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Loyalist Township Emergency Services

Loyalist Township Emergency Services. Fire Behaviour. FIRE BEHAVIOUR - INTRODUCTION.

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Loyalist Township Emergency Services

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  1. Loyalist Township Emergency Services FireBehaviour

  2. FIRE BEHAVIOUR - INTRODUCTION • As firefighters we have a responsibility to know how to “Prevent, Control and Extinguish” fires in the most efficient and effective methods possible. To fulfill that responsibility requires understanding of the fire theory, phases of fire, heat transfer and extinguishing methods. • With this knowledge in hand, we will be better prepared to effectively and safely extinguish fires.

  3. TERMS & DESCRIPTIONS • Flash Point – The minimum temperature at which a fuel gives off sufficient vapours to form an ignitable mixture of air near the surface. At this temperature the ignited vapours will flash, but will not continue to burn. • Ignition Temperature – The minimum temperature at which a fuel in air must be heated in order to start self sustained combustion without a separate ignition source. • Fire Point – The temperature at which a liquid will produce vapours sufficient to support combustion once ignited. The fire point is usually a few degrees above the flash point.

  4. TERMS & DESCRIPTIONS • Spontaneous Ignition – Decomposition of material produces quantities of heat. If this heat is contained the temperature will rise until it achieves the ignition temperature. • Vapour Density – The relative density of a gas as compared to air. Air has a value of 1.0 compared to natural gas 0.7 or gasoline 1.5. • Specific Gravity – The relative density of a liquid compared to water. Water has a value of 1.0 compared to gasoline 0.75 or bromic acid 3.2.

  5. METHODS OF HEAT TRANSFER TS 2–7 • Conduction — Point-to-point transmission of heat energy. E.g. spoon in hot water • Convection — Transfer of heat energy by the movement of heated liquids or gasses. E.g. upward travel of hot air & gases in stairwell or elevator • Radiation — 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

  6. OXIDIZING AGENTS TS 2–12a • Those materials that yield oxygen or other oxidizing gases during the course of a chemical reaction • Oxygen rich atmospheres — Those with oxygen concentrations exceeding 21% • Health care facilities • Industrial occupancies • Private homes (where occupants use liquid oxygen breathing equipment)

  7. OXIDIZING AGENTS (cont.) TS 2–12b • Oxygen deficient atmospheres — Those with oxygen concentrations lower than 21% • Storage tanks • Silos • Pipes and vaults • Other confined spaces • High altitudes

  8. FUEL CHARACTERISTICS TS 2–13a • Fuel — Material or substance being oxidized or burned in the combustion process • Pyrolysis — Chemical decomposition of a substance through the action of heat • Surface-to-mass ratio — Surface area of fuel in relation to its mass • Vaporization — Transformation of a liquid to its vapor or gaseous state

  9. FUEL CHARACTERISTICS (cont.) TS 2–13b • Flammable 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

  10. CHEMICAL HEAT ENERGY TS 2–14 • Most common source of heat is combustion reactions • 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 spontaneous ignition to occur • Sufficient heat production • Sufficient air supply • Sufficient insulation

  11. COMPARTMENT FIRE DEVELOPMENT TERMS TS 2–16 • Compartment — Enclosed room or space within a building • Compartment fire — Fire that occurs within a compartment • Fuel controlled — Amount of fuel available to burn is limited • Ventilation controlled — Amount of available oxygen is limited

  12. INCIPIENT (Beginning) STAGE TS 2–17 • The earliest phase of fire. • Flames are still small and the relative room temperature only slightly increased. The fire is burning fairly pure, producing mostly H20 and carbon dioxide CO2. The oxygen content in the room is only slightly reduced to around 20%.

  13. FREE BURNING STAGE TS 2–17 • During this stage oxygen rich air is drawn to flame as convection carries heat upwards in the confined area. Heated gases spread out at upper levels and ignite materials. Greatest heat is at the ceiling level ( 1300 F) and the least at the floor level. This is why we are taught to stay low and wear breathing apparatus. Oxygen concentration is lowered by still around 16%. As this type of fire progresses it will consume all of the oxygen in an area and could become a smoldering fire.

