On May 18, 2021, about 0653 local time, the towing vessel Mary Lynn, with a crew of six, was pushing two barges, transiting upbound near mile 176 on the Upper Mississippi River near St. Louis, Missouri, when a fire broke out in the engine room. A nearby Good Samaritan towing vessel and a St. Louis Fire Department fire boat helped put out the fire, which was extinguished at 0810. There were no injuries or pollution reported. Damage to the Mary Lynn was estimated at over $700,000.
determines that the probable cause of the engine room fire on board the towing vessel Mary Lynn was the overpressurization of the fuel day tank (which did not have an independent vent) and a main engine fuel return system when the fatigued chief engineer inadvertently left the day tank overflow valves to the storage tanks closed, which ultimately led to ignition of spraying diesel fuel from a main engine’s fuel system onto an uninsulated engine component.
Lessons Learned: Tank Ventilation
Subchapter M regulations for towing vessels require vessels built after 2000 to have vents for each fuel tank. Regulations for vessels ranging from small passenger vessels to cargo ships require that fuel tanks be independently vented from the highest point of the tank to atmosphere on a weather deck. Tank ventilation is important to ensure a valve line up error does not lead to the overpressurization of or vacuum in a fuel tank. Operators should be aware of their fuel tank ventilation system arrangements. On vessels without independent fuel day tank ventilation, it is critical to ensure proper valve position during transfer and operation of the fuel system.