How to answer "what is your highest certification level"?

[Manatee Diver]

First examples of that idea comes from aviation, bail out oxygen bottle designed for fighter pilots. It was strapped to the seat.

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Same concept still in use today for HALO jumps.


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The Spare Airs are literally helicopter bail out cylinders.

 

[scubadada]

...My redundant air is usually, whatever I need to safely surface at any point in the dive, and a little more than whatever a "third" would be in rule-of-thirds. A 19cu can "theoretically" do that from 130ft with safety stop and no panick. Intuitively, I don't like diving beyond 90ft solo with 19cu redundant, regardless my calculations...

Yes, it is personal. I am comfortable diving a 19 cu ft pony for all rec dives. A minute at 130 ft, 30 ft/min ascent, a 3 min SS, all at twice my average RMV is 16 cu ft. Leaves just under 500 psi buffer in the cylinder. Of course, push comes to shove on a no stop dive, you can ascend a bit faster and skip the SS. I very rarely solo dive deeper than 100 feet.

 

[SlugLife]

Yes, it is personal. I am comfortable diving a 19 cu ft pony for all rec dives. A minute at 130 ft, 30 ft/min ascent, a 3 min SS, all at twice my average RMV is 16 cu ft. Leaves just under 500 psi buffer in the cylinder. Of course, push comes to shove on a no stop dive, you can ascend a bit faster and skip the SS. I very rarely solo dive deeper than 100 feet.

You got me thinking, perhaps I should bounce-dive 130ft with a 80cu + 19cu. At depth, switch to 19cu, take 5 breaths at 130ft, surface at 20 to 30ft/min, 3min safety-stop, and see how much is left. Obviously, I'd have my mostly-full 80cu as my redundant. I know my "in theory" calculations, but why not verify in an non-emergency. It might be several weeks before I can do that test.

I could also test the 6cu at 60ft, same test. I haven't calculated it, but I'm guessing it'll hit 500psi around 2-min into the safety-stop.

 

[scubadada]

You got me thinking, perhaps I should bounce-dive 130ft with a 80cu + 19cu. At depth, switch to 19cu, take 5 breaths at 130ft, surface at 20 to 30ft/min, 3min safety-stop, and see how much is left. Obviously, I'd have my mostly-full 80cu as my redundant. I know my "in theory" calculations, but why not verify in an non-emergency. It might be several weeks before I can do that test.

I could also test the 6cu at 60ft, same test. I haven't calculated it, but I'm guessing it'll hit 500psi around 2-min into the safety-stop.

I have done that, but it was hard for me to breathe at twice my avg RMV for the whole time It's a lot of gas.

Alternatively, just do the same ascent profile on your AL80 or other cylinder starting at a known gas pressure and record your finish pressure to calculate the volume used. With an AL 80, a start pressure around 750 psi would be about the same as a 19

 

[ofg-1]

It was the early 70's. I don't remember which class I was the highest in.

 

[SlugLife]

I have done that, but it was hard for me to breathe at twice my avg RMV for the whole time It's a lot of gas.

Alternatively, just do the same ascent profile on your AL80 or other cylinder starting at a known gas pressure and record your finish pressure to calculate the volume used. With an AL 80, a start pressure around 750 psi would be about the same as a 19

Makes sense, and easy enough to calculate. I'll have to stop procrastinating and setup my air-integration, to get accurate numbers. Running the test at 125ft, 100ft, 75ft, and 50ft I'm guessing is about 2 tanks, but I'll bring more air and possibly run it several times. Obviously running 125ft on full tanks, scaling down from there.

As far as increased SAC rate, no reason to intentionally hyper-ventilate yourself, just multiply the volume used after.

 

[Wibble]

Practice using your redundancy before you need it for real.

When you do need it, life will be a lot easier because you know it works.

 

[Subcooled]

Practice using your redundancy before you need it for real.

When you do need it, life will be a lot easier because you know it works.

It is absolutely forbidden, despiced and dangerous to commence a dive with broken equipment.
Hence, the little rebel in me awakens, and I do just what you recommend:

People often see the broken equipment etc. but they do not see the safety precautions and the planned redundancy. This was done in a shallow quarry and the other reg was fine.

 

[stretchthepenn]

I did solo about 6 weeks before I did cavern/intro. The solo instructor is cave trained and knew I was doing my intro class soon. The mask off exercise involved following a line strung all around a big platform. I had no issues with that skill. Big confidence builder and made the same skill in my intro class go much smoother.

I probably got more out of solo class than if I I’d taken it after intro to cave.

I already had SM experience so that helped as well.

Much the same here, minus the cave-specific stuff.

I took the PADI Self-Reliant course before moving into the technical realm but after diving SM for a few years. The course was an excellent "soft" introduction to the technical diving mindset and skills, and my previous SM experience made some of the class much easier.

I did two supervised dives on day one of solo class. Day two was two SOLO dives. Boy, it was kinda freaky diving by myself the first time.

Yeah... That first intentional solo dive felt straight-up weird.

 

[jlcnuke]

I have done that, but it was hard for me to breathe at twice my avg RMV for the whole time It's a lot of gas.

Alternatively, just do the same ascent profile on your AL80 or other cylinder starting at a known gas pressure and record your finish pressure to calculate the volume used. With an AL 80, a start pressure around 750 psi would be about the same as a 19

A cave diver that passed away earlier this year posted an account of when he had an actual problem at depth a few years back. His RMV was more than 3 times his normal rate for an extended period during that incident (a dive that would normally consume less than 80 cuft used more than 300cuft recovering from an emergency). What happens in a real emergency is often much worse that how we think we'll deal with a situation.

Check out this report sometime... New to rebreathers - what do you recommend based on this?