The crew of a scuba diving boat that sank off the coast of Southern California made several attempts to rescue the 34 people who were trapped below decks by fire, but intense flames drove them back and all perished, federal authorities said Thursday. All those lost in the Labor Day tragedy aboard the Conception were sleeping in a bunkroom below the main deck when fire broke out around 3 a.m. The captain and four crew were above and survived, and one of the searing questions was whether they tried to help the others before saving themselves. The crew members told investigators in “very lengthy, detailed, comprehensive interviews” what Jennifer Homendy, a member of the National Transportation Safety Board, called a harrowing story of the moments after the fire erupted on the vessel.