Depth effect on sorb duration

JukkaO said:
Sorry to mix the discussion but how close the truth you get by measuring and calculating O2 consumption? It is not that depth related but it tells something about how much work you have done.
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It strongly correlates with CO2 production so that info should be at value. Doesn't some commercial units track the O2 feed rate via solenoid?
However produced CO2 by O2 consumption varies a lot by diet up to 30%.
 
JukkaO said:
Sorry to mix the discussion but how close the truth you get by measuring and calculating O2 consumption? It is not that depth related but it tells something about how much work you have done.
Click to expand...

In lab testing, CO2 is normally taken as 90% of O2 being consumed so for example, a test at 40RMV would assume 1.78 litres/min of O2 is consumed and this leads to 1.6 litres/min (90% of 1.78) of CO2 being produced

Other breathing rates are then a direct ratio from above numbers e.g. RMV of 22.5 litres/min would be 22.5/40 * 1.6 for CO2 production = 0.9 litres/minute

As we all know, O2 consumption is not affected by depth and is only related to how hard the diver is working. Although the above would therefore assume the same for CO2 this is not the full story as CO2 production can vary depending on the diet of the diver. The 90% calculation is an over estimation to cover all eventualities and ensure a safety factor due to the insidious nature of hypercapnia

All of the above help explain why scrubber durations quoted seem to be so much shorter than we in fact see in reality but as I mentioned previously, breakthrough can easily occur quickly when normal scrubber duration is exceeded and breathing rates are suddenly increased. Likewise, a scrubber which is starting to break through can start to work properly again if we help it by adding heat (very hard to achieve), reducing workload (could be easy but depends on situation) or reducing depth (could be easy, again depending on circumstances).

As we get shallower gas gets less dense and this helps the scrubber in 2 ways. Firstly the "interference" of the CO2 reacting with the lime due to other particles in the mix is less and therefore the scrubber can work more efficiently. Secondly, the thermal reaction of the scrubber is cooled less by less dense gas passing through it and again the efficiency is helped by the increased temperature (same reason a scrubber last longer in warm water!)

Hope above helps
Gar​
 
plazma said:
It strongly correlates with CO2 production so that info should be at value. Doesn't some commercial units track the O2 feed rate via solenoid?
However produced CO2 by O2 consumption varies a lot by diet up to 30%.
Click to expand...

From unreliable memory, the US Navy developed a system that used a temp stick and 02 consumption. DeltaP (or whatever they were called at the time) licensed it for use in the sentinel.
 
I did a dive without the scrubber O-ring in my Inspiration. Pre-breath and above 10m ok. Not that nice in 30m and after 10 minutes there, bail-out, back to loop in 6m and ok again. Just as Gar explained.
 
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