Oil Tanker

Terminology for tankers carrying oil



Means the Government of the State whose flag the ship is entitled to fly.

Anti-static additive

A substance added to a petroleum product to raise its electrical conductivity to a safe level above 50
picoSiemens/metre (pS/m) to prevent accumulation of static electricity.

Approved equipment

Equipment of a design that has been tested and approved by an appropriate authority, such as a
government department or classification society. The authority should have certified the equipment as
safe for use in a specified hazardous atmosphere.


The ignition of a combustible material without initiation by a spark or flame, when the material has
been raised to a temperature at which self-sustaining combustion occurs.


The connecting together of metal parts to ensure electrical continuity.

Brush discharge

A brush discharge is a diffuse discharge from a single blunt conductor that is more rapid than corona
and releases more energy. It is possible for a brush discharge to ignite gases and vapours.

Cathodic protection

The prevention of corrosion by electrochemical techniques. On tankers it may be applied either
externally to the hull or internally to the surfaces of tanks. At terminals, it is frequently applied to steel piles and fender panels.


Oil remaining on the walls of a pipe or on the internal surfaces of tanks after the bulk of the oil has
been removed.

Cold work

Work which cannot create a source of ignition.

You may want to read Purpose and scope of ISGOTT 

Combination carrier

A ship which is designed to carry either petroleum cargoes or dry bulk cargoes.

Combustible (also referred to as ‘Flammable’)

Capable of being ignited and of burning. For the purposes of this guide, the terms ‘combustible’ and
‘flammable’ are synonymous.

Combustible gas indicator

An instrument for measuring the composition of hydrocarbon gas/air mixtures, usually giving the
result as a percentage of the lower flammable limit (LFL).


The owner of a ship or any other organisation or person such as the manager, or the bareboat
charterer who has assumed the responsibility for the operation of the ship from the owner of the ship.
This includes the duties and responsibilities imposed by the ISM Code.

Competent Person

A person who has been adequately trained to undertake the tasks they are required to perform within
their job description. For personnel in the shipping industry they should be able to demonstrate this
competence by the production of certificates approved by the vessel’s Administration.


A diffuse discharge from a single sharp conductor (less than 5 mm in diameter) that slowly releases
some of the available energy. Generally corona is incapable if igniting a gas like propane or vapours
like those given-off by gasoline. Corona may ignite vapours like hydrogen or acetylene, which require much lower energies for ignition.

You may want to read Purpose and scope of ISGOTT  

Dangerous area

An area on a tanker which for the purposes of the installation and use of electrical equipment is
regarded as dangerous.

Designated Person Ashore

Under the ISM Code, is a person or persons ashore within a ship’s managing office (Company) with
direct access to the highest levels of management, who has or have the responsibility and the
authority to monitor the safety and pollution prevention aspects of the operation of each ship, and to
ensure that adequate resources and shore-based support are applied, as required.

Dry chemical powder

A flame 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.

Enclosed space

A space which has the following characteristics:
• Limited Openings for entry and exit;
• Unfavourable natural ventilation; and
• Is not designed for continuous worker occupancy.
This includes, but is not limited to, cargo spaces, double bottoms, fuel tanks, ballast tanks, pump
rooms, compressor rooms, cofferdams, void spaces, duct keels, inter-barrier spaces, engine
crankcases and sewerage tanks.

Entry permit

A document issued by a responsible person allowing entry into a space or compartment during a
specific time interval.

You may want to read Purpose and scope of ISGOTT  


See ‘Combustible gas indicator’.

Explosion-proof (also referred to as ‘Flame-proof’)

Electrical equipment is defined and certified as explosion-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.

Explosive range

See ‘Flammable range’.

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
flammable gas on the other side of the arrester.

Flame screen

A portable or fitted device incorporating one or more corrosion resistant wire woven fabrics of very
small mesh which is used for preventing sparks from entering a tank or vent opening or, for a short
time, preventing the passage of flame. (Not to be confused with ‘Flame arrester’).

