Lessons Learnt: Liquid cargo contamination during tank cleaning

Oil tanker in seaport with containerships

Vessel Type: Tanker

Incident description

This tanker was fixed to load three liquid chemical parcels, each consigned for discharge at different ports. No problems were experienced during loading or the sea passage and the parcel consigned for the first discharge port was delivered without incident. Upon arrival at the second discharge port, the vessel was instructed to anchor due to congestion at the terminal. The crew took this opportunity to carry out fresh water pre-washing of the five empty cargo tanks that had been discharged at the previous port and proceeded to connect the designated hoses between the deck fresh water pipeline and the individual tank washing machines. After the commencement of tank cleaning, the duty officer noticed that one of the hoses was incorrectly connected to a tank loaded with cargo consigned for the third port of discharge, thus allowing a large quantity of water to enter before the valve was closed. 


The high value chemical cargo in the tank was contaminated with water far in excess of specification limits and was rejected by the original consignee. Dealing with the contaminated cargo required a very expensive process of separate storage, refining at an alternative port and on-carriage on board another vessel. The incident would not have occurred had the crew properly checked and double checked that the correct connections were made and the appropriate system valves properly set up before commencing tank cleaning. These precautions are particularly critical when tank cleaning is conducted with the vessel in a partially laden condition. Apart from the financial impact of potentially very large contamination claims, erroneously admitting water and tank cleaning additives into the wrong tank may potentially result in a dangerous chemical reaction.

Lessons Learnt

  • Tank cleaning operations should always be carried out in strict compliance with documented shipboard procedures and guidelines, with which responsible officers should be fully familiar
  • Prior to commencement of cargo, ballast, tank cleaning or any other transfer operations, the correct setting up of pipelines, valves and blanks should be clearly stated in the operational plan and reviewed during the pre-work briefing of all officers and crew involved
  • Tank cleaning checklists must be diligently completed prior to commencement of operations
  • The setting up of lines and valves should be double checked by a responsible officer

Captain David Nichol

Senior Loss Prevention Executive (Greece)