Abstract
INTRODUCTION: Diving rebreathers use "scrubber" canisters containing soda lime to remove carbon dioxide (CO(2)) from the expired gas. Soda lime has a finite ability to absorb CO(2). We undertook an experiment to determine whether the manner of storage of a partly used scrubber affected subsequent CO(2) absorption. METHODS: An Evolution Plus™ rebreather was mechanically ventilated in a benchtop circuit. Respiratory minute volume was 45 L·min(-1) and CO(2) was introduced to the expiratory limb at 2 L·min(-1). The scrubber canister was packed with 2.64 kg of Sofnolime 797™. Scrubbers were run in this circuit for 90 minutes then removed from the rebreather and stored in packed form under one of three conditions: "open" (unsealed) for 28 days (n = 4); vacuum "sealed" in an airtight plastic bag for 28 days (n = 5); or open overnight (n = 5). Following storage the scrubber canisters were placed back in the rebreather and run as above until the PCO(2) in the inspired gas exceeded 1 kPa. The total duration of operation to reach this end-point in each storage condition was compared. RESULTS: The mean run times to reach an inspired CO(2) of 1 kPa were 188, 241, and 239 minutes in the open-28-day, the sealed-28-day and the open-overnight storage conditions, respectively. CONCLUSION: Rebreather divers should consider placing partially used soda lime scrubber canisters in vacuum-sealed plastic bags if storing them for longer periods than overnight. If a partially used scrubber canister is to be used again the next day then the storage modality is unlikely to influence scrubber efficacy.