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chemistry of fire

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Information about chemistry of fire
Science-Technology

Published on November 23, 2007

Author: DCA901

Source: authorstream.com

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Chemistry of fire:  Chemistry of fire Oxidation Kinds of oxidatin: 1- slow like rotten food 2-fast like fire What is fire? Slide3:  FIRE ABOARD USS INDEPENDENCE 1 - DEAD Slide5:  FUEL HEAT O2 FIRE TRIANGLE WHERE SURFACE GLOWING OR SMOLDERING IS OCCURRING: Heat Sources:  Heat Sources Chemical: Mixing chemicals such as acid and water in a manner that produces heat Spontaneous Ignition: Heating produced by organic materials with no external source of heat(Oily rags) Mechanical Friction: Heat produced when 2 objects rubbing together(Dry Bearings) Compressed Air: Diesel Combustion Electrical: High currents, Shorts Or Overloads Static Charge/Discharge: Spark produces heat when static is discharged to ground. Slide9:  FIRE TETRAHEDRON FOR FLAMING COMBUSTION TO OCCUR: Slide10:  FIRE TETRAHEDRON FOR FLAMING COMBUSTION TO OCCUR: COMBUSTION THRESHOLDS:  COMBUSTION THRESHOLDS Ignition Temperature ????? Minimum temperature at which self sustained combustion occurs without an external ignition source. Fire Point ?????? Temperature at which sufficient vapors are released to support continuous combustion once ignited. Flash Point ??????? Minimum temperature at which sufficient vapors are released to form an ignitable mixture. TEMPERATURE COMBUSTION THRESHOLDS:  COMBUSTION THRESHOLDS Lower Explosive Limit(LEL) Minimum percentage of flammable vapor in air which will burn. Below this mixture is to lean Upper Explosive Limit(UEL) Maximum percentage of a flammable vapor in air which will burn. Above this limit, mixture is too rich. Practical Combustion Thresholds:  Practical Combustion Thresholds Gasoline LEL=1.3% Diesel Fuel Marine(F-76)LEL=0.6% Lube Oil(2190)LEL=0.6% Flash Point -50F Boiling Point 90F Flash Point 140F Auto Ignition Temp >500F Flash Point >400F Boiling Point > 600F Auto Ignition Temp 853F Practical Combustion Thresholds:  Practical Combustion Thresholds Gasoline LEL=1.4% UEL=7.6% Diesel Fuel Marine(F-76)LEL=0.6% Lube Oil(2190)LEL=0.9% UEL=7% Flash Point -45F Flash Point 140F Auto Ignition Temp>450F Flash Point >400F Auto Ignition Temp 665F Auto Ignition Temp853F Jet Fuel(JP-5) LEL=0.6% UEL=4.6% Flash Point 140F Auto Ignition Temp 475f Hydraulic Oil(2110) Flash Point 325F Auto Ignition Temp 685F CLASSES OF FIRE:  CLASSES OF FIRE CLASS FUEL PREFERRED AGENT LIFE CYCLE OF A FIRE:  LIFE CYCLE OF A FIRE 4 STAGES GROWTH FULLY DEVELOPED DECAY For a flash-over or fully developed fire, the FFE provides only a few seconds of protection for escape. Self sustaining reaction:  Self sustaining reaction Burning vapor produces heat Heat releases and ignites more vapor FIRE DYNAMICS:  FIRE DYNAMICS GROWTH STAGE Earliest stage of a fire beginning with actual ignition. Fire limited to origin of ignition material. Flame temperature may be well above 10000F. Some heat being generated. Amount of heat will increase with the progress of the fire. FIRE DYNAMICS:  FIRE DYNAMICS GROWTH STAGE (cont’d) Sufficient oxygen and fuel are available for fire growth to a point where total involvement is possible. Heat carried to uppermost region of confined area. Heated gases spread laterally from the top and then down. FIRE DYNAMICS:  FIRE