It spread rapidly and flames blocked both exits out of the lower deck, where passengers and one crew member were sleeping in tight quarters, Santa Barbara County Sheriff Bill Brown said.
Flames roared through the boat of sleeping scuba divers so quickly that it appears none of the 34 people below deck could escape, authorities said Tuesday. This, as they ended their search without finding anyone who was missing still alive from the Labor Day tragedy off the Southern California coast.
It’s not known what started the fire.
National Transportation Safety Board member Jennifer Homendy said Tuesday that she was “100 percent confident” investigators would find the cause of the fire aboard the Conception, which caught fire before dawn Monday and sank near Santa Cruz Island.
She also said the NTSB planned to stay at the scene for up to 10 days and would look into safety measures aboard the boat, such as whether it had fire extinguishers, and will interview survivors, first responders, divers and others.
The captain and four crew members awake on the upper decks jumped off the front of the vessel, swam to an inflatable boat at the back and steered it to a ship anchored nearby.
Among those believed to be dead are five members of one family and the marine biologist leading the diving tour.
DNA will be needed to identify all the victims, and authorities will be using the same rapid analysis tool that identified victims of the deadly wildfire that devastated the Northern California town of Paradise last year, the sheriff said.
Officials have not released any victims’ names, but Brown said he had heard anecdotally that they ranged from teenagers to people in their 60s. He said most appear to have been from Northern California, including Santa Cruz, San Jose and the San Francisco Bay Area.
The 75-foot Conception was on the last day of a three-day excursion to the chain of rugged, windswept isles that form Channel Islands National Park in the Pacific Ocean west of Los Angeles. The fire broke out shortly after 3 a.m. Monday as the boat sat anchored in Platt’s Harbor off Santa Cruz Island.
The sheriff said all 34 victims were trapped on the boat’s lower deck when flames quickly blocked both a narrow stairway and an escape hatch leading to the upper decks.
“The one crew member who was not rescued appears to have been asleep in the sleeping area down below with the passengers,” Brown said.
It appears the crew sent multiple mayday calls, including one from the Conception in which a crew member could be heard saying he couldn’t breathe.
A later one came from the fishing vessel the Grape Escape after the crew reached it in their small boat. One of the vessel’s owners said he heard explosions as he watched the Conception go up in flames from about 100 yards away. Brown said the blasts could have been exploding scuba tanks or propane tanks.
The Conception, based in Santa Barbara Harbor, was owned by Santa Barbara-based Truth Aquatics, founded in 1974. A memorial at the harbor has quickly grown as mourners come to pay their respects.
Coast Guard records show the boat’s owners quickly addressed all safety violations from the last five years.
The Associated Press contributed to this report.