Fire Behavior

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PHYSICAL CHANGE

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A PHYSICAL CHANGE OCCURS WHEN A SUBSTANCE REMAINS CHEMICALLY THE SAME BUT CHANGES IN SIZE, SHAPE, OR APPERANCE.

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CHEMICAL REACTION

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A CHEMICAL REACTION OCCURS WHEN A SUBSTANCE CHANGES FROM ONE TYPE OF MATTER INTO ANOTHER, SUCH AS TWO OR MORE SUBSTANCES COMBINING TO FORM COMPOUNDS.

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OXIDATION

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OXIDATION IS A CHEMICAL REACTION INVOLVING THE COMBINATION OF AN OXIDER, SUCH AS OXYGEN IN THE AIR, WITH OTHER MATERIALS.

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MATTER

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ANYTHING THAT OCCUPIES SPACE AND HAS MASS

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WHAT ARE THE TWO FORMS OF ENERGY

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POTENTIAL ENERGY

AND

KINETIC ENERGY

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POTENTIAL ENERGY

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POTENTIAL ENERGY REPRESENTS THE AMOUNT OF KINETIC ENERGY THAT AN OBJECT CAN RELEASE AT SOME POINT IN THE FUTURE.

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KINETIC ENERGY

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IS THE ENERGY POSSESSED BY A BODY OF MATERIAL BECAUSE OF ITS MOTION.

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ENERGY

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ENERGY IS THE CAPACITY TO PERFORM WORK.

OCCURS WHEN A FORCE IS APPLIED TO AN OBJECT OVER A DISTANCE, OR WHEN A CHEMICAL, BIOLOGICAL OR PHYSICAL TRANSFORMATION IS MADE IN A SUBSTANCE.

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NFPA 921 ( FUEL)

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A MATERIAL THAT WILL MAINTAIN COMBUSTION UNDER SPECIFIED ENVIRONMENTAL CONDITIONS.

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COMBUSTION

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COMBUSTION IS A CHEMICAL PROCESS OF OXIDATION THAT OCCURS AT A RATE FAST ENOUGH TO PRODUCE HEAT AND USUALLY LIGHT IN THE FORM OF EITHER A GLOW OR A FLAME.

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HEAT (NFPA 921)

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HEAT IS A FORM OF ENERGY CHARACTERIZED BY VIBRATION OF MOLECULES AND CAPABLE OF INITIATING AND SUPPORTING CHEMICAL CHANGES OF STATE

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FIRE (NFPA 921)

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A RAPID OXIDATION PROCESS, WHICH IS A CHEMICAL REACTION RESULTING IN THE EVOLUTION OF LIGHT AND HEAT IN VARYING INTENSITIES.

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ENERGY IS MEASURED IN WHAT?

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JOULES

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A BRITISH THERMAL UNIT IS THE AMOUNT IF HEAT REQUIRED TO RAISE THE TEMPERATURE OF ONE POUND OF WATER ONE DEGREE FAHRENHEIT.

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1055 JOULES = 1 BTU

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REACTIONS THAT EMIT ENERGY AS THEY OCCUR ?

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EXOTHERMIC REACTIONS

EXAMPLE: FIRE

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REACTIONS THAT ABSORB ENERGY AS THEY OCCUR ARE ?

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ENDOTHERMIC REACTIONS

EXAMPLE: CONVERTING WATER TO STEAM

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PYROLYSIS

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PYROLYSIS IS THE CHEMICAL DECOMPOSITION OF A SOLID MATERIAL BY HEATING. PYROLYSIS OFTEN PRECEDES COMBUSTION.

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JOULES

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JOULES ARE DEFINED IN TERMS OF MECHANICAL ENERGY.

IT IS EQUAL TO THE ENERGY EXPENDED IN APPLYING A FORCE OF ONE NEWTON THROUGH THE DISTANCE OF ONE METER.

4.2 JOULES ARE REQUIRED TO RAISE THE TEMPERATURE OF ONE GRAM OF WATER ONE DEGREE CELSIUS.

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VAPORIZATION

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PHYSICAL PROCESS THAT CHANGES A LIQUID INTO A GASEOUS STATE.

THE RATE OF VAPORIZATION DEPENDS ON THE SUBSTANCE INVOLVED, HEAT, PRESSURE, AND EXPOSED SURFACE AREA.

