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GAS FIRES
Helen Verstraelen
FIRES: what you need to
remember
Fire safety aspects: prevention, protection,detection, combat
Transport of heat
Mecanism of a fire
Flamability, speed of reaction and explosion limits
Fire triangle, fire tetrahedron
Fire risk
Fire development
Fire classes
Causes of fire, fire prevention
Fire detection
Fire fighting: material, methods, installations,
DIFFERENT TYPES OF GASES
LNG: liquefied natural gases:
especially methane; relatively stable
LPG: liquefied petroleum gases:
especially butane and propane
relatively stable
Chemical gases: liquefied inflammable
gases: unsaturated and possible
unstable ex: ammonia, VCM
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CRITICAL TEMPERATURE /
PRESSURE
Critical temperature: the temperatureabove which a gas can not beliquefied, no matter what the pressure.There is no difference between theliquid and the gas: supercritical fluid
Critical pressure: pressure required forliquefaction at the critical temperature
Liquefaction possible by: Cooling down
Compressing (not above criticaltemperature)
Combination cooling and compressing
CRITICAL TEMPERATURE /
PRESSURE
CRITICAL TEMPERATURE /
PRESSURE
217.7374H2O
31.2
-119
132
critical temperature (C)
73.0CO2
49.7O2
111.5NH3
critical pressure (atm)1 atm = 1.01325 bar
gas
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TRANSPORTATION
Full pressure method: pressurised at
normal temperature. Cargo holds arespherical or cylindrical
Full refrigerated method: low T andpressure just above atmosphericalpressure. Material strength at lowtemperature is important
Semi-refrigerated (semi-pressurised)method: at the boiling temperature andcorresponding pressure
TRANSPORT
TRANSPORT
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METHANE
CH4444
Most important component of LNG
Transported at -165C (boilingtemperature) / 1.04 kg/cm
S.G. liquid: 0.474
S.G. gas: 0.554
Explosion limits: 5.3 - 14%
Flashpoint: low
Self ignition temperature: 595C
Safety and Risks of LNG TransportationSafety and Risks of LNG TransportationSafety and Risks of LNG TransportationSafety and Risks of LNG Transportation
LNG shipping so far has an excellent safetyLNG shipping so far has an excellent safetyLNG shipping so far has an excellent safetyLNG shipping so far has an excellent safetyrecordrecordrecordrecord
No shipboard fatalities over the life of theNo shipboard fatalities over the life of theNo shipboard fatalities over the life of theNo shipboard fatalities over the life of theindustry associated with cargoindustry associated with cargoindustry associated with cargoindustry associated with cargo
No major losses of cargo and only one minorNo major losses of cargo and only one minorNo major losses of cargo and only one minorNo major losses of cargo and only one minorLNG on board fire (lightning strike near ventLNG on board fire (lightning strike near ventLNG on board fire (lightning strike near ventLNG on board fire (lightning strike near ventriser, cargo tanks not affected)riser, cargo tanks not affected)riser, cargo tanks not affected)riser, cargo tanks not affected)
Two groundings resulting in major hullTwo groundings resulting in major hullTwo groundings resulting in major hullTwo groundings resulting in major hullbreaches without cargo lossbreaches without cargo lossbreaches without cargo lossbreaches without cargo loss
BUT you should never rest on your laurels. R&DBUT you should never rest on your laurels. R&DBUT you should never rest on your laurels. R&DBUT you should never rest on your laurels. R&D
programs should continue to search forprograms should continue to search forprograms should continue to search forprograms should continue to search forimprovements.improvements.improvements.improvements.
