Quote: (Originally Posted by Devon Rob)
Has anyone got a good LAYMANS explanation for handling the PO2 drop on SCR by ascent? All the technical explanations are making my head spin
and yes I do know it has to do with the reduced ambient pressure!
Ok, I'll give it a go, however I am not rebreather trained, so please take everything that I write on the subject as being a best guess.
On some SCRs (Like the halcyon) you have a system whereby a percentage of the loop volume is dumped overboard on each exhale. When you breath in again there is not enough gas, and so a regulator injects gas to fill up the space. This new gas contains O2, so the O2 level stays pretty constant (although lower than the % in the drive gas itself)
Now when you ascend, the gas expands, and so the regulator doesn't inject, and so no new O2 is injected. This causes the PPO2 to drop. The way around it is to manually dump more of the gas (for example by breathing the loop out through your nose)
Or at least that is how I understand it works.
J