CHAPTER 8 CARGO MEASUREMENT AND CALCULATION 187
8.1 Principles for liquefied gases.................................................................. 187
8.1.1 Special practices for gas cargoes................................................... 187
8.1.2 General. Density in air and density in vacuum................................ 188
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8.1.3 True density (apparent density)....................................................... 189
8.1.4 Relative density (specific gravity)................................................... 189
8.1.5 Apparent relative density (apparent specific gravity)...................... 190
8.1.6 LNG quantification........................................................................... 194
8.1.7 Shore measurement versus ship measurement............................. 191
8.2 Measurement of cargo tank volumes.................................................... 192
8.2.1 Trim correction................................................................................ 192
8.2.2 List correction.................................................................................. 193
8.2.3 Tape correction................................................................................ 193
8.2.4 Float correction................................................................................ 194
8.2.5 Tank shell contraction and expansion............................................. 194
8.3 Measurement of density......................................................................... 194
8.3.1 Density measurement methods...................................................... 194
8.3.2 Units of density................................................................................ 195
8.4 Ship/shore calculation procedures......................................................... 195
8.4.1 Outline of weight-in-air calculation.................................................. 195
8.4.2 Procedures using standard temperature......................................... 196
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8.4.3 Procedure using dynamic flow measurement................................ 197
8.5 Example — cargo calculation................................................................ 198
8.6 Other calculation procedures and measurement units.......................... 199
8.7 Cargo documentation............................................................................. 199
CHAPTER 9 PERSONAL HEALTH AND SAFETY 202
9.1 Cargo hazards........................................................................................ 202
9.2 Flammability........................................................................................... 205
9.2.1 Operational aspects......................................................................... 205
9.2.2 Emergency aspects......................................................................... 205
9.3 Air deficiency.......................................................................................... 205
9.3.1 Toxicity............................................................................................ 205
9.3.2 Asphyxia (suffocation)..................................................................... 207
9.3.3 Medical treatment............................................................................ 208
9.3.4 Oxygen therapy............................................................................... 209
9.4 Frostbite.................................................................................................. 210
9.5 Chemical burns....................................................................................... 211
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9.6 Transport to hospital............................................................................... 212
9.7 Hazardous atmospheres......................................................................... 212
9.7.1 The need for gas testing......................................................................... 212
9.7.2 Oxygen analysers................................................................................... 213
9.7.3 Combustible gas indicators..................................................................... 215
9.7.4 Toxicity detectors................................................................................... 217
9.8 Entry into enclosed spaces..................................................................... 218
9.8.1 Precautions for tank entry............................................................... 218
9.8.2 Procedures...................................................................................... 219
9.8.3 Rescue from enclosed spaces........................................................ 220
9.9 Personal protection................................................................................. 220
9.9.1 Breathing apparatus................................................................................ 220
9.9.2 Protective clothing.................................................................................. 222
CHAPTER10 EMERGENCY PROCEDURES 223
10.1 The principal hazards.............................................................................. 223
