Pollution incident during bunkering. Analysis, Findings, and Recommendations.
Incident Overview
A container vessel was conducting a routine bunkering operation at a port. The operation involved the transfer of 117 metric tonnes of very low sulphur fuel oil (VLSFO) from a bunker barge to the vessel’s designated bunker storage tanks. The Chief Engineer and the 2nd Engineer supervised the operation, assisted by engine ratings.
At 17:15, the bunker barge was alongside the vessel. Upon completion of the pre-bunkering procedures, the transfer started at 19:30.
At approximately 20:10, fuel was observed overflowing from the air vent from one of the bunker tanks. The emergency stop was activated, and the Ship Oil Pollution Emergency Plan (SOPEP) was initiated. Port authorities were notified. It was estimated that 400 litres of VLSFO spilled into the port’s waters.
Investigation Findings
A detailed investigation into the incident revealed several procedural, operational, and equipment-related shortcomings that contributed to the spill:
1. Procedural Deficiencies
- Lack of specified maximum bunkering pumping rate and delivery pressure: Neither bunkering checklists nor Safety Management procedures specified these limits.
- Bunkering checklists deficient: The checklists were not ship-specific and had confusing entries.
- Improper tank soundings: The Chief Engineer's tank level limit was set at 440 cm, but an overflow was observed at approximately 392 cm, suggesting improper tank soundings.
- Unspecified frequency of tank soundings during transfer: The frequency of tank soundings required during the transfer was not stipulated in shipboard bunkering procedures.
2. Operational Shortcomings
- High pumping rate: Unlike during previous bunkering operations, the vessel agreed with the bunker barge to deliver fuel at a rate of 100 MT/hour, which was too high given the vessel’s tank size and venting system.
- Delayed emergency response: A delay in activating the emergency stop may have contributed to the spill.
- Manual sounding issues: Level measurements of the tanks were done using long tape by dip sounding, which is prone to errors, instead of the commonly accepted practice of ullaging.
- Crew Competency Concerns: Some assigned roles in the bunkering procedure did not match the crew list, raising concerns about proper role assignments.
- Use of unapproved and outdated drawings and tank sounding tables. The vessel was using a simplified self-made tank sounding table that lacked important correction factors. The ship’s drawings did not reflect the actual construction of the bunker fuel transfer system.
- Oil Record Book (ORB) records deficient. The accidental oil spill was not recorded as per MEPC.1/Circ.736/Rev.2.
- Vent Pipe maintenance. There were no records of air vent pipe head regular maintenance. The air vent system may have been partially blocked or restricted, leading to increased backpressure and overflow.
3. Equipment and System Deficiencies
- Lack of high-level alarms: The vessel’s bunker tanks did not have high-level alarms installed.
- Lack of pressure monitoring: The bunker manifold lacked pressure and temperature gauges, preventing proper monitoring of the transfer process.
- Lack of maintenance: Pressure release valves installed on the system were not included in the Planned Maintenance System and may not have been checked for proper functioning regularly.
- Poor condition of deck scupper plugs: The deck scupper plugs were found to be loose and perished.
Recommendations
Based on the findings, the following corrective actions were recommended to prevent future incidents:
1. Procedural Revisions:
- Revise bunkering checklists to include:
- Maximum pumping rate and pressure limits.
- More detailed and standardised tank sounding procedures.
- Ensure all checklists and procedural documents are clear and straightforward to enhance crew understanding.
- Ensure that personnel assigned with bunkering operation duties are properly trained and certified and that their roles align with the crew list.
2. Equipment and System Improvements:
- Install high-level alarms in all bunker storage tanks and ensure they are included in the vessel’s planned maintenance system.
- Upgrade the bunker manifold by adding pressure and temperature gauges.
- Implement a routine inspection and cleaning program for vent pipes to prevent blockages.
- Ensure scupper plugs are inspected and replaced regularly to improve containment in case of overspill.
3. Operational Enhancements:
- Set up the maximum bunkering rate at 40 MT/hour (as observed in operations prior to the incident).
- Improve emergency response training to ensure quicker activation of the emergency stop procedure.
- Require the use of approved tank sounding tables that account for vessel’s trim and heel to prevent incorrect ullage measurements.
- Require that the vessel’s plans and drawings are revised and updated.
- Conduct an Oil Record Book (ORB) compliance review to ensure proper documentation of fuel transfers and accidental discharges.
Conclusion
This oil spill incident highlights the critical importance of robust bunkering procedures, well-maintained equipment, and trained personnel in preventing marine pollution. By addressing procedural gaps, improving equipment functionality, and enforcing better operational practices, similar incidents can be prevented, ensuring both compliance with international regulations and environmental protection.