Transcript 1.2 Principle of Fire Fighting

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;
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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).
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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
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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
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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
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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
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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:
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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.