18.10.1.1 A cargo emergency shutdown system shall
be fitted to stop cargo flow in the event of an emergency, either
internally within the ship, or during cargo transfer to ship or shore.
The design of the ESD system shall avoid the potential generation
of surge pressures within cargo transfer pipe work (see 18.10.2.1.4).
18.10.1.2 Auxiliary systems for conditioning the
cargo that use toxic or flammable liquids or vapours shall be treated
as cargo systems for the purposes of ESD. Indirect refrigeration systems
using an inert medium, such as nitrogen, need not be included in the
ESD function.
18.10.1.3 The ESD system shall be activated by
the manual and automatic initiations listed in table 18.1. Any additional
initiations shall only be included in the ESD system if it can be
shown that their inclusion does not reduce the integrity and reliability
of the system overall.
18.10.1.4 Ship's ESD systems shall incorporate
a ship-shore link in accordance with recognized standardsfootnote.
18.10.1.5 A functional flow chart of the ESD system
and related systems shall be provided in the cargo control station
and on the navigation bridge.
18.10.2
ESD valve requirements
18.10.2.1.1 The term ESD valve means any valve
operated by the ESD system.
18.10.2.1.2 ESD valves shall be remotely operated,
be of the fail-closed type (closed on loss of actuating power), be
capable of local manual closure and have positive indication of the
actual valve position. As an alternative to the local manual closing
of the ESD valve, a manually operated shut-off valve in series with
the ESD valve shall be permitted. The manual valve shall be located
adjacent to the ESD valve. Provisions shall be made to handle trapped
liquid should the ESD valve close while the manual valve is also closed.
18.10.2.1.3 ESD valves in liquid piping systems
shall close fully and smoothly within 30 s of actuation. Information
about the closure time of the valves and their operating characteristics
shall be available on board, and the closing time shall be verifiable
and repeatable.
18.10.2.1.4 The closing time of the valve referred
to in 13.3.1 to 13.3.3 (i.e. time from shutdown signal initiation
to complete valve closure) shall not be greater than:
where:
|
U
|
= |
ullage
volume at operating signal level (m3);
|
|
LR
|
= |
maximum
loading rate agreed between ship and shore facility (m3/h).
|
The loading rate shall be adjusted to limit surge pressure
on valve closure to an acceptable level, taking into account the loading
hose or arm, the ship and the shore piping systems, where relevant.
18.10.2.2 Ship-shore and ship-ship manifold connections
One ESD valve shall be provided at each manifold connection.
Cargo manifold connections not being used for transfer operations
shall be blanked with blank flanges rated for the design pressure
of the pipeline system.
18.10.2.3 Cargo system valves
If cargo system valves as defined in section 5.5 are also
ESD valves within the meaning of 18.10, then the requirements of 18.10
shall apply.
18.10.3
ESD system controls
18.10.3.1 As a minimum, the ESD system shall be
capable of manual operation by a single control on the bridge and
either in the control position required by 13.1.2 or the cargo control room,
if installed, and no less than two locations in the cargo area.
18.10.3.2 The ESD system shall be automatically
activated on detection of a fire on the weather decks of the cargo
area and/or cargo machinery spaces. As a minimum, the method of detection
used on the weather decks shall cover the liquid and vapour domes
of the cargo tanks, the cargo manifolds and areas where liquid piping
is dismantled regularly. Detection may be by means of fusible elements
designed to melt at temperatures between 98°C and 104°C, or
by area fire detection methods.
18.10.3.3 Cargo machinery that is running shall
be stopped by activation of the ESD system in accordance with the
cause and effect matrix in table 18.1
Table 18.1 ESD functional
arrangements
— Functional requirement.
18.10.3.4 .The ESD control system shall be configured
so as to enable the high-level testing required in 13.3.5 to be carried
out in a safe and controlled manner. For the purpose of the testing,
cargo pumps may be operated while the overflow control system is overridden.
Procedures for level alarm testing and re-setting of the ESD system
after completion of the high-level alarm testing shall be included
in the operation manual required by 18.2.1.
18.10.4
Additional shutdowns
18.10.4.1 The requirements of 8.3.1.1 to protect
the cargo tank from external differential pressure may be fulfilled
by using an independent low pressure trip to activate the ESD system,
or, as minimum, to stop any cargo pumps or compressors.
18.10.4.2 An input to the ESD system from the
overflow control system required by 13.3 may be provided to stop any
cargo pumps or compressors' running at the time a high level is detected,
as this alarm may be due to inadvertent internal transfer of cargo
from tank to tank.
18.10.5
Pre-operations testing
Cargo emergency shutdown and alarm systems involved in cargo
transfer shall be checked and tested before cargo handling operations
begin.