BASIC LIQUEFIED GAS TANKER FAMILIARIZATION COURSE NOTES

Gas Tanker Familiarization Course:-LGTF IMPORTANT NOTES



The material is arranged under nine main headings:
1. Introduction
2. Characteristics of cargoes
3. Toxicity and other hazards
4. Hazard control
5. Safety equipment and protection personnel
6. Pollution prevention
7. Emergency operations
8. Cargo equipment
9. Cargo operations
1. INTRODUCTION
TYPES OF CARGOES
Liquefied gas cargo
For economical marine transportation, gas is carried in a liquefied state. As a liquid, the volume to
weight ratio at atmospheric pressure is in the range of 650 times less than in the gaseous state.
Even so, the relative densities are low and vary between 0.42 (methane) and 0.97 (VCM).
Generally speaking, a liquefied gas is the liquid form of a substance which at ambient temperature
and atmospheric pressure would be a gas. Definition: A liquid which has a sturated vapour
pressure exceeding 2.8 bar absolute at 37.80C and certain other substances specified in the Gas
Codes.
Cargoes transported by gas tankers are listed in IMO’s Gas Carriers Code
Cargo Ship Type
Acetaldehyde 2G/2PG
Ammonia, anhydrous 2G/2PG
Butadiene 2G/2PG
Butane 2G/2PG
Butane/propane mixtures 2G/2PG
Butylenes 2G/2PG
Chlorine 1 G
Diethyl ether 2G/2PG
Dimethylamine 2G/2PG
Ethane 2 G
Ethyl chloride 2G/2PG
Ethylene 2 G
Ethylene oxide 2G/2PG
Ethylene oxide/propylene oxide mixture
(with ethylene oxide content less than 30% by weight) 2G/2PG
Isoprene 2G/2PG
Isopropylamine 2G/2PG
Methane 2 G
Methylacetylene/propadiene mixture 2G/2PG

Methyl bromide 1 G
Methyl chloride 2G/2PG
Monoethylamine 2G/2PG
Nitrogen 3 G
Propane 2G/2PG
Propylene 2G/2PG
Propylene oxide 2G/2PG
Refrigerant gases 3 G
Sulphur oxide 1 G
Vinyl chloride 2G/2PG
Vinyl ethyl ether 2G/2PG
Vinylidene chloride 2G/2PG
These cargoes can be divided into the following four groups:
1- liquefied natural gas, LNG
2- liquefied petroleum gas, LPG
3- liquefied ethylene gas, LEG
4- chemical gases and certain other substances
 LNG is liquefied natural gas from which impurities are removed
 The principal constituent of LNG is methane
 “Liquefied petroleum gas”-LPG- is a common name for petroleum gases, mainly propane
and butane
 LPG is produced from two sources:
1- from crude oil processing in refineries, or as a by-product of chemical plants
2- from natural gas streams or from crude oil at or close to production points
(wells/platforms)
 Liquefied ethylene gas – LEG – is produced by “cracking” of LPG
 Chemical gases are a group of liquefied gases produced through a chemical process
 Chlorine, ammonia and vinyl chloride monomer (VCM) as examples of chemical gases
 Certain other substances in the “borderland” between liquefied gas and chemicals are
carried on gas tankers
 Acetaldehyde and propylene oxide as examples of such cargoes
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Trial
 The two methods by which gas can be liquefied as:
1- liquefaction by removal of heat
2- liquefaction by pressurizing
 Liquefaction of gas cargoes on ships – other than fully pressurized ships – is done by
removal of heat
 The heat to be removed from the cargo is called “latent heat of condensation”
Gas carrier is a cargo ships constructed or adapted and used for the carriage in
bulk of any liquefied gas or other products listed in the table of chapter 19 IGC Code

