Ifsta Ch 5 Fire Behavior (2)

Essentials of Fire Fighting6th EditionFirefighter IChapter 5 — Fire BehaviorReplace with manual graphic on slide masterLearning Objective 1Explain the science of fire as itrelates to energy, forms of ignition,and modes of combustion.5–1Reality Check13:28:05Time 0Time 48 secondsTime 6 secondsTime 120 seconds1

Understanding the physical scienceof fire can help firefighter safety.Fire – Variety of forms Heat-producing chemical reaction between fueland oxidizerKnowledge can help Translate into practical knowledge of firebehavior Recognize what is happening – Predictpotential behavior5–3There are two types of changesfirefighters should chemicallysameSubstancechangesChanges insize, shape,appearanceFrom onetype of matterto another5–4The concept of energy is alsoimportant for firefighters to know.In heat defined asWork occurs when Increasingtemperature ofsubstance Force is appliedto object overdistance Substanceundergoeschemical,biological,physical change5–52

There are two forms of energy thatfirefighters should know about.Courtesy of Dan Madrzykowski, NIST5–6There are many types of energy and allcan change from one type to another. TypesIn fire behaviorpotentialchemicalenergy ound Converted to thermal Released as heat5–7You should also know about how tomeasure and the exchange of energy.Chemical, physicalchanges involveexchange of energyMeasurement Joules (J) in SI British thermalunit (Btu) incustomary Potential energy Released duringcombustion Converted tokinetic energy5–83

POWER . .is the Rate at which energy is expended.Expressed as Watts1 watt 1 joule / secondKilowatts and Megawatts commonly used1 horsepower 745 watts 12/13 DPSST, 2012 9There are two types of energyreactions that you should understand.5–10The process of ignition follows asequence of steps.Sufficient heat transfer Causes pyrolysis (solidfuels); vaporization (liquidfuels) Releases ignitable vapors orgasesFuel heated –Temperature increasesEnergy necessary forignitionContinues production,ignition so combustionreaction sustained Provided by external source Fuel can be heated untilignites5–114

Piloted and autoignition arethe two forms of ignition.5–12Fire and combustion require similarconditions to occur.Combustion –Chemical reaction,can occur without fireFire – One possibleresult of combustion5–13The fire triangle is the oldest andsimplest fire model.5–145

The fire tetrahedron represents theuninhibited chain reaction that mustbe present for fire to occur.5–15There are several materials that affectboth ignition and fire amingThe two types of combustion occurunder different circumstances.Gaseous fuelmixes withoxygen incorrect ratio,heated toignitiontemperatureFlamingBurning islocalized on ornear fuel’ssurface – Wherein contact withoxygen5–176

The products of combustiongenerate as fuel burns andchanges chemical composition.Thermal energyToxic smokeSmoke(Cont.)5–18The products of combustiongenerate as fuel burns andchanges chemical composition.Carbon monoxide (CO)Hydrogen cyanide (HCN)Carbon dioxide (CO2)(Cont.)5–19WARNINGSmoke is fuel and is always potentiallyflammable. Wear full PPE and SCBAanytime you work in smoke.5–207

The products of combustiongenerate as fuel burns andchanges chemical composition.Flame5–21REVIEW QUESTIONHow does the science of fire relateto energy, forms of ignition, andmodes of combustion?5–22Learning Objective 2Describe the impact of thermalenergy on heat, temperature, andheat transfer.5–238

Thermal energy (heat) is the energyelement in both fire models.Kinetic energytransfers from hightemperature to lowtemperaturesubstanceAlways in transitThermal kineticneeded to releasepotential chemicalenergy in fuelVibrates molecules infuel leading to breakdown, release ofvapors5–24You should understand the relationshipbetween heat and temperature. Heat- a formof energycapable ofinitiating andsupportingchemicalchanges andchanges ofstate5–25TempuratureMeasure of a materials ability to transferheat energy to other objects- thegreater the energy, the higher thetemperature.Measured in terms of degrees on aStandard Scale- Celsius or Fahrenheight What is the difference between thescales?1–269

The concept of transfer rate isinfluenced by several factors.Related to temperature differential – Thermal conductivityGreater temperature difference – Greater transfer rateHeat flux5–27There are several sources of thermalenergy you should recognize.ChemicalElectrical Resistance heating Overcurrent or overload Arcing SparkingMechanical5–28Understanding the concept of heattransfer can help in several ways.Understand transfer from initial fuelpackage to othersEstimate size of fire before attacking –Evaluate effectiveness of attackTransfer occurs from warmer to cooler– In a room full of fire, if you are in itheat is transferred to you5–2910

Conduction is the transfer of heatthrough and between solids.5–30Convection is the transfer of thermalenergy by circulation or movementof fluid (liquid or gas).5–31Radiation is the transmission ofenergy as an electromagnetic wave,without an intervening medium.5–3211

REVIEW QUESTIONWhat impact does thermal energyhave on heat, temperature, and heattransfer?5–33Learning Objective 3Recognize the physical states of fuel.5–34Fuel is the material or substanceoxidized or burned in combustion.Inorganic – Do not containcarbonOrganic – Contain carbon,other elements5–3512

The chemical content of fuelinfluences heat of combustionand heat release rate.Heat of combustion Total amount of thermal energy released when specificamount of fuel oxidized (burned)Heat release rates5–36Gaseous fuel can be the mostdangerous of all fuel types.5–37The properties of liquid fuel areimportant to understand.Mass, volumebut no shapeWill not expandto fill all ofcontainerWill flowdownhill, canpool in low areas5–3813

