All six crew members of the Conception were asleep when the scuba diving boat caught fire and sank off the coast of Southern California early on Sept. 2, killing 34 people, according to a federal report released on Thursday.

That finding, by the National Transportation Safety Board, suggests that the crew had failed to uphold a commitment to have someone awake.

“According to its certificate of inspection, the passenger vessel Conception was required to have a roving watch,” said Lisa Novak, a spokeswoman for the United States Coast Guard.

N.T.S.B. investigators are still trying to determine the cause of the fire and plan to look into regulations governing boats of this type, build and operation, it said in the two-page preliminary report on Thursday. The report describes attempts by five crew members to reach the 33 passengers and another crew member trapped below deck. The five crew members were sleeping on the top of the boat’s three levels, while the passengers and one crew member were asleep on the lowest level, within the hull, according to the report.