GAS TANKER TERMINOLOGY
Absolute temperature
The fundamental temperature scale with its zero at absolute zero and expressed either in
kelvin or degrees Rankine. One kelvin is equal to one Celsius degree or one centigrade;
one Rankine degree is equal to one Fahrenheit degree. To convert Celsius to kelvin, add
273.1 (e.g. 5oC = 278.1oK)
To convert Fahrenheit to Rankine, add 459.6 (e.g. 5
o
F = 464.6oR)
0
oK = 0
oR = 273.1oC = -459.6o
F
Absolute temperatures are used in most thermdynamic tables, charts and calculations. In
the SI system of measurement, Centigrade temperature units (i.e. oC or oK) are used.
Absolute zero
The temperature at which the volume of a gas theoretically becomes zero and all thermal
motion ceases. Generally accepted as being -273.16 °C or-459.69 °F.
BLEVE
Boiling Liquid Expanding Vapour Explosion. Associated with the mpture under fire
conditions of a pressure vessel containing liquefied gas.
Blind spots
Areas of the tank not reached by the tank washing machine water jets.
Boil-off
Vapour produced above the surface of a boiling liquid.
Boiling point
The temperature at which the vapour pressure of a liquid is equal to atmospheric
pressure. Boiling points, as quoted on the data sheets, are correct at a pressure of 760
mmHg, unless indicated to the contrary.
Boiling range
Some liquids which are mixtures, OR which contain impurities, boil over a range of
temperatures known as the boiling range. When this occurs, the range will be stated on
the relevant data sheet. The lower temperature is that at which the liquid starts to boil.
Bonding
The connecting together of metal parts to ensure electrical continuity.
Booster pump
A pump used to increase the discharge pressure from another pump (e.g. a main cargo
pump).
Bulk cargo
Cargo carried in cargo tanks and not shipped in drums, containers or packages.
Burning
Liquid petroleum does not burn, petroleum vapor burns. Danger increases according to
how quickly the product vaporizes. The lower the temperature at which a petroleum
evaporates, the more dangerous it is.

Calorie

The amount of heat necessary to rise one gram of water one degree centigrade at 

constant pressure of one standard atmosphere.

Canister-type breathing apparatus

A respirator consisting of mask and replaceable canister filter through which toxic air is 

drawn by the breathing effort of the wearer and the toxic elements are absorbed. A filter 

dedicated to the specific toxic contaminant gas must be used. May be referred to as 

"cartridge" or "filter" respirator.

Cargo area

That part of the ship which contains the cargo-containment system, cargo pump and 

compressor rooms, and includes the full beam deck area over the length of the ship 

above the cargo containment. Where fitted, cofferdams, ballast or 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.

Cargo conditioning

The maintaintaining of the cargo quantity without undue loss, of the cargo tank pressure 

within its n limits, and of the desired cargo temperature.

Cargo containment system

The arrangement for containment of cargo, including, where fitted, a primary and 

secondary barrier, associated insulation, interbarrier spaces and structure required for the 

support of elements.

Cargo handling

The loading, discharging and transferring of bulk liquid cargo.

Cascade reliquefaction cycle

A process whereby vapour boil-off from cargo tanks is condensed in a cargo condenser in 

which the coolant is an evaporating refrigerant such as Freon 22. The evaporating 

refrigerant then passed through a coventional seawater-cooled condenser.

Critical temperature

The temperature above which a gas cannot be liquefied by pressure alone.

Critical pressure

The pressure of a saturated vapour at the critical temperature, i.e. the pressure) cause 

liquefaction at that

The study of the behaviour of matter at very low temperatures.

Crossover valves

Athwartships tank lines joining the main line are known as crossover lines and the crossover 

valves separate the main lines from each other as well as separating individuals tanks. Thus 2P 

can be separated from 2C by a crossover valve. Briefly, master valve separate separates in a 

fore-and-aft direction and crossovers in the athwartships direction.

Cryogenics

The study of the behaviour of matter at very low temperatures.

Cyanosis

A bluish discoloration of the skin, particularly about the face and extremities, which 

usually occurs when the blood is not properly oxygenated by the lungs, and manifests 

itself particularly in the area of the mouth and ears.

Crystalline

A material formed in such a manner that its structure is arranged in a regular, repeated 

and interlocked pattern.

Dalton's Law of Partial Pressures

The pressure exerted by a mixture of gases is equal to the sum of the separate pressures 

which each gas would exert if it alone occupied the whole volume.

Dangerous area

An area on a tanker which, for the purposes of the installation and use of electrical 

equipment, is regarded as dangerous.

Dangerous cargo endorsement

Endorsement to a certificate of competency of a responsible officer for him to serve as 

such on a dangerous cargo carrier (i.e. oil or chemical or gas carrier).

Deepwell pump

Atype of centrifugal cargo pump commonly found on gas carriers. The prime mover, 

usually but not always an electric motor, is flange-mounted on top of the cargo tank and 

drives, through a long transmission shaft, the pump assembly located in the bottom of the 

tank. The discharge pipe surrounds the drive shaft and the bearings of the shaft are 

cooled and lubricated by the liquid being pumped.

Density

The mass per unit volume of a substance at a standard temperature and pressure. In the 

metric system, measured in grams per cubic centimeter, when it is equal to specific 

gravity

Deposit

An accumulation of unwanted materials in a system.

Dewpoint

The temperature at which the water vapour present in a gas saturates the gas and begins 

to condense.

