NomenclatureaConstantassociatedwitht-squaredfires,Q=at?AAreaArbAreaoffuel coveredbytheflameAITAutoignitiontemperatureA.H.VentilationfactorcDistance in radiation fraction equationcSpecific heatcSpeed of lightCHFCritical heat flux, threshold heat flux for piloted ignitiondDiameterdThicknessDDiameterDsMaximumfireballdiameterDmMassoptical density,pertainstovisibilityD.Opticaldensityper unit path lengthEEnergyffFrequencyFriction factor'F12ViewfactorFrFroudenumber,ratioofmomentumtobuoyantforce8hEarth'sgravitationalforceperunitmass,9.81N/kgConvective heat transfer coefficientHHeightHLSmoke layer heightHNNeutral plane heightHRPHeat release parameter,H/LHRRHeat release rate, same as Q1Intensity of lightkThermal conductivitykpcThermal inertia1LengthLHeat of gasificationLMaximumheightoffireballLLFlamelengthVisibility,distanceabletoseethroughsmokeLFLLowerflammabilitylimitmMassmMass of fuel burnedinMass lossorburningrate'i"Massburningflux,orburningrateperunit areaxxi
xxi Nomenclature a Constant associated with t-squared fires, Q a = t 2 A Area AF,b Area of fuel covered by the flame AIT Autoignition temperature A H o o Ventilation factor c Distance in radiation fraction equation c Specific heat c Speed of light CHF Critical heat flux, threshold heat flux for piloted ignition d Diameter d Thickness D Diameter Db Maximum fireball diameter Dm Mass optical density, pertains to visibility Do Optical density per unit path length E Energy f Frequency f Friction factor F12 View factor Fr Froude number, ratio of momentum to buoyant force g Earth’s gravitational force per unit mass, 9.81 N/kg h Convective heat transfer coefficient H Height HL Smoke layer height HN Neutral plane height HRP Heat release parameter, ΔHc /L HRR Heat release rate, same as Q I Intensity of light k Thermal conductivity kρc Thermal inertia l Length L Heat of gasification Lb Maximum height of fireball Lf Flame length Lv Visibility, distance able to see through smoke LFL Lower flammability limit m Mass m Mass of fuel burned m Mass loss or burning rate m ¢¢ Mass burning flux, or burning rate per unit area
xxiiNomenclatureila,maxMaximumairflowrateMass of COmcoisnokeMassflowrateof smokeMspeciesMolecularweightofspeciespPressure9Q9HeatChemical energyFlowrate of heatHeat flux, or q/AqierExternal radiantheatfluxfrom hot surroundingsimameIncident flameheat flux福QQReradiationheatfluxfromignitedsurfaceEnergyfromcombustionCombustion energyreleaserateof fireQQ*Zukoskinumber, Q*=PaCmTagDD?RHRelative humiditysStoichiometricairto fuelmass ratiousuallyfor complete chemicalreactionsSurface areatTimetDuration of burningtiTimeto reach1MW in f-squaredfiregrowthTTime to igniteTemperatureT.AirtemperatureT'sIgnition temperatureTSurfacetemperatureToAir or initial temperatureTRPThermal responseparameter, Equation 4.4UFLUpperflammablelimitVFlame spread velocityVOriginal fuel volume infireball equationswWidth of the fuelX华XFlame heightPyrolysis lengthFractionofchemical energyradiatedfromflameXspecisMoleorvolumefractionofspeciesinmixtureMass of species produced in combustion per mass of fuel suppliedYyspeciesYspeciesMassfractionofspeciesinmixtureN&Vertical heightThermal diffusivity,k/pc8,Flameforwardheattransferlengthinspread
xxii Nomenclature m a,max Maximum air flow rate mCO Mass of CO m smoke Mass flow rate of smoke Mspecies Molecular weight of species p Pressure q Heat Q Chemical energy q Flow rate of heat q ¢¢ Heat flux, or q A / q ¢¢ext External radiant heat flux from hot surroundings q ¢¢flame Incident flame heat flux q ¢¢rr Reradiation heat flux from ignited surface Q Energy from combustion Q Combustion energy release rate of fire Q* Zukoski number, Q Q a p c Ta a gDD * = r 2 RH Relative humidity s Stoichiometric air to fuel mass ratio usually for complete chemical reaction S Surface area t Time tb Duration of burning t1 Time to reach 1 MW in t-squared fire growth tig Time to ignite T Temperature Ta Air temperature Tig Ignition temperature Ts Surface temperature T∞ Air or initial temperature TRP Thermal response parameter, Equation 4.4 UFL Upper flammable limit V Flame spread velocity Vf Original fuel volume in fireball equations w Width of the fuel xƒ Flame height xp Pyrolysis length Xr Fraction of chemical energy radiated from flame Xspecies Mole or volume fraction of species in mixture yspecies Mass of species produced in combustion per mass of fuel supplied Yspecies Mass fraction of species in mixture z Vertical height α Thermal diffusivity, k/ρc δƒ Flame forward heat transfer length in spread