10.1.1 Flammability.................................................................................... 223
10.1.2 Vaporisation of spilled liquid............................................................. 224
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10.1.3 Toxicity and toxic products of combustion...................................... 230
10.1.4 Frostbite........................................................................................... 224
10.1.5 Brittle fracture.................................................................................. 224
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10.2 Liquefied gas fires................................................................................... 224
10.2.1 Fire detection................................................................................... 225
10.2.2 Jet fires............................................................................................ 225
10.2.3 Liquid (pool) fires.............................................................................. 225
10.2.4 Fires in compressor rooms.............................................................. 226
10.3 Liquefied gas fire-fighting........................................................................ 227
10.3.1 Alarm procedures............................................................................ 227
10.3.2 Extinguishing mediums.................................................................... 227
10.3.3 Training............................................................................................ 229
10.4 Emergency procedures.......................................................................... 229
10.4.1 The emergency plan........................................................................ 229
10.4.2 Ship emergency procedures........................................................... 230
10.4.3 Terminal emergency procedures.................................................... 231
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10.5 Emergency release and emergency shut-down.................................... 232
10.5.1 Emergency shut-down (ESD) —ship/shore links............................ 232
10.5.2 Emergency release systems (ERS)................................................ 232
10.6 Removal of ship from berth.................................................................... 233
10.7 Ship-to-ship cargo transfer..................................................................... 233
APPENDIX 1 References............................................................................................. 234
APPENDIX 2 Liquefied and Chemical Gases Covered by the IGC Code .................. 237
APPENDIX 3 Ship/Shore Safety Check List................................................................ 239
INDEX ................................................................................................................ 260
Figures and Tables
Inside front and back covers — LPG and LNG carriers (to scale)
Figure No. Title
1.1 Constituents of natural gas
1.2 Typical flow diagram for LNG liquefaction
1.3 Typical oil/gas flow diagram
1.4 Typical flow diagram — production of chemical gas
2.1 Molecular structure of some saturated hydrocarbons
2.2 Molecular structure of some unsaturated hydrocarbons
2.3 Molecular structure of some chemical gases
2.4 Solubility of water in butadiene
2.5 The polymerisation of vinyl chloride
2.5(a) Inhibitor information form
2.6 Temperature/heat diagram for varying states of matter
2.7 Characteristics of methane
2.8 Simple refrigeration — evaporation/condensation cycle
2.9(a) Boyle's Law for gases (constant temperature)
2.9(b) Charles' Law for gases (constant pressure)
2.9(c) Pressure Law for gases (constant volume)
2.10 Relationship between adiabatic and isothermal compression
2.11 Barometric method for measuring saturated vapour pressure
2.12 Characteristics of propane
2.13 Pressure/temperature relationship for hydrocarbon gases
2.14 Pressure/temperature relationship for chemical gases
2.15 Equilibrium diagram for propane/butane mixtures
2.16 Mollier diagram for propane
2.17 Flammable range for propane
2.18 Flammable vapour zones — a liquefied gas spill
2.19 Flammable limits of gas mixtures in air and nitrogen
3.1 Prismatic self-supporting Type 'A' tank — fully refrigerated LPG carrier
3.2(a) Self-supporting spherical Type 'B' tank
3.2(b) Self-supporting prismatic Type 'B' tank
3.3 Type 'C' tanks — fully pressurised gas carrier
3.4 Type 'C' tanks — semi-pressurised gas carrier with bi-lobe tanks
3.5(a) Gaz Transport membrane containment system — larger LNG carriers
3.5(b) Construction of the Gaz Transport membrane system
3.6(a) Technigaz membrane containment system — larger LNG carriers
3.6(b) Construction of the Technigaz membrane — Mark III
3.7 Compressor room/electric motor room on a gas carrier
4.1 Cargo tank dome piping arrangement — Type 'C' tank
4.2 Pilot-operated relief valve
4.3 Pump performance curves — a deepwell pump
4.4 Centrifugal pumps in parallel — combined characteristics
Figure No. Title
4.5 Centrifugal pumps in series — combined characteristics
4.6 Typical deepwell pump
4.7(a) Submerged motor pump for LPG
4.7(b) Typical LNG submerged motor pump assembly
4.8 Vertical booster pump
4.9 Horizontal booster pump
4.10 Cargo heater
