An engine room fire on a towing vessel was caused by a fatigued chief engineer who inadvertently left a main engine fuel return system overpressurize, according to a National Transportation Safety Board (NTSB) report.
The May 18, 2021, incident on the Upper Mississippi River near St. Louis, Missouri, involved no injuries but resulted in more than $700,000 in damage to the vessel, the Mary Lynn.
Less than 5 hours of sleep in 24-hour period
The Mary Lynn had just dropped off barges and was picking up another delivery as the chief engineer was performing regular maintenance on the main engine. While preparing for the delivery, the chief engineer – who had less than five hours of sleep in a 24-hour period – accidentally left the day tank overflow valves to the fuel storage tanks closed.
Just after the vessel left port, the starboard main engine failed and the captain turned back toward the port to allow the chief engineer to troubleshoot.
While troubleshooting, the chief engineer, who had 32 years of experience with this specific type of engine, opened the suction valves to a fuel storage tank and started a transfer pump, which he turned off during fueling and forgot to turn back on.
Thirteen minutes later, the Mary Lynn was moving again, but then the chief engineer saw a fuel filter sight glass bowl blow off the main engine fuel header, causing the fuel to spray and ignite.
A Good Samaritan towing vessel and a St. Louis Fire Department fire boat helped extinguish the fire.
Acute fatigue impacted attention, memory
NTSB investigators found the probable cause of the fire was the overpressurization of the fuel tank when the fatigued chief engineer inadvertently left the overflow valves to the storage tanks closed, leading to the ignition of spraying diesel fuel from a main engine’s fuel system onto an uninsulated engine component.
Fatigue “likely impacted the chief engineer’s attention, memory and performance of complex tasks.”
However, the chief engineer told investigators he didn’t feel tired at the time of the incident. This despite the fact that he reported receiving less than five hours of sleep in the 24 hours preceding the fire, consisting of a one-hour nap the previous afternoon and about three-and-half hours of sleep before waking earlier than his scheduled 5 a.m. watch to prepare for fueling. His longest continuous sleep was five hours on May 17, the day before the fire, from midnight to 5 a.m.
The NTSB report states that “given the engineer’s accumulated sleep debt over the previous 24 hours and waking early during an off-duty time when he would normally be asleep, the chief engineer was likely affected by acute fatigue.”
Effects of fatigue can include a reduction in vigilance, concentration, memory and reduced performance on complex or sequential tasks that require high levels of attention, all of which likely impacted the chief engineer’s attention, memory and performance of the complex task.