How much air to surface with?

[ev780]

I am probably just rationalizing personnel behavior but I believe that different diving conditions have different requirements and there is no one size fits all gas planning. Cave, Tech / planned DECO and low vis cold water diving would IMHO require much more stringent gas planning and reserve requirements over basic warm water drift diving in good vis like I do in Cozumel (AKA rec Bunny dives). I try to be up to 60' by around 500 PSIG and complete the SS requirement by 250 PSIG. At that point I may hang out until the boat comes around or until I reach the IP crack point on my 1st stage. I have always checked my regs in shallow water to see how they react to low pressure and with balanced regs have found them to draw to the end of the bottle. I want to know how they feel and flow at less than IP so that as a last fail safe I know when an OOA situation is immanent based upon feel and 'draw', in the event I was silly enough to not monitor one of my two gauges.

I read the whole thread and this is the best post of the bunch. It depends." Right answer.

I returned a tank to the dive shop at pennekamp in key largo with 200 psi.. The guy had a fit and told me that it is very dangerous to breath a tank that low... He also said " I should charge for a visual inspection to make sure no water got in the tank " I just started laughing after he returned the credit card to me...

Jim...

I think the water in the tank thing is an urban legend! I can't for one second believe that any human can breathe a tank dry enough through SCUBA equipment to get a tank to zero or negative pressure which is what is required to get water into a tank through that little hole in the valve! There has to be some amount of pressure to overcome all of the springs in the regulator to allow air to flow. All it takes is some positive amount and water will never enter a tank. Someday I will test my hypothesis.

I breathe tanks down to the end of my dive. Hitting the safety stop with 500 works for me. Although I am good on air and others usually end and I have plenty left. Of course as stated above if I am in an aggressive or challenging dive I give myself much more cushion.

 

[stuartv]

I think the water in the tank thing is an urban legend! I can't for one second believe that any human can breathe a tank dry enough through SCUBA equipment to get a tank to zero or negative pressure which is what is required to get water into a tank through that little hole in the valve!

What if you breathe it "dry" while you're at 30 feet, then descend to 90 feet (presumably, breathing off a different tank/pony), for some reason?

 

[BRT]

Yep, that would do it. So don't do that. Reality is that if you left 26 lbs over ambient in it at 30 no water would enter at 90. It will start to breath pretty hard at 26 so switch to your other supply when it still has 50 over ambient and you will be good below 140 without letting water in unless you have figured out a way to get water to move against pressure. If so I'd like a share of the patent.

 

[dumpsterDiver]

Are y'all advocating that everyone should dive with redundant buoyancy? So, for wetsuit divers, they should all use dual bladder BCs/wings?

No . you need to be able to survive a BC failure. Lotsa ways to do that. When you wear a thick wetsuit in deep water AND have little or no ballast to dump then you options become more limited. Having a bc with extra volumetric capacity is not related to redundancy. All. This should be obvious to you by now...with all those cards, dives and posts?????

 

[redacted]

What if you breathe it "dry" while you're at 30 feet, then descend to 90 feet (presumably, breathing off a different tank/pony), for some reason?

Yes, the tank that was being used by a diver who went OOA and drowned will probably need a VIS. But other scenarios which get water in a tank while UW are a bit hard to find.

Water gets in tanks from sloppy fill operations. Other sources are extremely unlikely.

 

[Freewillow]

Water may enter in the tank when the system is disconnected. So, as awap is saying awap, do not dry the valve of the tank and fill it up and you get water in the tank. When it comes to sucking dry a tank @ 10 feet and then go down to 90 feet with your second tank is a theoretical construction that I have a though time to consider in practice

For the "back up " on buyancy. If you are correctly weighted you do not need one. I can make it to the surface with an empty BCD at the end of a dive . Additional buyancy is provided - although this is not the reason I bring one - is my 5 gallons SMB .

 

[AfterDark]

Are y'all advocating that everyone should dive with redundant buoyancy? So, for wetsuit divers, they should all use dual bladder BCs/wings?

Naw, just carry a lift bag or have ditchable weights that be ditched in small increments.

 

[stuartv]

This should be obvious to you by now...with all those cards, dives and posts?????

Seriously? I ask a question to lead someone to realize they have made a statement that, either, is very subject to misunderstanding, or, that may not be completely correct, and you decide to adopt an interpretation that suggests I am truly ignorant and then attack me?

---------- Post added October 1st, 2015 at 08:34 PM ----------

Yes, the tank that was being used by a diver who went OOA and drowned will probably need a VIS. But other scenarios which get water in a tank while UW are a bit hard to find.

Water gets in tanks from sloppy fill operations. Other sources are extremely unlikely.

What part of "breathing off a different tank/pony" means that someone drowned?

Did you read the post I was responding to that said, essentially, there is NO WAY a person could empty a tank and have it get water in it?

When you are identifying risks and choosing what, if any, steps to take in risk mitigation, is it your normal practice to ignore physics with regard to what is possible, no matter how unlikely?

 

[redacted]

Seriously? I ask a question to lead someone to realize they have made a statement that, either, is very subject to misunderstanding, or, that may not be completely correct, and you decide to adopt an interpretation that suggests I am truly ignorant and then attack me?

---------- Post added October 1st, 2015 at 08:34 PM ----------



What part of "breathing off a different tank/pony" means that someone drowned?

Did you read the post I was responding to that said, essentially, there is NO WAY a person could empty a tank and have it get water in it?

When you are identifying risks and choosing what, if any, steps to take in risk mitigation, is it your normal practice to ignore physics with regard to what is possible, no matter how unlikely?

Your scenario make less sense than perhaps tying a rope on an empty tank and lowering it into the water. Might make more sense for the valve to loosen UW after the tank is empty.

Water in tanks come from careless fill operations 99.99% of the time.

Want to see how many scenarios you can come up with to account for the other 0.01 percent?

 

[dumpsterDiver]

Seriously? I ask a question to lead someone to realize they have made a statement that, either, is very subject to misunderstanding, or, that may not be completely correct, and you decide to adopt an interpretation that suggests I am truly ignorant and then attack me?
?

CONGRATULATIONS! You have been admitted into a very small and highly selective group of scuba divers.... You have now been added to my ignore list.

I would not be at all displeased if you reciprocated....

Breathing down a tank to empty at 30 feet and taking it to 90 feet and pressing the purge button...

What if a kitten removes the gas cap from my truck and crawls down into the fuel tank?

Do you SERIOUSLY worry about this stuff... Wait.. don't answer that..