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IGNITION (NFPA 921)

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THE PROCESS OF INITIATING SELF-SUSTAINED COMBUSTION.

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WHAT ARE THE TWO FORMS OF IGNITION ????

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PILOTED IGNITION AND AUTO IGNITION

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PILOTED IGNITION

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PILOTED IGNITION IS THE MOST COMMON AND OCCURS WHEN A MIXTURE OF FUEL AND OXYGEN ENCOUNTERS AN EXTERNAL HEAT (IGNITION) SOURCE WOTH SUFFICIENT HEAT OR THERMAL ENERGY TO START THE COMBUSTION REACTION.

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AUTOIGNITION (NFPA 921)

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AUTO IGNITION OCCURS WITHOUT ANY EXTERNAL FLAME OR SPARK TO IGNITE THE FUEL GASES OR VAPORS.

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WHAT IS A.I.T. ??

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AUTO IGNITION TEMPERATURE:

THIS IS THE LOWEST/MINIMUM TEMPERATURE AT WHICH A COMBUSTIBLE MATERIAL IGNITES IN AIR WITHOUT A SPARK OR FLAME (NFPA 921)

NOTE: THE AUTO IGNITION TEMPERATURE OF A SUBSTANCE IS ALWAYS HIGHER THAN ITS PILOTED IGNITION TEMPERATURE

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WHAT ARE THE TWO MODES OF COMBUSTION ?

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NON-FLAMING AND FLAMING

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NON-FLAMING COMBUSTION

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NON-FLAMING COMBUSTION OCCURS MORE SLOWLY AT A LOWER TEMPERATURE PRODUCING A SMOLDERING GLOW IN THE MATERIALS SURFACE.

OCCURS WHEN BURNING IS LOCALIZED ON OR NEAR THE FUELS SURFACE WHERE IT IS IN CONTACT WITH OXYGEN. EXAMPLES OF NON-FLAMING OR ALSO KNOWN AS SMOLDERING COMBUSTION INCLUDES BURNING CHARCOAL OR SMOLDERING WOOD OR FABRIC. .

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FLAMING COMBUSTION

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FLAMING COMBUSTION IS COMMONLY REFERRED TO AS FIRE BECAUSE IT PRODUCES A VISIBLE FLAME ABOVE THE MATERIALS SUFACE.

THIS OCCURS WHEN A GASEOUS FUEL MIXES WITH OXYGEN IN THE CORRECT RATIO AND IS HEATED TO IGNITION TEMPERATURE. ALSO FLAMING COMBUSTION REQUIRES LIQUID OR SOLID FUELS TO BE VAPORIZED OR CONVERTED TO THE GAS PHASE THROUGH THE ADDITION OF HEAT. WHEN HEATED, BOTH LIQUID AND SOLID FUELS WILL EMIT VAPORS THAT MIX WITH OXYGEN PRODUCING FLAMES ABOVE THE MATERIALS SURFACE IF THE GASES ARE IGNITED (THUS THIS GIVING YOU A CHEMICAL CHAIN REACTION) THE FIRE TETRAHEDRON ACCURATELY REFLECTS THE CONDITIONS REQUIRED FOR FLAMING COMBUSTION.

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FIRE TRIANGLE

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THE OLDEST AND SIMPLEST MODEL ILLUSTRATES THE THREE ELEMENTS NECESSARY FOR FIRE TO OCCUR: FUEL, OXYGEN, AND HEAT.

NOTE: REMOVAL OF ANY ONE OF THESE ELEMENTS AND THE FIRE WILL BE EXTINGUISHED.

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FIRE TETRAHEDRON

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RESULTED BY RESEARCH TO EXPLAIN FIRES INVOLVING CERTAIN TYPES OF SUBSTANCES AND THE TYPES OF AGENTS NECESSARY TO EXTINGUISH THEM.

THE FOUR SIDES OF THE TETRAHEDRON REPRESENT FUEL, HEAT, OXYGEN, AND SELF SUSTAINING CHEMICAL CHAIN REACTION.

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PASSIVE AGENTS

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ARE MATERIALS THAT ABSORB HEAT BUT DO NOT PARTICIPATE ACTIVELY IN THE COMBUSTION REACTION.

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WHAT ARE ON EOF THE MOST COMMON TYPES OF A PASSIVE AGENT??

