Even with searchlights, rescuers can barely see their own hands

The British submarine rescue team en route to the Barents Sea faces zero visibility, strong currents and buffeting waves. And when they eventually attempt a rescue, they may find the stricken Kursk already a watery tomb for at least some of those on board.

The British submarine rescue team en route to the Barents Sea faces zero visibility, strong currents and buffeting waves. And when they eventually attempt a rescue, they may find the stricken Kursk already a watery tomb for at least some of those on board.

Naval experts believe the cold is the greatest threat to the lives of the Russian crew combined with a build-up of pressure in the submarine caused by the flooding of the front compartments of the vessel.

"If crew members got wet when the front compartments were flooded, then they are at even greater risk of the cold causing hypothermia. The temperature is probably 2-4C, the temperature of the sea water at that depth," said Carol House, of the Environmental Medicine Unit at the Institute of Naval Medicine, Portsmouth.

The crew will start to suffer from hypothermia as body temperatures start to drop below 37C. At 35C, the metabolism will start slowing down and they will become lethargic and confused, said Dr Gavin Donaldson, of Queen Mary's and Westfield College, London, an expert on hypothermia.

"At 32C, they will become unconscious with their hearts eventually stopping as they get colder," said Dr Donaldson.

People can, he said, operate and breathe quite normally in air at oxygen levels down to 8 per cent (normal air contains 21 per cent oxygen), but the real danger to the crew is a build-up of suffocating levels of carbon dioxide.

Normal levels of carbon dioxide in the air are 4 per cent but once they reach 5 per cent, people experience headaches and nausea, and will pass out when it reaches 10 per cent," said Ms House.

Although few can imagine the terror of being trapped in the dark 500ft below sea level, Dr Stuart Turner, of the Traumatic Stress Clinic, London, said that the crew, althoughtrained to cope such events, will be experiencing extreme fear.

"Being trapped in a confined space with no means of escape is a very instinctive basic human fear and, despite their training, they will be very frightened," he said.

However Dr Turner said the chances of the men becoming hysterical or losing control would be very small. "Generally people who are in the middle of a disaster with their lives at stake do not develop a hysterical reaction," he said.

The physical conditions will be making the crew less and less aware of what has been happening to them.

"In a sense this is a relief," he said. "If there are some crew members dying of hypothermia or suffocation then the others will not be in a state either physically or mentally to take the full impact of what is happening and will not fully realise how close to death they are," he said.

The British rescue team, which has carried out numerous practice rescues but never a real operation, is made up of experts from the Scottish-based firm Rumic, which is contracted to the Royal Navy. A team of 27 left for Trondheim, Norway, yesterday morning from Prestwick airport. From there they will move on to the Barents. The team's self-propelled vessel will be used to clamp onto the Kursk and carry the trapped sailors to the surface in groups of 15 at a time.

In good conditions, the rescuers would expect each trip to the submarine to take 1.5 to 2 hours. They would require eight trips to bring up all 118 officers and crew. Chief pilot Tom Herron said: "Providing we can get the right connection between ourselves and the Kursk the job is not a problem. We have trained in worse conditions and we are constantly training in bad visibility and strong currents.