200042 Dangerous Incident after Tank Washing

11 Feb 2000 MARS

Dangerous Incident after Tank Washing
Report No. 200042

After discharging Naphtha, we had completed tank washing and gas freeing all tanks to prepare for the next cargo. At this time we did not know that we had a large leak on the hydraulic line leading to the decanting valve between the port and starboard slop tanks. Although the decanting line between these tanks should have been drained of Naphtha during tank washing, this was overlooked. If we had known that we would need to work on this valve, perhaps we would have given more importance to draining the decanting line.

After gas freeing and one of the crew entering the tank, the leak was found and the hydraulic line repaired. When the valve was being tested after repair, the pumpman and a cadet were in the tank at an intermediate landing on the ladder to observe it opening while the valve was operated from the cargo control room. In most ships, this valve is at the bottom of a long vertical line coming from the top of the slop port to the bottom of the slop starboard. When the valve was opened, Naphtha trapped in the vertical line rushed out, immediately filling the tank with a high concentration of gas. The pumpman and the cadet came out choking. Fortunately they had not been standing at the bottom of the tank or the incident would have been much more serious.

In addition to draining all lines during tank washing, I would also suggest that when operating valves for the first time, the crew should stand outside the tank, on deck, to observe anything wrong and only enter the tank to observe subsequent operations of valves.

Have you had any bad experiences with tank washing or other procedures? - Why not pass on the lessons learned?