Liquefied Gas Carrier

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Liquefied Gas carrier precautions & instructions for Openings in Deckhouses and Superstructures

Cargo vapour, whether toxic or flammable, should be vented to atmosphere with extreme caution, taking account of regulations and weather conditions.

Accommodation and machinery spaces contain equipment that is not suitable for use in flammable atmospheres and it is therefore important that petroleum gas is kept out of these spaces.

If doors have to be opened for access, they should be closed immediately after use. Where practical, a single door should be used for working access in port. Doors that must be kept closed should be clearly marked. Allowance must be made to permit doors and openings to be open if the vessel is storing provided there is no possibility of gas entering the accommodation and that doors do not remain open for longer than is necessary.

The accommodation air conditioning system is maintained on partial re-circulation during cargo operations. It is essential that the accommodation is kept under positive pressure to prevent the entry of hydrocarbon vapours. The operation of sanitary and galley extraction fans will cause a vacuum and therefore the gas detector is equipped for air conditioning system intakes must not kept fully closed in case of between the vessel and the terminal agreement

If the cargo vapour is heavier than air it may accumulate on deck and enter accommodation spaces. Standard precautions should therefore be observed. In some cases it may be possible to heat vapour before venting to reduce its density and assist dispersion. If such facilities are provided they should be used.

It is essential that the accommodation is kept under positive pressure to prevent the entry of hydrocarbon vapours. Intakes for air conditioning units are normally positioned in gas safe areas, and under normal conditions vapour will not be drawn into the accommodation.

A positive pressure will only be maintained if air intakes are open, and if all doors, portholes and other openings (including all those in the poop front first tier) are kept closed during cargo operations. Regulations require that certain portholes are fixed shut and openings positioned to minimise the possibility of vapour entry. The design features are not be impaired in any way. Doors are to be clearly marked if they have to be kept closed. It is particularly important that air lock doors are opened one at a time only, opening both doors together will activate an alarm and cause shutdown of equipment.

The air conditioning system should not be operated with intakes fully closed, that is in 100% recirculation mode, as the operation of extraction fans in the galley and sanitary spaces will reduce the pressure inside the accommodation to less than that of the ambient pressure outside.

There is a benefit from having a gas detection and/or alarm system fitted to air conditioning intakes. In the event that hydrocarbon vapours are present at the inlets, the ventilation system should be shut down and cargo operations suspended until such time as the surrounding atmosphere is free of hydrocarbon vapours.

Ethylene carrier underway

Fig: Ethylene carrier underway

Related Information:

  1. Vapour Characteristics of liquefied gases

  2. Low temperature effects of Liquefied gases

  3. Flammable vapours in cargo tanks and how to monitor safety limits

  4. Reactivity of liquefied gas cargo and safety guideline

Cargo Information - physical and chemical properties necessary for the safe containment of the cargo

Mooring requirements for gas carrier

Means of access to ship - gas carrier guideline

Standards for use of Mobile-phone in gas carrier

Precautions against abnormal weather or other conditions

Dispersal of vented cargo vapours

Engine and boiler room p0`recautions

Cargo Machinery Room Precautions

Ship’s Readiness to Move

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