Rebreathers, Pack Your Canisters Properly

While it may be old news to rebreather divers, a recent study points out why failing to pack the soda lime canister properly can lead to oxygen toxicity incidents, in which the presence of CO2 on inhalation was the precipitating factor. Researchers at the Israel Naval Medical Institute found that tilting or other movement of a loosely packed canister can lead to rearrangement of the free spaces, resulting in variations in channeling and considerable differences in CO2 scrubbing capacity. Pressure-packing the soda lime probably forces channels through the less dense granules and reduces the scrubbing efficiency. The study “The Effect of Over- or Underfilling the Soda Lime Canister on CO2 Absorption in Two Closed-Circuit Oxygen Rebreathers,” is printed in the Journal of the Undersea and Hyperbaric Medical Society, volume 35, number 3.