Chemistry of fire: Chemistry of fire
Kinds of oxidatin:
1- slow like rotten food
2-fast like fire
What is fire? Slide3: FIRE ABOARD
1 - DEAD Slide5: FUEL HEAT O2 FIRE TRIANGLE WHERE SURFACE
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
TO OCCUR: COMBUSTION THRESHOLDS: COMBUSTION THRESHOLDS Ignition
????? 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
Limit(LEL) Minimum percentage of flammable vapor in air which will burn. Below this mixture is to lean Upper
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
> 600F Auto
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
heat Heat releases
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
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
Leaves no residue
No reflash protection SMOTHERING AGENTS: SMOTHERING AGENTS CARBON DIOXIDE (cont’d)
Static electricity buildup
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
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
High velocity discharge
Frostbite CHEMICAL INTERRUPTION: CHEMICAL INTERRUPTION HALON 1301 (MONOBROMOTRIFLUORMETHANE)
Hydrogen fluoride STARVING: STARVING Jettison burning material
Isolate burning fuel from other fuel sources SUMMARY: SUMMARY Unit Introduction
Fire school brief
Facts / figures