LNG TRANSPORT
PROPANE
C2222H8888
Transported at -43C / 1.04 kg/cm
S.G. liquid: 0.583
S.G. gas: 1.55
Explosion limits: 2.1 - 9.5%
Flashpoint: - 105C
Self ignition temperature: 470C
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BUTANE
C4444H10101010
Transported at - 1C / 1.04 kg/cm
S.G. liquid: 0.602
S.G. gas: 2.9
Explosion limits: 1.8 - 8.5%
Flashpoint: - 60C
Self ignition temperature: 406C
LPG
MMMMixtureixtureixtureixture ofofofof gasesgasesgasesgases,,,, mainlymainlymainlymainly propanepropanepropanepropane andandandand butanebutanebutanebutane
SSSStored under pressure totored under pressure totored under pressure totored under pressure to keepkeepkeepkeep itititit in ain ain ain a liquidliquidliquidliquidstatestatestatestate
BBBBoiling pointoiling pointoiling pointoiling point ofofofof LPGLPGLPGLPG varies from aboutvaries from aboutvaries from aboutvaries from about 44C44C44C44Ctotototo 0C,0C,0C,0C, sosososo thethethethe pressure required to liquefy itpressure required to liquefy itpressure required to liquefy itpressure required to liquefy itisisisis considerableconsiderableconsiderableconsiderable
LPG isLPG isLPG isLPG is an attractive fuel for internalan attractive fuel for internalan attractive fuel for internalan attractive fuel for internal----combustion engines because it burns withcombustion engines because it burns withcombustion engines because it burns withcombustion engines because it burns withlittlelittlelittlelittle airairairair pollutionpollutionpollutionpollution andandandand little solid residuelittle solid residuelittle solid residuelittle solid residue,,,, ititititdoesdoesdoesdoes not dilute lubricantsnot dilute lubricantsnot dilute lubricantsnot dilute lubricants, and, and, and, and it hasit hasit hasit has a higha higha higha highoctaneoctaneoctaneoctane rating.rating.rating.rating.
ETHYLENE OXIDE
C2222H4444O
Transported at -11C / 1.04 kg/cm
S.G. liquid: 0.913
S.G. gas: 1.52
Explosion limits: 3 - 100%
Flashpoint: - 57C
Self ignition temperature: 429C
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GAS FIRE
EXPLOSION
Can be mechanical, chemical or nuclear Mechanical: no chemical reaction. Ex:
breaking of vessel containing compressedgas
Chemical: fast exothermic chemicalreaction. Ex: polymerisation, decomposition,fast burning, nuclear..
In case of leakage (gas, liquid) Mixture gas-air and no ignition
Mixture gas-air and immediate ignition: fire
Mixture gas-air and postponed ignition:
explosion
DEFLAGRATION / DETONATION
Deflagration most common
Speed of flames 1 to 1000 m/s (compared
to stationary observer)
Pressure: some bars
Detonation:
supersonic (compared to speed of sound in
non combusted gas in front of the flames)
1500 - 2000 m/s
Shock wave 15 20 bar
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DETONATION
Probability of detonation dependson type of fuel
Very reactive products likehydrogen acetylene or ethylenemight explode when an accidentoccurs
Detonation of a pure mixturemethane / air is not known
POSTPONED IGNITION
Depending on dispersion of gas
cloud
SPECIFIC GRAVITY
Gases transported by ships:
Liquid: lighter than water
Gaseous: often heavier than air, except for
methane, natural gas and ammonia
! Pay attention: influence of
temperature: methane at 110C is as
heavy than air
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SPECIFIC GRAVITY
1.562 at 34C
1.458 at 10 C
0.915 at 60C
0.568 at 104.C
0.599
0.873
0.823
0.464 at 164C
specific gravity liquid to
water (at 25C) or boiling
point
2.486Chlorine - Cl2
2.264Sulfur Dioxide - SO2
1.1763Hydrogensulfide - H2S
0.9683Ethylene(Ethene) -C
2H
4
2.0061Butane - C4H
10
2.6961Benzene- C6H
6
0.596Ammonia -NH3
