What form of redundant Gas supply is preferred?

[sylpha]

I used to dive with a single 12l and a pony, but i discovered the beauty of using twin 7l cylinders. (I'm sure Devon will take a sharp intake of breath when i say they are not manifolded ) I usually surface with 10 to 20 bar in one of them and at least 150 bar in the other (i i make sure i have enough gas in both cylinders to get to the surface including deco, but change to the lower cylinder as i begin my ascent). Then i change 1 cylinder for my second dive.

Of course if i'm doing something different from my usual max 30m dives then nitrox mixes have to be taken into account etc and i plan accordingly.

 

[seahorsey]

'I think the vast majority of solo dives are made in typical recreational single 80, vest BC. Maybe a majority of solo dives include a cutting device. '
True, and that may be why DAN has these insane figures that add up to '54 % of fatalities in 2009 were sustained while solo". But that won't be me. I'm an instructor and a little old lady (49 and 5.3") so I'm pretty safety conscious, and I know I need SOME redundancy. And yeah, I get it, manifolded doubles are the best thing since sliced bread, but frankly, they are also heavy, awkward and costly buggers, too, and I don't do the kind of dives where I would really need them. Yeah I do my backsquats religiously and can probably bench press my husband, but really, not everyone is cut out for doubles. As someone said so rightly, it's no good if you leave it on the dock because it's too much hassle. But good to know that there is a lot of consensus out there! The more people share their preferences, the clearer the picture gets. Big thanks, everyone, such a nice thread this is! Although the Spare Air company will probably hate all you manifolders and pony tamers...

 

[DevonDiver]

I used to dive with a single 12l and a pony, but i discovered the beauty of using twin 7l cylinders. (I'm sure Devon will take a sharp intake of breath when i say they are not manifolded)

LOL No sharp intakes of breath from me on this subject

I regularly dive independant doubles, as I have a set-up using a Custom Divers backplate that allows me to simply cam-band 2 cylinders direct to the backplate. It's a perfect solution for travelling...and twinset diving... using the resources of a (non-tech) diving centre.

I would always prefer to have properly banded cylinders. I would always prefer to have my cylinders manifolded. However, in reality, that isn't always possible. So... I just dive in the best configuration that I can...and that is often dictated by locally available resources.

I usually surface with 10 to 20 bar in one of them and at least 150 bar in the other (i i make sure i have enough gas in both cylinders to get to the surface including deco, but change to the lower cylinder as i begin my ascent). Then i change 1 cylinder for my second dive.

I found that I dove this way when I was in the UK. In an ideal world, I would want to 'balance' the pressure of the cylinders...taking equal amounts of gas from both by switching/alternating the cylinders during the dive.

However, for UK diving, it is not always possible/convenient to swap over both cylinders between dives. Sucking one down...and then slightly dipping into the second..still provides an element of redundancy and means you just need one spare cylinder to swap in before your second dive.

That would lead to some small issues (gas weight) that could affect your trim, but it's easily compensated for if you know how to use your wing properly.

I am not sure if I would suck a cylinder down to 10-20 bars, if I had a deco obligation. In the worst case scenario, where the reg on your second cylinder failed, then you might not have enough gas left in your first cylinder should you need to swap back to it.

Of course, the exact gas-switch times/pressures can (should) be calculated as part of a pre-dive plan.... and any deco trained diver would be wise enough to ensure that their redundancy (however obtained/configured) would be sufficient to cope with their full dive plan and prevent them ever having to break a ceiling.

 

[LeadTurn_SD]

'I think the vast majority of solo dives are made in typical recreational single 80, vest BC. Maybe a majority of solo dives include a cutting device. '
True, and that may be why DAN has these insane figures that add up to '54 % of fatalities in 2009 were sustained while solo". But that won't be me. I'm an instructor and a little old lady (49 and 5.3") so I'm pretty safety conscious, and I know I need SOME redundancy. And yeah, I get it, manifolded doubles are the best thing since sliced bread, but frankly, they are also heavy, awkward and costly buggers, too, and I don't do the kind of dives where I would really need them. Yeah I do my backsquats religiously and can probably bench press my husband, but really, not everyone is cut out for doubles. As someone said so rightly, it's no good if you leave it on the dock because it's too much hassle. But good to know that there is a lot of consensus out there! The more people share their preferences, the clearer the picture gets. Big thanks, everyone, such a nice thread this is! Although the Spare Air company will probably hate all you manifolders and pony tamers...

I have not read that report yet, and I'm not positive, but I think that figure is probably that the 54% fatalities occured during buddy separation (the diver was alone when he/she died), not with true solo divers?

I was just reading the DAN Asia/Pacific fatality report, it gives a good breakdown, and it lists:

49% as "Separated Before" (the fatality),
17% as "Separated During" (the fatality),
18% as "With Buddy" (when fatality occured),
16% as "Solo" when the fatality occured.

Those DAN Asia/Pacific numbers are probably representative of overall fatality percentages from everything I've read over the years.

Of the total fatalities, The question is whether of the 16% that were actually "solo", would redundancy have made a difference?

Would it have made any difference in the vast majority of fatalities, which at least began as buddy dives?

Best wishes.

 

[DevonDiver]

I think the only way to get to the heart of that is to assess the statistics of what caused the incident and the fatality.

That would show whether a reactive buddy and/or redundancy would have made a difference to the outcome.

 

[LeadTurn_SD]

I think the only way to get to the heart of that is to assess the statistics of what caused the incident and the fatality.

That would show whether a reactive buddy and/or redundancy would have made a difference to the outcome.

Yes.

If 16% of the fatalties apparently involved "true" solo divers, that concerns me, but doesn't really surprise me.

I doubt that 16% of all recreational dives are made by solo divers. I think true solo dives are a very small percentage of total dives.... Maybe 5%, or less?? Hard to say.

Maybe it is more than I think. I'm alone when I solo dive, so I couldn't really say

But if solo divers do make up of 16% of the fatalities, it would just confirm what we already know intuitively: In an emergency, a solo diver is probably at greater risk in certain situations. Some emergencies that might be surviveable with a good buddy at your side may be fatal if you are solo.

Best wishes.

 

[Doc Harry]

49% as "Separated Before" (the fatality),
17% as "Separated During" (the fatality),
18% as "With Buddy" (when fatality occured),
16% as "Solo" when the fatality occured.

So my take on these statistics is that, since 84% of fatalities occurred when buddy diving, it is safer to dive solo.

 

[aquaregia]

That would only be true if at least one sixth of all dives were solo.

 

[Doc Harry]

That would only be true if at least one sixth of all dives were solo.

HEY! It's my delusion and I can rationalize it if I want to!

 

[Lorenzoxs]

I used to go with eight SpareAirs straped to my waist, but people thought I was an aquatic suicide bomber....