Direct line system

The system is common on VLCCs (very large crude carriers) as it facilitates quick loading 

and discharging, the cargo being natural unrefined oil. The shorter pipe lengths and the 

fewer bends ensure that there is less loss of pressure due to pipeline friction during both 

operations and when discharging the line to a pump provides better suction.

The system is a cheaper to construct than the ring main and require less maintenance. 

Leaks are minimized as there are fewer washing time is also considerably shortened. 

However, as there is no circular system lines can be often difficult to wash and simply has 

to flush lines from the tanks with sea water

Drop valves
Each of the main tank pipelines has a counter part on deck and loading lines which lead
vertically from the deck lines to the tank lines are as known as drop lines. Each main line
has one or two drop lines and drop valves control the flow of oil in those lines.
Dry chemical powder
Aflame-inhibiting powder used in fire fighting.
Earthing (also referred to as ‘grounding’)
The electrical connection of equipment to the main body of the earth to ensure that it is at
earth potential. On board ship the connection is made to the main metallic structure of the
ship, which is at earth potential because of the conductivity of the sea.
Endothermic
Referring to a process which is accompanied by absorption of heat.
Entry permit
Adocument issued by a responsible person permitting entry to a space or compartment
during
aspedfictime interval.
Explosimeter
See "Combustible-gas indicator", but sometimes giving the result as a percentage of the
lower explosive limit (LEL) or ppm.
Explosion-proof (‘flame-proof’)
Electrical equipment is defined and certified as explosion-proof (flame-proof) when it is
enclosed in a case which is capable of withstanding the explosion within it of a
hydrocarbon gas/air mixture or other specified flammable gas mixture. It must also
prevent the ignition of such a mixture outside the case either by spark or flame from the
internal explosion or as a result of the temperature rise of the case following the internal
explosion. The equipment must operate at such an external temperature that a
surrounding flammable atmosphere will not be ignited thereby.
Explosive range
See “Flammable range”
Exothermic
Referring to a process which is accompanied by evolution of heat.
Explosive limit/range
See "Flammable range".
Evaporation
The change of a liquid into a vapor, not necessarily by boiling. Usually such vapors are
called gases.
Filling density (for liquefied gases)
The "filling density" is defined as the percent ratio of the weight of the liquid gas in a tank.
Fire point
The temperature at which a liquid continues to burn when ignited. This is always higher
than flash point (20-25oC depend of kind of petroleum products).
Flame arrester
A permeable matrix of metal, ceramic or other heat-resisting materials which can cool a
deflagration flame and any following combustion products below the temperature required
for the ignition of the unreacted flammable gas on the other side of the arrester.
Flame-proof
See "Explosion-proof".
Flame screen
A portable or fitted device incorporating one or more corrosion-resistant wire-woven
fabrics of very small mesh used for preventing sparks from entering a tank or vent
opening or, fora short time, preventing the passage of flame. (Not to be confused with a
flame arrester, see Instructor Manual section 1.4)
Flammable (also referred to as ‘combustible’)
Capable of being ignited and of burning. For the purposes of these guidance notes, the
terms "flammable" and "combustible" are synonymous.
Flammable limits
It is possible to have a mixture containing so much or so little petroleum vapor that it
cannot ignite. Mixtures which have reached these respectively have reached their Upper
Flammable Limit (UFL) or Lower Flammable Limit (LFL). (Also known as the Upper or
Lower Explosion Limit: UEL or LEL)
Flammable range (also referred to as ‘explosive range’)
The range of hydrocarbon gas concentrations in air between the lower and upper
flamrnable (explosive) limits. (UFL-LFL). Mixtures within this range are capable of being
ignited and of burning.
Flashlight (also referred to as ‘torch’)
A battery-operated hand lamp. An approved flashlight is one which is approved by a
competent authority for use in a flammable atmosphere.
Flashpoint
The lowest temperature at which a liquid gives off sufficient gas to form a flammable
gas mixture near the surface of the liquid. It is measured in the laboratory in standard
apparatus using a prescribed procedure.
Foam (also referred to as ‘froth’)
An aerated solution which is used for fire prevention and fire fighting.
Foam concentrate (also referred to as ‘foam compound’)
The full-strength liquid that is received from the supplier, which is diluted and processed
to produce foam.
Foam solution
The mixture produced by diluting foam concentrate with water before processing to make
foam.
Freezing point (melting point)
The temperatures at which the liquid stale of a substance is in equilibrium with the solid
state, i.e. at a higher temperature the solid will melt and at a lower temperature the liquid
will solidify. Freezing point and melting point may not always coincide, but they are
sufficiently close to enable the difference between them to be ignored for the purpose of
this Guide. (See "Supercooling")
Froth
See "Foam".
Gas
This term is used to cover all vapour or vapour/air mixtures.
Gas absorption detector
An instrument used for the detection of gases or vapours which works on the principle of
discolouring a chemical agent in the apparatus
Gas Codes
The Codes for the Construction and Equipment of ships carrying liquefied gases in bulk,
prepared and published by the International Maritime Organization.
Gas-dangerous space or zone
A space or zone within the cargo area which is not arranged or equipped in an approved
manner to ensure its atmosphere is at all times maintained in a gas-safe condition, or an
enclosed space outside the cargo area through which any piping passes which may
contain liquid or gaseous products unless approved arrangements are installed to prevent
any escape of product vapour into the atmosphere of that space.
Gas-free
A tank, compartment or container is gas-free when sufficient fresh air has been
introduced into itto lower the level of any flammable, toxic, or inert gas to that required
fora specific purpose, e.g. hot work, entry, etc.
Gas-free certificate
Acertificate issued by an authorized responsible person confirming that, at the time of
testing a lank, compartment or container, it was gas-free for a specific purpose.
Gas-freeing
The process of eliminating a hazardous or expolosive atmosphere from an enclosed area
by ventilation, washing, or chemical cleaning.
Gas-safe
A space not designated as a gas-dangerous space.
Gate cargo valve
Many manual valves are of the ‘gate’ type (sometimes known as ‘sluce valve’);
Gauze screen (sometimes called "flame screen")
A portable or fitted device incorporating one or more corrosion-resistant wire-woven
fabrics of very small mesh used for preventing sparks from entering an open deck hole, or
FORA SHORT PERIOD OF TIME preventing the passage of flame, yet permitting the
passage of gas.
Grounding
See "Earthing".
Halon
A halogenated hydrocarbon previously used in fire fighting which inhibited flame
propagation.
Hard arm
An articulated pipework arm used in terminals to connect shore pipework to ship manifold.
Harmful
A general descriptive term for injurious effects on health that may be caused by
chemicals.
Hazardous area
A hazardous area is one in which vapour may be present continuously or intermittently in
sufficient concentrations to create a flammable atmosphere or an atmosphere which is
dangerous for personnel.
Hazardous zone
See "Hazardous area".
Health hazard
A general descriptive term for the danger to the health of personnel presented by soire
chemicals.
Heat
There are three commonly used units of heat, namely the kilojoule (kJ), kilocalorie (kcal)
and the British Thermal Unit (BTU).
The preffered SI unit is the kilojoule. It is the amount of heat, measured in Joules,
required to raise the temperature of 1 kilogram of water by 1
oC.
Heat of fusion
Quantity of heat required to effect a change of state of a substance from solid to liquid
withoit change of temperature. (Latent heat of fusion).
Heat of vaporization
Quantity of heat required to effect a change of state of a substance from liquid to vapoi.'
without change of temperature. (Latent heat of vaporization).
Hidden areas
Surfaces which are concealed from the direct flow of a cleaning solution.

