#### huwporter

##### Contributor

The tissue loading equations are straightforward enough for a stage at a constant depth. They are the same Buhlmann equations as for open circuit, you just need to work out your PN2 and PHe after taking account of the PPO2 and the proportions of inert gasses in the diluent (code is Python):

Code:

```
TissueN2[cntr] = TissueN2[cntr]+(PN2-TissueN2[cntr])*(1-math.pow(2,(-1*(TimeInterval/HalftimesN2[cntr]))))
TissueHe[cntr] = TissueHe[cntr]+(PHe-TissueHe[cntr])*(1-math.pow(2,(-1*(TimeInterval/HalftimesHe[cntr]))))
```

Equally, ascent and descent phases are simple enough on OC, using the Schreiner equations together with the fractions of inert gas inspired:

Code:

```
TissueN2[cntr] = (FN2*(CurrentPressure-WaterVapour))+(DepthRate*FN2)*(MoveTime-(1/(math.log(2)/HalftimesN2[cntr])))-((FN2*(CurrentPressure-WaterVapour))-TissueN2[cntr]-((DepthRate*FN2)/(math.log(2)/HalftimesN2[cntr])))*math.exp(-1*(math.log(2)/HalftimesN2[cntr])*MoveTime)
TissueHe[cntr] = (FHe*(CurrentPressure-WaterVapour))+(DepthRate*FHe)*(MoveTime-(1/(math.log(2)/HalftimesHe[cntr])))-((FHe*(CurrentPressure-WaterVapour))-TissueHe[cntr]-((DepthRate*FHe)/(math.log(2)/HalftimesHe[cntr])))*math.exp(-1*(math.log(2)/HalftimesHe[cntr])*MoveTime)
```

However this assumes FN2 and FHe remain the same throughout the stage - which would only be true OC.

What I can't find are the equivalent equations for ascent/descent phases on CCR where not only is the pressure changing but so also are the FN2 and FHe - which are changing at a different rate to the pressure change...!

Every description of Buhlmann I've come across so far (multiple online including the Baker decolessons.pdf, Deco For Divers etc) only describe the OC equations. Yes, I could approximate it by dividing it in to small discrete steps but I'd prefer to use the exact equations if possible.

To save me trying to sweat it out with a pencil myself, does anyone happen to have the CCR equivalent for Schreiner?

Thanks for any leads...