fundamentals of fire
DESCRIPTION
Basic fire SafetyTRANSCRIPT
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Fundamentals of Fire SafetyPresented byKiran K. Joy
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FIRE SAFETY & PROTECTIONOutlineIntroductionFire ChemistryFire Classification.Extinguishing agentsControlling fire hazards
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OBJECTIVESKnow and Understand:
Basics of fire chemistryFire classesHow extinguishing agents work
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INTRODUCTIONFire is a substantial riskAnnual $2.2 billion lossOver 300 Workplace deathsOver 3%of workplace fatalitiesFire losses can be catastrophicFire hazards MUST be controlled to low level of probability, as losses are so high.
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CHEMISTRY OF FIREFire is a chemical reaction, in which substance (fuel) combines with oxygen. The reaction is exothermic and usually associated with emission of light and smoke
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CHEMISTRY OF FIREFour components of Combustion
1 OxygenAtmosphere (21% O2)Chemical Oxidizers
2 FuelSolids - Surface to mass ratio affects burn rate Liquids - Vapour burns, not liquidGases
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CHEMISTRY OF FIRE3 HeatHeat of CombustionOther sources of heat can cause ignitionChemical reactionDecaySlow oxidationSpontaneous combustionElectricity - arching, resistance heatingMechanical friction4 Chemical Chain reactionPropagation of free radicals
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CHAIN REACTION
H*
O*+H2
OH*
H*+O2
OH*+H2 H*
OH+H2
H2O
H2O
O+H2
H+O2
OH*+H 2 H2O
H*+O2
OH*
H2O
O*+H2
OH*+H2 OH*
H*
H*+O2
OH*
H*
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FLAMMABILITY LIMITSLower Explosive limits, LEL (LFL)The minimum concentration of vapour in air below which a spread of flame does not occur when the vapour is in contact with a source of ignition
Upper Explosive limits, UEL (UFL)The maximum concentration of vapor in air above which a spread of flame does not occur when the vapor is in contact with a source of ignition.
Explosive Range (Flammable range)
The spread between LEL & UELAcetone Explosive range 2.5 - 12.8 %
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EXTINGUISHING FIRESThe Fire Triangle- Four ComponentsOxygenHeatFuelChain Reaction
Removing any components stops the fire
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EXTINGUISHING FIRECoolingRemoves heat - Applying waterStarvationRemoving fuel - Shut off gas or liquid supply or pump liquid from burning tanksLimiting OxygenMechanical smotheringFoamDisplace oxygen with inert gasInterrupting Chain reactionCapture free radicals using an extinguishing agent
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EXTINGUISHING FIRESFire Classification- Extinguishing methods are based on Fire classClass AOrdinary Combustibles - e.g. - wood, paperExtinguish with WaterClass B Flammable LiquidsWater may aggravate a burning liquid fireExtinguish with foam, Chemical agent
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Extinguishing FiresFire Classification (Cont.)Class CFlammable gasesExtinguish by starvation or chemical agentsClass DCombustible metals firesExtinguish by smothering with dry powdersWater will cause burning metals to explodeClass F Fires involving cooking oil, animal fats etc.
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EXTINGUISHING AGENTSWaterRemoves heat from a fireStream spray or fogBest for class A firesSmothering & dilution of vapors due to generation of steamNot for Electrical or combustible metal fires
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EXTINGUISHING AGENTSFoam - Aqueous Film Forming Foam (AFFF)
Excluded oxygen from burning liquidFire can re-ignite if foam breaks down
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INERT GASESCarbon dioxide, Nitrogen etcDisplaces oxygen Potentially fatal due to O2 deficiency
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DRY CHEMICAL POWDERMono-ammonium Phosphate, Sodium or potassium bicarbonate type.For class A, B or C FiresInhibits chain reactionExcludes oxygen by coating surfaces
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INHIBITION OF CHAIN REACTION BY DCPWhen Dry Chemical Powder Decomposes-2NaHCO3 --------> Na2CO3 + H2O + CO2Na2CO3 ----------->Na2O + CO2Na2O + H2O -----> 2NaOHNaOH + H* -------> Na* + H2ONaOH + OH* -----> NaO* + H2ONaO * + H* --------> NaOHNa* + OH* --------> NaOH
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SummaryQuestions and AnswersWhich is the 4th element in the Fire Chemistry?Chain reaction. What do you mean by Class D type of Fire?Fires involving Na,Mg,Ti etc.What is meaning of term starvation?Removal of fuel
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True or False?Lower explosive limit :- The Maximum concentration (percentage) of a gas or a vapor in air capable of producing a flash of fire in presence of an ignition source.False.Water is the best ,suitable fire extinguishing medium for Class D fires.False .Wet chemical Fire Extinguishers
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THANK YOU
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