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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.
- Increased safety type with flame proofed enclosure, and
- Pressurized type
(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.
- Stop all cargo/ballast/bunkering operations immediately. Valves and tank openings must be
secured. Wherever possible, the fuel supply to the fire should be cut off.
- A limited outbreak of fire can often be dealt with by the portable extinguishers, but where
the fire is established, fixed smothering installations should be used.
- Early consideration must be given to the shutting down of systems by remote closing
devices, as necessary. Ventilation and forced draft fans must also be stopped, as necessary.
- Before any fixed smothering system is activated, it is essential that ;
i) All personnel have been accounted for, and none are in the space on fire.
ii) Ventilation fans to the space have been stopped
iii) Doors and vents are closed
- Boundary cooling should be used to control the temperature of the casing exterior and the
emergency fire pump used to supply the water system.
- In every case, all necessary precautions must be taken to prevent the fire spreading to
adjacent spaces. Consideration must be given to the fuel and lubricating oil pipes in the
vicinity of a fire which may become a fuel source.
- In the unlikely event that the fixed system is inoperable, and no progress is being made
with portable appliances, the only alternative is to endeavour to smother the fire by closing
down the entire space.
Fires in other machinery spaces should be dealt with in a similar manner, as per normal ship fire
fighting procedures.
Related Information:
- Engine room precautions
- Ships readiness to move
- Cargo emergency shutdown requirement for liquefied gas carrier
- Precautions against abnormal weather or other conditions
- 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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