UK MAIB issued its first Safety Digest of 2022, in which it describes an incident where seawater began flooding into the engine room, making the engineers evacuate the engine room and raise the alarm.
The incident
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.
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. 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 fitted 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.
Probable cause
After the accident, a technical investigation identified 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.
Lessons learned
- Procedure: The strainer lid was fitted with a test plug, provided to make sure the system was not still under pressure before the lid was removed. However, the engineers involved in this accident neither followed an approved procedure for the strainer clean nor opened the test plug and so were unaware of the faulty hull valve that meant the system was still open to sea pressure. Additionally, when they tried to remove the lid with a screwdriver, the absence of any leakage underpinned their assessment that the system was isolated.
- Check: Given that the hull valve indicated shut on the ballast control panel, it was reasonable of the engineers to assume this was correct. However, where there is doubt or, for instance, when reducing a system to single valve isolation to sea, it is good practice to visually inspect the valve’s mechanical position indicator as well as checking its remote indication. A further precaution is to loosen the nuts, then use wedges to crack the lid open; if water floods out, the retaining nuts can be retightened to seal the strainer lid.
