NTSB report finds lack of continuous monitoring an issue in fire on dive support vessel undergoing repairs

The dive support vessel Joseph Bisso, later renamed Iron Maiden (Photo: US Coast Guard)

The National Transportation Safety Board (NTSB) recently released its investigation report into an incident wherein a fire ignited on board the dive support vessel (DSV) Iron Maiden while it was undergoing repairs at a Louisiana shipyard on April 16, 2020.

At 01:10 local on the said date, a fire on board Iron Maiden occurred while the vessel was docked at Allied Shipyard in Larose, Louisiana.

Local firefighters extinguished the fire at 02:25. No one was aboard the vessel at the time of the fire, and no pollution or injuries were reported.

Damage to the vessel was estimated at greater than US$900,000.


The 163-foot (49-metre) Iron Maiden was built in 1978 at Halter Marine in Lockport, Louisiana, as an offshore supply vessel and was originally named Kathy Candies. It was purchased by Tiburon Marine in 2006, renamed Thrasher, and converted to a dive support vessel in 2007.

In May 2009, Bisso Marine Company purchased vessel, changed its name to Joseph Bisso, and continued dive support operations. In December 2019, the vessel was purchased by Blue Marlin, which renamed it Marlin Responder and later Iron Maiden, and intended to upgrade the vessel and return it to dive support operations.

Accident events

Iron Maiden was moved to Allied Shipyard on March 31, 2020. The vessel was to be drydocked for inspection by the US Coast Guard and American Bureau of Shipping (ABS) personnel so it could receive certification and return to operations.

While waiting for the drydock to become available, shipyard personnel worked on the vessel, and a marine chemist visited the vessel on three occasions to certify the interior tanks and voids as safe for workers and hot work.

On April 15, 2020, Iron Maiden was shifted 150 feet (45 metres) to a new berth, and the shipyard electrician reconnected the shore power electric cables and restored power. The electrician stated that he went aboard the vessel after the power was restored, found everything was operating, and departed.

Following the movement of Iron Maiden, Allied Shipyard workers entered the vessel at 08:00 to conduct hot work with acetylene torches on the starboard exhaust trunk under the bridge deck and on the forecastle deck by the starboard-side mooring/securing bitt. Both work areas were located directly above the generator room on the main deck.

The room had three diesel-engine-driven generators, which were secured. The number one generator was directly under the starboard exhaust fan (which was secured) and had a fire cloth over it for protection from falling sparks that could come down the exhaust trunk.

Shipyard employees working on the stack trunk and bulwark encountered thin metal while cutting with a torch, which caused blow-through, resulting in a hole in each area.

The shipyard foreman examined the generator room at approximately 09:30 and determined that the space was safe, since there was no indication of fire or smoke.

Service contractors were also on board the vessel cleaning the sewage tank, located on the deck directly below the generator room, so it could be certified for hot work by a marine chemist the next day.

After the hot work was completed on the exterior of the starboard exhaust trunk and the generator room was inspected by the shipyard foreman, two other shipyard employees entered the generator room at 10:00 to start removing the woodwork at the base of the generator room’s forward bulkhead, near the access hatch.

As the two shipyard employees were removing the woodwork, they discovered wastage (a hole) in the deck, which exposed them to the vessel’s sewage tank directly below. The two shipyard workers were told by the supervisor to leave the space because contractors were cleaning the sewage tank, so they departed the generator room at 14:00.

By 16:30, all work on Iron Maiden was concluded, and all shipyard workers departed the vessel. The vessel company representative left Iron Maiden about 17:35, leaving on board two vessel crewmembers, who finished eating dinner and left the vessel around 18:00 to return to their hotel for the evening.

The shore power to the vessel remained energised following the departure of the shipyard personnel, contractors, and the vessel crew.

On April 16, at 01:10, the Lafourche Parish Fire District dispatcher received a phone call from the Larose Bridge tender (located a short distance from the shipyard) reporting smoke and flames coming from a vessel at the shipyard.

