Stage Bottle Question

[Cheekymonkey]

I read everywhere that stage bottles should be worn in an off position so that they do not freeflow, and as one extra precaution to prevent you from inadvertantly breathing from the wrong bottle. My question then is what stops the water from invading the reg, do you pressurize the hoses prior to the dive and then turn off the bottle to just prevent this issue?

 

[cerich]

do you pressurize the hoses prior to the dive and then turn off the bottle to just prevent this issue?

yes, and even if you don't it's pretty unlikely to have water get all the way into the first stage to cause a problem.

 

[Cheekymonkey]

Thanks so much for the fast answer, so in that way, you wouldnt get instant feedback if you grabbed the wrong reg (bad senario in the first place), but would only be able to take 1-2 breaths.

 

[cerich]

correct, I also teach that the diver visually id the stage/deco bottle as correct then place the reg from that correct bottle in mouth, look at SPG on first stage of the ID'd bottle and breath from second stage. The needle on the SPG should drop, that is further confirmation you are breathing from the correct bottle. Turn the valve on now that that is done, enjoy the new gas. Your buddy is watching you do this and is further confirmation you are on the correct bottle. Wait a min (to stabilize/stow/any problems to creep up like a O2 seizure from wrong mix at depth) then signal your buddy to commence his/her gas switch and watch them.

 

[Doc Intrepid]

Turning off your sling bottles does in fact ensure that the bottle does not leak, however, it also helps ensure that you do not breath the wrong bottle when you are carrying multiple sling bottles. Occasionally a 2nd stage will discharge the gas in the hose during the dive, and water conceivably could back up into the hose. If this occurs just turn the tank back on, purge the 2nd stage, and turn the tank back off.

There is a careful procedure that divers should use to ensure, both visually and physically, that the reg they are placing into their mouth actually comes from the bottle they intend to breath (at that depth). As an aside, the process if performed correctly involves having your buddy watch while you switch gasses, then you watch while your buddy switches gasses. The final step in that process involves "turning on the tank"...and "if upon turning on the tank you can breath from the regulator in your mouth, then you have the correct regulator".

While I have no empirical evidence to cite, anecdotal evidence would suggest that some of the most dangerous times of a staged decompression dive are during gas switches. Divers frequently have indicated problems occurring during or as a result of gas switches. The process of switching sling bottles on ascent, then back to backgas before going onto O2 at 20', is worth a team's time to practice under more controlled conditions. Even issues such as 'stowing the hose' while other things are happening, you're deploying a jon line, you're trying to hang onto the anchor line in current, some other hoser kicks off your mask during the process, etc. can make a routine evolution more exciting than you may have imagined it would be.

FWIW. YMMV.


Edit:

Sorry cerich, we were typing at the same time...

 

[cerich]

In the 90's when tech diving became more mainstream there was an absolute rash of wrong gas switch diver deaths.

The method we both typed is IMHO the best one I have found and I've tried a few...

One thing that does creep up withtech divers using standard gases is the assumption that the tank actually has the standard gas for the MOD in it. I've known of a couple folks who got lax in checking every bottle before every dive and worked on assumption or trust in the content duct tape that another filled out. A bad and stupid practice.

 

[Cheekymonkey]

Thank you so much for the wonderful answers cerich and doc. The above checklist for switching to a stage bottle cerich was wonderful and as I begin the diving with oppotunities to practice this, I certainly will until it becomes habit as that does make perfect sense and seems to eliminate most problems right there.

Since I made the OP though, I guess i'll hijack it myself and move on towards your last post cerich about checkign the mix myself. I do habitually self check the mix since I have become a nitrox diver. But it made me wonder, my normal Open Water certification is PADI, and when we teach nitrox we teach to use the tables if the gas is within +1 or -1 percent of the gas the table was intended for. For instance the 32% mix I intended to get yesterday was actually about 31.1%, while this was exceptable for using 32% calculations through PADI, what are the feelings on this regarding beginning tech diving, is it still safe to plan with 32%. Obviously having 0.9 less O2 leaves you with a slightly deeper MOD, but will the minor loss of N2 offgassed between 31.1% and 32% cause problems in deco plans?

 

[cerich]

Hey Cheeky, do a tech couse before trying this stuff at home!

The variance is still there in tech except also with helium as well as O2.

 

[Doc Intrepid]

..."Obviously having 0.9 less O2 leaves you with a slightly deeper MOD, but will the minor loss of N2 offgassed between 31.1% and 32% cause problems in deco plans?"

In a word, "no".

Unless your team packs a T-bottle of O2 in a van when you drive off for the weekend (and fill your own tanks at destinations), you will be dependent on various dive operations for deco gas mixes. Most will be pretty close. Occasionally, if a T-bottle gets low for example, you may get a mix that is either too rich or too lean and you may want to re-run V-planner to see whether any variance might be wise in your dive plan.

Speaking only for myself, we try to build enough conservativism into the deco schedule that a < 1% variance in gas is not something we are concerned about. You control the things you can control to the best of your abilities, and you must deal with those things you cannot control. Each situation will need to be evaluated individually, but in general a < 1% variance is not something that will cause problems. Your ability to conduct a proper ascent, for example, is of far greater significance than a < 1% variance in your deco mix.

IMHO. YMMV.

 

[rjack321]

48.9% or 51.2% in lieu of exactly 50.0% deco gas is pretty normal. I don't start considering dumping the gas until its >2% off and even that's pretty conservative.

For backgas, I dive standard mixes. 21/35 or 18/45. Both use the same tables. So is 19/40 acceptable? I would use it (assuming no MOD issues) without hesitation.

23/34? Yup no changes.

17/50? OK now that's getting a bit outside the norm, but I would not modify my deco.

Thank you so much for the wonderful answers cerich and doc. The above checklist for switching to a stage bottle cerich was wonderful and as I begin the diving with oppotunities to practice this, I certainly will until it becomes habit as that does make perfect sense and seems to eliminate most problems right there.

Since I made the OP though, I guess i'll hijack it myself and move on towards your last post cerich about checkign the mix myself. I do habitually self check the mix since I have become a nitrox diver. But it made me wonder, my normal Open Water certification is PADI, and when we teach nitrox we teach to use the tables if the gas is within +1 or -1 percent of the gas the table was intended for. For instance the 32% mix I intended to get yesterday was actually about 31.1%, while this was exceptable for using 32% calculations through PADI, what are the feelings on this regarding beginning tech diving, is it still safe to plan with 32%. Obviously having 0.9 less O2 leaves you with a slightly deeper MOD, but will the minor loss of N2 offgassed between 31.1% and 32% cause problems in deco plans?