A small dry cargo vessel was in harbour and its engineers were investigating why ballasting operations were taking longer than normal. Their plan was to clean the ballast system’s seawater strainer and then check the ballast pump’s condition, reports MAIB Safety Digest.
Isolating the strainer
To isolate the strainer, the second engineer (2/E) went to the ballast control panel and shut the automatic butterfly hull valve between the hull inlet and the strainer. The hull valve indicated as shut on the ballast control panel.
Replacing the lid
The 2/E then went to the engine room and manually shut the isolation valve between the strainer and the pump. With the chief engineer present, the 2/E loosened the strainer lid’s retaining bolts and tried to lever the lid off with a screwdriver, but it would not budge. The engineers then rigged a chain block to the strainer lid, having completely removed all the bolts. As the weight came onto the chain block the strainer lid flew off and seawater began flooding into the engine room.
The engineers tried unsuccessfully to replace the lid, then decided to evacuate the engine room and raise the alarm. In the engine room, the water level rose over the bottom plates until the seawater pressure equalised and the vessel settled with the engine room partly flooded. The vessel was made watertight after a diver ftted an external patch over the hull valve.
Thereafter, the contaminated water was pumped out to road tankers for disposal and the vessel was dry docked for repairs. After the accident, a technical investigation identifed that the automatic butterfly hull valve was defective, and had remained partially open when indicated as shut on the ballast control panel.
This investigation also found that the strainer was clean but that a ballast pump defect had caused the slow ballasting operations. The company has provided a revised safe system of work for strainer cleaning.
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Source: MAIB Safety Digest