The following points are to be considered during “topping-off”:
- The pre-loading meeting must include agreement on the arrangements and notice required for “topping-off”. The number of valves to be closed during “topping-off” must be reduced to a minimum.
- The loading rate is to be reduced to a safe level. This will require a request to the shore to reduce the rate. Ship tank valves are not to be used to reduce the rate as this can lead to pressure surges or excessive pressure in the system.
- Portable MMC gauges must be used for “topping-off”. Remote gauges are not to be used for this purpose.
- Tanks not being loaded must be frequently checked for leakage.
- The final stages of filling tanks must be well staggered to make sure that only one tank is being “topped-off” at any one time. After “topping-off” individual tanks master valves must be shut,where possible, to provide two valve separation.
- One tank in each grade must always be kept as a “crash tank”. If a valve failure or major leak is experienced, so that a tank being “topped-off” cannot be closed off, the availability of a “crash tank” will provide space to divert the flow during an emergency reduction in rate or complete stoppage. The “crash tank” must always be the final tank to be loaded.
- On completion of loading, all tank valves are to be closed.
Points to pounder :
During “topping-off” operations vigilance is essential to ensure that a pollution incident is avoided.