DanDunfee

The discussions above seem to substantially UNDERESTIMATE expectable RMVs (and O2 consumption) which might occurr in a bailout situation, particularly one which might involve some panic, and especially if augmented by a CO2 or PPCO2 hit ( which might have caused the bailout in the first place.)

Heres some common RMV and O2 Consumption benchmarks:
Extracted / Interpolated From NOAA Diving Manual, 2001:
Work
Level...................................... Typical Swim....Typical O2
Description__ _____RMV, lpm__ __Speed,Knots_ _Cons., Lpm__
Light..................... 22.5........ ...... 0.6............... 1.1
Moderate............... 40.0 ...............1.0............... 1.8
Moderately Heavy.... 62.5............... 1.2............... 2.5
Heavy.................... 75.0............... 1.4............... 3.0
Extremely Heavy...... 90.0............... 1.6 ...............3.5

USN data are close enough to the NOAA data, to warrant not repeating here.

EC Spec. EN 14143 Test Criteria For Rebreathers. 2003:
Moderate.................40.0 ....................................1.8
Upper Test Criteria... 75.0......................................3.3 (Specifically selected to cover statistical probabilities for emergencies.
Still, less than the 90.0 and 3.5 actuals documented in the NOAA Manual above)

Remember that RMVs are typically quoted in STPD SE (Surface Equivalent) units. as they are above. For OC diving, they're the basis for at-depth, gas-demand estimates, as illustrated in Marks example above. For both OC and Rebreather diving the Physical, En-Situ RMVs are
not strongly influenced by depth. They are very strongly influenced by the divers physiological and psycological variability, and especially in heavy-work-load or hi-stress environments. Bailouts, especially those involving 'panic' and ' O2 or PPCO2 hit' elements, are especially threatening.

In this, and other, similar RBW threads dealing with bailout, many of the statements focus on 'normal values' , rather than 'emergency values' of breathing and consumption. Some divers exhude confidence, and others actually assert that they can exercise control and restore breathing and consumptions to normal levels veeery soon after an emergency incident, even those involving panic,.. so they don't need all that much bailout reserves. IMHO, this represents extreme naivete based on inadequate appreciation for how REALLY BAD a critical emergency bailout, with a panic element, potentially augmented by a PPO2 or PPCO2 hit, can get to be .

Its true that not every bailout will represent a panicky, critical, emergency situation...or not to every individual...and when they occurr, the critical, emergency conditions will typically not last throughout all the remaining dive period. .. HOWEVER..

Based on a substantial body (vs a few personal incidents) of RMV and O2 consumption data, and major studies of the effects of panic and confusion on divers highly-variable performance during critical emergencies,,,, it is quite reasonable that, under critical emergency / bailout conditions RMVs and O2 consumption can approach,... and potentially exceed ....SEs of 75 lpm and 3 lpm respectively for a significant portion of the remaining bailout period. !!! For OC bailouts the SE RMVs then need to be corrected to at-depth pressures per Mikes example, to estimate total OC gas consumption. Yes, the resultant numbers are large, but must not be naively ignored or dismissed by wishful thinking !!

It's sometimes not practicable to carry bailout reserves for every possible combination of worst-on worst-on worst case scenarios. This is especially true for bailouts near the end of deep, long dives ... therefore, significant compromises must sometimes be made, and with that comes increased probablistic risk. However the tradeoff estimates should, at least, start with the virtual certanty that emergency / bailout RMVs and gas consumptions will shoot up to levels well above 'normal' values. The critical questions, whose answers must be embedded in the pre-dive planning are....how high will they go??....and for how long ?? You, must choose those estimates for yourself..and assume the risks that go with the choices.

While one certainly needs to 'practice' switching off from primary to bailout gas sources to develop it as an intuitive / instinctive emergency procedure...this practice doesnt, and can't, simulate how bad it can become under real critical emergency conditions. IMHO it's extreme naivete to assume that it does for estimating your RMV and consumption in critical emergency conditions. I specifically disagree with use of a SE RMV of 40 as an initial emergency bailout estimate. It should be more like 75.

It remains then, for each diver to first ensure the thoroughness of his own training and education, then understand the implications and risks of each option,.. then make the benefit / risk tradeoff decisions, and imbed them in comprehensive pre-dive planning. I, personally, am a Conservative (Chicken , if you choose), and whenever practicable, I try hard to carry / provide sufficient bailout reserves to get myself (and hopefully my buddy) all the way back home. Failing that, I try hard to deduce the most probablistic risks based on: dive conditions & profile; dive buddy(s); and surface & underwater suport factors; make the best choices I know how at the time, and leave the rest to God.

Its a ' take-your-own-chances and pay-Davy Jones-his due" game. My basic philosophy is in my signature line below

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There are 'Bold' divers and old divers, but NO old, ' Bold ' divers