My AN/DP/Helitrox course

[kensuf]

I teach a working portion of 1.2, MOD of 1.4, max deco of 1.6 when diving OC. When diving CCR, I teach 1.2 and 1.0, depending on duration.

If adding 5 minutes of deco chills your willies to the point where you're willing to push CNS exposure, then tech diving isn't for you.

 

[Marie13]

I teach a working portion of 1.2, MOD of 1.4, max deco of 1.6 when diving OC. When diving CCR, I teach 1.2 and 1.0, depending on duration.

If adding 5 minutes of deco chills your willies to the point where you're willing to push CNS exposure, then tech diving isn't for you.

Look, I have no issue with it. Some of you (not you, Ken) seem to have no concept of running theoretical dives, looking at the numbers, and working things out. You seem to expect a fully formed tech diver to just appear, like Athena from Zeus’ head.

And, no, I just don’t take something as the gospel truth just because someone spouted it on the internet.

 

[BlueTrin]

I think @Marie13 is only asking questions about whether there is some basis for using 1.2 rather than 1.4, that seems a sensible to attitude to me to question things: it does not mean you disagree but that you are curious about the causes.

I’ll be asking the same question to my instructor after reading this thread.

 

[grantctobin]

Try out DiveSafe, it’s a very simple to use mobile app that can help estimate in a very visual way trimix , end, gas densities and such.... it has also a very advanced gas blending functionality.

It costs a bit, so try out the free recreational version first, DiveSafe Nitrox.

Using some technology to choose a good gas is not a bad idea

Are you shilling your software? A disclaimer might make this seem less sketchy.

 

[hxtk]

Regarding the ppO₂ limit, if you're looking for an authoritative source, the US Navy Dive Manual is published freely on the internet by NAVSEA. I don't think I've ever heard someone refer to the limits of the Navy manual as particularly conservative, but in revision 7, §3‑9.2.2 it prescribes a 1.3ata limit for ppO₂ in a "wet" diver as opposed to 2.4ata for a diver who is dry, i.e., in a hyperbaric chamber.

 

[Jack Hammer]

@Marie13
Most tech divers I know use 1.2 for their planned dive with 1.4 as a contingency. A lot of newer tech divers unknowingly do similar. The deck of the Hume is around 130'/40m with the bottom of cargo hold at about 148'/45m. When planning you use that max depth even though the bulk of the dive will be at the shallower depth. A lot of Great Lakes shipwrecks are like this so very little of your dive will actually be at 1.4. For that wreck I've typically used 18/45 (because that's what I keep in my doubles so they work in a wide range of depths). My last dive on the Hume I used a stage with 21/35 for my bottom portion, IIRC I used about 1800psi from it, not exactly a fortune in Helium.

 

[Scuba Cobra]

That helium stuff is $$$$, an END of 119ft is good enough! (joking). NAUI taught 25/17 for a few years as a standard mix - Bruce Weinke (RIP - he died this past weekend) was an advocate for this mix as the 17% was light enough to behave similar to nitrox. It never really caught on. In the cusp years between AG leaving GUE and starting UTD he taught for NAUI and bent the rules on 25/17 to make it 25/25 but never at 150ft. 25/25 is 100-130ft gas under that paradigm.

I have done Great Lakes dives with ENDs in the 120s. It might be cold but the vis is pretty good and there's plenty of ambient light down into the 250+ft range so its not hideously narc-ing to me.

I will admit that I have used 25% more than a few times at 150' for the same reason Marie13 had said, and being TDI worh the teaching of best mix etc..

I'm still FAR from the most experienced tech diver, so i spend alot of time reading and listening to those with more deco dives under their belts than i even have dives.

Part of what has made me want helitrox, thinking about all those times i was at 150' with 25% fighting hard currents with such a high working pp02 and dense gas.

Thankfully in japan its warm water and extremely well lit at those depths plus more. Still wish i could get a helitrox course to bring the gas density down to an END of 100'. At the end of the day helium is almost non existent in Japan, but inwant thenoption for my own safety.

 

[Marie13]

@Marie13
Most tech divers I know use 1.2 for their planned dive with 1.4 as a contingency. A lot of newer tech divers unknowingly do similar. The deck of the Hume is around 130'/40m with the bottom of cargo hold at about 148'/45m. When planning you use that max depth even though the bulk of the dive will be at the shallower depth. A lot of Great Lakes shipwrecks are like this so very little of your dive will actually be at 1.4. For that wreck I've typically used 18/45 (because that's what I keep in my doubles so they work in a wide range of depths). My last dive on the Hume I used a stage with 21/35 for my bottom portion, IIRC I used about 1800psi from it, not exactly a fortune in Helium.

Better?

 

[ChuckP]

Regarding the ppO₂ limit, if you're looking for an authoritative source, the US Navy Dive Manual is published freely on the internet by NAVSEA. I don't think I've ever heard someone refer to the limits of the Navy manual as particularly conservative, but in revision 7, §3‑9.2.2 it prescribes a 1.3ata limit for ppO₂ in a "wet" diver as opposed to 2.4ata for a diver who is dry, i.e., in a hyperbaric chamber.

@rjack321 and @kensuf

I was writing some long defense of 1.4 and wanting a better explanation of why 1.2 and bam there it is. The TDI books just refer to dialing back the PO2 if expecting heavy work or multiple dives over multiple days - no real tie of PO2 and He and Ox Tox........

Interesting reading and a good enough reason for the decrease.

 

[ScubaWithTurk]

Why not ask your instructor why plan for 1.4?
Do we always use the max fO2 allowable? When should we back off? long bottom times? short bottom times but long deco? cold? high work? uncertain max depth? high tide?

I believe these are questions all new tech divers should be asking their instructors. If we take, say the use of 1.4, as gospel, aren't we just trusting that it will all be ok without any discussion? Like a trust me dive.

When we understand that 1.4 is the high end for working dives, we should ask why not dial it back to something like 1.2. Run the plans for each and present them to the instructor and listen to what they say.

All part of being a thinking diver.

Keep up the hard work @Marie13. I look forward to hearing about the pool sessions and the dives.