Nomenclaturexxili8EmissivityAH.HeatofcombustionAMeans differenceKAbsorptioncoefficientofthesmokeorflameKsLight extinctioncoefficient, Equation 8.10入WavelengthDensitypBulk densityPbaStefan-Boltzmannconstant,5.67×10-11kW/m2-K4ΦParameterinEquation5.6@Equivalenceratio
Nomenclature xxiii ε Emissivity ΔHc Heat of combustion Δ Means difference κ Absorption coefficient of the smoke or flame κs Light extinction coefficient, Equation 8.10 λ Wavelength ρ Density ρb Bulk density σ Stefan–Boltzmann constant, 5.67 × 10–11 kW/m2 -K4 ϕ Parameter in Equation 5.6 Φ Equivalence ratio
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1EvolutionofFireScienceLearning ObjectivesUponcompletionofthischapter,youshouldbeableto:Describe what is fire·Identifyfireinhistory?DescribetheU.S.fire safetyinfrastructureand statistics·Describethehistoryoffireresearch·Describetheroleof sciencetopredictfire1.1IntroductionBefore there was life there was fire. It has left its imprint on history in manyways. We need to understand the role fire has played in history, includingprehistoric events as well. After all, fire has been around from the beginning.Creation mayhavebegun with nuclear reactions,but fire was an essentialconsequencetothedevelopmentoflife.Eventheancients revered fire,astheyimagined Prometheus stole it from Zeus and gave it to us mortals. PerhapsZeusknew wewould use it and abuse it, and so hepunished Prometheusseverely.Today, fire in the form of controlled combustion is an essential ingredi-ent of ourtechnology.We could not easily survive without the burningof coal, gas, and oil.For these reasons, the study of combustion for usefulpower is driven by marketforces that drivedeveloped world economies.Incontrast, the study of uncontrolled fire is motivated by clear risks to soci-ety and by societies having the means and desire to invest in such study.Consequently,weknowa lotless aboutfirethan controlled combustion.Fireevents arechronicled and recorded in proportion to the damage rendered1
1 1 Evolution of Fire Science Learning Objectives Upon completion of this chapter, you should be able to • Describe what is fire • Identify fire in history • Describe the U.S. fire safety infrastructure and statistics • Describe the history of fire research • Describe the role of science to predict fire 1.1 Introduction Before there was life there was fire. It has left its imprint on history in many ways. We need to understand the role fire has played in history, including prehistoric events as well. After all, fire has been around from the beginning. Creation may have begun with nuclear reactions, but fire was an essential consequence to the development of life. Even the ancients revered fire, as they imagined Prometheus stole it from Zeus and gave it to us mortals. Perhaps Zeus knew we would use it and abuse it, and so he punished Prometheus severely. Today, fire in the form of controlled combustion is an essential ingredient of our technology. We could not easily survive without the burning of coal, gas, and oil. For these reasons, the study of combustion for useful power is driven by market forces that drive developed world economies. In contrast, the study of uncontrolled fire is motivated by clear risks to society and by societies having the means and desire to invest in such study. Consequently, we know a lot less about fire than controlled combustion. Fire events are chronicled and recorded in proportion to the damage rendered