𝟎. 𝟓𝑨𝑫𝑯𝑫 𝟏 𝟐 [kg/s] Ventilation factor: 𝑨𝑫𝑯𝑫 𝟏 𝟐 ❖ All are empirical correlations with a large uncertainty Fire power or heat release rate (HRR) is controlled by incoming air and estimated by heat of oxidation (13.1 MJ/kg) 𝑯𝑹𝑹 = 𝒎ሶ 𝑶𝟐∆𝑯𝑶𝒙 ≈ 𝒀𝑶𝟐𝒎ሶ 𝒂∆𝑯𝑶𝒙 = 𝟏. 𝟓𝑨𝑫𝑯𝑫 𝟏 𝟐 MW
CompartmentFire Stage 3:Fully-DevelopedEstimatethefuelburningrateinthecompartmentfireBurningratecannotbedirectlymeasured inrealfire,but canbeestimatedbasedontheKawagoe'sLawHRR= mo2AHox=mpAH~ 1.5ApH,2 [MW]HRR1[kg]kg0.09ApH,25.5ApHDmbXAHcsminCombustionefficiency:x=0.8Heatofcombustion:2oMJ/kgforwoodEstimate theburning duration and fire-resistant requirementFuel loadmAt:mburning rate17FireScienceDrXinyan Huang
Fire Science 17 Dr Xinyan Huang Compartment Fire Stage 3: Fully-Developed Fully-developed 𝑯𝑹𝑹 = 𝒎ሶ 𝑶𝟐∆𝑯𝑶𝒙 = 𝒎ሶ 𝑭∆𝑯𝒄 ≈ 𝟏. 𝟓𝑨𝑫𝑯𝑫 𝟏 𝟐 [MW] 𝒎ሶ 𝒃 = 𝑯𝑹𝑹 𝝌ΔHc = 𝟎. 𝟎𝟗𝑨𝑫𝑯𝑫 𝟏 𝟐 kg s = 𝟓. 𝟓𝑨𝑫𝑯𝑫 𝟏 𝟐 kg min • Combustion efficiency: 𝜒 = 0.8 • Heat of combustion: 20 MJ/kg for wood Estimate the fuel burning rate in the compartment fire ▪ Burning rate cannot be directly measured in real fire, but can be estimated based on the Kawagoe’s Law Estimate the burning duration and fire-resistant requirement ∆𝒕 = 𝒎 𝒎ሶ = Fuel load burning rate
CompartmentFireStage4:DecayandCoolingHRRDecay isa resultofburnout,smothering,firefightingsuppression,andcoolingBackdraftExtinctionbyburnoutandsuppressionaretruedecayOxygenre-supply,Smothering(lackofO,)cancausetemporarydecaywhichcan re-growwithfreshairbybreakingwindow/doorandtriggerbackdraftsmotheringFlashoverTimeIgnitionburnoutHRR个BurnoutSuppressedFlashoverBumoutTimeIgnition18FireScienceang
Fire Science 18 Dr Xinyan Huang Compartment Fire Stage 4: Decay and Cooling Decay is a result of burnout, smothering, firefighting, suppression, and cooling ▪ Extinction by burnout and suppression are true decay ▪ Smothering (lack of O2 ) can cause temporary decay, which can re-grow with fresh air by breaking window/door and trigger backdraft HRR Time Burnout Suppressed HRR Time Oxygen re-supply Backdraft smothering
CompartmentFireStage4:DecayandCoolingContinuously cooling the building is important to prevent the structure collapse (Lecture 8)19FireScienceDrXinyan Huang
Fire Science 19 Dr Xinyan Huang Compartment Fire Stage 4: Decay and Cooling Continuously cooling the building is important to prevent the structure collapse (Lecture 8)