Boiler explosion highlights MGO challenges

30 Jun 2017
Inspection after the boiler explosion revealed waxy deposits in the unit's fuel line filter

Inspection after the boiler explosion revealed waxy deposits in the unit's fuel line filter

A safety bulletin from the UK Marine Accident Investigation Branch (MAIB) concerning a fatal explosion on the ‘Manhattan Bridge’ highlights the challenges of low-sulphur distillate fuel.

One engineer was killed and another badly injured in January, when an auxiliary boiler on the containership blew up. The bulletin noted that the vessel, which was berthing alongside a container terminal in Felixstowe, had been operating on marine gas oil (MGO) for several days prior to the incident, having switched from heavy fuel oil when it entered the North Sea ECA.

An examination of the boiler fuel system by the burner unit manufacturer identified the build-up of waxy deposits in the supply filter, sufficient to restrict the fuel flow. The formation of waxy deposits at low temperatures has been attributed to the increased paraffin content in some MGO. The bulletin noted that ‘industry reports indicate an increased incidence of boiler and marine diesel engine performance problems in colder waters following the implementation of the more stringent sulphur emissions limit [in 2015]’.

The MAIB also noted that the rules under which the bunkered MGO was sampled did not include the cloud point (CP) test measuring the temperature at which crystals visibly begin to form, or the cold filter plugging point (CFPP) test measuring the lowest temperature at which fuel of a given volume, drawn by vacuum through a standardised filter (45 micron) within a specified time (60 sec), continues to flow.

MAIB noted that these tests were only included under the 2017 version of the ISO 8217, which was introduced in March. The MGO loaded at Rotterdam in November 2016 was declared under the 2005 version of the standard. There was thus no way for the crew to know that the MGO, which later was shown to have a CFPP of 14˚C, would lead to wax formation if not properly heated in the 4˚C ambient air temperature at Felixstowe.

“It is essential that vessel operators carefully consider anticipated ambient air and sea temperatures that will be experienced during the voyage when purchasing low-sulphur MGO bunkers,” the bulletin concluded. Monitoring of MGO’s visual appearance, inspections of fuel filters, checking fuel system pressures and maintaining of tanks and pipework above CP and CFPP temperatures would control the risk, the MAIB noted.

The boiler explosion occurred while the second engineer and the oiler were trying to restart the boiler burner unit following a flame failure cut-out. The force of the explosion blew open the boiler burner unit door and propelled the burner’s air diffuser into the engine room.