Section 9 Environmental Control

901.

Environmental control within cargo tanks and cargo piping systems

1. A piping system is to be provided to enable each cargo tank to be safely gas-freed, and to be safely purged with cargo gas from a gas-free condition. The system is to be arranged to minimize the possibility of pockets of gas or air remaining after gas-freeing or purging.

2. A sufficient number of gas sampling points are to be provided for each cargo tank in order equately monitor the progress of purging and gas-freeing. Gas sampling connections are valved and capped above the main deck.

3. The system is to be arranged to minimize the possibility of a flammable mixture existing

to ad- to be

in the

cargo tank during any part of the gas-freeing operation by utilizing an inerting medium as an inter-

mediate step. In addition, the system is to enable the cargo tank to be purged with an inerting me- dium prior to filling with cargo gas, without permitting a flammable mixture to exist at any time within the cargo tank.

4. Piping systems which may contain cargo are to be capable of being gas-freed and purged as pro- vided in Pars 1 and 3.

5. Inert gas utilized in these procedures may be provided from the shore or from the ship.

902. Environmental control within the hold spaces

Hold spaces associated with cargo containment systems are to be inerted with suitable dry inert gas and kept inerted with make-up gas provided by a shipboard inert gas generation system or by ship- board storage which are to be sufficient for normal consumption for at least 30 days.

903.

Inerting

1. Inerting refers to the process of providing a non-combustible environment by the addition of com- patible gases, which may be carried in storage vessels or produced on board the ship or supplied from the shore. The inert gases are to be compatible chemically and operationally, at all temper- atures likely to occur within the spaces to be inerted, with the materials of construction of the spaces and the cargo. The dew points of the gases are to be taken into consideration.

2. Where inert gas is also stored for fire-fighting purposes, it is to be carried in separate containers and is not to be used for cargo services.

3. Where inert gas is stored at temperatures below 0°C, either as a liquid or as a vapour, the storage

and supply system are to be so designed that the temperature of below the limiting values imposed on it.

4. Arrangements suitable for the cargo carried are to be provided gas into the inert gas system.

5. The arrangements are to be such that each space being inerted controls and relief valves, etc. are to be provided for controlling

the ship’'s structure is not reduced

to prevent the backflow of cargo can be isolated and the necessary

pressure in these spaces.

904.

Inert gas production on board

1. The equipment is to be capable of producing inert gas with an oxygen content at no time greater than 5 % by volume. A continuous-reading oxygen content meter is to be fitted to the inert gas supply from the equipment and is to be fitted with an alarm set at a maximum of 5 % oxygen content by volume. Additionally, where inert gas is made by an onboard process of fractional dis- tillation of air which involves the storage of the cryogenic liquefied nitrogen for subsequent release, the liquefied gas entering the storage vessel is to be monitored for traces of oxygen to avoid possi- ble initial high oxygen enrichment of the gas when released for inerting purposes.

2. An inert gas system is to have pressure controls and monitoring arrangements appropriate to the cargo containment system. A means acceptable to the Society, located in the cargo area, of pre- venting the backflow of cargo gas are to be provided.

3. Spaces containing inert gas generating plants are to have no direct access to accommodation spaces,

service spaces or control stations, but may be located in machinery spaces. If such plants are lo- cated in machinery spaces or other spaces outside the cargo area, two non-return valves, or equiv- alent devices are to be fitted in the inert gas main in the cargo area as required in Par 2. Inert gas piping is not to pass through accommodation spaces, service spaces or control stations. When not in use, the inert gas system is to be made separate from the cargo system in the cargo area except for connections to the hold spaces.

4. Flame burning equipment for generating inert gas is not to be located within the cargo area.

Special consideration may be given to the location of inert gas generating equipment using the cat-

alytic combustion process.

5. Where a nitrogen generator system is installed, it is to comply with the relevant requirements in Pt 8, Annex 8-5 of the Guidance relating to the Rules.