Air backup for a nitrox dive?

[The Chairman]

I would go further to say there is no compelling reason to use a bailout bottle if you’re not using twins already.

I don't need a bailout bottle if I am diving doubles. I use a bailout if I'm diving a rebreather or diving solo and the minimum size would be an AL40 (>80cf on me rebreather). However, a bailout is never ever a part of my dive plan except as a redundancy. If I am carrying bottles to extend my dive, I call them stages and they will be AL80s. Typically, I'll be in a cave on sidemount if I'm diving stages and they will be the same mix. I don't dive helium mixes, so I don't have to worry about travel gasses, which are also referred to as stages. I do carry deco bottles quite often and they are usually AL40s but I have used AL80s depending on the dive.

 

[The Chairman]

Why? Well, when you're offshore and lose a little bit of gas with each dive,

Sounds more like a stage and not a bailout bottle. It's my opinion that bailouts should never be used to extend a dive and that they are there for an emergency only. My first bailout was an AL19. I sold it five years later as I decided AL40s were more appropriate, and realized that I had only ever breathed on it to test it prior to each dive. I vaguely remember it had 2800 or so in it on the initial fill of EAN36. The hydro had expired and the vis was 5 years out when I sold it, so the guy who bought it took it down for a hydro. He complained about all the black inside the tank. Wow. My O2 cleaned AL19 wasn't. I had already learned my lesson on dives I had done to 130 and such about the fact that my bailout wasn't really the appropriate mix for deeper dives. So, I have only filled my OC bailouts with air since then.

As a caveat, since I started using an SPG, I have yet to run out of air. Since I started rebuilding my own regs, I have yet to have a catastrophic failure at depth on a reg. The only time I have breathed on my bailout was during training or to test the reg/bottle before a dive. I simply won't use it to extend a dive and I pay attention to my gas supply, so it just sits there dive after dive.

I use a slightly different tactic on my rebreather. One of my bailouts is also my dil. I use a shrimp, which can easily switch between CC and OC, but I also have a second stage on each one as well and they are in sidemount configuration. The bailout in this case is for a possible malfunctioning rebreather and I carry enough gas to finish my dive. Clear as mud?

 

[CuzzA]

Sounds more like a stage and not a bailout bottle. It's my opinion that bailouts should never be used to extend a dive and that they are there for an emergency only. My first bailout was an AL19. I sold it five years later as I decided AL40s were more appropriate, and realized that I had only ever breathed on it to test it prior to each dive. I vaguely remember it had 2800 or so in it on the initial fill of EAN36. The hydro had expired and the vis was 5 years out when I sold it, so the guy who bought it took it down for a hydro. He complained about all the black inside the tank. Wow. My O2 cleaned AL19 wasn't. I had already learned my lesson on dives I had done to 130 and such about the fact that my bailout wasn't really the appropriate mix for deeper dives. So, I have only filled my OC bailouts with air since then.

As a caveat, since I started using an SPG, I have yet to run out of air. Since I started rebuilding my own regs, I have yet to have a catastrophic failure at depth on a reg. The only time I have breathed on my bailout was during training or to test the reg/bottle before a dive. I simply won't use it to extend a dive and I pay attention to my gas supply, so it just sits there dive after dive.

I use a slightly different tactic on my rebreather. One of my bailouts is also my dil. I use a shrimp, which can easily switch between CC and OC, but I also have a second stage on each one as well and they are in sidemount configuration. The bailout in this case is for a possible malfunctioning rebreather and I carry enough gas to finish my dive. Clear as mud?

Nope, not for extending dives. In real world practice if you do let's say 5 dives offshore and do an initial test breath, charge it, turn it off, something depressurizes the reg, burp a bit of gas splashing, charge, depressurize, repeat, repeat, repeat... You are using up gas which needs to be replaced. This is the reality of private offshore diving. So the simplest and most logical thing to do is whip it full with back gas since there's not a dive shop 100 miles offshore. My back mounted pony tank reg gets necklaced and is charged, ready for immediate use should I have a catastrophic failure of my back gas. I have a 13, 19 and 40. I choose the right tool for the job. The 13 is the 100 ft. or less tool, so it won't ever be taken down past its potential MOD. I also wouldn't dump the gas and pay for a new fill after each trip simply because it has a little more o2 than air.