Vaporization is the transformation ofa liquid to a vapor or gaseous state.Flammableliquids withhigh vaporpressurepresentspecialhazard5–39Solubility is a factor to considerregarding liquid fuels.Solubility Miscible – Mix in any– Extentproportionto which Hydrocarbon – Do notmixsubstance Polar solvents – Readilywill mixmixwith water5–40Density is also a factor toconsider regarding liquid fuels.Liquids lessdense than waterdifficult toextinguish withwater alone Fuel will not mix with water –Adding may disperse burningliquid Extinguish with appropriate agentWater-soluble mixwith agent – Avoid use with foams specificallydesigned for polar solventsBecome lesseffective5–4114

The properties of solid fuelinfluence the process of pyrolysis.5–42REVIEW QUESTIONWhat are the physical states thatfuel can be found in?5–43Learning Objective 4Explain the relationship betweenoxygen and life safety.5–4415

Oxygen is the primary oxidizingagent present at most fires.21 percent oxygentypicalAt normaltemperatures Materials can ignite, burnat concentrations as lowas 14 percentAmbient temperatureimpacts Nonflaming FlamingLimited oxygendiminishes flamingcombustionHigher oxygenconcentrations thannormal5–45Combustion occurs after a fuel hasbeen converted to a gaseous state andmixed with an oxidizer in proper ratio.5–46REVIEW QUESTIONHow do oxygen and life safety relateto one another?5–4716

Learning Objective 5Identify the products of selfsustained chemical reactions.5–48Self-sustained chemical reactionscreate several products.Combustion ofmethane and oxygenFlaming combustion Production of CO2,water Release of energy inform of heat, light Production of CO,formaldehyde Different free radicals Free radicals Will burn until fuel oroxygen exhausted Chemical flameinhibition occurswhen extinguishingagent applied5–49REVIEW QUESTIONWhat products of self-sustainedchemical reactions combine to makeflammable and toxic substances?5–5017

Learning Objective 6Explain the factors that affect firedevelopment.5–51Learning Objective 7Describe the stages of firedevelopment.5–52The stages of fire development occur inboth unconfined and confined fires.Courtesy of Dan Madrzykowski, NISTClickimage toplay(Cont.)Traditional – Lab development5–5318

The stages of fire development occur inboth unconfined and confined fires.Courtesy of Dan Madrzykowski, NISTClickimage toplayActual – Real world development5–54There are several factors that willaffect fire development.Fuel typeAvailabilityand locationof additionalfuel Affects heat release rateClass AClass BFires involving singletype of fuel rare Compartment fire asresult of gas leak Building configurationConstruction materialsContentsProximity of initial fire toexposed fuel sources(Cont.)5–55There are several factors that willaffect fire development.Compartmentvolume andceiling heightVentilation Large vs. small compartment High ceiling can makedetermining extent difficult All buildings exchange airfrom inside to outside Influences Can be increased or assisted Two forms of compartmentfires Changes(Cont.) HRR decreases/increases5–5619

There are several factors that willaffect fire development.Thermalproperties ofcompartmentAmbientconditions Insulation Heat reflectivity Retention High humidity, coldtemperatures Strong winds If window fails, dooropens on windward side Wind direction, velocity Cold temperatures Atmospheric air pressure(Cont.)5–57There are several factors that willaffect fire development.Fuelload On sceneonly estimate Knowledgeof REVIEW QUESTIONWhat different factors can impactfire development?5–5920

The incipient stage starts when theelements of the fire triangle cometogether and combustion begins.Courtesy of Dan Madrzykowski, NIST5–60The growth stage occurs as thefire transitions and is influencedby air in the compartment.Courtesy of Dan Madrzykowski, NIST5–61Thermal layering can also occurduring the growth stage.5–6221

Isolated flames and rapid transitionsmay also be a part of the growth stage.Courtesy of Dan Madrzykowski, NIST5–63The fully developed stage occurs whenall combustible materials are burning.Courtesy of Dan Madrzykowski, NIST5–64The decay stage brings combustion toa complete stop through two means.Courtesy of Dan Madrzykowski, NIST5–6522

REVIEW QUESTIONWhat are the stages of firedevelopment?5–66Learning Objective 8Recognize signs, causes, and effectsof rapid fire development.5–67Rapid fire development is responsiblefor numerous deaths and injuries.Protect yourself and your crew Recognize indicators Know conditions created by Determine best action to takebefore5–6823

Flashover occurs when combustiblematerials in a compartment ignitealmost simultaneously.Environment of roomchanges from two-layercondition to single wellmixed, untenable hotgas conditionTypically occurs duringgrowth stage – Mayoccur during fullydeveloped stageConditions duringTransition betweenpre-flashover to postflashover can occurrapidly Volume of fire can increaseto fill entire room Burning gases push out ofopenings5–69There are several common elementsin flashover to be aware of.Ignition ofexposedsurfacesTransition ion to a flashover isdetermined by two factors.Ventilation –Must havesufficient oxygenSufficient fuel,heat release rate5–7124

Firefighters should be aware ofseveral flashover ��72Backdraft is a change in ventilationthat results in explosively rapidcombustion of flammable gases.Courtesy of Bob Esposito5–73Firefighters should know aboutseveral backdraft indicators as well.BuildingFlameSmokeHeatAirflow5–7425