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Report: Uninsulated Exhaust Components Sparked Catastrophic Fire

miss dorothy
Image courtesy NTSB

Published Mar 14, 2022 3:36 AM by The Maritime Executive

The fire that completely destroyed the towboat Miss Dorothy was ignited by a spray of diesel fuel hitting uninsulated exhaust components, an National Transportation Safety Board (NTSB) investigation has concluded.

The incident involving Miss Dorothy occurred last March while the vessel was pushing 14 barges upbound on the Lower Mississippi River, north of Baton Rouge. A fire broke out in the engine room, and the eight crewmembers aboard attempted to fight it. They were unsuccessful and evacuated to the towboat's barge tow. No pollution or injuries were reported.

According to the NTSB, shortly after midnight fire alarms began to sound in the pilothouse and throughout the vessel. The pilot saw smoke and flames coming from the starboard main engine in the engine room, and the crew attempted to use fire hoses and handheld extinguishers to fight the fire. Shortly after, the chief engineer activated the ventilation shutdown and pulled the emergency fuel oil shutoff for the fuel tank that supplied the starboard main engine.

However, air continued to be drawn in through open engine room doors and other penetrations. In addition, the shutoff valve failed to close. Investigators later discovered that the metal cables connected to all four of the valves had been severed during the fire. 

As the fire continued to grow, the captain ordered abandon ship and the crew was rescued by a good samaritan vessel. The fire was extinguished several hours later.

Regulations for towing vessels require that “piping and machinery components that exceed 220°C (428°F)" must be insulated, the exhaust system aboard Miss Dorothy was uninsulated. Investigators found that the exhaust header leading from the individual cylinder heads to the exhaust manifold - which was subject to temperatures higher than 600°F - was not insulated, and this was near the suspected origin point of the fire. “NTSB investigators concluded it is likely that the uninsulated exhaust header acted as an ignition point for the atomized or spraying diesel fuel,” the report concluded. 

The board recommended that towing vessel owners and inspectors should examine high-heat engine room equipment to ensure that insulation is in place. 

The incident aboard Miss Dorothy is the latest of many engine room fires attributed to uninsulated components. In December 2017, towing vessel J.W. Herron experienced an engine room fire caused by leaking lube oil ignited off an exposed hot engine surface or a slipping clutch.