Essentials of Fire Fighting (4Th Edition-FF1)-Miscellaneous Fire Behavior Notes

CHEMICAL HEAT ENERGY

. Heat of combustion is the amount of heat generated by the combustion (oxidation) reaction. (FIRE) . Spontaneous heating is the heating of an organic substance without the addition of external heating. (OIL-SOAKED RAGS) . Heat of decomposition is the release of heat from decomposing compounds, usually due to bacterial action. (COMPOST PILE) . Heat of solution is the heat released by the solution of matter in liquid. (ACID IN WATER) . Electrical heat energy is heat produced by electricity. (ELECTRIC CURRENT) . Resistance heating refers to the heat generated by passing an electric current through a conductor such as a wire or an appliance. (OVERLOADED EXTENSION CORD) . Dielectric heating occurs as a result of the action of pulsating either DC or AC current at a high frequency on a nonconductive material. (MICROWAVE OVENS) . Leakage current heating occurs when a wire is not insulated well enough to contain all the current. (POOR INSULATION) . Heat from arcing is a type of electrical heating that occurs when the current flow is interupted. (WELDING ROD) . Static electricity is the buildup of positive charge on one surface and negative charge on another surface. (LIGHTNING)

MECHANICAL HEAT ENERGY

. Heat of friction is created by the movement of two surfaces against each other. (FRICTION) . Heat of compression is generated when a gas is compressed. (SCBA) . Nuclear heat energy is generated when atoms are either split (FISSION) or combined (FUSION). . Solar heat energy is heat generated by the sun in the form of electromagnetic radiation. (SUN)

FUEL-TO-AIR MIXTURE

. Once a fuel has been converted to a gaseous state, it must mix with an oxydizer to burn. . The mixture of the fuel vapor must be within the flammable limits for that fuel. . If there is too much fuel vapor, it is too rich to burn, if there is not enough, it is too lean to burn.

EXAMPLES OF FLAMMABLE RANGES

LOWER UPPER FUEL LIMIT % LIMIT % Gasoline vapor 1.4 7.6 Methane(Natural Gas) 5 15 Propane 2.2 9 .5 Hydrogen 4 75 Acetylene 2.5 100

HOT-SMOLDERING PHASE . When flames cease to exist because of the lack of oxygen in an airtight situation. . Burning is reduced to glowing embers. Structure is filled with dense smoke and gases. Air pressure from gases may cause smoke and gases to leak through small cracks and openings. . Room temperatures in excess of 1,000OF. . If air is not introduced, the fire will eventually burn out, leaving totally incinerated contents.

BACKDRAFT

. Also known as smoke explosion. Conditions are low oxygen, high heat, smoldering fire, and high fuel vapor concentrations. . Characteristics: Pressurized smoke exiting small openings, black smoke becoming dense gray yellow, confinement and excessive heat, little or no visible flame, smoke leaving structure in puffs or at intervals, smoke-stained windows, muffled sounds, and sudden rapid movement of air inward when opening is made. . Situation can be made less dangerous by ventilating at the highest point possible to allow heated gases and smoke to escape thus reducing the possibility of an explosion.

INCIPIENT PHASE

. Earliest phase of fire beginning with the actual ignition. . Oxygen content not significantly reduced.

. Fire is producing water vapor (H2O), carbon dioxide (CO2), and a small amount of sulphur dioxide

(SO2), carbon monoxide (CO), and other gases. . Fire may produce a flame temperature well above 1,000OF, yet the temperature in the room may be slightly increased. . Air approximately 20% oxygen.

ROLLOVER

. Takes place when unburned superheated combustible gases accumulate at the ceiling level in the incipient phase or early in the steady-state phase. These gases are pushed away from the fire area into uninvolved areas where they mix with oxygen and ignite when they reach there ignition temperatures. . Rollover continues until the source of the fire gases is extinguished.

STEADY-STATE PHASE

. Sometimes called free-burning phase. . Phase when sufficient oxygen and fuel are available for fire growth and open burning where total involvement is possible. . Early in this phase, oxygen rich air is drawn into the flame as convection carries the heat to the uppermost regions of the confined area. . Heated gases spread laterally from the top downward forcing cooler air to seek lower levels, and eventually igniting all combustible materials in the upper levels. . Early portion is the flame-spread phase. . Temperature in the upper regions can exceed 1,300OF. . Clear burning, caused by perfect burning conditions, is accompanied by high temperatures and complete combustion. Little or no smoke is given off. This usually only occurs with clean fuels such as methanol-based race car fuels. . Thermal columns occur with rapid air movements rising upward from the base of the fire. . Fire continues to burn until oxygen levels are diminished in which the fire then enters the hot- smoldering phase. The introduction of more oxygen will reinstate rapid burning.

HEAT TRANSFER

. The law of heat flow states that heat tends to flow from a hot substance to a cold substance. . Conduction is heat that is transferred from one body to another by direct contact of the two bodies or by an intervening heat-conducting medium. . Good conductors are aluminum, copper, iron. . Convection is the transfer of heat by the movement of air or liquid. Mushrooming occurs when heat contacts a surface. . Radiation is heat that travels where matter doesn’t exist. Radiated heat travels through space until it reaches an opaque object.

PRINCIPLES OF FIRE BEHAVIOR

. Fuel may be found in any of 3 states of matter, solid, liquid, or gas. Only gases burn. . Pyrolysis is the chemical decomposition of a substance through the action of heating. . The surface-to-mass ratio is the surface area of the fuel to the mass of the fuel. (CHIPPED WOOD- HIGH S-T-M RATIO) . Density is the measure of how tightly the molecules of a substance are packed together. . The density of liquids in relation to water is called specific gravity. . Volatility is the ease with which a liquid gives off vapor. . Vapor density is the density of gas or vapor in relation to air. . If vapor is less dense than air (air being a value of one), it will rise and tend to dissipate. . Every hydrocarbon except the lightest one, methane, has a vapor density greater than one, will sink, hug the ground, and flow into low lying areas. . Ethane, propane, and butane are examples of hydrocarbon gases that are heavier than air.