Flammable (also referred to as ‘Combustible’)

Capable of being ignited and of burning. For the purposes of this guide the terms ‘flammable’ and
‘combustible’ are synonymous.

Flammable range (also referred to as ‘Explosive range’)

The range of hydrocarbon gas concentrations in air between the lower and upper flammable
(explosive) limits. 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.


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 a laboratory in standard apparatus using a prescribed

Flow rate

The linear velocity of flow of liquid in a pipeline, measured in metres per second (m/s). The
determination of the Flow Rates at locations within cargo pipeline systems is essential when handling
static accumulator cargoes. (Also see ‘Loading rate’).

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 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.

Free fall

The unrestricted fall of liquid into a tank.


See ‘Foam’.

You may want to read Purpose and scope of ISGOTT  

Gas free

A tank, compartment or container is gas free when sufficient fresh air has been introduced into it to
lower the level of any flammable, toxic, or inert gas to that required for a specific purpose, e.g. hot
work, entry, etc.

Gas free certificate

A certificate issued by an authorised responsible person confirming that, at the time of testing, a tank,
compartment or container was gas free for a specific purpose.


See ‘Earthing’.


A halogenated hydrocarbon used in fire fighting which inhibits flame propagation.

Hazardous area

An area on shore which for the purposes of the installation and use of electrical equipment is
regarded as dangerous. Such hazardous areas are graded into hazardous zones depending upon the
probability of the presence of a flammable gas mixture.

Hazardous task

A task other than ‘Hot work’ which presents a hazard to the ship, terminal or personnel, the
performance of which needs to be controlled by a risk assessment process such as a Permit to Work

Hazardous zone

See ‘Hazardous area’.

You may want to read Purpose and scope of ISGOTT  

Hot work

Work involving sources of ignition or temperatures 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, and internal combustion

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.

Hydrocarbon gas

A gas composed entirely of hydrocarbons.

Inert condition

A condition in which the oxygen content throughout the atmosphere of a tank has been reduced to 8
per cent or less by volume by the addition of inert gas.

Inert gas

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

Inert gas plant

All equipment fitted to supply, cool, clean, pressurise, monitor and control the delivery of inert gas to
the cargo tank systems.

Inert gas system (IGS)

An inert gas plant and inert gas distribution system together with means for preventing backflow of
cargo gases to the machinery spaces, fixed and portable measuring instruments and control devices.


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

Insulating flange

A flanged joint incorporating an insulating gasket, sleeves and washers to prevent electrical continuity between ship and shore.

Interface detector

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

International Safety Management Code (ISM Code)

An international standard for the safe management and operation of ships and for pollution
prevention. The Code establishes safety-management objectives and requires a “Safety Management
System” (SMS) to be established by the “Company”.

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.

Loading over the top (also known as ‘Loading overall’)

The loading of cargo or ballast 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.

Loading rate

The volumetric measure of liquid loaded within a given period, usually expressed as cubic metres per
hour (m3/hr) or barrels per hour (bbls/hr).

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).

Material Safety Data Sheet (MSDS)

A document identifying the substance and all its constituents, providing the recipient with all
necessary information to safely manage the substance.The format and content of an MSDS for MARPOL Annex I cargoes and Marine Fuel Oils is prescribed in IMO Resolution MSC.150 (77).


A group of naturally occurring sulphur containing organic chemicals. They are present in some crude
oils and in pentane plus cargoes. They have a strong odour.

Mooring winch brake design capacity

The percentage of the minimum breaking load (MBL) of a new mooring rope or wire that a winch
carries, at which the winch brake is designed to render. Winch brakes will normally be designed to
hold 80% of the line’s MBL and will be set in service to hold 60% of the mooring line’s MBL. Brake
holding capacity may be expressed either in tonnes or as a percentage of a line’s MBL.

Mooring winch design heaving capacity

The power of a mooring winch to heave in or put a load on its mooring rope or wire. Usually
expressed in tonnes.

Naked lights

Open flames or fires, lighted cigarettes, cigars, pipes or similar smoking materials, any other
unconfined sources of ignition, electrical and other equipment liable to cause sparking while in use,
unprotected light bulbs or any surface with a temperature that is equal to or higher than the minimum
ignition temperature of the products handled in the operation.

