Redundancy on twin sets.

[Gareth J]

Actually Tbone's comment about diving with the manifold fully open go t me thinking.

Do all you boys in the New World dive with the manifold fully open?

 

[tbone1004]

Actually Tbone's comment about diving with the manifold fully open go t me thinking.

Do all you boys in the New World dive with the manifold fully open?

not all, but most do. I don't know of any that dive like where you're probably thinking

For those that are wondering where he's most likely thinking. One of the ways that some in the UK dive is with the valve fully closed for low viz diving. You breathe on one tank until it is basically empty or starts to breathe hard. Open the isolator and let them equalize, then make your ascent. You are give yourself half of your pressure to make the dive, then a quarter of your pressure to make the ascent/return, and you still have half of your total gas volume in the redundant tank. Useful before SPG's came about or if you are in some seriously sh!t viz.

 

[Gareth J]

For those that are wondering where he's most likely thinking. One of the ways that some in the UK dive is with the valve fully closed for low viz diving. You breathe on one tank until it is basically empty or starts to breathe hard. Open the isolator and let them equalize, then make your ascent. You are give yourself half of your pressure to make the dive, then a quarter of your pressure to make the ascent/return, and you still have half of your total gas volume in the redundant tank. Useful before SPG's came about or if you are in some seriously sh!t viz.

I think I am correct in saying that that is a 'ships diver' procedure used by the Navy (not sure if the USN does it).
Generally used, both for maintenance and clearance, under ship searching etc.

 

[taimen]

These days I'm not sure my shoulders would allow my to dive a conventional twinset with a high degree of confidence I could close the manifold quickly in an emergency. But then I dive CCR mostly these days so its academic, note the O2 cylinder is only ever open half to a turn at the most.

I have been wandering this... The valve drill requires some serious flexibility and definitely good shoulders. How large fraction of seasoned divers are actually able to perform the classic twinset valve maneuvers in a real emergency?

 

[tbone1004]

I have been wandering this... The valve drill requires some serious flexibility and definitely good shoulders. How large fraction of seasoned divers are actually able to perform the classic twinset valve maneuvers in a real emergency?

if they do what they're supposed to do? all of them. Most of the ones that I know manipulate all valves during their S-drills to make sure that they can reach them and that they are all fully open

 

[Gareth J]

I have been wandering this... The valve drill requires some serious flexibility and definitely good shoulders. How large fraction of seasoned divers are actually able to perform the classic twinset valve maneuvers in a real emergency?

Heres a solution some of my buddies use

Stoney28January2018(3 Of 46)January 28, 201828th, 2018, January, NickCharter, StoneyCove

• Gareth J
• Apr 1, 2018

Inverted Twinset

 

[taimen]

if they do what they're supposed to do? all of them. Most of the ones that I know manipulate all valves during their S-drills to make sure that they can reach them and that they are all fully open

Sure. Where I dive, doubles with isolator manifold is the most common configuration you see. Much more common than a single tank. And there are plenty of divers who do not start every dive with an S-drill... I am sure serious cave and tech people do. And they switch to rebreather or other configurations if i.e. shoulder problems prevent safe diving with doubles.

 

[KevinNM]

That was a categorical no, no, on my course.
An open solenoid failure with a fully open O2 valve would result in an O2 hit. We had to be able to shut down the O2 in a fraction of a second as we did a loop flush.

Hypoxia due to the valve rolling closed seems far, far more likely and dangerous. Most people can choose to not breathe for 30 seconds or so, and unless you get an insane O2 PP O2 toxicity takes a while.

 

[Gareth J]

Hypoxia due to the valve rolling closed seems far, far more likely and dangerous. Most people can choose to not breathe for 30 seconds or so, and unless you get an insane O2 PP O2 toxicity takes a while.

Kevin

Hypoxia?
You are on a set point of 1.3, say 1.1 if you are doing anything extreme, do you know how long it will take for the loop to drop to Hypoxic levels.
a/ You should have seen it on the handset.
b/ the HUD will be going nuts - flashing Red
c/ the alarm in my ear will be going ballistic.
All that way before you hit 0.7!

There's an outside chance on the the ascent, but if anything, you are paying far more attention on an ascent than at any other time, ascent is the time you really worry about hypoxic levels. Remember, its CCR not OC. One of the great luxury's of CCR is as a general rule you have time to react and resolve issues.
The high speed faults are hyperoxia really scary issues are a hyperoxic fit, or a CO2 hit. Both give you very little time. I've seen a Hyperoxic fit when I used to dive OC, its not funny. Guess what your PO2 is at 30m with a 100% O2 in the loop? I've had a small CO2 hit, (if you can call a CO2 hit small), thats really frightening, and you feel like **** for ages afterwards. (Not to mention, high CO2 generates paranoia anyway). The CO2 problem seems to have a quick onset because all the early symptoms are generally masked in a high PO2 breathing gas, so you are only aware very late in the day.

Gareth

 

[KevinNM]

I know of multiple people who died of hypoxia on rebreathers. I don't know of anyone who died due to suffering both the bizarre series of coincidences you postulate and then also refused to bail out when the loop became obviously nonviable.