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IN BUILDING CONSTRUCTION ONE OF THE MOST COMMOM PASSIVE AGENTS IS DRYWALL OR GYPSUM BOARD.

AS THE GYPSUM BOARD IS HEATED, THE MOISTURE IS VAPORIZED IN THE GYPSUM BOARD SLOWING THE INCREASE IN THE TEMPERATURE OF THE GYPSUM BOARD.

ANOTHER EXAMPLE OF A PASSIVE AGENT IS VEGETATION.

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WHAT ARE PARTS OF COMBUSTION ??

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PARTS OF COMBUSTION ARE MATERIALS PRODUCED AND RELEASED DURING BURNING.

THEY ARE OFTEN SIMPLY DESCRIBED AS HEAT (ENERGY RELEASE, THERMAL ENERGY) AND SMOKE (NEW SUBSTANCES) BECAUSE THESE ARE THE PRODUCTS THAT HAVE THE MOST EFFECT ON FIREFIGHTERS.

NOTE: THERMAL ENERGY GENERATED DURING A FIRE IS ONE PRODUCT OF COMBUSTION THAT HEATS ADJACENT FUELS AND MAKES THEM MORE SUSCEPTIBLE TO IGNITION. ( ANYTHING CAN BE AN ADJACENT FUEL FOR HEAT)

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WHAT IS SMOKE?

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SMOKE IS AN AEROSOL COMPROMISED OF GASES, VAPOR, AND SOLID PARTICULATES.

SMOKE IS THE PRODUCT OF INCOMPLETE COMBUSTION.

FOR EXAMPLE: COMPLETE COMBUSTION OF METHANE IN AIR RESULTS IN THE PRODUCTION OF HEAT, LIGHT, WATER VAPOR, AND CARBON DIOXIDE. HOWEVER IN A STRUCTURE FIRE, MULTIPLE FUELS ARE INVOLVED AND LIMITED AIR SUPPLY RESULTS IN INCOMPLETE COMBUSTION. THESE FACTORS RESULT IN EXTREMELY COMPLEX CHEMICAL REACTIONS PRODUCING A WIDE RANGE OF PRODUCTS OF COMBUSTION INCLUDING TOXIC AND FLAMMABLE GASES, VAPORS, AND PARTICULATES.

TESTS HAVE DETERMINED THAT THERE ARE OVER 20 IRRITANTS IN SMOKE, INCLUDING HYDROGEN CHLORIDE, FORMALDEHYDE AND ACROLEIN.

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WHAT IS CARBON MONOXIDE??

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CARBON MONOXIDE ALOS KNOWN AS (CO) IS A TOXIC AND FLAMMABLE PRODUCT OF THE INCOMPLETE COMBUSTION OF ORGANIC (CARBON CONTAINING) MATERIALS.

THIS GAS IS PROBABLY THE MOST COMMON PRODUCT OF COMBUSTION ENCOUNTERED ON STRUCTURE FIRES.

CARBON MONOXIDE ACTS AS A CHEMICAL ASPHYXIANT BY BINDING WITH THE HEMOGLOBIN IN THE BLOODSTREAM PREVENTING CELLULAR DISTRIBUTION OF OXYGEN THROUGHOUT THE BODY.

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HYDROGEN CYANIDE (HCN)

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A TOXIC AND FLAMMABLE SUBSTANCE PRODUCED IN THE COMBUSTION OF MATERIALS CONTAINING NITROGEN. HCN ALSO ACTS AS A CHEMICAL ASPHYXIANT BUT WITH A DIFFERETN MECHANISM OF ACTION. HCN ACTS TO PREVENT THE BODY FROM USING OXYGEN AT THE CELLULAR LEVEL.

HYDROGEN CYANIDE IS A SIGNIFICANT BYPRODUCT OF THE COMBUSTION OF POLYURETHANE FOAM, WHICH IS COMMONLY USED IN FURNITURE AND BEDDING.

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CARBON DIOXIDE (ALSO KNOWN AS CO 2)

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CARBON DIOXIDE IS A PRODUCT OF COMPLETE COMBUSTION OF ORGANIC MATERIALS. CO2 ACTS AS A SIMPLE ASPHYXIANT BY DISPLACING OXYGEN. CARBIN DIOXIDE ALSO ACTS AS A RESPIRATORY STIMULANT, INCREASING RESPIRATORY RATE.

