Bailout gas.....how much is enough?

[deep_al]

First of all I believe in always carrying all of my bailout, not because I think team bailout is majorly flawed, but because I dont have a ccr buddy that I dive with enough to make team bailout a legitimate plan. 

Team bailout isnt for the average dive though, its for the dives that require it.  Carrying 2 80s is no problem, especially since, without a 7ft hose, you can sling bottles on both side (right=rich, left=lean).  The issue arises when you enter a situation where your using your rebreather to its full potential.  Plan a 20-25 min, 350+ft dive and figure the bailout requirements. Youll need at least 4 bottles, deep bailout, intermediate deco gas, another deco gas, and O2.  You need a good deal of your deep bailout to make up for your high breathing rate from the stressful situation, so you'll probably want an 80 of that, then you'll need a very full 80 of say 20/30 to get you up to your next gas, then you'll just about empty an 80 of 50%, and youll get out of the water with a nearly empty 80 of O2. 

Now Im not saying saying you cant carry 4 80s on a dive, but four 80's of bailout would get you out of the water by the skin of your teeth, remember that a CO2 issue or a total flood that would force you off the loop is going to effect your normal sac rate by quite a lot. This bailout is also assuming that you plan your bailout with the same deco you normally dive with.  You could use a really steep GF for your bailout tables that would get out out of the water a little quicker, but I would consider shortening your deco stops a last ditch effort. Ive been told: you can get un-bent, but not un-drowned.

In the end, RB's dont have that many failure modes that would require you to get off the loop.  Your bailout is your bailout, its your last ditch effort to get to the surface.  Its like a pilot and his parachute, hes not gonna jump out of the plane untill he knows there is no way its going to survive the landing.  Loop flushes, using off board gas, flying the unit manually (for you eCCR guys), and SCR are all ways to keep you on the loop and off of OC, because if you bailout and something else goes wrong where do you go then?

Theres no reason for a CCR diver to not carry enough bailout gas down to 250-300ft after that things could get a little stressful, without team bailout. 

There is a certain level of trust for, or better yet, understanding of your RB you need to develop in order to go into the major dives that require huge amounts of bailout.  As you practice diving your CCR you get to know how it acts, you learn about the cell readings and the sounds you should be hearing.  With a manual rebreather you even get a feeling for how the PO2 should change based on how long you add O2. 

For example, my cell #3 was always a little slow compared to the other 2, and I always kept an eye on it, last weekend it was reading really low in air (0.14) during calibration 100% O2 at 1atm it made 38 millivolts instead of the 48ish millivolts of the others. During the dive it read a little lower than the other two (about 0.15-0.2), and when I did an O2 flush at 20 feet it jumped to reading high (about 0.3 above the other two).  The point is that I expected that cell to fail me at some point, and I was ready for it. 

The point Im getting at is that you develop an understanding of your rebreather and that understanding lets you decide how you react to different failures.  If one of my other cells had suddenly read 0.3 high while I was at 200ft, my reaction would have been very different (dil flush, and evaluation), but I knew this was coming and I knew it wouldn't be something to worry about. 

That all being said Im still new at deep trimix dives and haven't gone to a depth where I feel uncomfortable carrying my own bailout.  But with the right teammate I have no problem dividing up my bailout for dives that require it. 

Sorry for the rant, but it is an interesting subject, especially the failure modes of rebreathers and the thought process behind completely bailing out to OC, since this significantly controls your thoughts of bailout supplies.

-Al

PS hey Mike what RB did you decide on? 'boris?