FIRE AND SAFETY PRINCIPLES OF FIRE FIGHTING PRINCIPLE OF FIRE FIGHTING INTRODUCTION • A fire can be extinguished by destroying one or more of the elements of the fire tetrahedron. • If the chain reaction is broken, resulting, reduction in vapour and heat production will extinguish the fire. If the fuel, oxygen or heat is removed, the fire will die out • Fire extinction, in principle, consists of the limitation or removal of one or more of four factors of the fire tetrahedron, and the methods of extinguishing classified as follow; – – – – Starvation (fuel) Smothering (oxygen) Cooling ( heat) Interrupt the chain reaction Starvation • Defines as the reduction or removal of the fuel supply. • If the unburn fuel is taken away from the immediate vicinity of a fire, the fire does not extend to the unburn fuel. • If it is in a liquid form or gas, turn off supply valve or shut down the supply of fuel, and therefore extinguish the fire Smothering • Reducing the oxygen level in the air to below 16%, which will then die when the surrounding oxygen is used up. • The extinction of fire by shutting of doors, hatches and appropriates ventilation valves or shutters is a result of smothering. • Other method is by application of extinguishing agents such as foam, carbon dioxide, dry chemical powder and dry powder for metal fires Smothering: to separate the fuel from the oxygen. This can be considered as an attack on the edge of the fire tetrahedron where the fuel and oxygen sides meet Cooling • The most commonly used method is to removed the heat. • Water is a very effective heat absorber and radiation feedback when properly applied.As a result, the chain reaction is indirectly attacked both on the fuel surface and the flame. • The production of vapour and radiant heat is reduced • Boundary cooling is one way of keeping all external sides of fire zones cooled with water spray to prevent spreading by conduction. Cooling: to reduce the temperature of the fuel below its ignition temperature. This is direct attack on the heat side of the fire tetrahedron. Interrupt chain reaction • Fire can be extinguished by breaking the chain reaction. • It normally direct attack the molecules structure or breaking down of compounds formed during the chain reaction process. • The extinguishing agents commonly used to attack the chain reaction and inhabit combustion are dry powders and halons. Chain breaking: to disrupts the chemical reaction process that sustains the fire Additional • Oxygen dilution; to reduce the amount of available oxygen below that needed to sustain combustion. This is an attack on the oxygen side of the tetrahedron CO2 HEAT OXYGEN FUEL CHAIN REACTION Fire Fighting Medium FIRE EXTINGUISHING AGENTS Factors affecting choice of extinguishing agents: • RIGHT CHOICE OF AGENT IS VERY IMPORTANT • • • • • • SINCE IT WILL BE MORE EFFICIENT THAN OTHERS Efficiencies Electrical conductors Dangerous to personnel Toxic level Effective / danger than fire itself Type of fire involve Selecting the wrong agents could: • Transfer electrical hazards • Toxic and dangerous to operator • Do more damage than the fire itself • Unable to extinguish the fire • Create bigger fire spread • Do increase rate of combustion • Promote an explosion / uncontrolled situation FIRE EXTINGUISHING AGENTS Water • • • • • • • • Abundantly available lowering temperature below ignition point Great cooling effects smothering action, starving the fire of oxygen Turn into steam – smothering effect (oxygen starvation) Best for class A – deep penetration to fire seat Excellent boundary cooling Non toxic, non irritant Water (cont/….) • causing water damage • possibility of endangering the stability of the • • • • ship