AN investigation into the deaths of two Royal Navy submariners under the Arctic ice on Wednesday is concentrating on blocked vents in an emergency air-producing system as the cause of the tragedy, The Herald has learned.

The dead men were named last night as Paul McCann, 32, and Anthony Huntrod, 20, based at Devonport, Plymouth.

A third sailor was slightly injured when a self-contained oxygen generation (Scog) "candle" exploded in a forward compartment on HMS Tireless, one of Britain's nuclear-powered hunter-killer fleet.

Naval sources said yesterday the investigation team's initial findings pointed to a rapid build-up of pressure in the square-shaped Scog canister, which is designed to burn chlorate at high temperatures to produce lifesaving oxygen.

The sailors had set off one of the candles in the boat's forward escape compartment. The canister containing it blew up a few minutes later.

A naval source said: "These things are ignited by striking a primer and burn extremely hotly, giving off enough oxygen through vents in the canister to supply breathable air. A kilo of the chlorate releases enough oxygen to keep a man alive for six or seven hours.

"The chlorate candle is seeded with iron powder to bring the burn temperature to about 600C inside the container. It looks like the vents may have been blocked. It would go off like a grenade in that confined space."

The Scog system is used on exercises to produce oxygen when the attack boats are "running silent" to avoid detection by surface warships' sonar. The usual electrical air-conditioning system potentially produces enough noise to give away the submarine's position.

HMS Tireless was operating with USS Alexandria, another attack submarine, on a routine exercise designed to test warfighting techniques in Arctic waters.

The British boat surfaced immediately after the explosion, to allow the injured sailor to be flown to a hospital in Anchorage, the Alaskan state capital, where he is expected to make a full recovery.

A Royal Navy spokeswoman said the use of Scogs on the fleet's Trafalgar-class submarines had been "restricted" until safety checks were carried out.