For three days prior to the event, the divers underwent compression in a chamber on board the Igor Belousov rescue ship. They then undertook the dive and placed a Russian flag at the site. The are now undergoing decompression and won't be able to leave the diving chamber until November 18.
Last year, navy divers conducted an experimental descent in a diving bell from the Igor Belousov to a depth of 317 (1,040 feet) meters. Earlier, the Navy's record depth was 200 meters (656 feet) - the dive took place in 2001. Nitrogen narcosis becomes a hazard to divers breathing air below 30 meters (98 feet), and special breathing gas mixtures are needed below 60 meters (200 feet) to lessen the risk of this and oxygen toxicity.
Early experiments carried out by Comex divers using special breathing gas involved an open-sea dive to 501 meters (1,644 feet) in 1977. The open-sea diving depth record was achieved in 1988 by a team of Comex divers who performed pipeline connection exercises at a depth of 534 meters (1,752 feet). The divers were exposed to ambient pressures over 50 times that of atmospheric pressure on the surface.