Non-volatile petroleum

Petroleum having a flash point of 60oC or above, as determined by the closed cup method of test.

Odour threshold

The lowest concentration of vapour in air which can be detected by smell.


See ‘Combination Carrier’.

You may want to read Purpose and scope of ISGOTT  

Oxygen analyser/meter

An instrument for determining the percentage of oxygen in a sample of the atmosphere drawn from a
tank, pipe or compartment.

Packaged cargo

Petroleum or other cargo in drums, packages or other containers.


An electrical sensor unit fitted in a flammable gas detector for measuring hydrocarbon vapours and
air mixtures within the flammable range.


A document issued by a responsible person which allows work to be performed in compliance with
the vessel’s Safety Management System

Permit to work system

A system for controlling activities that expose the ship, personnel and the environment to hazard. The
system will provide risk assessment techniques and apply them to the varying levels of risk that may
be experienced. The system should conform to a recognised industry guideline.


Crude oil and liquid hydrocarbon products derived from it.

Petroleum gas

A gas evolved from petroleum. The main constituents of petroleum gases are hydrocarbons, but they
may also contain other substances, such as hydrogen sulphide or lead alkyls, as minor constituents.


Oil is considered to have three phases in which it can exist depending on the grade of oil and its
temperature. The three phases are the solid phase, the liquid phase and the vapour phase. The
phases do not exist in isolation and operators must manage the carriage of oil with an understanding
of the combinations of the phases of oil in the cargo being carried.

Pour point

The lowest temperature at which a petroleum oil will remain fluid.

Pressure surge

A sudden increase in the pressure of the liquid in a pipeline brought about by an abrupt change in
flow rate.

Pressure/vacuum relief valve (P/V valve)

A device which provides for the flow of the small volumes of vapour, air or inert gas mixtures caused
by thermal variations in a cargo tank.

You may want to read Purpose and scope of ISGOTT  


The introduction of inert gas into a tank already in the inert condition with the object of:
(1) further reducing the existing oxygen content; and/or
(2) reducing the existing hydrocarbon gas content to a level below which combustion cannot be
supported if air is subsequently introduced into the tank.

Pyrophoric iron sulphide

Iron sulphide capable of a rapid exothermic oxidation causing incandescence when exposed to air
and potential ignition of flammable hydrocarbon gas/air mixtures.

Reid vapour pressure (RVP)

The vapour pressure of a liquid determined in a standard manner in the Reid apparatus at a
temperature of 37.8oC and with a ratio of gas to liquid volume of 4:1. Used for comparison purposes
only. See ‘True Vapour Pressure’.

Relaxation time

The time taken for a static charge to relax or dissipate from a liquid. This time is typically one half
minute for static accumulator liquids.

Responsible officer (or person)

A person appointed by the employer or the master of the ship and empowered to take all decisions
relating to a specific task, having the necessary knowledge and experience for that purpose.


Equipment to assist or restore the breathing of personnel overcome by gas or lack of oxygen.

Safety Management System (SMS)

A formal documented system, required by the ISM Code, compliance with which will ensure that all
operations and activities onboard a ship are carried out in a safe manner.

Self stowing mooring winch

A mooring winch fitted with a drum on which a wire or rope is made fast and automatically stowed.

Settling time

The time it takes for tank contents to stop moving once filling has stopped. The movement can be
because of thermal currents, solids and/or water settling or of gas bubbles rising. Typically this time
is 30 minutes.


The International Convention for the Safety of Life at Sea, as amended from time to time.

Sounding pipe

A pipe extending from the top of the tank to the bottom through which the contents of the tank can be
measured. The pipe is usually perforated to ensure the level of liquid in the pipe is the same as the
level of liquid in the body of the tank and to prevent the possibility of spillages. The pipe should be
electrically bonded to the ship’s structure at the deck and at its lower end.

Sour crude oil

A crude oil containing appreciable amounts of hydrogen sulphide and/or mercaptans.