0.5537 / between 0.6 and
0.7
Methane- CH4
/ natural
gas
specific gravity gas to airgas
DISPERSION OF GAS
DISPERSION OF GAS
Neardeckhouses
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DISPERSION OF GAS
Near
deckhouses
CONTRIBUTING FACTORS
The consequences of a gasfire/explosion depend on: Type of fuel and atmosphere
Dimensions gas cloud and concentration
Mixture
Place of ignition
Power of ignition
Dimension, position and type of venting
Position and dimension of equipment andstructural elements
CONSEQUENCES GAS
LEAKAGE
42 % explosion of gas clouds (inside
and outside)
35 % fire
22 % explosions (uncontrolled
reactions, BLEVES, mechanical
explosions, explosions in equipment
1% evaporation / dilution in air (by
wind)
Garrisson 1988
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PRESSURE JET FIRE
Fire of gas leakage under
pressure : pressure jetfire
VENT MAST FIRE
POOL FIRE
Fire of pool of liquid gaspool fire
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POOL FIRE
Refrigerated transport
About 30% of the leaked product willevaporate; whats left will form a pool
Low temperature may give cracks inthe vessels construction: Spray waterto protect the metal and to avoidheating of the construction
Gas fire: speed of flames 3 x speed offuel fire
POOL FIRE
The flames will be blown away by the
wind
Methane: height flames approximately
3x to 4x diameter pool
Important: reduction of heat effect
Heat will be dangerous over 100C
(electrical isolation will melt at
130C)
POOL FIRE
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POOL FIRE
Pay attention for convection heat(air or water)
Pay attention for radiation heat: Near seat of fire 170 kW/m
Skin problems at 4.7 kW/m
Second degree burns at 6.2 kW/m
Most flammable products catch fire at12 kW/m
FLAMABLE GAS
SENSORS
FLAMABLE GAS
SENSORS
Two ceramic beads (pellistors) withembedded platinum coils are heated to~450C. One pellistor is impregnated with acatalytic material that, at the given
temperature, oxidizes the gas (O(O(O(O2222 must bemust bemust bemust bepresent!!!!)present!!!!)present!!!!)present!!!!) and thus forms additional heatwhich can be detected by measuring theresistance of the platinum coil. Using aWheatstone bridge with a second,deactivated pellistor as a reference, thebridge current is approximatelyproportional to the gas concentration inthe 0%100% range of the lower explosivelimit (LEL).
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FLAMABLE GAS
SENSORS
Advantages: can be calibrated for very largerange of flammable gasses. Methane is often
used for calibration, calculations give resultsfor other gasses, using enthalpy (heatreleased during combustion)
Mixture of flammable gasses: calibrate forleast sensitive gas. That way the detector willerr on the side of safety
Disadvantage:in the presence of lead, sulphur,silicone vapours, halogens the sensor can loseall sensitivity
FLAMABLE GAS
SENSORS
FLAMABLE GAS
SENSORS
The IR measuring principle is based onthe fact that gas molecules are excitedby IR light of a certain wavelength and
so produce vibrations while partlyabsorbing energy from the light.
Compared to the original IR lightintensity, the attenuated intensitywithin a defined fixed optical path is ameasure for the gas concentration. Asecond beam with a wavelength notabsorbed by gas can be used tomeasure the original IR light intensity.
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FLAMABLE GAS
SENSORS
Fluctuation of power of the IR
source, contamination of the mirror
or window, as well as faults caused
by dust or aerosol in the air, affect
the 2 detectors similar
Can be used in a O2 low or free
admosphere!!
