Case 11
Major Oil Spill in Sydney HarbourNarrative
The1991-built Italian tanker Laura D’Amato was alongside in Sydney, Australia, discharging a cargo of crude oil from some cargo tanks and the two slop tanks using No 2 pump. During the course of events the mate thought the level of the slop tanks was falling too slowly and decided to expedite the process by opening the crossover valves on the main sea line to connect No 3 cargo line to No 2 pump. Five minutes later one of the shore workers smelled hydrogen sulphide, and saw an oil slick between the ship and the shore. The mate stopped the cargo, initially expecting a burst hose or some other trouble in the shore terminal.
The mate went ashore to see if he could locate the source, and was shown where oil was welling to the surface on the vessel’s port side. Back on board he checked all the valves in the pump room, and found both the sea-chest valves unexpectedly open. An attempt was made to shut them, but because the large manually-operated butterfly valves were “back seated” open, it needed two men using a large wheel spanner to do so. Once done the leak stopped.
The investigation focused on finding out why the sea-chest valves were open.
A month before the accident, Lauro D’Amato had loaded her cargo in Jebel Dhanna, where an independent cargo surveyor inspected her. During the inspection he was shown two ‘sealed’ valves, and was told they were the closed sea-chest valves. He tried to turn them in a clockwise direction and, finding they didn’t move, assumed they were shut. His attention was not drawn to the valve indicator, nor did he look for it. He re-sealed the valves and left the pumproom. The ship sailed for Sydney once loading was complete.
On arrival at Sydney, the ship/shore checklist was completed as normal and the discharge started. A vetting inspector, acting on behalf of a leading oil company, recalls seeing the sea chest valves sealed with a loop of twine joined by a red plastic seal connecting the two valve handles. He, like several others, assumed they were shut and sealed. They were all mistaken and Sydney Harbour suffered a major oil spill.
Procedural and mechanical safeguards failed to prevent the accident.
The most likely source of oil pollution in tanker operations is from overfilling cargo tanks, the valves at the ship’s loading manifold and sea valves connected to the ship’s cargo pipeline system. On board Laura D’Amato the sea crossover line was also part of the cargo pipeline system, and on this occasion the two sea-chest valves were open.
The Lessons
1 . Laura D’Amato’s pump room piping system had no positive means of isolating the sea chest from the cargo system. This accident would not have happened had a spectacle piece, blank or removable spool piece been used to isolate the cargo system.
2. The assumption that valves are closed because a seal has been attached can be flawed. In this case the investigation found that in all probability a seal which had supposedly been in place for four months, had in fact been temporarily removed during a ballast passage. Forensic evidence shows that this seal had been tampered with. The valves had been hard opened and the seal replaced – with the valves still in the open position. The surveyor in Jebel Dhanna assumed they were shut, and resealed them without further checking.
3. The ship’s staff should not have perpetuated the assumption that the valves were shut just because of the seal. The mate and the pumpman should have made a proper inspection, the valve indicators should have been checked, and an air-pressure test should have been carried out on the sea chest valves before any cargo was loaded.
Footnote
This article is based on an Australian Marine Incident Investigation Unit’s report and features in this Safety Digest with the kind permission of the Australian Transport Safety Bureau.