If I had to guess I would say its about casuality control with a ccr failure i cant think of much else that would be different. I have often thought about that. any staged bottles for oc would be needed for both divers. perhaps you only need them for one diver. I had always heaqrd that CCR's are a no no in caves because of hte degree of penetration that exceeded the amount of support equipment normally used with OC.
You can easily go farther than the amount of bailout you can carry. An average scrubber and with 3L steels will provide anywhere from 6-10 hours of use under ideal circumstances. Very few people drive their unit that hard, I certainly don't.
There are several bailout strategies that are employed depending on the depth and length of penetration. It's generally split into two categories, self-sufficient bailout, where each diver carries their own bailout to get them to the surface safely, and team bailout, of which there are often several types.
Individual bailout is obviously the safest as every team member carries and/or stages enough gas to have a total failure of all units on the dive. However, on big dives the volume of gas can become cumbersome and unwieldy. Often setup dives are done beforehand to stage gas so the actual volume carried by each diver is less as there are bottles staged along the line. Quite frequently divers will drop gas at various intervals so that at max penetration, they carry a bare minimum of bailout, but they will be able to pickup gas and drop bottles on the way back out. This always leaves gas within a short swim, with less drag for a faster exit as you are not carrying out extra tanks. You can go back and get the the empties later. Not always possible, but it is a usable strategy in some circumstances.
Team bailout uses several strategies, everything from bailout being split so that only one diver can have a failure and everyone else stays on the loop, every diver spreading out that gas load, but that has little margin of error. Another is a quasi-team bailout where total carried is more gas than needed for one guy to get out, but it may not be optimized for the amount of gas needed or the decompression requirement. In this case, each diver may carry a deep bailout gas, one diver carries an intermediate gas, one carries a shallow travel gas, and other deco gas is staged, etc. (this is a VERY simplified explanation btw). This is all worked out beforehand, and in the event of two failures, due to gas contents, the team may be forced to split in order to complete all their deco, but overall the volume is enough for more than one unit failure.
It's all dependent on the depth, length of penetration, amount of decompression, environmental considerations, access to alternative exits, etc. For example, two AL80's in Mexico will pretty much get you to any exit with plenty of volume to spare. That's 2 hours of gas to find a hole in the jungle, and pretty much anybody doing a CCR cave dive in Mexico should be familiar enough to find a place to get out. There are very few swims where you are more than 2 hours from your own entrance, if not one of the myriad of other cenotes that get you to the big scuba tank above the water line. Because of the depth, decompression obligations are little to nonexistent, and you're typically on EAN32 at least. However, this doesn't always hold true, and a dive to the Wakulla Room in The Pit is going to require substantially more gas because of the required deco involved. Diving in Florida in a high flow cave is a whole other set of circumstances to deal with, and due to bailout constraints, what would be a 4 hour dive in Mexico on CCR, might be a 1 hour dive in Florida with required deco, and substantially shorter penetration. It's all environmentally dependent.
Keep in mind rebreather bailout gas management is different from normal OC gas management. While we use at MINIMUM, the rule of thirds during an OC dive, on a CCR, you have the entire gas volume to get you out, so each bailout tank provides you essentially 3 times the available time/distance of a single tank, all things being equal. We don't dive to those extremes, you absolutely don't run your margins that thin, but it illustrates the point. Actual OC gas goes a lot farther when on CCR than when OC cave diving.
It's important to note that I am not espousing any particular method of bailout gas management. It's a decision that the individual or the team needs to make.