The first fire trucks arrived at the shipyard at 01:18, and firefighters discovered smoke coming from the starboard side of Iron Maiden‘s pilothouse. The fire extended from the main deck up to the pilothouse, encompassing the generator room and the living spaces on the forecastle deck.

The responding firefighters boarded the vessel and fought the fire with water hoses. At 02:25, the fire was extinguished with no injuries.

At about 09:00, shipyard personnel found an area still emitting smoke behind the fuel tank the starboard side of the generator room, but it was “dug up” by shipyard personnel and quickly extinguished with water from a garden hose.

Additional information

There was no crewmember or shipyard worker staying on board Iron Maiden during the night of fire. The vessel’s fire detection system was secured while work was being conducted within the vessel to prevent false alarms from smoke and dust.

In addition, there was no shipyard policy or vessel owner policy in place to have shipyard personnel or vessel crewmembers conduct safety rounds after hours when there was no work being done on the vessels at the shipyard.

On April 16, fire investigators from the LaFourche Parish Fire District attended Iron Maiden to investigate the cause of the fire. They noted extensive damage to the generator room, as well as significant damage to the passageway outside the generator room and living quarters (located above the generator room).

In addition, the investigators noted smoke damage to the mess area and the galley (located forward of the generator room) and the interior stern section of the pilothouse (located two decks above the generator room). They also noted sections of burned exterior paint around the starboard smoke trunk and pilothouse.

Within the generator room, the most severe damage was observed on the forward bulkhead near the access hatch from the passageway. The bulkhead area with the most extensive damage was where the charger, alarm panel, and generator button start-stop panel were mounted.

According to the fire investigator’s report, “The fire started in the generator room on the wall area common to the mess area.” They could not rule out the possibility of an electrical short as the potential source of the fire but were unable to determine the cause of the fire.


The hot work on the starboard exhaust trunk and starboard area of the forecastle deck was completed at 09:00 on April 15. After the completion of the hot work, a shipyard supervisor inspected the area, identifying no flame or smoke.

During the remainder of the day, shipyard and contract personnel worked in and around the generator room until 16:30, and there were no observations of flame or smoke within the area. Crewmembers remained on board Iron Maiden until 18:00 and made no reports of or smoke prior to departing the vessel.

Based on the location of the hot work and the initial location of the fire within the generator room (as determined by the LaFourche Parish Fire District investigator’s report), the hot work conducted on board the vessel was not the source of the fire.

While there was extensive damage throughout the generator room, the fire pattern and damage indicated that the area of ignition where the fire started was the forward bulkhead.

Because the battery charger, alarm panel, and generator push button start-stop panel were in the area of fire ignition identified by fire investigators, one of these components may have been the source of the fire as the result of an electrical short. However, the exact location of the source of the fire could not be identified by fire investigators.

At some point, as the fire grew, the wood paneling and furniture in the space above the generator room ignited. After the wood and other combustible items caught fire, they provided a path for the fire to expand from the generator room up into the living quarters.

With the vessel’s fire detection system secured for the shipyard period and no continuous or periodic scheduled monitoring of the vessel by shipyard or owner personnel, the fire was able to spread undetected.

Probable cause

The NTSB determines that the probable cause of the fire aboard Iron Maiden was an electrical short from an unidentified source located on the forward bulkhead within the generator room. Contributing to the undetected propagation of the fire was the lack of continuous monitoring of the vessel while it was docked at the shipyard.

Fire and flooding are risks for both crewed and unattended vessels. To protect personnel, property, and the environment, it is good marine practice for owners, operators, and shipyard managers to coordinate and implement some form of continuous monitoring for vessels undergoing maintenance in a shipyard, in lay-up, or in some other inactive period without regular crews aboard.

Continuous monitoring can consist of scheduled security rounds and/or active monitoring with sensing and alarm systems.

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