Kaffphine,
Just courious, amoung the "don't need more air then you need. nothing well maintained breaks down" crowd. Do you use a pony.. doubles? And if the dive plan is so well thought out, then what's the problem with the extra conservistism.
Stuff breaks down all the time.. which is why every technical diver fiercely advocates redundancy. Redundancy is wonderful and necessary. Conservatism is wonderful and necessary. Buddies, the rule of thirds, backup lights, and dual-post gas delivery systems are all a requirement for good diving. No one ever, ever said that a good dive plan prevents problems: the dive plan doesn't prevent problems, it provides methods to solve them safely. Lights will go out, hoses will burst, mask seals will fail, etc. All technical divers are acutely aware of these failure modes. You'll notice our gear choices and our techniques above and below water are specifically aimed at mitigating those known risks.
So, the operative questions are:
1. "How can I make my equipment redundant?"
2. "How can I make my diving more conservative?"
The answer to 1 is almost universally a good set of doubles and a good set of regs. They're more reliable, simpler, easier, and more cost effective than a pony setup.
Consider, for example, a person tying himself to a car seat with a piece of rope: it will indeed provide some safety benefit in a crash, but it comes bundled with a variety of new problems, like entrapment and difficulty. The proper solution is to use a well-engineered, well-thought-out seatbelt system with accessible releases, tensioners, and inertial locks. This system provides all of the desired goals (safety) without introducing any new problems.
The analogy is easily extended to ponies. The pony DOES solve the problem of providing redundant gas. Unfortunately, though, like the piece of rope around the car seat, it comes bundled with its own host of new problems. It has an additional, third, second stage regulator. It cannot be shared without buddy-breathing. It it difficult to stow properly. It is difficult to deploy easily. It is an entanglement hazard. A good set of doubles provides the desired goal (redundant gas) without introducing any new problems.
You'll find this a very common issue with many divers: they buy some bit of gear to eliminate some perceived risk, without noticing the three new risks the piece of gear itself produces.
The answer to number 2 is somewhat more complex. Proper training, equipment, and well-rehearsed emergency plans reduce inherent risks to very small levels. This in itself is a type of conservatism.
- Warren