4.10(a) Examples of indirect cooling cycles
4.11 (a) Single-stage direct reliquefaction cycle
4.11(b) Mollier diagram — single-stage direct reliquefaction cycle
4.12(a) Two-stage direct reliquefaction cycle with inter-stage cooling
4.12(b) Mollier diagram — two-stage direct reliquefaction cycle
4.13 Simplified cascade reliquefaction cycle
4.14 Sulzer oil-free compressor
4.15 Linde oil-free compressor
4.16 Typical rotor for an oil-free screw compressor
4.17 Typical purge gas condenser system
4.18 Flow diagram of an inert gas generator
4.19 Saturated water content of inert gas
4.20 Drying of inert gas
4.21 The membrane system for producing nitrogen
4.22 Intrinsic safety using Zener barriers
4.23 Float level gauge
4.24 Nitrogen bubbler level gauge
4.25 Differential pressure level gauge
4.26 Electrical capacitance level gauge
5.1 Typical gas carrier loading arm
5.2 Loading arm operating envelope
5.3 Quick connect/disconnect coupling
5.4 Powered emergency release coupling (PERC)
5.5 Roots blower typically used for vapour return
5.6 LPG loading terminal — vapour return using a shore based blower
5.7 Fully pressurised storage in horizontal cylindrical tanks
5.8 Rock cavern LPG storage
5.9 Salt cavern LPG storage
5.10 Semi-pressurised storage in spheres
5.11 Typical single-wall tank — LPG storage
5.12 LNG tank — concrete bund
5.13 LNG tank — double-wall
5.14 Double containment steel tank for LPG
5.15 LPG tank — earth berm
5.16 In-ground tank for LNG
5.17 Bursting disc for surge pressure relief
5.18 Flow diagram for reliquefaction within an LPG terminal
5.19 LNG receiving terminal — vaporiser/sendout
5.20 A positive displacement meter
5.21 A turbine meter
5.22 A prover loop
7.1 Air drying — operational cycle
7.2 Inerting cargo tanks by the displacement method
7.3(a) Gassing-up cargo tanks using liquid from shore
7.3(b) Gassing-up cargo tanks using vapour from shore
7.4 Cargo tank cool-down using liquid from shore
7.5 Loading with vapour return
7.6 Loading without vapour return
7.7 Cargo refrigeration at sea
Figure No. Title
7.8 Combined ship and shore pumping characteristics — single pump
7.9 Illustration of static head and friction head
7.10 Combined ship and shore pumping characteristics — parallel pumps
7.11 Discharge without vapour return
7.12 Discharge with vapour return
7.13 Pipeline diagram of a cargo booster pump and heater
7.14 Removal of cargo liquid residue by pressurisation
7.15 Inerting of cargo tanks
7.16 Aeration of cargo tanks
8.1 Cargo calculations — correction for trim
8.2 Cargo calculations — correction for list
9.1 Patient label
9.2(a) Oxygen indicator — circuit diagram
9.2(b) Oxygen indicator — plan view
9.2(c) A polarographic cell
9.3(a) Combustible gas indicator — circuit diagram
9.3(b) Combustible gas indicator — calibration graph
9.4 Infrared gas analyser
9.5 Toxic gas indicator
9.6 Maritime safety card with safety check list
10.1 Pool fire configurations
Table No. Title
1.1 Physical properties of some liquefied gases
2.1 Synonyms for the main liquefied gases
2.2 Chemical properties of liquefied gases
2.3(a) Chemical compatibilities of liquefied gases
2.3(b) Previous cargo compatibilities of liquefied gases
2.4 Inert gas compositions
2.4(a) Factors affecting lubrication
2.5 Physical properties of gases
2.6 Conversion factors for units of pressure
2.7 Calculation for molecular mass of a gas mixture
2.8 Ignition properties for liquefied gases
2.9 Flammability range in air and oxygen for some liquefied gases
3.1 Typical insulation materials
8.1 ASTM 56 (short table)
9.1 Health data — cargo vapour
9.1 (a) Health data — cargo inhibitors
9.2 Additional health data — cargo liquid
9.3 Liquefied gas groups — for medical first aid purposes
9.4 Enclosed spaces on gas carriers
Definitions
The definitions listed in this section relate to their usage within this book. Other publications may use similar terms with different interpretations.
Absolute Pressure
The absolute pressure is the total of the gauge pressure plus the pressure of the surrounding atmosphere .
Absolute Temperature
The fundamental temperature scale with its zero at absolute zero and expressed in degrees Kelvin. One degree Kelvin is equal to one degree Celsius or one degree Centigrade. For the purpose of practical calculations in order to convert Celsius to Kelvin add 273. It is normal for the degree Kelvin to be abbreviated in mathematical formulae to 'K' with the degree symbol being omitted.
Absolute Zero
The temperature at which the volume of a gas theoretically becomes zero and all thermal motion ceases. It is generally accepted as being -273.16°C.
Activated Alumina
A desiccant (or drying) medium which operates by adsorption of water molecules (see 4.7.1).
Adiabatic
Describes an ideal process undergone by a gas in which no gain or loss of heat occurs (see 2.1).
Aerating
Aerating means the introduction of fresh air into a tank with the object of removing toxic, flammable and inert gases and increasing the oxygen content to 21 per cent by volume (see 7.9.4).
Airlock
A separation area used to maintain adjacent areas at a pressure differential. For example, the airlock to an electric motor room on a gas carrier is used to maintain pressure segregation between a gas-dangerous zone on the open deck and the gas-safe motor room which is pressurised.
