201937 Settling tank overflows on deck

28 May 2019 MARS 2019

During routine rounds while in port, the deck watch officer noticed oil on the poop deck. The alarm was raised and cleanup activities begun, as did the search for the oil source. It was found that the contents of a fuel oil settling tank had overflowed from the vent pipe located in the funnel. The overflowing oil then spilled on to the lower decks through the drain pipes and scuppers.

The company investigation into the factors contributing to the incident discovered that the settling tank was fitted with a float-type
liquid level indicator. This had, among other features, a high-level alarm and an auto-stop function to assist in the automatic transfer of
fuel to the settling tank. The tank level gauge became stuck while the transfer pump was running in auto mode. This caused first the auto-stop function and then the high-level alarm to remain inactive even as the tank filled to overflowing. It was also found that a final safety barrier had been disabled by crew during the last voyage.

The settling tank overflow line to another fuel tank had been blanked off to mitigate the risk of contaminating low-sulphur fuel.

Lessons learned

  • Vessels are fitted with numerous automatic systems. These are usually equipped with safety barriers that must not be disabled, otherwise negative consequences can arise.
  • Notwithstanding automatic processes, crew members should conduct regular inspection rounds to maintain safety.
  • Regular draining of tank level columns will help prevent clogging caused by sludge accumulation, which in this instance may have been a contributory factor in the gauge becoming stuck.