Unsuitable for electrical fire – good conductor fire in cargoes - emit flammable gases when wet condition Not extinguish low flash point fires Cause explosion when in contact with certain chemicals Steam • Smother fire Replace air in protected • • • • • • compartment until insufficient oxygen level Not suitable for “well established” fire – steam will condense Condense steam acts as water Must be continuously supply until fire completely extinction. To be injected at lower level – lighter than air Not very effective agent No longer fitted in new building Carbon dioxide (CO2) • Smothering action – replace the air in • • • • protected compartment - insufficient by diluting oxygen Non corrosive Non electrical conductors Leaves no residue Consider easy to store Carbon dioxide (CO2) • Quality not deteriorate with ages • Immediately available even dead ship • Most substances – 12 ~ 16% O2 will sufficient to stop combustion • For smouldering solid materials - 5% O2 contents reqd for fire extinction. • Particularly suitable for enclosed spaces Carbon dioxide (CO2) • used only in enclosed spaces • limited quantity on board • not lowering the temperature • Evacuation reqd before flooding the space • Highly asphyxiating and slightly toxic • 9% concentration cause unconscious • Little cooling effect Carbon dioxide (CO2) • Danger of reignition if readmitted too quick • Generate static electricity during discharge – sufficient to produce spark • Unsuitable as inerting medium for cargo tank and pump room • Heavy storage container / comprehensive maintenance • Disperses easily – undetectable • colourless When CO2 no longer available / being used up: • Prepare fire watch system • Increase crew awareness • Extra precaution taken • More simulation, discussion, drill, practices to carry out • More safety on hotwork Halon • • • • • • Inhibiting effect by stopping chain reaction used only in enclosed spaces limited quantity onboard used in lower concentrations than carbon dioxide not directly dangerous for trapped personnel Breaks down in a fire into toxic components FOAM • EFFECTIVE AGENT FOR FIRE INVOLVING • • • • • LIQUIDS. FORMED LAYER OF SMALL BUBBLES – SEALED FUEL SURFACE & PREVENT VAPOURISATION AND ACCESS OF AIR. NORMALLY LIMITED QUANTITY ONBOARD & SERVING AGES. HAVE SOME COOLING EFFECT. SOME FOAMS CAUSING VARYING DEGREES OF WATER DAMAGE. 2 MAIN TYPES – CHEMICAL & MECHANICAL. CHEMICAL FOAM • PRODUCED BY INTERACTION OF ALUMINIUM SULPHATE & SODIUM BICARBONATE. • FOAMING AGENT/ STABILISER (MAGNESIUM STEARATE) NORMALLY ADDED. • WHEN MIXED TOGETHER, CO2 RELEASED AND PERFORMED 2 PURPOSES: – FILLING FOAM BUBBLES. – PROJECTING THE FOAM FROM CONTAINER IN CONTINUOUS JET. • SO, FOAM IS A MASS OF CO2 BUBBLES. • DETERIORATE IN STORAGE. MECHANICAL / AIR FOAM • MIXING A FOAM CONCENTRATE WITH WATER • • • IN CORRECT PROPORTION. RESULTANT FORCED THRU SPECIAL NOZZLE & BRANCH PIPE (APPLICATOR). TURBULENCE OCCURRED RESULTANT AIR BEING INTRODUCED TO AGITATE THE CONCENTRATE INTO SMALL AIR FILLED BUBBLES. 4 MAIN TYPES OF AIR FOAM: PROTEIN FOAM • FROM ANIMAL WASTE PRODUCT (BLOOD/HOOF & HORN) WITH STABILISER ADDED. • CREAMY COLOUR & UNPLEASANT SMELL. • SOLUTION IS MIXTURE OF 3% OF CONCENTRATE TO 97% OF WATER. • EXPANSION RATION 8 : 1. FLUOROPROTEIN FOAM • NORMAL PROTEIN FOAM WITH FLUORINE COMPOUND ADDED. • SUPERIOR THAN NORMAL PROTEIN FOAM & MUCH MORE EXPENSIVE. • PROBLEM WITH FOAM – WHEN PROJECTED ONTO BURNING FUEL, IT SUBMERGES BEFORE RISING TO FLOAT ON SURFACE, SOMETIMES BUBBLES ITSELF BURNS DUE TO CONTAMINATION WITH FUEL. • THIS DOES NOT HAPPEN TO FLUOROPROTEIN FOAM FUEL DOES NOT ADHERE TO IT. (FLUORIN IS A PART OF HALON COMPONENTS. SYNTHETIC FOAM • SIMILAR TECHNOLOGY TO HAIR SHAMPOO & LIQUID • • • • DETERGENT. SOLUTION – 5% CONCENTRATE & 95 WATER. WHITE COLOUR & LESS PERSISTENT THAN PROTEIN FOAM. SUPERIOR TO NORMAL FOAM, LESS EFFICIENT THAN FLUOROPROTEIN FOAM. VERY FLEXIBLE & CAN PRODUCED: – LOW EXPANSION FOAM (UP TO 12:1). – MEDIUM EXPANSION FOAM (UP TO 150:1). – HIGH EXPANSION FOAM (UP TO 1000:1). ** MORE THAN 1000:1 IS UNSUITABLE – TOO THIN, AFFECT SMOTHERING & COOLING. • LOW EXPANSION – APPLIED BY MONITOR / HAND HELD HOSES & APPLICATOR – PROJECTED OVER CONSIDERABLE DISTANCE. – FOAM WILL SCATTER IF TOO FAR. • MEDIUM EXPANSION – HANDHELD ONLY, RANGE UP TO 15 METER. – OPERATORS MUST WELL PROTECTED INCLUDING BA SET. – SUITABLE FOR FIRE IN ENCLOSED SPACES. • HIGH EXPANSION – – – – – CANNOT PROJECTED AT ALL. LED THRU DUCT / ALLOW TO FREE FALL. USED TO ENTIRELY FILL COMPARTMENT UNDER FIRE WHEN CONTACT WITH FIRE – FLASHED TO STEAM. GOOD COOLING EFFECT, EXCELLENT SHIELD AGAINST RADIANT HEAT – PREVENTING SPREAD OF FIRE. – EFFECTIVE AGAINST FIRE INVOLVING LOW FLASH POINT LIQUID WHICH DIFFICULTY DISSOLVE IN WATER. – PRODUCED BY SPRAYING THE SOLUTION ONTO FINE MESH NYLON SCREEN. – AIR IS INTRODUCED BY LARGE FAN TO FORM HUGE MASS OF BUBBLES AT 1200 TO 5400 CUBIC FT / MIN DEPENDING ON SIZE. Why not to exceed 1000? • Too thin for bubbles to form • Affecting: – Smothering – Cooling ACQUEOUS FILM FORMING FOAM (AFFF) • a.k.a. LIGHT WATER • FLUOROCHEMICAL BASED METTING AGENT & ABILITY • • • • • • TO FLOAT ON FLAMMABLE LIQUID WHICH HAVE LOWER DENSITY THAN WATER. SOLUTION – 6% CONCENTRATE & 94% WATER. DRIVEN THRU CONVENTIONAL AIR FOAM MAKING EQUIPMENT. EXPANSION RATION OF 8 TO 10:1. SPREAD RAPIDLY OVER SURFACE. ACTION – ENHANCES EXTINCTION & PREVENT FLASH BACK EVEN FOAM BLANKET IS RUPTURED. MOST EFFICIENT BUT VERY EXPENSIVE. ALCOHOL FOAM • NORMAL FOAM UNSUITABLE FOR FIRE INVOLVING WATER MISCIBLE LIQUID: – ALCOHOL ~ METHYL, ETHYL, ISOPROPYL – ESTER ~ ETHYL ACETATE – KETONES ~ ISOPROPYL ETHER, DIETHYL ETHER • ABSORB WATER FROM FOAM – BUBBLES • • COLLAPSED. A.k.a. ALL PURPOSES FOAM – CAN USED ON ORDINARY HYDROCARBON LIQUID FIRES. HOWEVER, QUANTITY REQD MAY HIGHER THAN PROTEIN FOAMS. FOAM FOR MARINE USE • MUST SUITABLE FOR USE WITH SEA WATER. • MUST CAPABLE TO MAINTAIN AN EFFECTIVE SEAL OVER FUEL SURFACE – REIGNITION DOES NOT OCCUR AT ANY POINT (BACK BURN). • FLUOROPROTEIN FOAM HAS A GOOD BACK BURN CHARACTERISTIC. Foam • • • • • • • smothering action by blanketing the fire limited quantity onboard choice of heavy, medium and light foams each type required own nozzle of foam generator light foams used only in enclosed spaces having some cooling effect some foams causing varying degrees of water damage Chemical powder • inhibiting effect by stopping the chain reaction • limited quantity onboard • causing damage to electrical and electronic equipment Starvation • cutting off fuel supply - situation: – Engine room fire involving burst oil pipes – Gas fires • cutting off fuel supply – methods: – closing supply valve – stopping pumps – dropping (emptying) high tanks Smothering • limiting the ingress of air: – – – – stopping fans closing dampers and doors Fire / smoke travel Possibility for back draught AUTO IGNITION TEMP MIN TEMP WHICH THE GENERATED VAPOUR WILL IGNITE SPONTANEOUSLY WITHOUT ANY EXTERNAL SOURCE OF IGNITION. AI TEMP FOR FO & LO ARE LOWER THAN THOSE OF LIGHTER FRACTION BECAUSE CERTAIN PROPS IN LIQUID COMPOSITION METHANE BENZENE ACETYLENE CYLINDER OIL 700ºC 742ºC 422ºC 420ºC SUBSTANCE WITH LOW AI TEMP HAS HIGHER FLASH POINT CONT/.. • THEREFORE WHEN CARRYING CARGO: – LOW AI & HIGH FP – TO ENSURE THE SPACE ABOVE THE LIQUID LEVEL DOES NOT CONTAIN EXPLOSIVE MIXTURE. – HIGH AI & LOW FP – NOT TO OVERHEAT THE FUEL EXCESSIVELY WHICH RESULT IN SPONTANEOUS IGNITION.