If they are using that single off board cylinder as their only diluent supply, they effectively aren’t carrying bailout, just one big Dil bottle.
Sidewinder 2.0 spotted at BOOT
- Thread starter Haaginheimer
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In a cave and especially a long penetration, you need plenty of bailout volume and some redundancy. Diving two bailouts of the same type is very common, as is sidemounting them with bungees to keep them under control. the last thing you want is a vertical cylinder catching on the roof and jamming you. Similarly when in restrictions.
Two bailouts (or more) give you more options and safety regardless of the rebreather.
Sidewinder-style rebreathers would normally be dived with two sidemount cylinders and a small backmounted oxygen cylinder.
It started to become more popular when units like the sidekick came out and some people now seem to think it's ok to do with units that don't have onboard dil. It's dangerours not only for cave diving but also for deep ow diving where you use a deep mix. When you have a LP hose blow or some other issue with the 1. stage, you're without dil and without BO. When you do shallow cave dives you also lose suit gas and gas for the wing... and in many caves you have depth changes on the way out. Even some of the tourist caves in france have depth changes of 100 ft or more.
It's done for convenience but it's putting all eggs in one basket.
Doing a cave dive on one 80 for dilout is bananas (especially for someone who trains instructor) ... doing a trimix dive that way is not quit as bad but not much better either.
We can agree that using a single bailout in caves is not a good idea. Whilst most dive planning is for one failure, the cave environment does mean that you could be on "bottom" bailout for a long time as you actively exit, so you must have some bailout redundancy. The GUE-style JJ has redundancy too.
For deep dives it is a different matter. Moderate depths mean you're carrying two stages of bottom bailout and deco 'bailout'. Redundancy here is probably team based. For deeper MOD3 dives then it's the variety of different bailout gases you need: deep, intermediate, deeper deco, shallow deco. There's also other safety mechanisms such as all divers decompressing on the trapeze.
^^ this.
Traditionally, rebreathers have onboard DIL. When people are diving alpinist, that is without an external bailout bottle, all of their eggs are in one basket. Even though they may be able to get a couple of hits of breathable gas from that onboard DIL (via open loop) in the event of a CCR failure, losing that DIL bottle (reg failure, burst disk failure, whatever) and they've now lost their bailout - let's hope they don't have a loop failure on their way up. This is why most people diving traditional rebreathers also carry a bailout bottle.
When you move to a DILout config, it's basically the same as just having a large DIL bottle. You need to also consider a separate source of bailout isolated from that DILout bottle.
It is often quite apparent to see people on boats doing deeper dives when it's clear they're carrying insufficient bailout. Hard to make that discussion on a boat.
Redundancy for suit inflate gas is also important. Separate suit inflate cylinder with the backup being the shallow deco gas.
211ratsbud
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I mean, this makes me feel like lp 50's are inadequate and i should be rocking 85's on the side of my thing now. 
It's that "s" and potentially that Lola manifold that make your case
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