Stray Welding Current May Have Caused $1.2M Total Loss

The National Transportation Safety Board has released its analysis of a fire that destroyed a small passenger / research vessel in Homer, Alaska last year. Though hot work occurred inside the vessel before the blaze, NTSB ruled this common fire hazard out, and concluded that an electrical fault was responsible for ignition. 

At noon on January 19, 2023, a fire broke out in a stateroom aboard the 100-foot passenger vessel Qualifier 105, which was being stored on shore at a yard in Homer, Alaska. Local firefighters responded and put out the fire, and no injuries or pollution were reported, but extensive internal damage forced the owners to declare the vessel a total loss. The cost came to an estimated $1.2 million.

Qualifier 105 was an aluminum-hulled Subchapter T boat built in 1970 and used commercially for research work and private charters. The NTSB has closely scrutinized fire safety aboard vessels of this class since the deadly fire aboard the aging "T-boat" Conception in 2019, which claimed the lives of 33 people. 

After the 2022 Alaska summer season, the boat was hauled out and put on blocks at the Northern Enterprises Boat Yard in Homer. There were no known issues with the vessel's mechanical or electrical systems when it was put in storage for the winter, the owners told NTSB. 

Over the next few months, the owners carried out typical drydock maintenance, including repairs to a starboard fuel tank and to the hull. The Coast Guard attended the vessel for a drydocking examination. Shore power provided electricity for work during the day, and it was shut off at night. 

On the day of the fire, the port engineer began preparing for a day's work on the boat. He turned on the breakers for the heating system and the lighting, and he conducted a safety briefing with the welding team scheduled to work on the vessel that day - a crewmember serving as fire watchman and two welders (both contractors). They were tasked with reinstalling deck plate over top of the head in one of the aft staterooms. As they worked, the roving fire watchman made rounds. 

At about 1155, the watchman noticed a "strange haze" from the ladderway between the salon on the main deck level and the aft stateroom compartment. He went down to investigate and found flame coming from a bunk in stateroom J, one of seven in the aft compartment. The welding machine was located in this compartment - as it had been for months - but the welders were working in the head, separated by two bulkheads and eight feet from the location of the fire. 

He alerted the welders to the blaze, and one of them went over to investigate. He saw a small palm-sized flame on the bunk, smoke between a layer of protective plastic sheeting (installed for the job) and the overhead, and pieces of the plastic falling down onto the bunks. He grabbed a fire extinguisher, and directed the other welder to go up the stairs to check on the salon area. There was heavy smoke in the salon, and the smoke was quickly filling up the passageway belowdecks. The welder bravely got down on his back and slid to the stateroom in order to discharge the extinguisher, but this had no effect. He escaped the compartment, and had the presence of mind to shut off and remove an exhaust fan as he left. 

The fire quickly engulfed the salon, starting on the starboard side. Homer's volunteer fire department responded immediately, arriving at 1211, and they extinguished the blaze by 1415.  

There were no known sources of heat in stateroom J. The welding machine was recovered intact and undamaged, and the welders were working in a different compartment, so NTSB ruled out hot work as a direct cause of the fire. The agency concluded that the blaze started in the overhead, where the welder had noticed plastic sheeting dripping down. 

The agency suggested that it is possible that stray welding current from the spool gun back to the welding machine's work clamp may have overheated a wire in the vessel's electrical system. There was a ten-foot distance between the gun and the clamp, and the return current would have had to pass through the aluminum structure in between. However, investigators could not determine this for certain. There were also several electrical boxes in stateroom J, which could have been the source of a fault and the start of a fire. 

The source was likely electrical in nature but could not be conclusively determined, NTSB said. Once the fire started, the damage accelerated because of the extensive use of combustible materials in the accommodations space (wood trim, plywood and carpeting throughout, including the bulkheads and drop-ceiling overheads) - a common and allowable interior construction method for an older "T-boat."

NTSB included a cautionary note on the potential for stray welding current to overheat unintended conductors, like the wires of an electrical distribution system. The agency advised following best practice and placing the work clamp as close as possible to the area of the welding, rather than 10 feet away.