DYNAMICS GROWTH STAGE (cont’d) Cooler air forced to lower levels. Upper region can exceed 13000F. Slide21:  FIRE DYNAMICS CIRCULATION THERMAL BALANCE / ROLLOVER THERMAL COLUMN 1200 0 F 900 0 F 600 0 F 0 FIRE DYNAMICS:  FIRE DYNAMICS FLASHOVER Simultaneous ignition of all contents of the compartment. Normally occurs when the upper gas layer reaches 11000F. Flashover can also occur in the space above the fire. Can usually be prevented by proper fog application or venting. FIRE DYNAMICS:  FIRE DYNAMICS FULLY DEVELOPED STAGE All combustibles in the space have reached their ignition temperature. Burning rate limited by the amount of oxygen available in the air for combustion. Unburned fuel in the smoke may burn as it meets fresh air in adjacent compartments. FIRE DYNAMICS:  FIRE DYNAMICS FULLY DEVELOPED STAGE (cont’d) Structural damage to exposed steel normally occurs. Normally inaccessible by hose teams. Best fought using indirect attack. FIRE DYNAMICS:  FIRE DYNAMICS DECAY STAGE Available oxygen is consumed or reduced to a point where there is insufficient oxygen to react with fuel. Flame may cease to exist if the area is sufficiently airtight. Burning reduced to glowing embers FIRE DYNAMICS:  FIRE DYNAMICS DECAY STAGE (cont’d) If fire continues to smolder, compartment will fill with dense smoke and gases and temperatures could reach well over 10000C. Intense heat and high concentration of fire gases could produce suitable conditions for a backdraft explosion. EXTINGUISHING METHODS:  EXTINGUISHING METHODS COOLING AGENTS:  COOLING AGENTS WATER Three forms when using the Vari-nozzle Straight stream Narrow angle fog Wide angle fog High Pressure Water Mist SMOTHERING AGENTS:  SMOTHERING AGENTS AQUEOUS FILM FORMING FOAM (AFFF) Lighter than most liquid fuels Provides vapor barrier Commonly used on Class “B” fires Clear, amber colored liquid 6% concentrate to 94% water HAS SOME COOLING AFFECT DUE TO WATER CONTENT SMOTHERING AGENTS:  SMOTHERING AGENTS CARBON DIOXIDE Inert gas, heavier than air Preferred agent for Class “C” fires Non-conductive Non-corrosive Leaves no residue No reflash protection SMOTHERING AGENTS:  SMOTHERING AGENTS CARBON DIOXIDE (cont’d) Hazards Static electricity buildup Suffocation Frostbite SMOTHERING AGENTS:  SMOTHERING AGENTS AQUEOUS POTASSIUM CARBONATE (APC) Used in the Range Guard system Reacts with burning fat / cooking oil to produce a non-combustible soap-like material that provides a vapor barrier on the surface of the cooking oil. CHEMICAL INTERRUPTION:  CHEMICAL INTERRUPTION POTASSIUM BICARBONATE (PKP) Chemically alters combustion Quick flame knockdown No reflash protection Commonly used in conjunction with AFFF Personnel Hazards May cause temporary breathing difficulty May interfere with visibility CHEMICAL INTERRUPTION:  CHEMICAL INTERRUPTION HALON 1301 (MONOBROMOTRIFLUORMETHANE) Extremely effective for Class “B” fires Somewhat effective for Class “A” fires No reflash protection Hazards High velocity discharge Extremely noisy Local turbulence Frostbite CHEMICAL INTERRUPTION:  CHEMICAL INTERRUPTION HALON 1301 (MONOBROMOTRIFLUORMETHANE) Hazards (cont’d) Toxic decomposition Hydrogen bromide Hydrogen fluoride STARVING:  STARVING Jettison burning material Isolate burning fuel from other fuel sources SUMMARY:  SUMMARY Unit Introduction Fire school brief Facts / figures Fire terminology Extinguishing agents Extinguishing techniques

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