Poseidon CCR dives: Nitrogen loading

Paul Sargent paul.lionseye at icloud.com
Fri Nov 7 03:46:34 PST 2014

On 7 Nov 2014, at 10:36, Robert Helling <helling at atdotde.de> wrote:

> Now, in the CCR case, things are a bit more complicated as there is not _the_ current cylinder, there are two, diluent and oxygen. For the purpose of deco calculation (and anything that is related to what gas is the diver currently breathing), I would still argue that the “current” cylinder should be the diluent as we have to know the diluent for fill_pressures to determine the breathing gas. 

I would say that the notion of the “Current Cylinder” being the diluent works well. It’s the only gas that might ever change during a CCR dive. That is, you may change diluent, but you’ll never change from O2 to something else. 

Also if you look at the three types of SCUBA equipment that exist from a philosophical point of view:
OC Equipment allows you to take a gas, breath it once, and vent it.
SCR Equipment allows you to take a gas, breath it ’n’ times, and vent it.
CCR Equipment allows you to take a gas, breath it a infinite number of times, with no venting (in theory)
It’s fairly obvious (to me) that the common element is the breathing gas / drive gas / diluent gas, but for some reason we call it different things. The difference on SCR / CCR is the mechanisms employed to extend that gas. It just so happens that a CCR has an O2 supply to make it work, almost the same way that it could have a battery.* It’s a resource you track, and make sure it doesn’t run out, but apart from that it’s of little interest. (I’d actually be tempted not to have it as part of the normal gas list for this reason. Instead have it in it’s own special area.)

I think you’ll find more commonality in the code for different dives types if you go this way.


* Of course, what makes CCR more complex is that we take advantage of the O2 supply to mix an ideal inspired gas, so that’s no longer constant. If it wasn’t for that, gas consumption rate would be the only difference between the 3.
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