COLORLESS, ODORLESS, HEAVIER THAN AIR GAS THAT NEITHER SUPPORTS COMBUSTION NOR BURNS; USED IN PORTABLE FIRE EXTINGUISHERS AS AN EXTINGUISHING AGENT TO EXTINGUISH CLASS B OR C FIRES BY SMOTHERING OR DISPLACING THE OXYGEN.

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WHAT IS FLAME CONSIDERED TO BE??

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FLAME IS ALSO CONSIDERED TO BE A PRODUCT OF COMBUSTION. FLAME IS THE VISIBLE, LUMINOUS BODY OF A BURNING GAS.

NOTE: WHEN A BURNING GAS IS MIXED WITH THE PROPER AMOUNTS OF OXYGEN, THE FLAME BECOMES HOTTER AND LESS LUMINOUS. THE LOSS OF LUMINOSITY IS CAUSED BY MORE COMPLETE COMBUSTION.

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THERMAL ENERGY

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THERMAL ENERGY IS THE KINETIC ENERGY ASSOCIATED WITH THE RANDOM MOTIONS OF THE MOLECULES OF A MATERIAL OR OBJECT; OFTEN USED INTERCHANGEABLY WITH THE TERMS HEAT AND HEAT ENERGY. MEASURED IN JOULES OR BTU'S.

THE WORD HEAT IS A MORE COMMONLY USED TERM FOR THERMAL ENERGY.

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Thermal energy continued....

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HEAT IS THE THERMAL ENERGY NEEDED TO RELEASE THE POTENTIAL ENERGY IN A FUEL. HEAT BEGINS TO VIBRATE THE MOLECULES IN A FUEL. AS THE MOLECULES BREAK DOWN AND RELEASE VAPORS, THE VAPORS CAN IGNITE AND RELEASE THERMAL ENERGY. THIS NEW SOURCE OF THERMAL ENERGY BEGINS TO HEAT OTHER, UNINVOLVED. FUELS CONVERTING THEIR ENERGY AND SPREADING THE FIRE.

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TEMPERATURE

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TEMPERATURE IS THE MEASUREMENT OF THE AVERAGE KINETIC ENERGY IN THE PARTICLES OF A SAMPLE OF MATTER.

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WHAT ARE THE DIFFERENT SOURCES OF THERMAL ENERGY?

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CHEMICAL, MECHANICAL, ELECTRICAL, LIGHT NUCLEAR, AND SOUND ENERGY ARE ALL SOURCES OF THERMAL ENERGY. THEY CAN ALL TRANSFER HEAT AND CAUSE THE TEMPERATURE OF A SUBSTANCE TO INCREASE.

CHEMICAL, ELECTRICAL, AND MECHANIICAL ENERGY ARE COMMON SOURCES OF HEAT THAT RESULT IN THE IGNITION OF FUEL.

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SELF HEATING

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SELF HEATING IS THE RESULT OF EXOTHERMIC REACTIONS, OCCURRING SPONTANEOUSLY ON SOME MATERIALS UNDER CERTAIN CONDITIONS, WHEREBY HEAT IS GENERALIZED AT A RATE SUFFICIENT TO RAISE THE TEMPERATURE OF THE MATERIAL.

NOTE: SELF HATING IS ALSO A FORM OF OXIDATION, IS A CHEMICAL REACTION THAT INCREASES THE TEMPERATURE OF A MATERIAL WITHOUT THE ADDITION OF EXTERNAL HEAT. NORMALLY, THERMAL ENERGY IS PRODUCED SLOWLY BY OXIDATION AND IS LOST TO THE SURROUNDINGS ALMOST AS FAST AS IT IS GENERATED. THE PROCESS CAN BE INITIATED OR ACCELERATED BY A EXTERNAL HEAT SOURCE SUCH AS SUNSHINE.

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SPONTANEOUS IGNITION

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SPONTANEOUS COMBUSTION IS THE INITIATION OF COMBUSTION OF A MATERIAL BY AN INTERNAL CHEMICAL OR BIOLOGICAL REACTION THAT HAS PRODUCED SUFFICIENT HEAT TO IGNITE THE MATERIAL.

