Why extra air when solo?

[Stoo]

I only dive 5-10 feet in my warm crystal clear stone lined fish pond with no plants, and rocky entry steps.
(not really...)
But the solo redundant air rules, or recommendations..., seem extreme.
What am I missing? Should we reexamine the solo rules in light of my 10' fish pond diving.

At some point, the question becomes a a little silly.

Obviously. Almost as silly as logging that as a dive.

 

[Stoo]

Far more common situations would be LP hose failure or an unrecoverable free flow, in which case the backup second stage on your back gas is not useful - you need to go to your alternate gas supply and ascend.

I assume you're talking about a single tank with an "octopus" 2nd. Certainly with doubles, an isolator and the regs, neither of those situations is difficult to resolve. Isolate, shut down a post and make plans to end the dive.

 

[doctormike]

I assume you're talking about a single tank with an "octopus" 2nd.

Yeah, that was the OP's question.

 

[pauldw]

but the OP was asking about diving 10 or 20 feet

Yeah, and was also curious about what exactly the equipment-related dangers are, or other dangers, that would make a pony bottle, for example, important in that kind of just-off-the-rocks diving. First stage failure? Entanglement? In other words, not just an affirmation of belief (as in, I believe only X kind of diving is appropriate), but specifics on WHY appropriate to relatively shallow water.

 

[MichaelMc]

Yeah, and was also curious about what exactly the equipment-related dangers are, or other dangers, that would make a pony bottle, for example, important in that kind of just-off-the-rocks diving. First stage failure? Entanglement? In other words, not just an affirmation of belief (as in, I believe only X kind of diving is appropriate), but specifics on WHY appropriate to relatively shallow water.

The same air failure causes exist as are at depth (human failure, debris clogged valve, o-ring fail, free flow, ...). That does not change by being shallow.

If they combine with entanglement, how many seconds can you afford to get free and then ascend? How long can you operate without a breath? Are you calm under stress? Is it really clear sand? How far up is an easy swim?

If we're not talking 20'-ish shallow, any N2 loading for that fast ascent?

Not sure anyone here has a good image of your dive site except you. Is it "20' over bare sand"? That is fairly easy to describe. But you haven't said that. Is it "Well, some rocks, some small ledges with cracks, some kelp"? There it is hard to quantify the entanglement risk. How many is 'some'? As you move away from 20'-ish over bare sand, redundancy becomes a safer default.

Diving normally with a buddy has weight and costs X. Diving redundant when you have no buddy adds Y, to cost at least. The weight and cost are easy to quantify. The risks are hard to quantify.

Which dice you roll for the dive is up to you.

 

[Storker]

My favorite Heinlein quote (from "The Moon is a Harsh Mistress") is:
TANSTAAFL

Shamelessly stolen by Larry Niven and used repeatedly in his "Ringworld" series.

 

[Angelo Farina]

I keep my position. For minimal depth and solo diving, I find fully acceptable to NOT use a pony, and to rely on just ONE cylinder of air.
But it must have two valves, and two separate complete regs. If one free flows, or the 1st stage fails, you just close its valve and use the other.
This means that the valves must be easily accessible, and for this everyone has its preferred arrangments: some prefer side mount, I love my very old back-mount harness which allows me to get the valves in front of my mask in less than one second.
What I find unsafe is to connect two second stages to just one first stage, without another completely independent reg...
This is widely employed in some countries, but I did always find it unsafe, for any kind of diving. What's the benefit of not using a second, independent first stage?

 

[TMHeimer]

The same air failure causes exist as are at depth (human failure, debris clogged valve, o-ring fail, free flow, ...). That does not change by being shallow.

If they combine with entanglement, how many seconds can you afford to get free and then ascend? How long can you operate without a breath? Are you calm under stress? Is it really clear sand? How far up is an easy swim?

If we're not talking 20'-ish shallow, any N2 loading for that fast ascent?

Not sure anyone here has a good image of your dive site except you. Is it "20' over bare sand"? That is fairly easy to describe. But you haven't said that. Is it "Well, some rocks, some small ledges with cracks, some kelp"? There it is hard to quantify the entanglement risk. How many is 'some'? As you move away from 20'-ish over bare sand, redundancy becomes a safer default.

Diving normally with a buddy has weight and costs X. Diving redundant when you have no buddy adds Y, to cost at least. The weight and cost are easy to quantify. The risks are hard to quantify.

Which dice you roll for the dive is up to you.

Probably repeating myself but yes, entanglement when in 20' water. But I know I can easily do a CESA from 30', so factors other than entanglement are probably of little concern. Different story at 100'. Depth matters a whole lot.

 

[pauldw]

I keep my position. For minimal depth and solo diving, I find fully acceptable to NOT use a pony, and to rely on just ONE cylinder of air.
But it must have two valves...

Not that I want to sound stupid, but how to you put two first stages on one tank?

 

[johndiver999]

The same air failure causes exist as are at depth (human failure, debris clogged valve, o-ring fail, free flow, ...). That does not change by being shallow.

If they combine with entanglement, how many seconds can you afford to get free and then ascend? How long can you operate without a breath? Are you calm under stress? Is it really clear sand? How far up is an easy swim?

If we're not talking 20'-ish shallow, any N2 loading for that fast ascent?

Not sure anyone here has a good image of your dive site except you. Is it "20' over bare sand"? That is fairly easy to describe. But you haven't said that. Is it "Well, some rocks, some small ledges with cracks, some kelp"? There it is hard to quantify the entanglement risk. How many is 'some'? As you move away from 20'-ish over bare sand, redundancy becomes a safer default.

Diving normally with a buddy has weight and costs X. Diving redundant when you have no buddy adds Y, to cost at least. The weight and cost are easy to quantify. The risks are hard to quantify.

Which dice you roll for the dive is up to you.

What is the probability that a solo diver would become badly entangled AND simultaneously experience a failure of the air supply? These are two independent events and the probability of both occurring is 0.00*1 times 0.00*1 - you get to pick what the * equals. Worrying about something like that is not something I will engage in.

If a diver gets badly tangled and spends a bunch of time (and air) trying to get free, the exit strategy would be to remove the scuba unit, leave it on the bottom and swim up 20 feet. That is really a pretty simple skill and no diver should be going in the water solo unless they are very confident that they could complete this task without any significant stress.

I think the chance of tripping and falling and getting knocked out in 6 inches of water while scrambling over slippery rocks and while wearing heavy scuba gear is a much more significant risk. Getting out is often worse than going in because you are tired and often cold and possibly stiff.

Trying to minimize the risk of a slip and fall is the primary reason why I would not carry additional weight (like a pony bottle) on such a dive. Once the diver is in the water, the drag and/or weight is inconsequential.