The National Transportation Safety Board (NTSB) has released an investigation report on an incident where a fire erupted aboard the small passenger vessel Qualifier 105, which was stored ashore for the winter at Northern Enterprises Boat Yard in Homer, Alaska, on January 19, 2023.
The incident
On January 19, 2023, a fire started in stateroom J, below the main deck of the Qualifier 105, which was on blocks for several months in the Northern Enterprises Boat Yard in Homer, Alaska. At the time the fire started, welders were on board performing aluminum hot work, cleaning up the area around a fuel tank that had been repaired and tested the day before, and reinstalling the deck in a head that was directly above the fuel tank.
While hot work can generate sparks and molten material that can ignite combustible materials, the two welders, who were working 8 feet from stateroom J,
where the fire was discovered by the fire watch, did not find any signs of a fire after or while conducting their work. Therefore, the hot work was not the source of the fire. The fire watch and welder 1 each saw a small flame on two different bunks in stateroom J—the first sign of a fire observed. Those small flames were likely caused by hot droplets of plastic sheeting—used to protect the carpet-covered, plywood drop ceiling above—that had melted and caught fire from heat or fire between the aluminum overhead and the drop ceiling. Therefore, it is likely that the initial ignition source and the eventual fire in stateroom J originated from the overhead. The accommodation spaces contained combustible materials—including carpet, wood framing, and plastic sheeting—in the overhead and on the bulkheads that further fueled the fire.
Stray welding current—a fault condition where current goes through unintended conductors, such as metal framing or wires, and back to the return
terminal of a welding machine—can result in heating and cause fires. On board the Qualifier 105, the welding machine work clamp (the return current clamp) was connected to an aluminum cross member below the deck in stateroom J, about 10 feet from the point of welding. The return current had to travel through the vessel’s aluminum structure and/or conducting wires from the spool gun’s electrode back to the work clamp. The aluminum structure would have served as a conductor, and the resulting current in the structure may have found its way into the vessel’s electrical system. An electrical wire in the overhead of stateroom J could have served as an unintended conductor and become overheated and eventually led to a fire. However, investigators could not definitively determine that stray welding current caused wires to overheat. Additionally, there were several wires and electrical boxes in stateroom J that may have been energized and become a potential electrical ignition source due to a fault. Therefore, the exact ignition source could not be determined.
Conclusions
Probable Cause
The National Transportation Safety Board determines that the probable cause of the fire aboard the passenger vessel Qualifier 105 was an undetermined electrical source that ignited a stateroom ceiling. Contributing to the extent of the fire damage was the substantial use of combustible materials composing the stateroom ceilings and bulkheads throughout the vessel’s accommodation spaces.
Lessons Learned
Taking Precautions for Stray Welding Current
Stray welding current is a fault condition in which current goes through unintended conductors and back to the return terminal of a welding machine; it can
cause fires by overheating wires. To avoid potential fires caused from stray welding current, maintenance personnel, owners, and operators should follow industry practice to place the work clamp (the return current clamp) of the welding machine as close as possible to the point of welding.