NOTE: IN ORDER FOR SELF HEATING TO PROGRESS TO SPONTANEOUS COMBUSTION, THE MATERIAL MUST BE HEATED TO ITS AUTO IGNITION TEMPERATURE.

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HYDROCARBON FUELS

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HYDROCARBON FUELS ARE FUELS SUCH AS GASOLINE, DIESEL, AND FUEL OIL. THESE ARE ALL LIGHTER THAN WATER AND DO NOT MIX WITH WATER.

NOTE: LIQUIDS THAT ARE LIGHTER THAN WATER ARE MORE DIFFICULT TO EXTINGUISH USING WATER AS THE SOLE EXTINGUISHING AGENT. BECAUSE IT WILL NOT MIX WITH WATER, ADDING WATER TO THE LIQUID FUEL MAY DISPERSE THE BURNING LIQUID INSTEAD OF EXTINGUISHING IT, WHICH COULD POTENTIALLY SPREAD THE FIRE TO OTHER AREAS.

`

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POLAR SOLVENTS

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POLAR SOLVENTS ARE LIQUIDS SUCH AS ALCOHOL, METHANOL, ETHANOL, KETONE AND LAQUER. WILL MIX READILY WITH WATER.

NOTE: SINCE THESE FUELS MIX READILY WITH WATER, WHEN BURNING THEY CAN MIX WITH AN EXTINGUISHING AGENT CAUSING THE AGENT TO BECOME LESS EFFECTIVE. TO AVOID THIS MIXTURE, FIRE FIGHTING FOAMS SPECIALLY DESIGNED FOR POLAR SOLVENTS SHOULD BE USED.

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WHAT IS FLAMMABLE (EXPLOSIVE) RANGE ?

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FLAMMABLE (EXPLOSIVE) RANGE IS THE RANGE BETWEEN THE UPPER FLAMMABLE LIMIT AND LOWER FLAMMABLE LIMIT IN WHICH A SUBSTANCE CAN BE IGNITED.

NOTE: FOR COMBUSTION TO OCCUR AFTER A FUEL HAS BEEN CONVERTED INTO A GASEOUS STATE, IT MUST BE MIXED WITH AIR (OXIDIZER) IN THE PROPER RATIO. HENCE: FLAMMABLE (EXPLOSIVE) RANGE.

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LOWER FLAMMABLE LIMIT

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LOWER FLAMMABLE LIMIT IS THE LOWER LIMIT AT WHICH A FLAMMABLE GAS OR VAPOR WILL IGNITE AND SUPPORT COMBUSTION.

NOTE: CONCENTRATIONS THAT ARE BELOW THE LFL ARE SAID TO BE TOO LEAN TO BURN.

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UPPER FLAMMABLE LIMIT

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UPPER FLAMMABLE LIMIT IS THE UPPER LIMIT AT WHICH A FLAMMABLE GAS OR VAPOR WILL IGNITE.

NOTE: CONCENTRATIONS THAT ARE ABOVE THE UFL ARE SAID TO BE TOO RICH TO BURN.

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FREE RADICALS

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FREE RADICALS ARE ELECTRICALLY CHARGED, HIGHLY REACTIVE PARTS OF MOLECULES.

NOTE: AS FLAMING COMBUSTION OCCURS, THE MOLECULES OF METHANE AND OXYGEN BREAK APART TO FORM FREE RADICALS. FREE RADICALS COMBINE WITH OXYGEN OR WITH THE ELEMENTS THAT FORM THE FUEL MATERIAL PRODUCING INTERMEDIATE COMBUSTION PRODUCTS (NEW SUBSTANCES), EVEN MORE FREE RADICALS, AND INCREASING THE SPEED OF THE OXIDATION REACTION.

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CHEMICAL FLAME INHIBITION

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EXTINGUISHMENT OF A FIRE BY INTERRUPTION OF THE CHEMICAL CHAIN REACTION.

EXAMPLE: THIS OCCURS WHEN AN EXTINGUISHING AGENT, SUCH AS DRY CHEMICAL OR HALON-REPLACEMENT AGENT, INTERFERES WITH THE CHEMICAL REACTION, FORMS A STABLE PRODUCT, AND TERMINATES THE COMBUSTION REACTION.

