The tissue loading equations are straightforward enough for a step 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]))))

[/CODE]

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)

[/CODE]

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, lizardland (thanks Stuart), Deco For Divers etc) only describe the OC equations. Yes, I could fudge it by dividing the stage in to small discrete steps but I'd prefer to use the exact equations if possible.

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

Thanks for any leads... ]]>

There seems to be a fair amount of support for nitrox in alis and trimix in steels because the lower gas density offsets the weight penalty with the benefit of a less bulky more streamlined cylinder.

I just wondered why GUE would stick with ali if steels make more sense for trimix fills. ]]>