Simulated high altitude diving experiment for the underwater construction operation

The simulated dive experiments were conducted at the high altitude of 4500 meters and 5000 meters, for the requirement of diving operation in the lakes at the altitude of 4442 meters for the construction of large-scale hydroelectric power station. The high & low pressure chamber-complex was used, and 15 professional divers participated in the experiment. The divers were stayed at the altitude of 4500 and 5000 meters for 7-9 days. Totally 85 persons-times of dives to the depths of 30-50 meters were operated; they stayed under the water for 30-90 minutes while processing physical activities. During the experiment, we studied the pressurization procedure, decompression table, and physiological functions of the divers. The results indicate that, although the relative pressure differences between the surface and underwater was larger at high altitude than at sea level, the appropriate prolongation of the compression time was able to prevent the difficulty in pressure regulation for the divers to avoid the injury of middle ear. Four tables of the decompression A, B, C and D was calculated with Haldane's theory, and the speed of decompression increased in the order from A to D. The safest procedure was C, and there was no decompression sickness and bubbles in body of the divers. The methods of decompression included underwater stage decompression, surface decompression, oxygen-breathing decompression, and repetitive diving decompression. The surface decompression was the most suitable method for the high altitude, as it could greatly decrease the time in the cold water for the divers. The power spectrum analysis of EEG (electroencephalogram) indicated that, when the divers were exposed to the altitude of 5000 meters, the delta activity in EEG increased, alpha and beta activity decreased. And the delta activity decreased, the alpha and beta activity increased while diving during a dry condition. According to the diving and decompression procedure studied under simulated conditions, 272 person-times of diving training and underwater operations were processed in a high altitude hydroelectric power station at the altitude of 4442 meters, including photographing, video-recording, measuring, and drilling. There were no signs and symptoms of decompression sickness and bubbles.