3.1 Atmospheric Management 101
While we’ve focused considerable attention on hardware and the mechanics of such hardware, inherent to rebreather diving is the fundamental premise of managing an ‘atmosphere’. When all goes as intended, the machine does all the work. However, things can go awry – a leak, a sudden change in depth, a failed gas injection mechanism, increased work/labor, or decreased work/labor – and all require the diver to intervene to avoid an undesirable physiological stimulus.
As humans breathe, two things happen:
1. Oxygen is consumed, with the rate of oxygen consumption varying based on the workload, or amount of exercise. Typically, oxygen is consumed by humans at rates from 0.25 liters per minute (LPM) (rest) to 2 LPM (very hard work). These rates also vary based on fitness of the diver.
2. Carbon dioxide is produced as a byproduct of our oxygen metabolism, very close to a 1:1 ration with oxygen consumption.
Rebreathers mechanically regulate oxygen injection into the breathing loop at a rate matching the pilot’s metabolic rate and chemically remove carbon dioxide produced within the scrubber bed. When all systems are set properly during the pre-dive sequence, both oxygen injection and carbon dioxide removal are essentially on autopilot, only requiring the diver to monitor gauges to verify the atmosphere is stable. As pointed out previously, a target pO2 of 1.0 bar can be set while purging the breathing loop with pure oxygen at the surface. This is a very easy and convenient way to start the dive and provides a benchmark from which to gauge pO2 fluctuations.