The sequential method is a process by which a ballast tank intended for the carriage of ballast water is first
emptied and then re-filled with replacement ballast water to achieve at least a 95% volumetric exchange.
Where the sequential method is utilized, each tank is to be discharged until the suction on the ballast pump
is lost. To assist in sediment control, it is recommended that a small percentage of seawater (approximately
5% of the tank’s volume) be pumped into the tank for flushing purposes and then removed prior to refilling
the tank to complete the exchange.
The intent of this additional flushing of the tank is to assist in the removal of sediments that may accumulate at
the bottom of the tank. Scientists have proven that aquatic organisms and pathogens when entrapped in the
sediments may re-emerge and develop when the tank is refilled with mid ocean water.