ABSTRACT
Early in a pneumatic-caisson project, which lasted for 36 working days with working pressures ranging from 3.2 bar at the beginning to 4.2 bar in the end, the average bends rate was as high as 3.24% in a split-shift working pattern, i.e. two 2-hour compressed air working periods separated by a one-hour surface interval per day. To solve the high rate of bends in response to a request from the site manager when the working pressure had reached 3.6 bar, the working pattern was switched to a single shift of 3 hour’s working time per day, using a modified Blackpool decompression schedule. The bends rate was reduced to 1.83%. Then, following our recommendation, oxygen breathing after surfacing in the caisson works further decreased the rate of bends to 0%. Bubble detection using the ultrasound Doppler method revealed that bubble appearance was also less in the single shift than the split shift. When the working pressure exceeded 4.1 bar towards the end of the work, however, the bends rate increased to 4.35%. After rescheduling the decompression procedure, the rate of bends was reduced to 2.11%, suggesting the necessity of further shortening the work time and/or redesigning the decompression schedule.
