The number #1 rule for diving a rebreather is to ALWAYS KNOW YOUR PPO2! This can be monitored using the HUD and/or the controller. It is important to check both often and confirm that the PPO2 values agree. It you cannot read the PPO2 values or it for any reason you are unsure of the true PPO2 in the loop you must bail out to an independent, open circuit bailout system.
It is important to remember that YOU are the engine that drives the breathing gas through the loop. You are using your lungs to push and pull gas through the unit. Proper functioning depends on this constant flow of gas. Breathing should be slow, deep, and continuous with no pauses. Pausing between breaths can cause PPO2 spikes because injected 02 does not flow across the sensors without the gas being
“pushed” across them. If the injected 02 does not reach the sensors quickly enough, the controller will continue to add more 02 to try to maintain the setpoint. This can cause more 02 than necessary to be injected and lead to a spike once breathing is resumed and all of the injected oxygen hits the sensors at once.
It is also important to exhale completely to prevent CO2 buildup in your body. Shallow breathing does a poor job of expelling CO2 and can lead to hypercapnia. Breathing too fast can also be problematic as this does not allow proper dwell time of the exhaled gas in the scrubber (commonly referred to as “over breathing” the scrubber). Strive for a slow, steady breathing rhythm.
It is best to maintain a minimal loop volume when diving. This is achieved when a full inhalation does not quite trigger the ADV. Too much gas in the loop can have a negative effect on breathing effort and buoyancy control.