There are conflicting reports concerning a recent Russian nuclear submarine accident. One such report has the culprit as a failure of the fire protection system to actuate. The second account has the failure as the spurious actuation of the fire protection system.

Twenty people were killed on board a Russian nuclear submarine, the navy said on Sunday, in an accident that exposed the gap between the Kremlin’s ambitions and its military capability.

The accident, which happened while the submarine was on sea trials in the Pacific Ocean, was the deadliest to hit Russia’s navy since the Kursk nuclear submarine exploded beneath the Barents Sea in 2000, killing all 118 sailors on board.

Prosecutors investigating the latest incident said they suspected the victims died after inhaling a toxic gas used as a fire suppressant when the vessel’s fire extinguishing systems went off unexpectedly.

It was not clear why the portable breathing gear usually issued to Russian submarine crews did not save them. A navy spokesman said the nuclear reactor was not damaged and the vessel was now in port.

“Twenty people died,” the Prosecutor-General’s Office said in a statement. “Results of a preliminary investigation show that death occurred as a result of freon gas entering the lungs.”

It appears that the later account is correct. The sailors died of suffocation when freon (a Dupont brand name for refrigerant) made the atmosphere uninhabitable.

The victims suffocated after the submarine’s fire-extinguishing system released Freon gas, said Vladimir Markin, an official with Russia’s top investigative agency. He said forensic tests found Freon in the victims’ lungs.

Seventeen civilians and three seamen died in the accident and 21 others were hospitalized after being evacuated to shore, Dygalo said, adding that none of the injuries were life-threatening.

“The submarine’s nuclear reactor was operating normally and radiation levels were normal,” Dygalo said, explaining that the accident affected two sections of the submarine closest to the bow.

Markin’s agency, the Investigative Committee under the Prosecutor General’s office, has launched a probe into the accident, which he said will focus on what activated the firefighting system and possible violations of submarine operating rules.

Lev Fyodorov, a top Russian chemical expert, agreed that the Freon pushed oxygen out, causing those inside to die of suffocation. But he wondered why the individual breathing kits that everyone on board is supposed to have did not keep people from dying.

“People on board the sub may have failed to use their breathing equipment when they found themselves in an emergency,” he told the AP.

Igor Kurdin, a retired navy officer who heads an association of former submariners, told Ekho Moskvy radio that the high death toll probably resulted from shipyard workers who lacked experience in dealing with the breathing kits.

A siren warning the crew that the firefighting system was turning on also may have failed, RIA Novosti quoted an unidentified navy official as saying, so those on board might not have realized that Freon was being released until it was too late.

U.S. submarines use primarily Halon as a fire suppressant, and the combustion and thermal decomposition products are designed to be limited to less than lethal concentrations given the short bursts of release of the gas.

The design on board the Russian submarine sounds dubious and the system apparently lacked in construction quality assurance. The gap between the Kremlin’s ambitions and capabilities is wide, and this latest accident is a long line of malfunctions that have plagued the Russian Navy, not the least of which is the Kursk accident.