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 Inc. 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.

The NTSB did not mention potential charges, which would be part of the criminal investigation.

An attorney who represented a Maine lobster boat captain charged in the deaths of two crew members who fell overboard when his boat flipped in high seas, said he suspects prosecutors reviewing the information will ask if there was a watchman and, if not, what the captain had said or done.

“No watch? A boat that far offshore?” Michael Turndorf asked. “I think that fits the statute. I would be surprised if those are the real circumstances that somebody doesn’t get charged.”

The NTSB says one of the crewmembers on the upper deck awoke to a noise and saw flames rising from the middle deck. He alerted the rest of the crew as the captain issued a panicked mayday call to the Coast Guard.

The crew, finding the ladder to the main deck on fire, jumped down — one breaking a leg in the process. They tried to reach the others through a window but couldn’t open it. They were forced to jump overboard when they became “overwhelmed by smoke.”

The captain and two crewmembers swam to the vessel’s stern and reboarded the boat, according to the report. They opened the engine room’s hatch but didn’t find any fire. With other access routes blocked, they launched the boat’s skiff and picked up the other two crewmembers and went to a nearby vessel.

Once aboard, the captain continued to send mayday calls as two crewmembers returned to the Conception to search for survivors near the burning wreckage.

There were none.

(AP)