Safety stop deco bottle

[Doc]

I've never heard of this. Can you even suck air out of a second stage at depth if the first stage is on the surface? That doesn't seem possible; don't both stages have to be close to the same ambient pressure for the system to work?

You profile avatar looks like it was shot on the Nekton. I guess not, but where was it shot?

The Nektons have a second dangling at the 15' hang bar.

 

[8thElementDiver]

I've never heard of this. Can you even suck air out of a second stage at depth if the first stage is on the surface? That doesn't seem possible; don't both stages have to be close to the same ambient pressure for the system to work?

To clarify, Blackwood was answering 'No' to your 2nd question; the answer to the first question is 'yes'. In fact, you could use some sort of snuba arrangement for a 20-15' safety stop. (Hell, you could even use just a hose connected to the surface air, but it would feel like you were breathing at an altitude of 18,000 feet.)

For the OP: when I dove the wreck of the Chaudiere in British Columbia, the dive boat hung a bottle at our safety stop. But the captain made it crystal clear that it was for emergencies only--no sucking your tank dry on the wreck, figuring you could use the bottle for a long safety stop.

Personally, I don't know if I'm a fan of hanging a bottle. Even if you do use it during an emergency, you still have that last 15-20 feet to the surface. Unless they can bring the hang bottle with them, most divers using the bottle would ascend too rapidly from their safety stop.

Plus, the whole 'emergency use only' dictum clouds the issue. Someone running out of air at depth is probably not going to take the trouble to find the ascent line where the bottle is hanging from, even if they are sharing air with their buddy--they're going straight for the surface. Someone on the ascent line with only 50 psi would likely think it's not an emergency situation, and would therefore skip using the bottle and instead just cut the safety stop short--after all, the safety stop is 'optional' and the diver doesn't want to get chewed out by the boat captain (or feel like a turd in front of his buddies). So in the end, the bottle just hangs like a dead octopus tangled in the ascent line, which everyone knows about but pretends is not there.

 

[Jim Baldwin]

Ok just a quick question...

How many of you diving with a group or just buddied up leave a stage bottle at the recommended decompression safety stops during your dives for emergency? Do you feel a need for this or what circumstance would make you use, or not use one. I have been on a few deep dives with charters but have never seen these used.

The first time I saw a hang tank being used I was diving off a six pack boat out of Pensacola. A couple of years later I saw the same thing in the Cayman Islands. These were all just recreational dives and were there just to make sure that divers had plenty of air for their safety stop.

I could certainly see a benefit for new divers doing AOW dives or just deeper dives. I harp on my students to monitor their air supply but for them knowing there is extra not only from a buddy but 20 feet under the boat is probably reassuring.

IMHO if you're doing deco dives then you need to have that extra gas clipped off under you arm and your buddy's not on an anchor rope or drapped over the side of a boat.

Ever got back to where the anchor line was suppose to be and find the anchor and the boat gone? I have.

 

[8thElementDiver]

THIS[/URL] kind of protocol, so it is not ever an issue for me or my buddies.

No offense intended, but that seems like a rather arrogant attitude, especially coming from an ER doc!

 

[Dr Dive]

Common practice on some liveaboards, example being the Nekton boats. They have a tank and multiple regs hanging at the same depth as the hang bar for safety stops. Interesting thing is that, even with the tank available, few if any divers push their tanks to the limit and depend on the hang bottle to complete the safety stop. Some do take a few extra minutes to photo the various creatures hanging out under the big SWATH hulls and use the hang bottles to stretch a few minutes. With unlimited diving, there is less pressure to push limits. With just two dives on a trip, some may be tempted. Seems to be a rare occurrence to see them on day boats, I agree.

 

[texdiveguy]

Ok just a quick question...

How many of you diving with a group or just buddied up leave a stage bottle at the recommended decompression safety stops during your dives for emergency? Do you feel a need for this or what circumstance would make you use, or not use one. I have been on a few deep dives with charters but have never seen these used.

The only good bottle hung (in this case 'slung') is the one you carry with you throught the entire dive profile. If you feel the need to have contingency gas on the dive then it should be kept with you! Nothing wrong hanging a bottle from the boat either in the off chance someone might require its use.

 

[sambolino44]

You profile avatar looks like it was shot on the Nekton. I guess not, but where was it shot?

The Nektons have a second dangling at the 15' hang bar.

The picture was taken at Iles Lavezzi on the boat of Club de Plongee de Barakouda, out of Bonifacio, Corsica. They had a bar at 15', but no cylinders.

The first stage doesn't care about the ambient pressure. It cares about the tank (internal) pressure.

I had a snappy response to this, but I decided it sounded too mean. Instead I'll just say: you are incorrect. The 1st stage reduces the cylinder pressure to the IP, which is around 150 PSI relative to the ambient pressure at the 1st stage. Pressure is relative. If it's relative to a hard vacuum, then you can call it absolute. But generally, when we talk about pressure, we are talking about pressure on one side of a barrier relative to the ambient pressure on the other side of the barrier.

Now that I think about it, as long as the second stage is only 15' deep, then you're only reducing the IP that the 2nd stage would normally have at that depth by about 7 PSI, so I guess it would work. But it sure seems strange to me to buy a 20' LP hose to rig up a system you have to suck on instead of just hanging a regular rig off the side of the boat.

Any comments from anybody who's actually used a rig like this?

 

[sambolino44]

...(Hell, you could even use just a hose connected to the surface air...

If you can suck air down a hose from 15' below the surface, that's something I think we'd all like to see. Why don't you film yourself doing that and educate us all?

 

[sambolino44]

...
Personally, I don't know if I'm a fan of hanging a bottle. Even if you do use it during an emergency, you still have that last 15-20 feet to the surface. Unless they can bring the hang bottle with them, most divers using the bottle would ascend too rapidly from their safety stop.

Plus, the whole 'emergency use only' dictum clouds the issue. Someone running out of air at depth is probably not going to take the trouble to find the ascent line where the bottle is hanging from, even if they are sharing air with their buddy--they're going straight for the surface. Someone on the ascent line with only 50 psi would likely think it's not an emergency situation, and would therefore skip using the bottle and instead just cut the safety stop short--after all, the safety stop is 'optional' and the diver doesn't want to get chewed out by the boat captain (or feel like a turd in front of his buddies). So in the end, the bottle just hangs like a dead octopus tangled in the ascent line, which everyone knows about but pretends is not there.

I agree with you on this part.

 

[TSandM]

No offense intended, but that seems like a rather arrogant attitude, especially coming from an ER doc!

I'm not sure why you'd be surprised at arrogance from a physician . . . But, in fact, that wasn't intended to be arrogant. It was actually intended to get the link into the thread so people would see it. There would almost never be a need for a hang tank, if people were educated properly on how to plan gas for their dives. I was lucky enough to run into somebody who opened my eyes.