  14. FLASHOVER STAGE TS 2–19a • Transition between growth stage and fully developed fire stage; is not a specific event • Preflashover condition — Radiant heat (red arrows in visual) from the hot ceiling gas layer heats combustible materials, producing vapors (green arrows in visual)

  15. FLASHOVER STAGE (cont.) TS 2–19b • Just prior to flashover — • Temperatures rapidly increase • Additional fuel packages become involved • Fuel packages release combustible gases • Flashover occurs when compartment temperature exceeds 900F (483C) and all combustible surfaces and gases are burning

  16. FULLY DEVELOPED STAGE TS 2–20 • All combustible materials are involved in fire • Burning fuels release maximum amount of heat; produce large volumes of fire gases • If fire becomes ventilation controlled, large volumes of unburned fire gases are likely to flow into adjacent spaces where they may ignite if air is more abundant

  17. SMOULDERING STAGE TS 2–21 • This phase will occur after a fire has consumed all of the available oxygen in an area. Flames cease to exist due to low concentrations of oxygen and dense smoke is produced. • The oxygen is below 15% and temperature is above 1000 F. Glowing embers and dense smoke and gases are forced through cracks under pressure. • This phase of fire will lead to a Backdraft instantly if oxygen is allowed to enter the area prior to smoke and gases being vented. • Ventilation must be undertaken immediately upon arrival and prior to any fire fighting personnel trying to enter the area.

  18. FACTORS THAT AFFECT FIRE DEVELOPMENT TS 2–22 • Initial fuel package • Size • Composition • Location • Additional target fuels • Availability • Location • Ventilation openings • Size • Number • Arrangement • Compartment volume • Compartment’s thermal properties • Ceiling height

  19. FLAMEOVER / ROLLOVER TS 2–23 • Condition where flames move through or across the unburned gases during a fire’s progression and roll across the ceiling • Involves only fire gases, not the surfaces of other fuel packages (flashover)

  20. THERMAL LAYERING OF GASSES TS 2–24 • Thermal layering — Tendency of gases to form layers according to temperature • Heat stratification — Hottest gases form top layers; cooler gases form bottom layers • Thermal balance — No disruption of heat stratification • Thermal imbalance — Disruption of heat stratification (hot gases mix throughout the compartment)

  21. TEMPERATURE REDUCTION TS 2–25 • Is used on solid fuels and liquid fuels with high flash points • Is most common method of extinguishment • Reduces temperature of high flash point fuels • Creates negative heat balance • Cools with water

  22. TEMPERATURE REDUCTION TS 2–25 • Cooling or quenching reduces a materials ability to give off vapours to support combustion. • Water is best agent available (water expands 1700 x cubic foot). • Solid fuels and liquid fuels with high flash point can be extinguished by cooling. • Fuels with lower flash points cannot be cooled sufficiently.

  23. FUEL REMOVAL TS 2–26 • Is used on solid, liquid, or gas fuels • Stops flow of liquid or gaseous fuel • Moves solid fuel out of fire path • Allows fire to consume all fuel

  24. FUEL REMOVAL TS 2–26 • Turn off supply – propane, natural gas • Pump flammable liquids away. • Remove portions of material – grass fires • Water will dilute some materials – ethyl alcohol • Foam can contain flammable vapours • Flammable gases can be diluted with inert gas – CO2 or Nitrogen

  25. OXYGEN EXCLUSION OR DILUTION TS 2–27 • Is used on solid, liquid, or gas fuels • Prevents air from reaching fuel (smothering) • Dilutes or displacing oxygen with an inert gas

  26. OXYGEN EXCLUSION OR DILUTION TS 2–27 • Smothering or blanketing fire. • Introducing inert gas in fire or separating O2 from fire.

  27. INHIBITION OF CHAIN REACTION TS 2–28 • Is used on gas and liquid fuels • Uses dry chemicals and halogenated hydrocarbons • Interrupts chemical chain reaction (stops flaming)

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