[abstract] DEVELOPMENT OF A SCRUBBER GAUGE FOR CLOSED-CIRCUIT DIVING.

Abstract

BACKGROUND: Currently a diver breathing on a closed-circuit underwater breathing apparatus (rebreather) has no way to know how much CO2 absorbency remains during a dive. Time limits are established for assumed workloads, but they have to be conservative. Therefore, in most cases a dive might be safely extended if the performance of the scrubber could be known in real time. Similarly, a dive might need to be shortened to avoid excessive CO2 exposure from unexpectedly poor absorbent performance or a workload that is greater than anticipated. A CO2 sensor is of limited use: since typically no CO2 leaves the scrubber until late in a dive, such a sensor would not allow any predictions. MATERIALS AND METHODS: Since the absorbent releases heat when CO2 is absorbed, temperatures were recorded at selected sites inside the scrubber of a rebreather. Unmanned testing was performed at several minute ventilations at the full range of depths, water temperatures, and absorbents. CO2 was measured in the diver’s inspired gas. RESULTS: The temperature recordings from more than 200 dives were analyzed, and a method that gives readings on a gauge that is essentially independent of depth, temperature, and minute ventilations was developed. The gauge, which has a read-out like a car’s fuel gauge, predicted the endurance time with an error that was typically less than 10% even early in both unmanned and manned dives. CONCLUSIONS: A gauge that shows the remaining capacity of a CO2 scrubber has been developed. It provides real-time knowledge of scrubber activity and may allow better planning, thereby resulting in enhanced safety, flexibility, mission duration, and diver confidence, as well as reduced cost. ACKNOWLEDGMENT: Funding was provided by the Office of Naval Research, Ocean Engineering and Marine Systems.