FireFire BehaviourBehaviour

Loyalist Township Emergency ServicesLoyalist Township Emergency Services

FIRE BEHAVIOUR - INTRODUCTIONFIRE BEHAVIOUR - INTRODUCTION

• As firefighters we have a responsibility to know how As firefighters we have a responsibility to know how to “Prevent, Control and Extinguish” fires in the most to “Prevent, Control and Extinguish” fires in the most efficient and effective methods possible. To fulfill that efficient and effective methods possible. To fulfill that responsibility requires understanding of the fire responsibility requires understanding of the fire theory, phases of fire, heat transfer and extinguishing theory, phases of fire, heat transfer and extinguishing methods.methods.

• With this knowledge in hand, we will be better With this knowledge in hand, we will be better prepared to effectively and safely extinguish fires.prepared to effectively and safely extinguish fires.

TERMS & DESCRIPTIONSTERMS & DESCRIPTIONS

• Flash PointFlash Point – – The minimum temperature at which a The minimum temperature at which a fuel gives off sufficient vapours to form an ignitable fuel gives off sufficient vapours to form an ignitable mixture of air near the surface. At this temperature mixture of air near the surface. At this temperature the ignited vapours will flash, but will not continue to the ignited vapours will flash, but will not continue to burn.burn.

• Ignition TemperatureIgnition Temperature – – The minimum temperature The minimum temperature at which a fuel in air must be heated in order to start at which a fuel in air must be heated in order to start self sustained combustion without a separate ignition self sustained combustion without a separate ignition source.source.

• Fire PointFire Point – – The temperature at which a liquid will The temperature at which a liquid will produce vapours sufficient to support combustion produce vapours sufficient to support combustion once ignited. The fire point is usually a few degrees once ignited. The fire point is usually a few degrees above the flash point.above the flash point.

TERMS & DESCRIPTIONSTERMS & DESCRIPTIONS

• Spontaneous IgnitionSpontaneous Ignition – – Decomposition of material Decomposition of material produces quantities of heat. If this heat is contained produces quantities of heat. If this heat is contained the temperature will rise until it achieves the ignition the temperature will rise until it achieves the ignition temperature.temperature.

• Vapour DensityVapour Density – – The relative density of a gas as The relative density of a gas as compared to air. Air has a value of 1.0 compared to compared to air. Air has a value of 1.0 compared to natural gas 0.7 or gasoline 1.5.natural gas 0.7 or gasoline 1.5.

• Specific GravitySpecific Gravity – – The relative density of a liquid The relative density of a liquid compared to water. Water has a value of 1.0 compared to water. Water has a value of 1.0 compared to gasoline 0.75 or bromic acid 3.2.compared to gasoline 0.75 or bromic acid 3.2.

METHODS OF HEAT TRANSFERMETHODS OF HEAT TRANSFER

• ConductionConduction — Point-to-point transmission of heat energy. E.g. spoon in hot water

• ConvectionConvection — Transfer of heat energy by the movement of heated liquids or gasses. E.g. upward travel of hot air & gases in stairwell or elevator

• RadiationRadiation — Transmission of energy as an electromagnetic wave without an intervening medium. E.g. heat waves that travel in a straight line until it reaches a solid object

TS 2–7

OXIDIZING AGENTSOXIDIZING AGENTS

• Those materials that yield oxygen or other Those materials that yield oxygen or other oxidizing gases during the course of a chemical oxidizing gases during the course of a chemical reactionreaction

• Oxygen rich atmospheresOxygen rich atmospheres — Those with oxygen concentrations exceeding 21%

Health care facilities

Industrial occupancies

Private homes (where occupants use liquid oxygen breathing equipment)

TS 2–12a

OXIDIZING AGENTS OXIDIZING AGENTS (cont.)(cont.)

• Oxygen deficient atmospheres — Oxygen deficient atmospheres — Those with oxygen concentrations lower than 21%

Storage tanks

Silos

Pipes and vaults

Other confined spaces

High altitudes

TS 2–12b

FUEL CHARACTERISTICSFUEL CHARACTERISTICS

• FuelFuel — Material or substance being oxidized or burned in the combustion process

• PyrolysisPyrolysis — Chemical decomposition of a substance through the action of heat

• Surface-to-mass ratioSurface-to-mass ratio — Surface area of fuel in relation to its mass

• VaporizationVaporization — Transformation of a liquid to its vapor or gaseous state

TS 2–13a

FUEL CHARACTERISTICS FUEL CHARACTERISTICS (cont.)(cont.)

