Liter Flow and Mix Selection in Semiclosed-Circuit Scuba

摘要

Development of closed-circuit deep-diving breathingg apparatus is still in its infancy, and today, the most widely used breathing apparatus for saturation diving is the semiclosed-circuit scuba. The U. S. Navy, with its Mark VI, VIII, and IX semicolsed rigs, has done considerable development and hyperbaric evaluation of equipment, and a variety of semiclosed-circuit breathing apparatus is now being manufactured commercially. Although it is known that the semiclosed-circuit scuba is an economical rig for deep work, no anlaysis of the apparatus and its theoretical behavior has been published to date. Flow selection is done by prepared tables, manufacturers' recommendations, and approximate rules of thumb, and has been imperfectly understood by many users. This paper presents an analysis of the system, relating all of the variables to one another. Equations are presented to permit calculation of liter flow, mix, oxygen usage, and partial pressure of oxygen. A graphical method is presented which allows rapid selection of proper gas mixture and liter flow. Use of the graphical 'Liter Flow and Mix Selector for Semiclosed-Circuit Scuba' should reduce greatly the confusion which presently exists in this field.