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FIRE BEHAVIORFIRE BEHAVIOR
ILLINOIS OSFM
FIREFIGHTER III
TERMS
• Heat Measurement– BTU
• Amount of heat required to raise the temperature of 1 pound of water 1 degree F
– Fahrenheit -Celsius• 32o water freezes 0o
• 212o water boils 100o
– Calorie• Amount of heat needed to raise the temperature of one
gram of water, one degree Celsius
TERMS
• Flash Point– min. Temp. liquid gives off sufficient vapor to ignite
momentarily at surface.
• Fire Point– temp. at which vapor gives off sufficient vapor to
support combustion once ignited
• Ignition Temperature– min. temp. a fuel, in air, must be heated to start self-
sustained combustion w/o an outside ignition source
TERMS
• Law of Specific Heat– The measure of the heat absorbing capacity of a
substance– Amount of heat transfer is measured in BTU’s– Specific heat represents the amount of heat
needed to raise the temp of a specified quantity of a material and an equal amount of water.
TERMS
• Law of Latent Heat of Vaporization– Quantity of heat absorbed by a substance when it
changes from a liquid to a vapor– Raising temp of 1 pound of water from 60o to 212o
requires 152 BTU’s– To change water at 212o to steam requires an
additional 970 BTU’s of heat energy (latent heat)– Latent heat explains potential extinguishing
capacity of water
Law of Latent Heat of Vaporization
• Example
– 1 gallon of water = 8.33 lbs..
– 1 pound of water from 60o to 212o =152 BTU
– 152 x 8.33 = 1266 BTU / gal of water
– 970 (latent heat) x 8.33 = 8080 BTU / gal
– 1266 + 8080 = 9346 BTU / gal of water
• 100 GPM fog nozzle has potential extinguishing capacity of 934,600 BTU / min.
HEAT SOURCES
• CHEMICAL– Heat of Combustion
• Oxidation reaction
• varies depending on material
• some materials burn hotter
– Spontaneous Heating• Organic Substances
• occurs where sufficient air not present and insulation prevents heat dissipation
– oil soaked rags
HEAT SOURCES
• CHEMICAL– Heat of Decomposition
• Release of heat from decomposing compounds
• Usually bacterial action
• Compost pile
– Heat of Solution• Heat released by the solution of matter in liquid
• Some acids
HEAT SOURCES
• MECHANICAL HEAT ENERGY
– Friction• Movement of two surfaces against each other
– brakes , grinding
– Compression• Generated when a gas is compressed
– diesel engine
– filling an SCBA bottle
HEAT SOURCES
• ELECTRICAL– Resistances Heating
• Generated by current passing through a conductor
• Increased if wire not large enough– Overloaded extension cord
– Leakage Current Heating• Wire not insulated well enough to contain current
• Current leaks out and heats surrounding materials– Outlet in wall mounted to stud
HEAT SOURCES
• ELECTRICAL– Heat from arcing
• Occurs when current flow is interrupted
• May be from a switch or loose connection – arc welding
– Static Electricity• Build-up of + charge on one surface and a - charge on the
another surface
• Lightning
• Excess of 60,000oF
EFFECTS OF HEAT & PRESSURE ON CONFINED GASES
• Charles Law – Gas will expand or contract in direct proportion
to change in temperature– If gas is confined, pressure will change in direct
proportion to the temperature
EFFECTS OF HEAT & PRESSURE ON CONFINED GASES
• Boyles Law– Pressure of a gas is inversely proportional to its
volume at a given temperature– Relates to the compressibility of a gas– Relates to the effect temperature and volume
have on pressure inside a pressurized container
EFFECTS OF HEAT & PRESSURE ON CONFINED GASES
• Heat of Compression– Generated when a gas is compressed
FINELY DIVIDED FUELS
• Surface to mass ratio– Ratio of surface area of the fuel to the mass of
the fuel– Ratio increases, fuel particle become
smaller/finely divided-easier to ignite– Surface area increases, heat transfer is easier
FINELY DIVIDED FUELS
• Surface to Mass Ratio– Positioning
• Vertical is best for fire spread
– Moisture Content– Arrangement (air)
• material packed tight vs.. pile of skids
FIRE BEHAVIOR & BUILDING CONSTRUCTION
• Type I– Compartmentize a fire– Primary fire hazard is contents– Protection may be compromised
• opening in firewalls/HVAC dampers
– Type II• Primary fire hazard is contents
• Heat build-up can cause structural failure
• Fire extension = roof collapse
FIRE BEHAVIOR & BUILDING CONSTRUCTION
• Type III– Fire and smoke spread in concealed spaces– Heat may be conducted to concealed areas
through finish materials
• Type IV & V– Massive amount of combustibles-structural
members– High heat given off-serious exposures hazards
FIRE BEHAVIOR & WILDLAND FIRES
• Fuels– Ground Fuels
• twigs, leaves, needles
– Surface Fuels• living vegetation-
• grass, brush, limbs
– Crown Fuels• Suspended and upright
– Separated from ground fuels by free air space
FIRE BEHAVIOR & WILDLAND FIRES
• Factors affecting fire behavior– Fuel size-small fuel burns faster
– Compactness-compacted burns slower
– Continuity-fuels close together spreads fire faster
– Volume-more fuel higher heat
– Wind- ^ intensity, fresh air
– Temperature-Affects wind, related to humidity, dries
FIRE BEHAVIOR & WILDLAND FIRES
• Factors affecting fire behavior– Relative Humidity-moisture content in dead fuels
– Precipitation-moisture content
– Steepness of slope-affect rate and direction of fire spread
– Slope aspect- southern exposures burn faster
– Canyons - increase wind velocity
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