Oxygen dosage principles in rebreathers. Subreport 1: Systems modelling

Five basic techniques for oxygen dosage in rebreather systems have been analysed theoretically. Models has been constructed to describe the oxygen fraction in the system over time, depth and the user´s oxygen consumption. There are operational systems on the market for all the described technologies. Thus it can be stated that all techniques can be made to function satisfactory from a physiological point of view. Where problems arise to keep the oxygen partial pressure within physiologically acceptable limits, operational procedures are used to limit the extent of the problems. The systems have often been optimised for a certain depth and give at that depth relatively longer exposure times for direct ascent compared to other systems. Also systems tend to be relatively more efficient at either great depth or shallow and not both.