View Full Version : i feel stupid but..

08-23-2007, 20:23
what does it mean when i see stage bottles and so on?

ScubaToys Larry
08-23-2007, 20:28
Stage bottles are extra bottles that you hang on the rope for "staged decompression" on the way up. Perhaps you are going to do a very long deep dive where you can't come straight to the surface, so you hang a tank at 50 feet, come up to that depth and have some air there for 20 minutes, then up to the 20 foot mark, etc.

And then these tanks probably will not have air... but different nitrox mixes calculated for the best off-gassing for the various depths.

They will many times have big lettering on the side of what depth they are for so someone does not make the mistake of breathing the wrong mix at the wrong depth which could be deadly, or not beneficial -- depending which way you goofed up.

There a simple layman version... without going into any fancy calculations for mixes and depths. Hope that helps!

08-23-2007, 20:30
thanks so are they to be used for deep dives such as past 100 feet?

08-23-2007, 20:36
yeah, after around 130ft you really want to look at different mixtures (IE: nitrox)

And if you are U/W for a long time, or you are down way deep, you cannot just come straight up.

Check your tables for being beyond Z :)

ScubaToys Larry
08-23-2007, 20:39
Well.. yes and no. Anytime you will be deep enough for a long enough period of time that you can't come straight to the surface - they could come in handy.

For example... even a 60 foot dive. We know our tables say I can stay for about 50 - 55 minutes (depending on whose table you look at). But let's assume I'm a research diver excavating an archaeological site, and I want to spend an hour and a half there. I can't come straight up as I'd get bent. So instead, I go up to about 35 feet, and use an extra "stage bottle" that is tied off on a rope there because it has some nitrox in it and my tanks I was using at depth are getting low. After 30 minutes there, I move up to 15 feet and breathe some pure oxygen in another stage bottle for some more time, until I've cleared enough nitrogen to go to the surface.

And some of the dive computers now, like the Oceanic VT3, and work off 3 different tanks and 3 different mixes and swap between them during the dive.

ScubaToys Larry
08-23-2007, 20:43
yeah, after around 130ft you really want to look at different mixtures (IE: nitrox)

And if you are U/W for a long time, or you are down way deep, you cannot just come straight up.

Check your tables for being beyond Z :)

Actually for deep dives like 130 feet, you can't use nitrox - at least not your basic 32% nitrox. Oxygen becomes toxic at depth, so you can only use nitrox in the shallower depths. If diving very deep, you get rid of some of the oxygen and actually lower the O2 percentage. But you would get narcosis with extra nitrogen in there, so they mix in some helium as well. That's why when you watch the shows where the deep divers are in a recompression chamber, they are talking like the chipmunks.

So then for deep they are using "tri-mix".

08-23-2007, 20:49
thanks for clarifying that Larry


08-23-2007, 21:53
Stage bottles can be used to simply extend a dive as in "travel" gas. They can be slung off a harness (That's what the D-rings are for) shoulder to hip. This provides additional breathing gas and or deco gas.
Cavers will sling bottles and breath off them during penetration and drop them off in stages along the way clipped off to the guide line. They will then use them again during the exit.
The gas mix will all depend on the dive plan.

Edit: Speaking with a cave diving buddy this morning, I was reminded that "stage bottles" not only get you back up with a different gas (see Larry's post above), they can get you down with a different gas. Example, for a very deep dive, a diver's trimix will have a smaller PPO (less oxygen) to avoid CNS (ox tox) at depth. The PPO however may not be enough to sustain the diver at more shallow depths. So the diver will breath the richer mix (stage) on the way down and then switch to his back gas at the appropriate depth.
On the return trip, he will then switch to the richer (stage) mix for travel and deco. (again, see post above)
This IS technical and depends on the plan.

08-23-2007, 21:55
cool im sure that there is trainig for using stage bottles as i assume it would be considered technical diving correct?

08-23-2007, 21:59
that is correct. when you get in past AOW into caves, deep penetration, DEEP dives etc... it becomes more tech.

08-23-2007, 22:00
cool thanks for the clarification

08-23-2007, 22:09
Here you go.
I was trying to find this link.


edit: note that these terminologies and uses cross over as in "staged decompression" for example where the "staged" bottles contain deco gas.

08-23-2007, 22:15
thanks bro