That is troubling to hear you had black stuff in your tank. I VIP my tanks each year to ensure they are clean and free from defects. I wouldn't pay extra money to fill a pony with EANx even if it we're not to ever go past it's mod.

 

[Fastmarc]

So, how do you rig a donkey? and what size?

I think you need to review your course materials. As stated on page 102, redundant tanks above 19cf are referred to as 'horses' not 'donkeys' as you incorrectly remembered.
Hope this will avoid confusion in the future.

 

[caruso]

Let’s face it, this is a stupid argument because if you’re at 40m and have 40% EAN you’re doing something wrong not the equipment.

Agreed. Safe diving.

 

[caruso]

The Rouses were nicknamed the Bicker Brothers, they made everyone on the boats uncomfortable

and it killed them

I read the book. They weren't killed because they bickered with each other. They ran into trouble on a deep wreck, it is presumed part of a wall collapsed trapping the son and dad overextended his bottom time to free him and they both got bent.

 

[EFX]

I think the book you're referring to is "Shadow Divers". As I recall the father and son took turns buying the trimix. I can't remember whose turn it was but he didn't want to pay for the trimix so he got air. The dive was +200 ft on the, at the time, the unidentified sub U869. They got narced and I think the son got trapped and the father helped free him which extended their time. After exiting the sub they couldn't find their deco cylinders and being low on air just surfaced and became critically bent. The father died on the boat. The son made it to a barometric chamber but died later. What a tragedy.

The root cause was not paying for the trimix which if they had it they would have been more clear headed, which possibly would have helped them find their deco tanks.

 

[NAM001]

Say I have Spare Air (the air model, not nitrox) and I have an OOA situation on a nitrox dive. Am I correct in assuming that it's safe to switch to the 20.9% backup for my ascent? I can't wrap my head around it at the moment.

IMO first we have to assertain the situation.
You are no longer diving and you are in an emergency situation.
Next next air never hurt anyone short term.
3rd It takes dime to exchange gas in the lungs to get a full replacement of a new gas mix. Probably more time that it takes to get to the surface and for sure if you do it at a faster rate.
4th if the spare air is all you have ...... thats all you have you have more issues with not enough gas and not what quality the air is.

A lot of rules are going to go out the window. 30 ft / min gone you need to get to 20 as quickly as you can with in reason. otherwise your spare air is out on the way to 60'.

Right or wrong i would beet fns to 20 even at 100 ft per minute ans stay there untill the spare air started to breath a little harder and then hit the surface. In other words use 1 cuft to get to 20 ft and another couple of minutes or so to let your compartments catch up with you for a bit. get on the surface and call it a day and monintor for symptoms. at 100 ft you can empty a 3 cuft in 2/3 minutes but at 30 it can take you up to perhaps 2 minutes. 20 fteven longer.

As mix goes the only aspect you have issues with is O2 level and that problem decreases as you go up. I think the general concensus is that you use air for emergency surfacing in rec diving.

 

[caruso]

IMO first we have to assertain the situation.
You are no longer diving and you are in an emergency situation. .

I think they're still diving.

 

[happy-diver]

Open your mind mate and read it again, perhaps twice

What happened in the water and in the sub, well it's all assumed
but what is not presumed is these guys operated under a spirit of criticism
and on the day neither wanted to dive, indeed it seems the entire trip was a Monkey ****

and due to their typical style of less brain than brawn interaction, they goaded each other into it

So yes their bickering killed them thanks.

I read the book. They weren't killed because they bickered with each other. They ran into trouble on a deep wreck, it is presumed part of a wall collapsed trapping the son and dad overextended his bottom time to free him and they both got bent.