LOS ANGELES • All six crewmembers were asleep aboard a scuba diving boat off the Southern California coast when a fire broke out in the middle of the night, killing 34 people who were trapped in a bunkroom below the main deck, federal investigators announced Thursday.

The National Transportation Safety Board’s preliminary report that said five crew members were sleeping in their quarters behind the wheelhouse on the second deck and another below deck when the fire broke out. All but one survived the inferno.

The cause of the blaze has yet to be determined.

Boats like the Conception, which caught fire around 3 a.m. on Sept. 2 and sank, are required to have a crewmember keep watch at night. Federal authorities are conducting a criminal investigation into the deadly fire off the coast of Santa Barbara and could bring charges under a statute known as seaman’s manslaughter.

The law predates the Civil War and was enacted to punish negligent captains, engineers and pilots for deadly steamboat accidents that killed thousands.

The victims on the Conception ranged from a girl celebrating her 17th birthday with her parents and a friend, to a 26-year-old crewmember who was thrilled by her recent promotion to deckhand. Others included the marine biologist who led the three-day tour and couples who shared a love of the water.

Coast Guard records show the Conception passed its two most recent inspections with no safety violations. Previous customers said the company that owns the vessel, Truth Aquatics, and the captains of its three boats, were very safety conscious. An attorney for Truth Aquatics did not immediately respond to an email request for comment on the NTSB preliminary report.

Truth Aquatics filed a lawsuit last week in U.S. District Court under a pre-Civil War provision of maritime law that allows it to limit its liability.

As crews work to recover the wreckage of the burned-out Conception from the bottom of the sea, the Coast Guard has issued additional safety recommendations in the wake of the tragedy, such as limiting the unsupervised charging of lithium-ion batteries and the use of power strips and extension cords.

The NTSB report Thursday provided few additional details and noted investigators have only interviewed three of the five surviving crew members, who said no mechanical or electrical issues had been reported prior to the fire.

A memorial for the victims of the Conception is seen on the Santa Barbara Harbor in Santa Barbara, Calif., this week. Authorities served search warrants at the Southern California company that owned the scuba diving boat that caught fire and killed 34 people on Sept. 2

the associated press