This time last year, the drama of the ill-fated Russian submarine the Kursk and its 118 crew was unfolding, writes Zahra Akkerhuys.

As the international rescue operation unfolded, the world watched, hoped and prayed they would survive.

But on August 22, 2000, news came through that everyone on board the Kursk, a relatively modern submarine, must be dead as the vessel had flooded.

Ever since the sinking, debate has raged about what caused the Kursk to sink in water 100 metres deep. Initial theories from the Russian Navy that it struck another vessel, possibly American, have generally been dismissed, given the dearth of evidence supporting the claim.

Scientific observations showed there had been first a small, then a larger, disturbance to seismic activity in the Barents Sea at the time when the Kursk went missing.

Scientist Dr Barry Mellor, who lives in Bicester and runs chemical research and consultancy firm Edotek, is one of the world's leading experts in propellants and he has come up with a theory of what is most likely to have happened on the Kursk. This theory was backed yesterday by the Russian Navy's deputy commander, Vice-Admiral Mikhail Barskov, at a briefing in London.

Working in his laboratory at Westcott Venture Park, about eight miles from Bicester, Dr Mellor conducted experiments to show how a fault in one of the hydrogen peroxide-filled torpedoes on board the Kursk could have triggered first the small, then a larger explosion.

Dr Mellor, who earlier this month appeared on a BBC Horizon programme looking at the sinking of the Kursk, says hydrogen peroxide has not been considered for use in British torpedoes since early trials in 1955 ended in the Sidon disaster, when 13 people were killed when a submarine sank off the south coast after the explosion of a torpedo, packed with the liquid.

The concentration of hydrogen peroxide used in torpedoes is up to 95 per cent. Such a concentration has a tremendous capacity for fuelling a fire - a submariner's nightmare.

Dr Mellor explains it was the reaction between the hydrogen peroxide and metal and the subsequent build-up of gas that caused the torpedo to violently explode, shattering much of the front of the double-hulled submarine.

Initially, it may not have triggered the warhead, fixed onto the end of a torpedo.

He says: "On the Kursk there would have been a torpedo room with a stockpile of torpedoes. If one goes off it will set off the others. I believe one of the torpedoes failed because the hydrogen peroxide had leaked out onto the casing of the torpedo.

"When hydrogen peroxide comes into contact with certain metals it is incredibly explosive and a great deal of gas is produced.

"The leakage and build-up of gas would have triggered the first explosion and probably a small fire, maybe killing a few men outright.

"Then, the fire would have become so intense that warheads exploded, two and a half minutes later, shattering the front of the submarine, destroying everything inside, and filling it with water. The men who survived both explosions, in the back of the submarine, would eventually have died through a lack of oxygen."

The human tragedy of what happened on board the Kursk is not lost on him on Dr Mellor.

"I think it would have been absolutely hellish on board at that time. The crew would have been badly shaken by the first explosion, but the impact of the second would have been unimaginable.

"To have been on board at that time would, I am quite sure, have been horrific," he says, almost in a whisper.

An international team of divers is working on the floor of the Barents Sea, bolting cables to the 490-ft submarine so it can be hoisted to the surface on September 15.

The $65m salvage project aims to fulfil a promise Russian president Vladimir Putin made to the families of the crew to bury them on shore as well as giving the Russians the chance to retrieve the two nuclear reactors that were on board the submarine when it sank and which could potentially trigger a large-scale ecological disaster.

Although the operation won't bring the submariners back, their burial and an understanding of how and why they died may offer some comfort to their families.

All Dr Mellor can hope is that vital lessons have been learned from what he believes happened, and that it will help prevent a similar tragedy.