Accidental Mixing of Different Fuel Oils

What happened?

A vessel was at anchorage waiting for the pilot. The engine room was manned and the main engine ready for manoeuvring. The duty engineer informed the bridge that two valves on the fuel transfer line were kept open overnight. These were the valve for Ultra Low Sulphur Fuel Oil tank no 6 (starboard) and valve for Heavy Fuel Oil tank no.6 (Centre starboard).

It was observed on the remote gauging system that the quantity of fuel in the Ultra Low Sulphur Fuel Oil tank no 6 (starboard) was considerably less than the previous day.

What went wrong? What were the causes?

All valves on the fuel transfer line were closed and soundings were taken for all tanks. It was found that 57 tonnes of Ultra Low Sulphur Fuel Oil from tank no.6 (S) had been accidentally transferred by gravity to Heavy Fuel Oil tank no.6 (CS), due to the initial higher level in the first tank (tank no.6 (S)).

Samples from tank no.6 (CS) and ULSFO settling tank were taken and landed ashore for urgent sample analysis.

Results from the laboratory confirmed that fuel was contaminated due to mixing.

Our member noted the following:

• There was financial and reputational loss:
  • cost for urgent sample analysing
  • company’s reputation with the shipowner;
• The immediate cause was carelessness – failure to operate the fuel valve correctly;
• Causal factors identified were inadequate supervision or management – a lack of adequate oversight and monitoring;
• The root cause identified was inadequate compliance with existing procedures.

What actions were taken?

Persons involved were referred back to company procedures, and a notice with the fuel oil transfer procedures displayed near the operating panel.

Members may wish to refer to the following incidents:

• Isolation of fuel tanks
• Cargo contamination causing LTIs during clean-up
• Near-miss: Engine room flooding