Investigators said deadly freon gas killed 20 people on a Russian nuclear-powered submarine Sunday when the fire safety system accidentally kicked in during a sea trial in the Sea of Japan, dpa reported.
It was unclear what activated the fire-extinguishing system and the military has launched further investigations, a spokesman for Russia's top investigatory committee, Sergei Markin, was quoted by news agencies as saying.
The system is designed to discharge the Freon gas coolant, which kills instantly, as the most serious of three safety methods to fight fires aboard.
High-ranking Russian officials were cited by Ria-Novosti as saying the system shut down two sections on the bow of the ship they identified as an Akula II class Nerpa attack submarine.
The atomic reactor was undamaged and radiations levels aboard the vessel were normal, a Russian Naval spokesman said early. The submarine has put into port in Russia's Far East near the city of Vladivostok, news agencies said.
Markin added in televised remarks that 14 civilians workers with a ship-building firm and six sailors were killed, citing preliminary information. Another 22 others were hospitalized after being evacuated by a destroyer overnight, he said.