Personal CO₂ scrubbing device for use in a disabled submarine

Introduction: In the sunken submarine, a breakdown in the power supply can disrupt the provision of fresh air and the absorption of CO₂. A personal device based on a breathing mask and the soda lime canisters used in the submarine is proposed for CO₂ absorption. Methods: In an unmanned experiment, a breathing simulator provided a flow of air at 8.7 L·min^-1 and a carbon dioxide output of 20.9 L·h ^-1, which passed through either one or two 3.8-kg canisters of soda lime. In the manned experiment, four subjects wore the breathing mask, which was connected to two 3.8-kg canisters of soda lime placed in a bag, and remained for 24 h in a sealed hyperbaric chamber. They inspired the chamber atmosphere and expired via the canisters. Results: In the unmanned experiment, the concentration of CO₂ when a single canister was used reached 1% after 8 h, 2% after 22 h, and 2.5% after 37 h. With two canisters connected in sequence, the concentration of CO₂ reached 1% after 48 h, while the pressure at the entrance to the canisters did not exceed 0.7 cm H₂O. In the manned experiment, the CO₂ concentration decreased over the first 12 h from its initial value of 1.3%, stabilizing during sleep at 0.75%. Discussion: The personal carbon dioxide absorption device lowered the ambient CO₂ level over a period of 24 h, and could maintain this level for a further 24 h. Keeping CO₂ at a low level has an advantage over the peaks of 3% obtained with absorbent LiOH curtains, where elevated pressure and increased PCO₂ may have an adverse effect on the survivors. Some of the crew can remain active without using the device, while the others do the job of clearing the carbon dioxide for the whole crew.