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FUEL CONTROLLED

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A FIRE WITH ADEQUATE OYGEN IN WHICH THE HRR (HEAT RELEASE RATE) AND GROWTH RATE ARE DETERMINED BY THE CHARACTERISTICS OF THE FUEL, SUCH AS QUANTITY AND GEOMETRY.

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VENTILATION CONTROLLED

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A FIRE WITH LIMITED VENTILATION IN WHICH THE HRR OR GROWTH IS LIMITED BY THE AMOUNT OF OXYGEN AVAILABLE TO THE FIRE.

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HRR (HEAT RELEASE RATE)

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TOTAL AMOUNT OF HEAT RELEASED PER UNIT TIME. THE HRR IS MEASURED IN KILOWATTS AND MEGAWATTS OF OUTPUT.

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AMBIENT CONDITIONS

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AMBIENT CONDITIONS ARE COMMON, PREVAILING, AND UNCONTROLLED ATMOSPHERIC WEATHER CONDITIONS.

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STAGES OF FIRE

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INCIPIENT STAGE

GROWTH STAGE

FULLY DEVELOPED STAGE

DECAY STAGE

FLASHOVER

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INCIPIENT STAGE

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THE FIRST STAGE OF THE BURNING PROCESS.

THIS PROCESS STARTS WITH IGNITION WHEN THE THREE ELEMENTS COME TOGETHER AND THE COMBUSTION PROCESS BEGINS. AT THIS POINT THE FIRE IS SMALL AND CONFINED TO THE MATERIAL (FUEL) FIRST IGNITED.

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PLUME

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THE COLUMN IF HOT GASES, FLAMES, AND SMOKE RISING ABOVE A FIRE. (ALSO CALLED CONVECTION COUMN, THERMAL UPDRAFT, OR THERMAL COLUMN)

NOTE: DURING THE INITAL (INCIPIENT STAGE) OF FIRE DEVELOPMENT, RADIANT HEAT WARMS THE ADJACENT FUEL AND CONTINUES THE PROCESS OF PYROLYSIS. A PLUME OF HOT GASES AND FLAME RISES FROM THE FIRE AND MIXES WITH THE COOLER AIR IN THE ROOM.

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CEILING JET

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A RELATIVELY THIN LAYER OF FLOWING HOT GASES THAT DEVELOPS UNDER A HORIZONTAL SURFACE AS A RESULT OF PLUME IMPINGEMENT AND THE FLOWING GAS BEING FORCED TO MOVE HORIZONTALLY.

NOTE: AS THE PLUME REACHES THE CEILING; HOT GASES BEGIN TO SPREAD HORIZONTALLY ACROSS THE CEILING IN WHAT FIREFIGHTERS HAVE HISTORICALLY CALLED MUSHROOMING; HOWEVER, IN SCIENTIFIC OR ENGINEERING TERMS IT IS REFERRED TO AS CEILING JET.

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GROWTH STAGE

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THE SECOND STAGE IN FIRE DEVELOPMENT.

AS THE FIRE TRANSITIONS FROM THE INCIPIENT STAGE TO THE GROWTH STAGE, IT BEGINS TO INFLUENCE THE ENVIRONMENT WITHIN THE COMPARTMENT AND HAS GROWN LARGE ENOUGH FOR THE COMPARTMENT CONFIGURATION AND AMOUNT OF VENTILATION TO INFLUENCE IT.

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THERMAL LAYERING

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THERMAL LAYERING ( ALSO REFERRED TO AS HEAT STRATIFICATION AND THERMAL BALANCE)

IS THE OUTCOME OF COMBUSTION IN A CONFINED SPACE IN WHICH GASES TEND TO FORM INTO LAYERS, ACCORDING TO TEMPERATURE, WITH THE HOTTEST GASES FOUND AT THE CEILING AND THE COOLEST GASES AT FLOOR LEVEL.

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NEUTRAL PLANE

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THE LEVEL AT A COMPARTMENT OPENING WHERE THE DIFFERENCE IN PRESSURE EXERTED BY EXPANSION AND BUOYANCY OF HOT SMOKE FLOWING OUT OF THE OPENING AND THE INWARD PRESSURE OF COOLER, AMBIENT TEMPERATURE AIR FLOWING IN THROUGH THE OPENING IS EQUAL.

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FULLY DEVELOPED STAGE

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THE FULLY DEVELOPED STAGE OCCURS WHEN ALL COMBUSTIBLE MATERIALS IN THE COMPARTMENT ARE BURNING.

