Summary
On December 11, 2015, about 1740 local time, a fire broke out in the electrical control room for the aft winches aboard the freighter Alpena while the vessel was dry docked undergoing work. Shipyard workers evacuated the vessel and notified the local fire department who extinguished the fire. No one was injured, but the Alpena sustained nearly $4 million in damage.
Findings
On December 16, 2015, the fire chief led investigators through the various fire affected spaces. A subsequent survey report stated that the ongoing welding activities showed “no evidence of being connected to the fire.” Rather, the fire appeared to have started in the electrical control room and subsequently spread to the steering gear flat and paint locker located in the aft section of the engine room. The fire also spread to the dining room, galley, and several staterooms located on the main deck.
Based on both the Coast Guard and the local fire department investigations, the most likely cause of the fire was an electrical fault in the wiring from the electrical control panel to the aft winch. The electrical system for the aft winch was original to the vessel and complied with regulations for original equipment; however, it did not have the more extensive circuit protection that modern shipboard electrical systems have. (According to the Coast Guard, planned postaccident modifications to the Alpena would feature additional circuit protection in accordance with current regulations.) The power cable to the aft winch was completely melted for a length of 10–15 feet. Similar conductors in the same wiring bundle were not damaged, which led investigators to believe that this specific conductor experienced a fault of some kind rather than being destroyed by the heat of the ensuing fire. As further evidence to support this conclusion, the same cable’s sheathing and insulation had signs of significant deterioration on the boat deck, several decks above where the fire started, where the aft winch is located. This area of the vessel was not affected by the fire.
Fire department investigators noted that an electrical fault at the winch (which would have resulted in high current flow in the wiring circuit) could have possibly caused further electrical faults in the winch circuit resulting in a switchboard/fuse overload.
Another potential fault source could have been caused by chafing, which damages the protective sheathing and reduces the thickness of a conductor’s insulation jacket over time. The wiring in the electrical control room had areas susceptible to chafing, specifically where the wires passed through sheet metal unprotected from its rough edges. According to the Coast Guard, the fire damage prevented full assessment of the pre-existing adequacy of this through-metal passage; however, planned postaccident modifications would feature protection for wire passage points.
Investigators found no evidence that the fire was associated with the ongoing shipyard work or with any of the daily work being attended to by the ship’s crew living aboard.
Probable Cause
The National Transportation Safety Board determines that the probable cause of the fire aboard the Alpena was a fault in the electrical wiring providing power to the aft anchor winch.
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Source: NTSB
