Liquefied Gas Carrier

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Cargo Machinery Room Precautions on board Liquefied Gas carrier

Cargo vapour, whether toxic or flammable, should be vented to atmosphere with extreme caution, taking account of regulations and weather conditions. Cargo vapour may be present in cargo pump or compressor rooms, and gas detection systems are installed to warn of its presence. In ships carrying cargoes whose vapours are lighter than air (e.g. ammonia) and heavier than air (e.g. LPG) gas detector points are fitted at high and low levels and the relevant detector points should be used for the cargo carried.

Ventilation systems are provided to disperse any vapour that may collect in the pump or compressor room. The space should be ventilated for at least ten minutes before cargo operations begin and throughout their duration, and also if liquid or vapour leakage is suspected. Ventilation systems should be maintained carefully; if the fans fitted are of non-sparking design their design features should not be modified in any way.

Lighting systems in cargo machinery rooms must be certified flame proof. It is essential to ensure that such systems are properly maintained. Additional lighting, if required, should be of a suitably safe type.

Gas-tight bulkhead gland seals and air lock doors to cargo machinery electric motor rooms should be carefully checked and maintained to ensure that cargo vapour does not enter.

Electric motors for driving cargo compressors are normally separated for those spaces by a gas tight bulkhead or deck. However, the IMO code permits where operational or structural requirements are such as to make it impossible to fit gastight bulkheads then electric motors of the following certified safety type may be installed.
(1) Records should be available of the pressure testing of cargo condensers and of the calibration of cargo system instrumentation.

(2) The compressor and motor rooms should be clean and free of combustible material.

(3) The compressor room ventilation system should be maintaining negative pressure.

(4) The motor room ventilation system should be maintaining positive pressure and operating satisfactorily.

(5) If the motor room access is located in a gas-hazardous area, it should be provided with an air-lock suitably alarmed to warn of both doors being opened at the same time. Airlocks and alarms should be in good order.

(6) If pressure in the air-lock is lost, should the shutdown system operate correctly.

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.

Procedure to follow in the event of a compressor house or motor room fire

These spaces are equipped with portable extinguishers (Dry Powder and / or CO2), smothering systems (generally CO2), water hose systems and possibly bulk dry chemical powder units. In the event of a fire, the initial alarm will be activated either automatically by the fire detection system, or manually by the person discovering the fire.

Fires in other machinery spaces should be dealt with in a similar manner, as per normal ship fire fighting procedures.

Related Information:

  1. Engine room precautions

  2. Ships readiness to move

  3. Cargo emergency shutdown requirement for liquefied gas carrier

  4. Precautions against abnormal weather or other conditions

  5. Dispersal of Vented Cargo Vapours

More info pages

Cargo conditioning, reliquefaction and boil-off control requirement for a liquefied gas carrier

Cargo Containment Systems in Liquefied Gas Carriers

cargo emergency shutdown requirement

damage stability guideline for liquefied gas carriers

Various Cargo handling equipments onboard

Cargo hoses connection guideline

Documents accompanying a liquid gas cargo

How LNG transferred from shore to ships cargo tanks ?

Cargo operation guideline onboard a liquefied gas carrier

Cargo piping Systems in Liquefied Gas Carriers

cargo planning requirement

cargo and pumproom safety precautions

cargo stripping guideline

Emergency response for cargo system leaks

Emergency response for cargo tank rupture

Risk of overfilling of cargo tank during loading onboard a liquefied gas carrier

Preparation for cargo transfer

cargo transfer between vessels- safety guideline

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