During his presentation at the last GREEN4SEA Conference, Mr. David Nichol, Senior Loss Prevention Executive at Thomas Miller (Hellas) Ltd., focused on bunker spills, examining their root causes and what loss prevention measures can be implemented to combat them. Mr. Nichol noted that spills into the marine environment relating to bunkering operations continue to occur with worrying regularity.

Bunkering operations are routine and yet critical, high risk operations which require to be carefully planned and performed by the crew in accordance with established shipboard procedures.

Although the vast majority of bunker transfers are performed without incident, very occasionally, things can and do go wrong. A loss of containment by reason of a tank overflow or leakage from pipeline or transfer hose failures may result in oil spilling overboard and polluting the marine environment.

UK P&I Club claim records indicate a recent increase in the number of pollution incidents relating to bunkering operations or internal bunker transfers. So what’s the problem?

We can all agree that oil spills are bad news on a number of different levels, not least for their potential to inflict serious damage to marine ecosystems and particularly when involving viscous heavy fuel oils. Even relatively minor incidents may result in very high value claims for recovery of pollutants, clean up, restoration operations and third party damages potentially running into seven figure dollar sums. In addition, ship owners and crews may also be exposed to heavy fines and criminal prosecution.

Our experience suggests that in only a minority of cases do spills occur due to failure of the hoses or pipelines, which are required to be pressure tested on a periodic basis. Furthermore, the general standard of maintenance of shipboard deck bunker pipeline systems has much improved.


The majority of bunker spills occur as a result of a tank overflowing. The oil is discharged from the tank air vent heads and flows into a containment box or saveall, which then overflows on to the deck. The oil accumulates on the deck and if a sufficient quantity is released, it may then spill over the raised guttering at the deck edge. This is when the real trouble starts. Oil flows down the ship’s side and onto the water surface, which can then be distributed widely by river or sea currents, going on to oil port structures or other shore features and amenities.

We can consider a simple but quite typical case study:

A container ship was stemmed to receive 450 MT of fuel oil. The chief engineer was in overall charge of the operation, which was delegated to the second engineer. A bunkering plan was prepared and pre-bunkering preparations and checklists were completed. The tanks nominated to receive the bunkers were a set of port and starboard side tanks located outboard of a set of port and starboard centre tanks. When all was ready, pumping was commenced but 15 minutes later oil started flowing from the starboard centre tank. By the time pumping was stopped, oil had filled the saveall, accumulated on deck and spilled over the deck containment into the dock.

This resulted in an expensive bill for clean-up operations and a fine imposed on the master and chief engineer, both of whom were removed from the vessel for interrogation by the local authorities.

So what went wrong?

Instead of opening the starboard side tank valve, the engineer opened the adjacent valve to the centre tank which was nearly full, demonstrating how a simple mistake can lead to serious consequences. It probably didn’t help that the valves are not very distinctly labelled but the correct valve set up should nevertheless have been checked and double checked during pre-bunkering procedures.

The common causes of tank overflow can be summarised as follows and should not necessarily be taken in isolation as they it may occur due to a combination of these factors:

  • Failure to properly set up the pipeline system valves: The main issue here is flow of bunkers being directed to where it is not intended.
  • Failure to diligently monitor tank levels during bunkering: Not just the nominated tanks but also other tanks in the system.
  • Transfer of bunkers at an excessive rate or pressure: This risks exceeding the design pressure or capacity of the system and will also increase operational stress on the crew.
  • Air lock: Where air becomes trapped in the tank due to excessive pumping rate, trim or list causing a sudden unexpected discharge of mist or oil from the tank ventilator.
  • Malfunction of valves: This may be associated with deficient valve testing or maintenance.

Most incidents can be traced back to human error. The main underlying factors associated with spills may be summarised as follows:

  • Complacency: Its routine, we’ve done it hundreds of times; what can possibly go wrong!
  • Inadequate planning and neglect to comply with operational procedures: It is not usually the documented procedures that are at fault but a failure to observe them.
  • Poor communication on board and between ship and barge: This is a common feature of bunker spills, where no effective means of communication is established either internally on board or with the barge, seriously compromising the ability to respond quickly and efficiently in the event of an incident.
  • High work load – simultaneous operations and demands: Bunkering often takes place concurrently with cargo operations, taking stores, or inspections and surveys, imposing high demands on the crew.
  • Fatigue: Not unrelated to the above – bunkering operations may be performed over a period of many hours and at night but there may also be other factors contributing to fatigue.
  • Maintenance failures: There have been incidents of overflow attributable to faulty bunker system valves or defects in tank level gauging systems.
  • Poor design: Inadequate arrangement of tank air vents and very small capacity savealls.

Key loss prevention measures: 

  • Familiarisation with bunkering systems and procedures:Delegating responsibility for the conduct of a bunkering operation or transfer to the newly joined junior engineer is probably asking for trouble.
  • Diligent planning and completion of check lists: The procedural checks should be physically performed by the responsible person, not casually ticked off. This does not mean the checklist being completed on the chief engineer’s office PC!
  • Adequate safety margins: The maximum loading volumes of the tanks should be clearly stated in the SMS, typically around 85 - 90% of capacity. In a recent incident, the bunkering plan called for some tanks to be filled in excess of 95%.
  • Pre-work briefing: This should include all involved engine and deck personnel, giving the opportunity to discuss the plan so everyone knows what is expected of them and that emergency procedures are fully understood.
  • Establish and continue to test communications: Emergency stop signals should also be mutually understood between ship and barge.
  • Check and double check pipeline system valves: The set-up of valves should be independently checked by another of the officers involved in the operation and confirmed.
  • Closely monitor and record tank levels: Not neglecting other tanks in the system at all stages of bunkering, particularly when nearing the topping off stage.
  • Beware of over-reliance on remote gauging systems and alarms: This has been a feature of two recent bunker spill incidents where the gauges were misinterpreted or were faulty.
  • Agree, regulate and confirm pumping rates: Ensure that the rate is slowed down at critical stages, particularly commencement of pumping, when nearing changeover of tanks and at completion.
  • Do not let other tasks compromise safe bunkering operations: Crew should not be distracted from their core duties.
  • If in doubt – suspend the operation: Better to absorb a small amount of off-hire hire than risk a very expensive pollution claim.


The views expressed in this article are solely those of the author and do not necessarily represent those of SAFETY4SEA and are for information sharing and discussion  purposes only.

View Capt. David Nichol’s presentation on Bunker Spills during the last GREEN4SEA Conference herebelow

David Nichol is a master mariner with 39 years of experience in the shipping industry. After sea service on tankers, bulk carriers and OBO’s, he worked as a ship surveyor and marine consultant for 18 years performing a wide range of casualty investigations, ship inspections and cargo surveys, with the majority of assignments being P&I related. From 2010, he was employed as a P&I Club senior claims executive before joining the loss prevention department of the UK P&I Club 3 years ago. David is based is the UK Club’s Piraeus office assisting members with loss prevention advice, training and education initiatives, as well as carrying out regular shipboard P&I risk assessments.