Loyalist Township Emergency Services
Fire Behaviour
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.
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.
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.
TS 2–7
METHODS OF HEAT TRANSFER
• 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
TS 2–12a
OXIDIZING AGENTS
• 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)
OXIDIZING AGENTS
(cont.)
• Oxygen deficient atmospheres — Those with
oxygen concentrations lower than 21%
 Storage tanks
 Silos
 Pipes and vaults
 Other confined spaces
 High altitudes
TS 2–12b
TS 2–13a
FUEL CHARACTERISTICS
• 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
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
TS 2–14
CHEMICAL HEAT ENERGY
• 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
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
TS 2–17
INCIPIENT (Beginning) STAGE
• 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%.
TS 2–17
FREE BURNING STAGE
• 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.
TS 2–19a
FLASHOVER STAGE
• 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)
FLASHOVER STAGE
(cont.)
• 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
TS 2–19b
TS 2–20
FULLY DEVELOPED STAGE
• 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
TS 2–21
SMOULDERING STAGE
• 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.
FACTORS THAT AFFECT
FIRE DEVELOPMENT
TS 2–22
• Ventilation openings
 Size
 Number
 Arrangement
• Initial fuel package
 Size
 Composition
 Location
• Compartment volume
• Additional target
• Compartment’s
thermal properties
• Ceiling height
fuels
 Availability
 Location
TS 2–23
FLAMEOVER / ROLLOVER
• 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)
TS 2–24
THERMAL LAYERING OF GASSES
• 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)
TS 2–25
TEMPERATURE REDUCTION
• 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
TS 2–25
TEMPERATURE REDUCTION
• 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.
TS 2–26
FUEL REMOVAL
• 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
TS 2–26
FUEL REMOVAL
• 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
TS 2–27
OXYGEN EXCLUSION OR DILUTION
• Is used on solid, liquid, or gas fuels
• Prevents air from reaching fuel (smothering)
• Dilutes or displacing oxygen with an inert gas
TS 2–27
OXYGEN EXCLUSION OR DILUTION
• Smothering or blanketing fire.
• Introducing inert gas in fire or separating O2
from fire.
TS 2–28
INHIBITION OF CHAIN REACTION
• Is used on gas and liquid fuels
• Uses dry chemicals and halogenated
hydrocarbons
• Interrupts chemical chain reaction (stops
flaming)