Hold space
The space enclosed by the ship's structure in which a cargo containment system is
situated,
Hot work
Work involving sources of ignition or temperature sufficiently high to cause the ignition of
a flammable gas mixture. This includes any work requiring the use of welding, burning or
soldering equipment, blow torches, some power-driven tools, portable electrical
equipment which is not intrinsically safe or contained within an approved explosion-proof
housing, sand-blasting equipment, or internal-combustion engines.
Hot-work permit
A document issued by a responsible person permitting specific hot work to be done
during a specific time interval in a defined area.
Humidity-absolute
Mass of water vapour present in unit volume of the atmosphere, usually measured as
grams per cubic meter. It may also be expressed in terms of the actual pressure of the
water vapour present.
Hydrate
White, snow-like, crystalline substance formed at certain pressures and temperatures by
hydrocarbons containing water.
Hydrate inhibitors
An additive to certain liquefied gases that is capable of depressing the temperature at
which
hydrates begin to form. Typical depressants are methanol, ethanol, isopropyi alcohol, etc.
Hydrocarbon gas
A gas composed entirely of hydrocarbons.
Hydrolysis
The decomposition of a compound by the agency of water (H-OH) into two parts, one part
then combining with hydrogen (H) from the water and the other part with the hydroxyl
(OH).
Hydrocarbon gas
A gas composed entirely of by hydrocarbons. Hydrocarbons are an organic compounds
consisting of Hydrogen and Carbon.
Hygroscopic tendency
The tendency of a substance to absorb moisture from the air.
IACS
International Association of Classification Societies.

