NTSB: Muffler Cracks Caused Towboat Fire

Around 9:30 a.m. on June 26, 2022, a fire broke out aboard the mv. Mary Dupre, which was pushing one barge of biodiesel along the Gulf Intracoastal Waterway (GIWW) west of Freeport, Texas. The towboat, built in 1974 and part of the Dupre Marine Transportation fleet since 2013, had left Port Comfort, Texas, the day before and was en route to Houston with a crew of four on board, including a relief captain, a pilot and two deckhands.

At the time of the fire, with the Mary Dupre eastbound on the GIWW near Mile 408 (west of Harvey Lock), the pilot, who was off watch and in his stateroom, awoke to the sound of a smoke alarm and the smell of smoke. According to a report by the National Transportation Safety Board (NTSB), released June 15, the relief captain heard “a smoke detector beep” from his post in the wheelhouse, while the off-watch deckhand was awakened by a “burnt smell.”

After notifying the captain in the wheelhouse, the pilot and both deckhands went to the pilot’s stateroom to investigate the smoke. “When they entered the stateroom,” the NTSB report stated, “they observed smoke coming out from the overhead. According to the captain, the crew members believed the smoke was coming from an engine exhaust leak.”

By 10 a.m., the three crew members began tearing off the wood paneling from the ceiling of the stateroom. They used their cell phones to record video of smoke coming out from overhead. “A deckhand looked into the open overhead and observed ‘small flames coming out [of] the walls,’” the NTSB report stated. A deckhand discharged a fire extinguisher into the opening, but the trio was unable to battle the fire behind the stateroom’s wooden bulkhead. “Additional interior spaces began to fill with smoke,” according to the NTSB report.

Moving outside, the crew members discovered smoke coming from the starboard exhaust stack and the starboard engine room ventilation air outlet. They also noticed that the paint on the outside of the stack was blistering.

The captain reached out to nearby vessels, Dupre Marine and the U.S. Coast Guard, and by about 10:20 a.m., the mv. Ave Maria arrived on the scene to take control of the Mary Dupre’s barge. Soon thereafter, the wheelhouse aboard the Mary Dupre began filling with smoke, and by 10:55 a.m., the crew abandoned the Mary Dupre aboard the vessel’s skiff.  By 11:30 a.m., the Mary Dupre crew boarded the Ave Maria, where they watched the Mary Dupre’s house become engulfed in flames.

According to the NTSB report, several towing vessels in the area arrived to apply water to the burning Mary Dupre. A salvage company arrived on scene at around 3:35 p.m., with the team describing the fire as “smoldering.” The team boarded the Mary Dupre and extinguished the fire. By 7 that evening, another vessel began towing the Mary Dupre to a shipyard. The vessel arrived by about 10 p.m. The Mary Dupre was later declared a “total constructive loss,” with damage estimated at about $1 million.

A local fire marshal, the Coast Guard and the NTSB inspected the Mary Dupre while it was at the shipyard. The inspection team noted that “in both the wheelhouse and on the second deck, all wood framing, furniture, paneling and joinery, as well as all paint and combustibles, were destroyed, completely consumed by fire and heat.” On the main deck, combustibles in the galley and crew quarters were described as “partially burned.” In the engineroom, “there was no damage to the main engines, generators or other machinery,” the NTSB report stated.

Problem In The Stack

When inspectors examined the Mary Dupre’s starboard stack, the team discovered a crack in the weld below the upper flange of the muffler. In addition, the exhaust blanket around the starboard muffler was disconnected on the inboard side. The wall in the pilot’s stateroom shared a common bulkhead with the stack, with wooden framing and paneling affixed directly to the common bulkhead. Thus, the team concluded the cracked weld in the muffler, combined with the failed exhaust blanket, allowed hot exhaust gas to build up in the stack, which in turn “caused an ignition of combustible materials on an adjoining wall.” The NTSB noted that the exterior paint’s maximum temperature resistance was 750 degrees and that the temperature required to ignite wood is 480 degrees.

On the day of the fire, the crew inspected the Mary Dupre for fire hazards, in accordance with company policy. “However, the visual inspection did not include the exhaust muffler because the size of the stack space did not allow for personnel to enter the space,” the NTSB report stated. The NTSB concluded that the probable cause of the fire aboard the Mary Dupre was “undetected cracks in the starboard muffler,” which allowed exhaust gases to heat wooden structure affixed to the common bulkhead to the point of ignition. “Contributing to the extent of the fire damage was the substantial use of combustible materials in the joinery, outfitting and furnishings in the accommodation spaces,” the report said.

The NTSB report noted that, while inland towing vessels are inspected according to Subchapter M, “these regulations currently do not require vessel owners to incorporate structure fire protection on their vessels.”

“Structure fire protection” includes the use of fire-resistant materials and insulation.

After the fire, Dupre Marine “completed an investigation report, developed lessons learned and instituted corrective actions,” the NTSB said. According to the NTSB, Dupre Marine stated the Mary Dupre was the only vessel in its fleet with staterooms adjacent to the stacks. The company told the NTSB that, in the future, drydocking procedures for any acquired vessel with a similar design would “include muffler inspections within the stack spaces.”