• Flammable rangeFlammable range — Range of concentrations of fuel vapor and air in which combustion will occur

Lower flammable limit (LFL) — Minimum concentration of fuel vapor and air that supports combustion

Upper flammable limit (UFL) — Concentration of fuel vapor and air above which combustion cannot take place

TS 2–13b

CHEMICAL HEAT ENERGYCHEMICAL HEAT ENERGY

• Most common source of heat is combustion Most common source of heat is combustion reactionsreactions

• Self-heating (spontaneous heating) — Self-heating (spontaneous heating) — Chemical energy that occurs when a material increases in temperature without the addition of external heat

• Conditions that must be present for Conditions that must be present for spontaneous ignition to occurspontaneous ignition to occur

Sufficient heat production

Sufficient air supply

Sufficient insulation

TS 2–14

COMPARTMENT FIRE COMPARTMENT FIRE DEVELOPMENT TERMSDEVELOPMENT TERMS

• CompartmentCompartment — Enclosed room or space within a building

• Compartment fireCompartment fire — Fire that occurs within a compartment

• Fuel controlledFuel controlled — Amount of fuel available to burn is limited

• Ventilation controlledVentilation controlled — Amount of available oxygen is limited

TS 2–16

INCIPIENT (Beginning) STAGEINCIPIENT (Beginning) STAGE

• The earliest phase of fire.The earliest phase of fire.

• Flames are still small and the relative room Flames are still small and the relative room temperature only slightly increased. The fire is temperature only slightly increased. The fire is burning fairly pure, producing mostly H20 and burning fairly pure, producing mostly H20 and carbon dioxide CO2. The oxygen content in the carbon dioxide CO2. The oxygen content in the room is only slightly reduced to around 20%.room is only slightly reduced to around 20%.

TS 2–17

FREE BURNING STAGEFREE BURNING STAGE

• During this stage oxygen rich air is drawn to During this stage oxygen rich air is drawn to flame as convection carries heat upwards in the flame as convection carries heat upwards in the confined area. Heated gases spread out at upper confined area. Heated gases spread out at upper levels and ignite materials. Greatest heat is at the levels and ignite materials. Greatest heat is at the ceiling level ( 1300 F) and the least at the floor ceiling level ( 1300 F) and the least at the floor level. This is why we are taught to stay low and level. This is why we are taught to stay low and wear breathing apparatus. Oxygen concentration wear breathing apparatus. Oxygen concentration is lowered by still around 16%. As this type of fire is lowered by still around 16%. As this type of fire progresses it will consume all of the oxygen in an progresses it will consume all of the oxygen in an area and could become a smoldering fire.area and could become a smoldering fire.

TS 2–17

FLASHOVER STAGEFLASHOVER STAGE

• Transition between growth stage and fully Transition between growth stage and fully developed fire stage; is not a specific eventdeveloped fire stage; is not a specific event

• Preflashover condition — Preflashover condition — Radiant heat (red arrows in visual) from the hot ceiling gas layer heats combustible materials, producing vapors (green arrows in visual)

TS 2–19a

FLASHOVER STAGE FLASHOVER STAGE (cont.)(cont.)

• Just prior to flashover — Just prior to flashover —

Temperatures rapidly increase

Additional fuel packages become involved

Fuel packages release combustible gases

• Flashover occurs when compartment Flashover occurs when compartment temperature exceeds 900temperature exceeds 900F F (483(483C)C) and all and all combustible surfaces and gases are burningcombustible surfaces and gases are burning

TS 2–19b

FULLY DEVELOPED STAGEFULLY DEVELOPED STAGE

• All combustible materials are involved in fireAll combustible materials are involved in fire

• Burning fuels release maximum amount of Burning fuels release maximum amount of heat; produce large volumes of fire gasesheat; produce large volumes of fire gases

• If fire becomes ventilation controlled, large If fire becomes ventilation controlled, large volumes of unburned fire gases are likely to volumes of unburned fire gases are likely to flow into adjacent spaces where they may flow into adjacent spaces where they may ignite if air is more abundantignite if air is more abundant

TS 2–20

SMOULDERING STAGESMOULDERING STAGE

• This phase will occur after a fire has consumed all of the This phase will occur after a fire has consumed all of the available oxygen in an area. Flames cease to exist due to available oxygen in an area. Flames cease to exist due to low concentrations of oxygen and dense smoke is low concentrations of oxygen and dense smoke is produced.produced.

• The oxygen is below 15% and temperature is above 1000 The oxygen is below 15% and temperature is above 1000 F. Glowing embers and dense smoke and gases are F. Glowing embers and dense smoke and gases are forced through cracks under pressure.forced through cracks under pressure.

• This phase of fire will lead to a Backdraft instantly if This phase of fire will lead to a Backdraft instantly if oxygen is allowed to enter the area prior to smoke and oxygen is allowed to enter the area prior to smoke and gases being vented.gases being vented.

