According to reports, the explosion that destroyed a tanker and killed 21 crew in 2004 was caused by the captain's unsafe order to his crew to open vapor-filled cargo tanks for cleaning, the Coast Guard said in a report Tuesday. Opening the hatches on 22 empty tanks caused the highly flammable vapors to escape onto the deck, where the crew of the Bow Mariner was working, according to the report. A spark ignited the mixture of air and vapors from a gasoline additive, the investigators said. The investigation also found that Capt. Efstratios Kavouras abandoned ship without sending a distress call or trying to save his crew, contributing to the high death toll. The 570-ft.