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DECAY STAGE

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where the fire begins to cool and die as fuel and/ or ventilation run out of supply.

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CONSUMPTION OF FUEL

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AS THE FIRE CONSUMES THE AVAILABLE FUEL IN THE COMPARTMENT AND THE HEAT RELEASE RATE BEGINS TO DECLINE, IT ENTERS THE DECAY STAGE. IF THERE IS ADEQUATE VENTILATION, THE FIRE BECOMES FUEL CONTROLLED. THE HEAT RELEASE RATE WILL DROP, BUT THE TEMPERATURE IN THE COMPARTMENT MAY REMAIN HIGH FOR SOME TIME. DURING THIS STAGE, THE FLAMMABLE PRODUCTS OF COMBUSTION CAN ACCUMULATE WITHIN THE COMPARTMENT OR ADJACENT SPACES.

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LIMITED VENTILATION

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WHEN A FIRE ENTERS THE DECAY STAGE DUE TO A LACK OF OXYGEN, THE RATE OF HEAT RELEASE ALSO DECLINES. HOWEVER, THE CONTINUING COMBUSTION REACTION (BASED ON AVAILABLE FUEL AND THE LIMITED OXYGEN AVAILABLE TO THE FIRE) MAY MAINTAIN AN EXTREMELY HIGH TEMPERATURE WITHIN THE COMPARTMENT. TEMPERATURE DECREASES BUT PYROLYSIS CAN CONTINUE. UNDER THESE CONDITIONS, A LARGE VOLUME OF FLAMMABLE PRODUCTS OF COMBUSTION CAN ACCUMULATE WITHIN THE COMPARTMENT.

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FLASHOVER

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WHERE THE COMBUSTIBLE MATERIALS IN THE COMPARTMENT AND THE GASES PRODUCED BY PYROLYSIS IGNITE ALMOST SIMULTANEOUSLY; THE RESULT IS FULL ROOM INVOLVEMENT. FLASHOVER TYPICALLY OCCURS DURING THE GROWTH STAGE OF A FIRE BUT MAY OCCUR IN THE FULLY DEVELOPED STAGE.

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FLASHOVER INDICATORS

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BUILDING INDICATORS- FLASHOVER CAN OCCUR IN ANY BUILDING, INTERIOR CONFIGURATION, FUEL LOAD, THERMAL PROPERTIES, AND VENTILATION WILL DETERMINE HOW RAPIDLY IT CAN OCCUR

SMOKE INDICATORS- RAPIDLY INCREASING VOLUME, TURBULENCE, DARKENING COLOR, OPTICAL DENSITY, AND LOWERING OF THE HOT GAS LEVEL.

AIRFLOW INDICATORS- HIGH VELOCITY AND TURBULENCE, BIDIRECTIONAL MOVEMENT WITH SMOKE EXITING AT THE TOP OF DOORWAY AND FRESH AIR MOVING IN AT BOTTOM , OR PULSING AIR MOVEMENT.

HEAT INDICATORS- RAPIDLY INCREASING TEMPERATURE IN THE COMPARTMENT, PYROLYSIS OF CONTENTS OR FUEL PACKAGES LOCATED AWAY FROM THE FIRE, DARKENED WINDOWS, OR HOT SURFACES.

FLAME INDICATORS- ISOLATED FLAMES IN THE HOT GAS LAYERS OR NEAR THE CEILING.

ROLLOVER- A CONDITION WHERE THE UNBURNED FIRE GASES THE AHAVE ACCUMULATED AT THE TOP OF A COMPARTMENT IGNITE AND FLAMES PROPAGATE THROUGH THE HOT-GAS LAYER OR ACROSS THE CEILING.

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ROLL OVER

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ALTHOUGH ROLLOVER WILL GENERALLY PRECEDE FLASHOVER, IT DOES NOT ALWAYS RESULT IN FLASHOVER.

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BACKDRAFT

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THE EXPLOSIVE BURNING OF HEATED GASES THAT OCCURS WHEN OXYGEN IS INTRODUCED INTO A COMPARTMENT THAT HAS A HIGH CONCENTRATION OF FLAMMABLE GASES AND A DEPLETED SUPPLY OF OXYGEN DUE TO AN EXISTING FIRE.