Failure prevention

• An indicating dye in the soda lime. It changes the colour of the soda lime after the active ingredient is consumed. For example, a rebreather absorbent called "Protosorb" supplied by Siebe Gorman had a red dye, which was said to go white when the absorbent was exhausted. With a transparent canister, this may be able to show the position of the reaction "front". This is useful in dry open environments, but is not useful on diving equipment, where:
  • A transparent canister would likely be brittle and easily cracked by knocks.
  • Opening the canister to look inside would flood it with water or get unbreathable outside gas in circuit.
  • The canister is usually out of sight of the user, e.g. inside the breathing bag or inside a backpack box.
• Temperature monitoring. As the reaction between carbon dioxide and soda lime is exothermic, temperature sensors, most likely digital, along the length of the scrubber can be used to measure the position of the front and therefore the life of the scrubber.
• Diver training. Divers are trained to monitor and plan the exposure time of the soda lime in the scrubber and replace it within the recommended time limit. At present, there is no effective technology for detecting the end of the life of the scrubber or a dangerous increase in the concentration of carbon dioxide causing carbon dioxide poisoning. The diver must monitor the exposure of the scrubber and replace it when necessary.
• Carbon dioxide gas sensors exist, but they are not sensitive enough to be used in a rebreather - the scrubber "break through" occurs quite suddenly and the diver shows symptoms before the sensor indicates a dangerous build-up of carbon dioxide. Even if a sensitive carbon dioxide sensor is developed, it may not be useful as the primary tool for monitoring scrubber life when underwater, because mixed gas rebreathers allow very long dives where long decompression stops may be needed: knowing that the rebreather will begin to deliver a poisonous breathing gas in five minutes may not be useful to a diver needing to carry out an hour or more of decompression stops.