Spontaneous combustion

The ignition of material brought about by a heat producing (exothermic) chemical reaction within the
material itself without exposure to an external source of ignition.

Spread loading

The practice of loading a number of tanks simultaneously to reduce the velocity of the cargo in the
pipelines serving individual tanks to avoid static electricity generation when loading static accumulator cargoes.

Static accumulator oil

An oil with an electrical conductivity less than 50 picoSiemens/metre (pS/m), so that it is capable of
retaining a significant electrostatic charge.

Static electricity

The electricity produced by dissimilar materials through physical contact and separation.

You may want to read Purpose and scope of ISGOTT  

Static non-accumulator oil

An oil with an electrical conductivity greater than 50 picoSiemens/metre (pS/m), which renders it
incapable of retaining a significant electrostatic charge.


The final operation in draining liquid from a tank or pipeline.


A ship designed to carry liquid petroleum cargo in bulk, including a combination carrier when being
used for this purpose.

Tank cleaning

The process of removing hydrocarbon vapours, liquid or residue from tanks. Usually carried out so
that tanks can be entered for inspection or hot work.

Tension winch (automated or self tensioning mooring system)

A mooring winch fitted with a device which may be set to automatically maintain the tension on a
mooring line. The use of such an automatic system is not usually permitted on tanker berths.


A place where tankers are berthed or moored for the purpose of loading or discharging petroleum

Terminal representative

A person designated by the terminal to take responsibility for an operation or duty.

Threshold Limit Value (TLV)

Airborne concentrations of substances under which it is believed that nearly all workers may be
exposed day after day with no adverse effect. TLV’s are advisory exposure guidelines, not legal
standards, that are based on industrial experience and studies.
There are three different types of TLV’s:
• Time Weighted Average (TLV-TWA) — the airborne concentrations of a toxic substance
averaged over an 8 hour period, usually expressed in parts per million (ppm).
• Short Term Exposure Limit (TLV-STEL) — the airborne concentration of a toxic substance
averaged over any 15 minute period, usually expressed in parts per million (ppm).
• Ceiling (TLV-C) – The concentration that should not be exceeded during any part of the working

Topping off

The operation of completing the loading of a tank to a required ullage.

Topping up

The introduction of inert gas into a tank which is already in the inert condition with the object of raising the tank pressure to prevent any ingress of air.


See ‘Flashlight’.


The degree to which a substance or mixture of substances can harm humans or animals.
‘Acute toxicity’ involves harmful effects to an organism through a single short term exposure.
‘Chronic toxicity’ is the ability of a substance or mixture of substances to cause harmful effects over
an extended period, usually upon repeated or continuous exposure, sometimes lasting for the entire
life of the exposed organism.

You may want to read Purpose and scope of ISGOTT  

True vapour pressure (TVP)

The true vapour pressure of a liquid is the absolute pressure exerted by the gas produced by
evaporation from a liquid when gas and liquid are in equilibrium at the prevailing temperature.


The space above the liquid in a tank, conventionally measured as the distance from the calibration
point to the liquid surface.

Upper flammable limit (UFL)

The concentration of a hydrocarbon gas in air above which there is insufficient oxygen to support and
propagate combustion. Sometimes referred to as upper explosive limit (UEL).


A gas below its critical temperature.

Vapour emission control system (VECS)

An arrangement of piping and equipment used to control vapour emissions during tanker operations,
including ship and shore vapour collection systems, monitoring and control devices and vapour
processing arrangements.

Vapour lock system

Equipment fitted to a tank to enable the measuring and sampling of cargoes without release of
vapour/inert gas pressure.

Volatile petroleum

Petroleum, having a flash point below 60oC as determined by the closed cup method of testing.

Water fog

A suspension in the atmosphere of very fine droplets of water usually delivered at a high pressure
through a fog nozzle for use in fire fighting.

Water spray

A suspension in the atmosphere of water divided into coarse drops by delivery through a special
nozzle for use in fire fighting.

Work permit

A document issued by a responsible person permitting specific work to be done, in a defined area,
during a specified time period.

Reference ISGOTT 5th edition