FIRE FIGHTING
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FIRE
FIGHTING
FIRE FIGHTING
Water deluge systemfor protection
FIRE FIGHTING
Water monitors
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FIRE FIGHTING
Powderextinghuishing
FIRE FIGHTING
DO NOT EXTINGUISH !!!!! ExceptDO NOT EXTINGUISH !!!!! ExceptDO NOT EXTINGUISH !!!!! ExceptDO NOT EXTINGUISH !!!!! Except
when the seat if the fire is isolatedwhen the seat if the fire is isolatedwhen the seat if the fire is isolatedwhen the seat if the fire is isolatedand the surface is reducingand the surface is reducingand the surface is reducingand the surface is reducing
OROROROR
To safe human life
When the outpouring of the gas can
no longer be controlled by water fog
When fear for expansion exist
FIRE FIGHTING
Goal of fire fighting is thecooling down of: Seat of fire
Dangerous zone downwind (turning of thevessel might be necessary
Equipment exposed to radiation heat
Determine in advance the areas thatneed cooling
Attack the fire from the weather side
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WATER
Seldom used for extinguishing, more for
protection. Never to be used on a liquefied gas pool
(spreading)
Use large jet
Spray a water film on the surfaces thatneed protection
Good housekeeping of the installation isessential (corrosion, ice, salt,...)
EFFECT OF WATER
Extinguishing effect on fire: Cooling: very limited when flashpoint
is lower than the water temperature
Suffocating: volume steam = 1700 xvolume liquid
Emulsification: when not soluble inwater
Dilution: when soluble in water. Use8 20 l/min/m
EFFECT OF WATER
Control of combustion: Even when the fire can not be
extinguished, it can be controlled
Continuous supply of water is necessary:20 l/min/m of the surface on fire
Protection of surfaces: containers: > 10 l/min/m exposed surfaces
superstructure: > 4 tot 10 l/min/m
cables: 12 l/min/m
others: > 10 l/min/m
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EFFECT OF WATER
Prevention of expansion of the fire:
Depending of type of fuel: about 10% of
what is necessary to extinguish the fire
Use the fog position of the nozzles
Immediate availability important
Closed valves need also be cooled
Try to direct the gas cloud and avoid
contact with sources of ignition.
POWDER
3 types often used: Sodium bicarbonate
Potassium bicarbonate
Urea potassium bicarbonate
Very effective for small LNG and LPGfires
Use the powder until all the flames areextinguished
Keep cooling down after extinguishment
POWDER
Gas codes require fixed dry powdersystem which can deliver powder to anypart of cargo area with fixed monitors
and hand held hoses Also jetty manifolds often protectedwith portable or fixed dry powdersystems
Effective for Gas fires on deck
Jet fires on holed pipes
Used for vent mast fires
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POWDER
Every powder has its ownproperties
When used with foam: make surethat the powder does not degradethe foam
When used with water: make surethat the powder does not disolvesin the water
MECHANISM
FIRST:
inhibiting chain reaction (absorption
of free radicals in combustion
process)
Start the reaction by the generation of
active radicals CH2222, OH, O and H
Na en K salts combine with H and OH to
make them rare
Ammonia salts provoke an endothermic
polymerisation reaction
MECHANISM
SECOND: Decrease evaporation by reducing the
radiation heat
Inerting by reducing the oxygen level andwith the production of CO2222
Slowing down the fire due to the formationof a surface film
Negligible cooling effect. Beware forre-ignition. cool down hot surfaceswith water before extinguishing withdry powder.
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POWDER ON BOARD
Never change the type of powder
without consulting the constructor /
designer
Never mix deferent types of powder
Powder can not always be used (not
almighty): not for metal fires, cellulose
nitrate, class A fires if the complete
surface can not be covered with the
fire (no cooling effect)
DISADVANTAGES
When used on electronically equipment,an almost irremovable membrane can beformed at higher T (above 127C) ofhumidity > 50%
Erosion is possible
Visibility almost zero while using powder
Powder can cause breathing difficulties.When used on large surfaces, evacuationis needed
Exercises are necessary for the correctuse of powder
FOAM
Mostly used on surface of pool fires
(when confined in bunded area):
Reduces vaporisation rate
Intensity of the pool fire is limited
Foam depth at least 1 or 2 meter is needed
High expansion foam of about 500 to 1
expansion rate has proven to be the bestfor this purpose
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FOAM
Used on un-ignited pool fires:
Reduces extend of gas cloud Stable foam can freeze at the interface of the
foam-gas cloud and will so reducevaporisation rate. Make sure the right foam isused. If it breaks down into the liquid, it mayincrease the vaporisation rate.
