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