Gas-Dangerous Space or Zone

A space or zone (defined by the Gas Codes) within a ship's cargo area which is designated as likely to contain flammable vapour and which is not equipped with approved arrangements to ensure that its atmosphere is maintained in a safe condition at all times. (Refer to the Gas Codes for a more detailed definition) (see 3.5).

Gas-free Certificate

A gas-free certificate is most often issued by an independent chemist to show that a tank has been tested, using approved testing instruments, and is certified to contain 21 per cent oxygen by volume and sufficiently free from toxic, chemical and hydrocarbon gases for a specified purpose such as tank entry and hot work. (In particular circumstances, such a certificate may be issued when a tank has been suitably inerted and is considered safe for surrounding hot work.)

Gas-free Condition

Gas-free condition describes the full gas-freeing process carried out in order to achieve a safe atmos­phere. It therefore includes two distinct operations: Inerting and Aeration.

(Note: — In some gas trades the expression 'Gas-free' is used to denote a tank which is just Inerted. Some gas carrier operations can stop at this stage; for example prior to special drydockings or cargo grade changes. However, in this book this condition is described as an 'Inert condition' and the expression Gas-free is reserved for the condition suited to tank entry or for hot work, as described on the Gas-free certificate).

Gas-Freeing

The removal of toxic, and/or flammable gas from a tank or enclosed space with inert gas followed by the introduction of fresh air (see 7.9.3).

Gassing-up

Gassing-up means replacing an inert atmosphere in a tank with the vapour from the next cargo to a suitable level to allow cooling down and loading (see 7.3).

Gas-Safe Space

A space on a ship not designated as a gas-dangerous space.

Hard Arm

An articulated metal arm used at terminal jetties to connect shore pipelines to the ship's manifold (see 5.1).

Heel

The amount of liquid cargo retained in a cargo tank at the end of discharge. It is used to maintain the cargo tanks cooled down during ballast voyages by recirculating through the sprayers. On LPG ships such cooling down is carried out through the reliquefaction plant and on LNG ships by using the spray pumps (see 7.8).

Hold Space

The space enclosed by the ship's structure in which a cargo containment system is situated.

Hydrates

The compounds formed by the interaction of water and hydrocarbons at certain pressures and temperatures. They are crystalline substances (see 2.7).

Hydrate Inhibitors

An additive to certain liquefied gases capable of reducing the temperature at which hydrates begin to form. Typical hydrate inhibitors are methanol, ethanol and isopropyl alcohol (see 2.7).

IACS

International Association of Classification Societies.

IAPH

International Association of Ports and Harbors.

ICS

International Chamber of Shipping.

IMO

International Maritime Organization. This is the United Nations specialised agency dealing with maritime affairs.

Incendive Spark

A spark of sufficient temperature and energy to ignite a flammable gas mixed with the right proportion of air.

Inert Gas

A gas, such as nitrogen, or a mixture of non-flammable gases containing insufficient oxygen to support combustion (see 2.5).

Inerting

Inerting means:

(i) the introduction of inert gas into an aerated tank with the object of attaining an inert condition suited to a safe gassing-up operation.

(ii) the introduction of inert gas into a tank after cargo discharge and warming-up with the object of: —

(a) reducing existing vapour content to a level below which combustion cannot be supported if aeration takes place

(b) reducing existing vapour content to a level suited to gassing-up prior to the next cargo

(c) reducing existing vapour content to a level stipulated by local authorities if a special gas-free certificate for hot work is required — see the note under gas-free condition (see 7.2.3/7.9.3).

Insulation Flange

An insulating device inserted between metalic flanges, bolts and washers to prevent electrical continuity between pipelines, sections of pipelines, hose strings and loading arms or other equipment (see 5.1.4).

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.

Intrinsically Safe

Equipment, instrumentation or wiring is deemed to be intrinsically safe if it is incapable of releasing sufficient electrical or thermal energy under normal conditions or specified fault conditions to cause ignition of a specific hazardous atmosphere in its most easily ignited concentration (see 4.8).

ISGOTT

International Safety Guide for Oil Tankers and Terminals (see Appendix 1 — Reference 2.4).

Isothermal

Descriptive of a process undergone by an ideal gas when it passes through pressure or volume variations without a change of temperature.

Latent Heat

The heat required to cause a change in state of a substance from solid to liquid (latent heat of fusion) or from liquid to vapour (latent heat of vaporisation). These phase changes occur without change of temperature at the melting point and boiling point, respectively (see 2.10.1).

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