Introduction

The purpose of the Emergency Shutdown (ESD) and Tank Protection System (TPS) is for the protection of personnel, equipment and the environment from injury, damage or pollution when at sea or in port.

The ESD system is a requirement of the IMO international code of the construction and equipment of vessels carrying liquefied gases in bulk, IGC Code and the SIGTTO industry guidance for ESD arrangements and a Ship Shore Link (SSL) communication system for liquefied gas carriers.

The SSL is fitted to protect the vessel and the shore terminal in the event of a cryogenic incident or a fire risk on the vessel or at the terminal.

It is vitally important at all stages of the carriage of LNG that the operation can be quickly and safely suspended automatically or manually in the event of an emergency.

Such emergency situations can be listed as:

• LNG leakage on the vessel or shore, or between vessels.
• Cargo tank over-filling during loading or transfer.
• Fire on the vessel or shore, or other vessel.
• Excessive movement of the vessel relative to the shore.
• Low pressure in the vessel’s cargo tanks.

During transfer of LNG, any emergency action taken on board the vessel or ashore can have serious repercussions respectively ashore or on the vessel, therefore, intercommunication between the shore and the vessel is absolutely necessary. This also includes all ship to ship transfer operation, where each vessel is similarly fitted with alarms and trips.

An integrated emergency shutdown circuit, electric ‘Fail-Safe’ type, incorporates alarm contacts together with manually-operated switches and fusible switches in series on the vessel. The actuation of any one of them will de-energise the circuit and initiate the ESD.

The SSL connection is provided on the port and starboard midships for the LNG terminal and is to be connected to the shore before starting cargo operations and remain connected throughout the cargo operation.
During ship to ship transfer, a similar arrangement is made between the vessels.

The SSL connection is either an electrical wired connection, fibre optic or pneumatic hose connection. The electrical signal sends a constant satisfactory signal and is used to transmit ESD data. The pneumatic hose connection is used to confirm a constant pressure, and if this fails, then this initiates the ESD and is initiated from either the vessel or the shore.

In the event of an emergency, such as a fire or a heavy cargo leakage, the officer on watch, or one of the watchkeepers on deck, will immediately initiate an ESD by pressing one of the ESD pushbuttons distributed on deck and raise the alarm in accordance with the vessel’s safety instructions.

The ESD will also be initiated by one of the following:

• Manual activation by personnel using the ESD pushbuttons.
• Fusible links around each tank dome, manifold and cargo machinery room in case of fire with delay of 5 seconds.
• Ship/shore activation of their ESD system (electric, fibre optic or pneumatic) with delay of 2 seconds.
• Vapour main pressure very low 0.3kPa(g) with delay of 5 seconds.
• Cargo tank pressure very low 2kPa(g) with delay of 5 seconds.
• Cargo tank extremely high level 99.4% with delay of 5 seconds.
• Electric power failure with delay of 5 seconds.
• Cargo hydraulic oil pressure low-low 9MPa(g) with delay of 10 seconds.
• Manifold ESD solenoid valve power failure with delay of 5 seconds.
• Master gas valve ESD solenoid valve power failure with delay of 5 seconds.
• Control air pressure low 0.5MPa(g).

All time delays are adjustable.Emergency Shutdown Activation

The initiation of an ESD will lead to the following:

• Stop the cargo pumps (4 sets).
• Stop the spray pumps (4 sets).
• Stop the fuel gas pumps (2 sets).
• Stop the emergency cargo pump (1 set).
• All ESD manifold valves will close.
• All cargo tank filling valves will close.
• All cargo tank spray valves will close.
• The master fuel gas valves to main engines, generator engines and GCU will close.
• ESD signal to shore (by electric/optical/pneumatic signal).
• The high duty compressors will trip.
• The low duty compressors will trip.
• The LNG and forcing vaporisers will stop.
• Gas combustion unit will trip.

Note: Once an ESD is activated, acknowledge all alarms but do not reset the system until investigations are concluded.

Shore Emergency Shutdown
Whilst there is mainly only one vessel ESD operating in port, for the terminal there is a second level of ESD, a shore ESD. A shore ESD can only be initiated by the terminal, either manually or automatically if the vessel moves outside of the permissible movement envelope for the manifold hard arms.

Therefore, should the moorings become slack to the extent that the vessel moves along the jetty outside of the shore arms limit, a shore ESD may be initiated.

Additionally, if there is a threatened danger, such as a fire at the terminal, that may affect the vessel, or fire on the vessel that may affect the terminal, the shore ESD system could also be initiated by the terminal.

Initiation of the shore ESD system will result in the same shutdown actions as the vessel’s ESD, but will then initiate a dry detachment of the shore arms from the vessel.

The shore hard arms have a Powered Emergency Release Coupling (PERC) as part of their construction. This section of the hard arm is located just above the Quick Release Connection (QRC) to the vessel’s manifold and consists of two ball valves just above the elbow part of the arms.

In the event of a shore ESD being initiated, these two valves will close automatically and then the upper part of the hard arm will detach at the joint which lies between the two ball valves, this leaves the lower part of the shore arm remaining attached to the vessel. The release of the arm may result in a small shower of liquid LNG being released due to the space between the two ball valves.