The Nerpa submarine was undergoing sea trials Saturday in the Pacific when the fire suppression system spewed out freezing and toxic liquefied Freon gas that asphyxiated victims and sent another 21 to hospital. The Nerpa returned to its home port Sunday after the accident under it’s own power, escorted by rescue vessels.

The Nerpa was at sea with a crew of 208 – nearly three times the usual Akula crew of 73. The majority of this crew were from the special civilian trial crew from the shipbuilding yard at Komsomolsk-na-Amur, where construction on the Nerpa began in 1991.

Funding shortages halted construction on the Nerpa for 15 years beginning in the 90s. But the sub was taken out of moth balls and construction on it completed at the Amur Ship Building and Repair Yard in order for the Russian Navy to lease it to the Indian navy, the top Russian business dailies Vedomosti and Kommersant, and Delhi’s India Express, all reported Tuesday.

Eighty-one of those aboard were Russian Naval seamen. The rest were inexperienced civilians, who constituted 17 of the 20-strong death toll.

Some of the 21 survivors interviewed told Russia Television they were caught completely unawares.

"A siren blared and Freon came streaming in immediately," shipyard worker Viktor Rivk said on Russia’s NTV television, speaking from a hospital bed in the Pacific coast port of Vladivostok. He was visibly enfeebled and exhausted and the bridge of his nose was bruised.

Russian submarines use Freon gas, a powerful anti-oxidant to extinguish fires in the closed and sealed quarters of a submarine, Alexander Nikitin, a former submarine captain who heads Bellona’s St. Petersburg offices said.

By thus sucking the oxygen out of the air, fires are extinguished. But the consequences are lethal if crew members are not alerted beforehand to don their personal breathing apparatus, or run for the nearest stationary breathing post with which submarines are equipped.

Fire alarm sounded after Freon dump
But other survivors said the siren warning the crew that the firefighting system was about to be activated might somehow have been delayed, NTV reported.

According to seaman Denis Kashevarov, the alarm sounded after the Freon came streaming into the bow compartment of the submarine, where most of the dead and injured were located at the time of the accident. He said a second wave of Freon came shortly afterward and he passed out.

The Russian daily Komsomolskaya Pravda quoted another survivor, Sergei Anshakov, who also said the alarm went off only after gas began to pour. A duty officer on the intercom then ordered everyone aboard to don breathing kits, Anshakov said, as quoted by the newspaper.

Anshakov said some of the victims may have died because they were sleeping immediately under the stream of Freon, or because they panicked, or couldn’t immediately reach their personal breathing apparatus.

Rivk told NTV that "practically everyone" in his section had breathing gear, but some may have failed to put it on quickly.

Russian Navy and investigative commission differ over accident’s cause
Russian officials blamed the accident  – which was the worst on a Russian sub since the 2000 Kursk disaster killed 118 sailors – on a fire-safety system malfunction. Navy spokesman Capt. Igor Dygalo told Russia’s Interfax newswire that there had been no fire and that the fire system was somehow tripped in error.

But the state-run RIA-Novosti news agency cited an unidentified official on the government panel investigating the incident as saying Tuesday that the system had been in working order. The panel is investigating whether there had indeed been a fire on board, RIA Novosti reported.

Navy experts have said that the overcrowding aboard the submarine that resulted from having both a navy and a trial crew aboard, and human error, may have contributed to the accident, the Associated Press reported.

Sea trials pose special risks
Former submariners told AP that sea trials always pose increased safety risks because of the large number of unqualified people on board. They say every person on board must permanently carry an oxygen kit, but many civilian workers may not have had the experience necessary to use them.

A former submarine captain quoted by Komsomolskaya Pravda noted that the vast majority of those killed in the accident were civilian workers – and that they were the least experienced or educated in dealing with emergencies at sea.

"I know from my own experience that instructions given to industrial personnel taking part in tests are a formality," the daily Komsomolskaya Pravda quoted retired Captain Nikolai Markovtsev as saying.

"Quite often they walk through a sub like they walk through their plant, without carrying breathing kits."

Breathing kits were available for everyone on the submarine, according to an official on the investigative commission, AP quoted the commission as saying.