Manned Test and Evaluation of Morgan Breathing System 2000 (MBS 2000) Oxygen Monitoring System

The MBS 2000 is an O2 rebreather intended for O2 decompression use in a dry chamber. Users purge the breathing loop with O2 at preset intervals. An O2 monitoring system (OMS) may reduce the purging needs or indicate needs for more frequent purging. The OMS for the MBS 2000 consists of a sensor (R10-DN) for partial pressure of O2, but a decision on the need to purge is based on fraction of O2. Since the water vapor content may be more than 10%, the water vapor present must be considered when conversions are made. An R10-DN is sensitive to temperature and is likely to be somewhat nonlinear at the high partial pressures of O2 expected. The OMS indicates a sufficient O2 level by a green light; a red light indicates that purging is needed (switchover at 85%). Manned dives to verify all the functions were required. Twelve military divers participated in the Institutional Review Board?approved manned test of the OMS. Tests lasted 60 minutes at 60 feet of seawater (fsw) and then 60 min at 30 fsw. OMS readings were compared to those of a laboratory-quality O2 analyzer. Compensations for temperature sensitivity and nonlinearity were made for each R10-DN. Oceaneering (Hanover, MD) and Dive Lab (Panama City Beach, FL) delivered the OMS parts. The average number of purges was 6.2 (range 0?14) in the first 30 min, a level dropping to an average of 2.7 (range 0?5) in the second 30 min period at 60 fsw. At the 30 fsw stop the average was 2.5 (range 0?4.5) purges per 30 min. Data on O2 from 10 test divers were used. Differences in readings of the OMS and the Rosemont were calculated for each test diver, and the average was ?0.01% (range +3.2 to?1.7%). The current purge procedure will not notify users who have a stable inspired O2 level between 85 and 90%. Adding a time limit will be sufficient. The MBS 2000 OMS worked well, and its readings compared well with those of the O2 analyzer.