Foam will not extinguish a liquefied gasfire.
Needs to be applied to substantial depth.This is not easy on ships and thereforeonly found on terminals and not on gascarriers.
INERT GAS
Preventional
measures with
IG generator:
Permanently
inerting ofinterbarrier
spaces or
cargo related
spaces
METHANE
CO2
High pressure bottled CO2 in case
of fire in enclosed space
Ventilation stopped, space closed Evacuation needed
CO2 injection produces electrostatic
charging (be aware when used as
precautionary measure in flammable
atmosphere)
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STATIC ELECTRICITY CO2
Incidents:
While attempting to inert a jet fuel tank, byusing a portable CO2 fire extinguisher, anexplosion occurred and killed two navy firemen.
On board a tanker, four people were killed in anexplosion while inerting a naphtha tank usingCO2 cylinders.
In Bitburg, Germany, twenty-nine people werekilled as a result of an explosion whilewitnessing the demonstration of a newlyinstalled CO2 fire-extinguishing system for apartially filled jet fuel tank.
STATIC ELECTRICITY CO2
When liquid CO2 expands up to absolute pressures of lessthan approximately 5 bars, the result is the formation ofsmall particles of solid CO2 (dry ice). As the two-phasesolid/gas flows through the piping, static charges areproduced by the particles rubbing against other particles,between themselves, piping and equipment.
These charges accumulate in the zones that are notearth/grounded at the end of the pipelines, most often invalves and nozzles. The size of these fields, can reachvalues of between 50 and 180 kV/m.
Similarly, static electricity can be generated by the dryice particles after they leave the discharge nozzle.
The pressure and impurities in the CO2, equipmentmaterials in transfer line hoses, etc. all influence the
generation of static electricity.
CO2
Used into safety relief valves or
vent mast fires (after shut down)
CO2 is not a cooling agent.Boundaries must be cooled with
water as re-ignition is possible
with the introduction of oxygen.
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EMERGENCY PROCEDURES
Ship procedures, communication is
vital Plans should deal with:
Missing or trapped personnel
Collision
Grounding
water leakage into hold or interbarrier space
Cargo containment leakage
Cargo connection rupture, pipeline fracture orcargo spillage
Fire in non cargo areas
Fire following cargo leakage
Fire in compressor or motor room
EMERGENCY PROCEDURES
Terminal procedures: Less standardised than on ships
Command of an on-site incident controller,often overtaken by port authority
Incident plans Cargo spillage or fire on board a ship alongside ajetty
Cargo spillage or fire while loading or receivingcargo
Cargo spillage or fire not associated with loadingor receiving cargo
EMERGENCY PROCEDURES
Emergency shut down (ESD)
ship/shore link
Exist on all gas carriers and largeterminals
Communication is essential
Loading: first terminal ESD, then ship
Unloading: first ship ESD, then terminal
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EMERGENCY PROCEDURES
Emergency release systems (ERS) Hand arms
First alarm between predetermined limits
(movements of ships): safe shut down
Second alarm outside these limits:disconnection with limited spillage
2 ball or butterfly valves close in 5 seconds
release coupling opened
arm swings by counter balance
Break-away couplings for hosesFor smaller terminals which work with hoses
EMERGENCY PROCEDURES
EMERGENCY PROCEDURES
Removal of ship from berth Burning ship alongside is less a
hazard if kept alongside where shoreservices can provide assistance
In case of an emergency within theterminal, safe practice to removeship to prevent involvement
Consultation master, terminal, portauthority
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EMERGENCY PROCEDURES
Ship-to-ship transfer Communication between ship
masters vital
One ship can use emergencyresources of other
Sometimes separation better optionto minimise overall risks and allowunobstructed access by fire tugs andsalvage services