ICS 

International Chamber of 

Shipping.

IEC

International Electrotechnical Commission.

Ignition temperature

The lowest temperature at which 

combustion (with fire) can occur 

spontaneously without any heat supply from 

outside.

IMO

International Maritime Organization, the United Nations specialized agency dealing with

maritime affairs.

Incendive spark

A spark of sufficient temperature and energy to ignite a flammable vapour.

Inert condition

A condition in which the oxygen content throughout the atmosphere of a tank has been

reduced to 8% or less by volume by addition of inert gas.

Interface detector

An electrical instrument for detecting the boundary between oil and water.

Inert gas

A gas or a mixture of gases, such as flue gas, containing insufficient oxygen to support 

the

combustion of hydrocarbons.

Inert gas distribution system

All piping, valves and associated fittings to distribute inert gas from the gas plant to cargo 

tanks, to vent gases to atmosphere and to protect tanks against excessive pressure or

vacuum.

Inert gas plant

All equipment specially fitted to supply, cool, clean, pressurize, monitor and control 

delivery of

inert gas to cargo tank systems.

Inert gas system (IGS)

An inert gas plant and inert gas distribution system together with means for preventing 

bacK-flow of cargo gases to the machinery spaces, fixed and portable measuring 

instruments and control devices.

Inerting

The introduction of inert gas into a tank with the object of attaining the inert condition.

Ingestion

The act of introducing a substance into the body via the digestive system.

Inhibited chemical

A chemical to which an inhibitor or additive has been added.

Inhibitor

A substance used to prevent any chemical reaction.

Insulating flange

A flanged joint incorporating an insulating gasket, sleeves and washers to prevent 

electrical continuity between pipelines, hose strings or loading arms.

Interbarrier space

The space between a primary and a secondary barrier of a cargo containment system, 

whether or not completely or partially occupied by insulation or other material.

Interface detector

An electrical instrument for detecting the boundary between oil and water.

INTERTANKO

International Association of Independent Tanker Owners.

Intrinsically safe

An electrical circuit or part of a circuit is intrinsically safe if any spark or thermal effect 

produced normally (i.e. by breaking or closing the circuit) or accidentally (e.g. by short 

circuit or earth fault) is incapable, under prescribed test conditions, of igniting a prescribed 

gas mixture.

Irritating liquid

A liquid which, on direct contact with the eyes or skin, will cause, injury, burns or severe 

irritation.

Irritating vapour

A vapour which will cause irritation of the eyes, nose, throat and respiratory tract. Such 

vapours generally are immediately evident.

ISGOTT

International Safety Guide for Oil Tankers and Terminals. Published jointly by ICS, 

OCIMF andlAPH.

Isothermal

When a gas passes through a series of pressure and/or volume variations without change 

of temperature, the changes are called "isothermal".

Latent heat

The heat required to cause a change in phase of a substance from solid to liquid (latent 

heat of fusion) or from liquid to vapour (latent heat of vaporization). 

Liquefied gas

A liquid which has a saturated vapour pressure exceeding 2.8 bar absolute at 37.8 °C 

and certain other substances specified in the IMO Codes.

LNG

Liquefied Natural Gas, the principal constituent of which is methane.

Load-On-Top (LOT)

This term refers to the process of demulsifying and settling a cleaning slop to separate 

the oil and water phases. After separation, the oil-free water phase is discharged 

overboard and the oil phase is saved and combined with the new cargo of oil.

Loading overall

The loading of cargo or ballast "over the top" through an open-ended pipe or by means of 

an open-ended hose entering a tank through a hatch or other deck opening, resulting in

the free fall of liquid.

Lower flammable limit (LFL)

The concentration of a hydrocarbon gas in air below which there is insufficient 

hydrocarbon to support and propagate combustion. Sometimes referred to as "lower 

explosive limit (LEL)".

LPG

Liquefied Petroleum Gas. Mainly propane and butane, and can be shipped separately or 

as amixture. 

MAC value

Maximum allowable concentration. Expressed in ppm (parts per million). This is a 

concentration of a certain substance in the air, which is the maximum allowable exposure 

for working for a normal person without danger.

Main deck

The steel deck forming the uppermost continuous watertight deck.

Manifold valves

Valves in a tanker's piping system immediately adjacent to the ship/shore connecting 

flanges.

MARVS

Maximum Allowable Relief Valve Setting of a cargo tank.

Mechanical hoists

Air driven winches attached to shear legs that can be 

situated over tank cleaning holes or tank lids to lift out the 

buckets of sludge from tank bottoms.