Fundamentals of Fire SafetyPresented byKiran K. Joy

FIRE SAFETY & PROTECTIONOutlineIntroductionFire ChemistryFire Classification.Extinguishing agentsControlling fire hazards

OBJECTIVESKnow and Understand:

Basics of fire chemistryFire classesHow extinguishing agents work

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.

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

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

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

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*

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 %

EXTINGUISHING FIRESThe Fire Triangle- Four ComponentsOxygenHeatFuelChain Reaction

Removing any components stops the fire

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

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

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.

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

EXTINGUISHING AGENTSFoam - Aqueous Film Forming Foam (AFFF)

Excluded oxygen from burning liquidFire can re-ignite if foam breaks down

INERT GASESCarbon dioxide, Nitrogen etcDisplaces oxygen Potentially fatal due to O2 deficiency

DRY CHEMICAL POWDERMono-ammonium Phosphate, Sodium or potassium bicarbonate type.For class A, B or C FiresInhibits chain reactionExcludes oxygen by coating surfaces

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

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

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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