FIRE 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 32 o water freezes0 o 212 o water boils100 o –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 60 o to 212 o requires 152 BTU’s –To change water at 212 o 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 60 o to 212 o =152 BTU –152 x 8.33 = 1266 BTU / gal of water –970 (latent heat) x 8.33 = 8080 BTU / gal – = 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 60,000 o F

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