Membrane-supplied nitrox saturation: Design and dynamic modeling for life-support in construction diving

The research reported here studied using membrane gas separation to supply diving and atmosphere gases in nitrox saturation diving systems. It relied on computational simulations and compared eight methods for suitability. Of the eight methods, only one was unable to provide suitable gases (Temperature Control). All seven of the remaining methods were able to provide and maintain either a suitable chamber atmosphere or excursion diving gases. When compared against each other in a Challenger/Defender elimination process (compression energy cost was used as the criteria), Partial Recycle emerged as the best choice for the chamber atmosphere. Membrane Turn-Down and Two Stage Compression emerged as suitable for supplying an excursion diver. The computational model process included developing a new membrane modeling approach to include transient dynamic response. That model revealed that typical time constants involved in membrane gas separation are orders of magnitude faster than other components in a saturation system; therefore, membrane dynamics can be ignored in further modeling study. This research also reviewed existing literature and technical nitrox saturation specifications. A modified set of nitrox saturation specifications specifically tailored to construction diving operations evolved.