It was Russia’s worst naval accident since torpedo explosions sank another nuclear-powered submarine, the Kursk, in the Barents Sea in 2000, killing all 118 seamen aboard.
The victims died of poisoning from Freon gas that was released Saturday when the fire-extinguishing system accidentally turned on, said Sergei Markin, an official with Russia’s top investigative agency.
Markin suggested there could be violations of operating rules, which points to human error.
The submarine itself was not damaged and travelled back to its base on Russia’s Pacific coast under its own power yesterday, said Russian Navy spokesman Captain Igor Dygalo.
The nuclear reactor that powers the sub was operating normally and radiation levels in the sub were also normal. The submarine returned to Bolshoi Kamen, a Navy base near Vladivostok.
Mr Dygalo said the deaths and injuries were due to the “unsanctioned activation” of the firefighting system in the two sections of the submarine closest to the bow.
17 civilians and three seamen died in the accident and 21 others were hospitalised after being evacuated to a destroyer that brought them to shore, Mr Markin said, revising earlier casualty figures.
Mr Dygalo said the submarine had 208 people aboard, including 81 servicemen. It was to be commissioned later this year.
Saturday’s accident came as the Kremlin is seeking to restore Russia’s naval reach, part of a drive to show off the nuclear-armed country’s clout amid strained ties with the West.