[Saturation diving system at high altitude]

Practical saturation diving was firstly performed at high altitude in Japan in 1987. Its work was to change the screen which had covered the pipeline of a hydroelectric dam located 850 meters above sea level, the same operation had been conducted in 1992 and in 1993, 2 times each year (Total = 5 operations) after the work. The saturation dives have lasted from six to eight days on 4 occasions and 13 days (Total duration = 4075 minutes) on 1 occasion, since the initial pressurization until the end of the last decompression. In each operation, there had always been involved 3 divers. They have been compressed to an equivalent depth of 45-73m in the deck decompression chamber (DDC), briefed for work and transferred to the submersible decompression chamber (SDC), which was then submersed to 53-78m of depth. Wearing heated suit and breathing Heliox (both at the same temperature as the inside of the SDC), the divers have been locked out to perform their tasks, all monitored and supervised by the use of a remotely operated vehicle (ROV). The works have run uneventful and successfully until the end. The water temperature had been higher than the expected, i.e. 9-13 degrees C in all occasions. The inside conditions of the chamber had been the following: partial pressure of nitrogen was from 0.78 ATA; partial pressure of oxygen was from 0.35 to 0.40 ATA; partial pressure of carbon dioxide was less than 0.005 ATA; the inside temperature of the SDC was from 26 to 30 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)