Ratio deco på RB?
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Jag läste en lång tråd i går kväll som började med något helt annat än vad den nu hamnar om.
Tråden handlar nu om UTD´s rebreather MX90 och hur de dyker den maskinen.
Andrew Gerogitsis har själv svarat i tråden och ett av dessa inlägg fastnade jag för.
Det handlar om Ratio deco, enlig honom så använder de sig av det på Rebreather dyk, hur fungerar det?
Som jag har fått lära mig så använder man standardgaser för att det ska fungera och där har du PO2 som ökar med djupet.
I en RB så får du helt andra mixer än det du har i diluent flaskan även om du har en standardgas där.
Om man dyker enligt Andrews sätt så spikar han PO2 och sen låter det falla. Vad har jag missat?
The addition of diluent is generally enough as is "real" diving, not theoretical diving, you are adding diluent based on volume changes and depth changes and it seems to enough to maintain your desired PPO2. We do not try to dive a "constant" PPO2 at depth as it is unnecessary for "our" decompression profile. Again a fundamental difference between UTD/DIR and others, is we use ratio deco and do not concern ourselves with maintain a perfect 1.2 or whatever else people set as setpoints. We adjust the PPO2 as needed. Generally above 1.0 for shorter dives and so constantly adjusting the PPO2 is unnecessary. Hence the reduced workload. I dove saturday to the 150'/45m "range" for 30mins bottom time, using a 21/35 for diluent. In reality I touched the O2 once at depth in 30 mins.
En kille räknade sedan ut hur han vad tuvngen att göra för att det stämmer med det han skriver ovan.
I actually don't see any problem with diving a manual CCR - the arguments as to why are valid, and it's how most of us learnt to dive CCR. I am a bit curious about you O2 addition and ppO2 management, so I've tried to understand the dive you quote above.
Assuming an O2 consumption of 1 l / minute, you will have consumed 30 litres of O2 at 1atm or 5 to 6 litres at depth. As you said you added O2 once, can we assume that you arrived at the bottom, consumed 3 litres, added 3 litres, consumed three litres, then started your ascent?
Being generous, lets assume your loop holds 12l of free gas. (that's a long way from minimum loop, but possible).
Let's also assume you breathed the loop down to a PPO2 of 0.3. I wouldn't do it, but its still fairly safe.
So that's 9l of loop volume with a PPO2 of 0.3 = approx 1/2 litre of O2 in the loop.
then you add the 3l of O2 you will need for respiration for the next 15 minutes.
Now you are back to 12l in the loop, of which 3.5 litres is O2 - approx 30%
Now an fO2 of 30% = a ppO2 of 1.65 at 45m.
I'm not sure I buy this. Are you really saying that the way you dive is to have a big loop volume, hit the bottom at a ppO2 of 1.65, let it decay to 0.3, bump it up to ppO2 of 1.65 again, let it decay to 0.3 again, then do whatever it is you do to ascend?
With a smaller, more reasonable, loop volume, the figures just get worse - you need to be either pushing the PPO2 higher, or letting it drop lower.
By complete co-incidence, the last dive I did was for about 30 minutes bottom time at depths between 40m and 55m on a completely manual rebreather. (a Prism with the electronics turned off due to flat battery / user stupidity.) I actually tend to agree that a completely manual rebreather is no big deal, and not significantly more work than a CMF or even ECCR. However I'd suggest that the prudent way to dive it is to both check ppO2 and inject a small squirt of O2 every minute or so. That's certainly how I did it - you get the rhythm of injecting to maintain a reasonably tight ppO2 - between 1.2 and 1.4 is my preferred window for that sort of dive. That way even in a no vis situation you can continue for a while without ppO2 getting dangerous.
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 Ratio deco på RB?
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Erik Rådström | 2010-09-07 09:39 |
  Hela tråden finner ni här! | Erik Rådström | 2010-09-07 09:40 |
| Sv: Ratio deco på RB? | Mark Dougherty | 2010-09-07 14:39 |
| Sv: Sv: Ratio deco på RB? | Erik Rådström | 2010-09-07 14:53 |
| Sv: Sv: Sv: Ratio deco på RB? | Tomas Persson | 2010-09-07 15:11 |
| Sv: Sv: Sv: Ratio deco på RB? | Mark Dougherty | 2010-09-07 15:17 |
| Sv: Sv: Sv: Sv: Ratio deco på RB? | Andreas Brodow | 2010-09-07 16:10 |
| Deco-on-the-fly CCR | Peter Steinhoff | 2010-09-07 16:35 |
| Sv: Ratio deco på RB? | Jakob Selbing | 2010-09-07 19:34 |
| Sv: Sv: Ratio deco på RB? | Ola Nordquist | 2010-09-07 21:58 |
| Sv: Sv: Sv: Ratio deco på RB? | Ola Nordquist | 2010-09-07 22:30 |
| Sv: Sv: Sv: Sv: Ratio deco på RB? | Mark Dougherty | 2010-09-08 07:49 |
| Sv: Sv: Sv: Sv: Sv: Ratio deco på RB? | Jakob Selbing | 2010-09-08 08:30 |
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