Approved Equipment
Equipment of a design that has been type-tested and approved by an appropriate authority such as a governmental agency or classification society. Such an authority will have certified the particular equipment as safe for use in a specified hazardous atmosphere.
Auto-ignition Temperature
The lowest temperature to which a liquid or gas requires to be raised to cause self-sustained spontaneous combustion without ignition by a spark or flame (see 2.20).
Avogadro's Law
Avogadro's Hypothesis states that equal volumes of all gases contain equal numbers of molecules under the same conditions of temperature and pressure.
BLEVE
This is the abbreviation for a Boiling Liquid Expanding Vapour Explosion. It is associated with the rupture, under fire conditions, of a pressure vessel containing liquefied gas (see 2.20).
Boil-off
Boil-off is the vapour produced above the surface of a boiling cargo due to evaporation. It is caused by heat ingress or a drop in pressure (see 4.5).
Boiling Point
The temperature at which the vapour pressure of a liquid is equal to the pressure on its surface (the boiling point varies with pressure) (see 1.1).
Booster Pump
A pump used to increase the discharge pressure from another pump (such as a cargo pump) (see 4.2).
Bulk Cargo
Cargo carried as a liquid in cargo tanks and not shipped in drums, containers or packages.
Canister Filter Respirator
A respirator consisting of mask and replaceable canister filter through which air mixed with toxic vapour is drawn by the breathing of the wearer and in which the toxic elements are absorbed by activated charcoal or other material. A filter dedicated to the specific toxic gas must be used. Sometimes this equipment may be referred to as cartridge respirator. It should be noted that a canister filter respirator is not suitable for use in an oxygen deficient atmosphere (see 9.9.1).
Carbamates
A white powdery substance produced by the reaction of ammonia with carbon dioxide (see 7.2).
Carcinogen
A substance capable of causing cancer.
Cargo Area
That part of the ship which contains the cargo containment system, cargo pumps and compressor rooms, and includes the deck area above the cargo containment system. Where fitted, cofferdams, ballast tanks and void spaces at the after end of the aftermost hold space or the forward end of the forwardmost hold space are excluded from the cargo area. (Refer to the Gas Codes for a more detailed definition).
Cargo Containment Systems
The arrangement for containment of cargo including, where fitted, primary and secondary barriers, associated insulations, interbarrier spaces and the structure required for the support of these elements. (Refer to the Gas Codes for a more detailed definition) (see 3.2).
Cascade Reliquefaction Cycle
A process in which vapour boil-off from cargo tanks is condensed in a cargo condenser in which the coolant is a refrigerant gas such as R22 or equivalent. The refrigerant gas is then compressed and passed through a conventional sea water-cooled condenser (see 4.5.2).
Cavitation
A process occurring within the impeller of a centrifugal pump when pressure at the inlet to the impeller falls below that of the vapour pressure of the liquid being pumped. The bubbles of vapour which are formed collapse with impulsive force in the higher pressure regions of the impeller. This effect can cause significant damage to the impeller surfaces and, furthermore, pumps may loose suction (see 4.2).
Certificate of Fitness
A certificate issued by a flag administration confirming that the structure, equipment, fittings, arrangements and materials used in the construction of a gas carrier are in compliance with the relevant Gas Code. Such certification may be issued on behalf of the administration by an approved classification society (see 3.7.1).
Certified Gas Free
A tank or compartment is certified to be gas-free when its atmosphere has been tested with an approved instrument and found in a suitable condition by an independent chemist. This means it is not deficient in oxygen and sufficiently free of toxic or flammable gas for a specified purpose.
Cofferdam
The isolating space on a ship between two adjacent steel bulkheads or decks. This space may be a void space or ballast space.
Condensate
Reliquefied gases which collect in the condenser and which are then returned to the cargo tanks.
Compression Ratio
The ratio of the absolute pressure at the discharge from a compressor divided by the absolute pressure at the suction.
Critical Pressure
The pressure at which a substance exists in the liquid state at its critical temperature. (In other words it is the saturation pressure at the critical temperature) (see 2.12).
Critical Temperature
The temperature above which a gas cannot be liquefied by pressure alone (see 2.12).
Cryogenics
The study of the behaviour of matter at very low temperatures.
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