The dive boat Conception smolders at sunrise on Sept. 2, 2019, before sinking. (National Transportation Safety Board)

The LA Times reports that the deadly fire that broke out four years ago aboard the Conception dive boat, killing 34 people, started in a plastic trash can on the main deck, a confidential report reviewed by The Times shows.

Investigators with the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) built a full-scale mock-up of the middle deck of the 75-foot vessel in their quest to determine the fire’s point of origin and cause. They conducted a series of burn tests at their Maryland research lab, which concluded the blaze began in a rubbish container and then quickly spread. Within minutes, the boat’s main salon was in flames, the testing showed.

The findings shed new light on the deadliest maritime disaster in modern California history, adding to the mystery surrounding its cause. However, due to ongoing criminal and civil court proceedings related to the incident, the report has not been publicly disclosed.

The fire broke out in the early hours of September 2, 2019, while the 75-foot wooden-hulled Conception was anchored off Santa Cruz Island. As the flames engulfed the boat, five crew members who were asleep in the wheelhouse were awakened by shouts of “Fire! Fire!” Shortly after 3 a.m., the boat’s 33 passengers and another crew member found themselves trapped below deck.

Initial investigations by the National Transportation Safety Board (NTSB) focused on the charging areas where divers plugged in lithium-ion batteries. One crew member suspected that the phone-charging station might have sparked the fire. However, ATF investigators honed in on a 23-gallon Rubbermaid Slim Jim garbage bin located under the main deck stairs as the point of origin.

The report, authored by ATF Special Agent Derek J. Hill in January 2021, outlined the meticulous examination of the fire scene, witness statements, pre-fire and fire photographs, and conducted test fires. The investigators concluded that the fire originated in the garbage container under the staircase.

Polyethylene trash cans are a known fire risk, and new Subchapter T boats are required to have noncombustible waste receptacles in all compartments. Conception was an older vessel and was exempt from this standard.

Maritime Executive notes that though they have narrowed down the location, investigators still cannot be sure of the exact cause of ignition. It could have been something inside the trash can, but could also have been another source located nearby. However, there was no evidence supporting the theory that charging batteries had sparked the blaze. 

Captain Jerry Boylan, who was in charge of the Conception, has been charged with 34 counts of manslaughter for allegedly failing to use a roving watch commander while the passengers were sleeping, as required by Coast Guard regulations. Boylan, who denies any wrongdoing, is scheduled to be tried in federal court next month.

The Conception was one of three dive boats operated by Truth Aquatics out of Sea Landing in Santa Barbara, California, and was launched in 1981. The boat had three decks:  a main deck containing the galley and salon; an upper deck with a wheelhouse and sun deck; and a lower deck with a bunkroom. 

Five crew slept on the upper deck while 33 divers slept in bunks on the lower deck bunk room. Access to the lower deck was limited to a single steep and narrow stairway from the main deck and a small emergency exit hatch. When a fire broke out on the main deck salon, the divers in the bunkroom were trapped on the lower deck and died. One crew member aboard also died.

As we posted in November of 2019, the dive boat Conception was a death trap. Officials said the vessel was in full compliance with inspections and other regulations at the time of the fire.