Research on nitrogen-oxygen saturation diving with repetitive excursions

For some tasks of underwater operation the need for longer dive duration and more working divers necessitates the use of saturation diving techniques with excursions. Saturation diving with excursion has high working efficiency. A collaborative experiment with Chinese Underwater Technology Institute, American National Office of Research Undersea Program and Hamilton Research Ltd. was conducted at our Institute in Shanghai. The main experiment objectives were to assess the longer, deeper repetitive excursions during nitrogen-oxygen saturation situation, oxygen exposure management, nitrox saturation decompression after excursions and performance aspects. Four Chinese professional experienced divers were saturated at 25 msw for 5 days at the hyperbaric facility, where they did 15 air excursions to depths between 50 and 75 msw, for duration up to 240 min. Decompression from excursions to the storage were mostly no-stops, but 5 required stops for 3 to 116 min. Saturation decompression began with the "precursory" ascent following a brief return to 25 msw. Doppler bubble detection showed some bubbles of Spencer Grade II and occasionally III, following excursions and during saturation decompression, especially after muscle flexing. No symptoms of decompression sickness were reported: one diver was more of fatigued on one occasion than other times. Oxygen exposure reached its peak of 3103 Oxygen Toxicity Units on Day 6. The only subjective symptom of oxygen toxicity was mild and transient numb fingertips. No significant change was seen in vital capacity.