Mailing List Archive Mailing List Archive
> The advantage of the stationary cycle mehod is that the VO2 can be > calculated at a worst case scenario, i.e., at 1.0 ATA. You should also be > able to get workload up to a level that is nearly impossible underwater. I agree. > This is not a theoretical model, if the diver passes out, then you know > the capacity of the system was exceeded! Only if the person is using the actual SCR unit at the time, with appropriate flow rates, etc. Maybe I misunderstood your original post - I thought you were suggesting that a diver calculate his/her VO2 using something other than the actual SCR to be used, and then plug than number into the SCR equation to extrapolate actual PO2 at different workload. My suggestion was to bypass all the calculations, and just go see what the actual PO2 is on the real unit, in real-world conditions, at various workloads. If you see what your PO2 is at 30 feet, and it drops below 0.4 atm, then you know your rig would be hypoxic on an ascent to the surface. > Finally no one who "teaches" > rebreather courses can claim that they can't afford to do this for *each* > student. I agree that an in-water test might be closer to the "real" > thing, but again it's a worst case scenario within minimum risk at the > surface. I am also not sure that any pPO2 meter is going to be more or as > accurate as measuring actual consumption (watching the cylinder gauge) at > the surface. I wasn't suggesting that they use the PO2 levels to calculate VO2, I was suggesting cutting straight to the chase and see what really happens on the unit in real-world conditions. I agree with you about the expense thing. > Let's assume that the FiCO2 is stable and constant (a really big, > effective canister), but the tidal volume falls. Now this shouldn' > happen for any given depth as the over-ride should kick in and > compensate. But say that the diver is dropping like a (Bill) stone - > 100 ft/min. Then the reservoir bag may not deliver the volume of gas > required to ventilate the diver. i.e., 500 - 750 cc/breath minimum. Then > you retain CO2, because you don't have enough "breath" to blow it off. The tidal volume would only fall if A) the diver was breathing incorrectly (i.e., hyperventilation) or B) the counterlungs bottom-out on inhalation. Yes, the counterlungs do bottom out on inhalation during a fast descent, but if they are not compensated for either automatically or manually, then I think CO2 buildup is low on the list of concerns for the diver. In my experience, it's extremely obvious if you are not getting a full breath on a rebreather. I guess what I'm trying to say is that this is an important consideration, but not one that involved the input flow rate of a SCR. Aloha, Rich Richard Pyle deepreef@bi*.bi*.ha*.or* ******************************************************************* "WHATEVER happens to you when you willingly go underwater is COMPLETELY and ENTIRELY your own responsibility! If you cannot accept this responsibility, stay out of the water!" *******************************************************************
Navigate by Author:
[Previous]
[Next]
[Author Search Index]
Navigate by Subject:
[Previous]
[Next]
[Subject Search Index]
[Send Reply] [Send Message with New Topic]
[Search Selection] [Mailing List Home] [Home]