• Ventilation must be undertaken immediately upon arrival Ventilation must be undertaken immediately upon arrival and prior to any fire fighting personnel trying to enter and prior to any fire fighting personnel trying to enter the area.the area.

TS 2–21

FACTORS THAT AFFECTFACTORS THAT AFFECT FIRE DEVELOPMENT FIRE DEVELOPMENT

• Ventilation openingsVentilation openings

Size

Number

Arrangement

• Compartment volumeCompartment volume

• Compartment’s Compartment’s thermal propertiesthermal properties

• Ceiling height Ceiling height

TS 2–22

• Initial fuel packageInitial fuel package

Size

Composition

Location

• Additional target Additional target fuelsfuels

Availability

Location

FLAMEOVER / ROLLOVERFLAMEOVER / ROLLOVER

• Condition where flames move through or Condition where flames move through or across the unburned gases during a fire’s across the unburned gases during a fire’s progression and roll across the ceilingprogression and roll across the ceiling

• Involves only fire gases, not the surfaces of Involves only fire gases, not the surfaces of other fuel packages (flashover)other fuel packages (flashover)

TS 2–23

THERMAL LAYERING OF GASSESTHERMAL LAYERING OF GASSES

• Thermal layering — Thermal layering — Tendency of gases to form layers according to temperature

• Heat stratification — Heat stratification — Hottest gases form top layers; cooler gases form bottom layers

• Thermal balance — Thermal balance — No disruption of heat stratification

• Thermal imbalance — Thermal imbalance — Disruption of heat stratification (hot gases mix throughout the compartment)

TS 2–24

TEMPERATURE REDUCTIONTEMPERATURE REDUCTION

• Is used on solid fuels and liquid fuels with high Is used on solid fuels and liquid fuels with high flash pointsflash points

• Is most common method of extinguishmentIs most common method of extinguishment

• Reduces temperature of high flash point fuelsReduces temperature of high flash point fuels

• Creates negative heat balanceCreates negative heat balance

• Cools with water Cools with water

TS 2–25

TEMPERATURE REDUCTIONTEMPERATURE REDUCTION

• Cooling or quenching reduces a materials Cooling or quenching reduces a materials ability to give off vapours to support ability to give off vapours to support combustion. combustion.

• Water is best agent available (water expands Water is best agent available (water expands 1700 x cubic foot).1700 x cubic foot).

• Solid fuels and liquid fuels with high flash point Solid fuels and liquid fuels with high flash point can be extinguished by cooling.can be extinguished by cooling.

• Fuels with lower flash points cannot be cooled Fuels with lower flash points cannot be cooled sufficiently.sufficiently.

TS 2–25

FUEL REMOVALFUEL REMOVAL

• Is used on solid, liquid, or gas fuelsIs used on solid, liquid, or gas fuels

• Stops flow of liquid or gaseous fuelStops flow of liquid or gaseous fuel

• Moves solid fuel out of fire pathMoves solid fuel out of fire path

• Allows fire to consume all fuelAllows fire to consume all fuel

TS 2–26

FUEL REMOVALFUEL REMOVAL

• Turn off supply – propane, natural gasTurn off supply – propane, natural gas

• Pump flammable liquids away.Pump flammable liquids away.

• Remove portions of material – grass firesRemove portions of material – grass fires

• Water will dilute some materials – ethyl alcoholWater will dilute some materials – ethyl alcohol

• Foam can contain flammable vapoursFoam can contain flammable vapours

• Flammable gases can be diluted with inert gas Flammable gases can be diluted with inert gas – CO2 or Nitrogen– CO2 or Nitrogen

TS 2–26

OXYGEN EXCLUSION OR DILUTIONOXYGEN EXCLUSION OR DILUTION

• Is used on solid, liquid, or gas fuelsIs used on solid, liquid, or gas fuels

• Prevents air from reaching fuel (smothering)Prevents air from reaching fuel (smothering)

• Dilutes or displacing oxygen with an inert gasDilutes or displacing oxygen with an inert gas

TS 2–27

OXYGEN EXCLUSION OR DILUTIONOXYGEN EXCLUSION OR DILUTION

• Smothering or blanketing fire. Smothering or blanketing fire.

• Introducing inert gas in fire or separating O2 Introducing inert gas in fire or separating O2 from fire.from fire.

TS 2–27

INHIBITION OF CHAIN REACTIONINHIBITION OF CHAIN REACTION

• Is used on gas and liquid fuelsIs used on gas and liquid fuels

• Uses dry chemicals and halogenated Uses dry chemicals and halogenated hydrocarbonshydrocarbons

• Interrupts chemical chain reaction (stops Interrupts chemical chain reaction (stops flaming)flaming)

TS 2–28