DIR- Generic Why use GUE nitrox only

[jadairiii]

On balance, I favour the argument that oxygen is less narcotic at the pressures we can safely breathe because there is a substantial gap between inspired and tissue PO2 due to metabolism in the tissues that matter for a narcotic effect. In contrast, the gap between inspired and tissue tensions of nitrogen in the brain is almost zero because the brain is a very fast tissue. Having said that the functional difference in narcotic effect is probably quite small. If we really want to avoid narcosis, then breathing helium is the key.​

In the end, Oxygen is "narcotic", may be less than N2, but still narcotic. The rub is O2 is metabolized.

That was what I was taught in my first Mix class in 1998, but as a side note to keeping PpO2's low on the working part of the dive.

 

[boulderjohn]

Research on saturation divers indicates that any tissue fully saturated at 20 feet or less can go directly to the surface. You essentially cannot get DCS at that depth, no matter how long you stay there. Extra oxygen does you no good, so I don't see a benefit to nitrox on a 20 foot dive, especially if you have to pay extra for it.

Do astronauts on space rockets get the bends? I heard a rumor that they pre-breathe oxygen prior to launch to prevent this. That would be like breathing 100% oxygen at 6 metres before you surface. Kind of. (Not really though? lol)

Astronauts and U2 pilots do prebreathe oxygen prior to flights. It is not because the oxygen is doing them any special favors. They do that to eliminate nitrogen from their body. The rapid increase in altitude is still a problem. I spoke with someone who consults for both NASA and the Pentagon on DCS issues, and he is convinced pretty much every one of them is mildly bent on every flight.

 

[Blackcrusader]

Single dive - not too many benefits aside from less fatigue (N2 sat?). Multiple dives - different story

I am 24 dives into a 30 dive vacation over 10 days. All on 21%. I've done same thing on nitrox and never felt any different.
Only thing is nitrox restricts MOD and can't be used for deep dives.

 

[leadduck]

I don’t know the royal «we» you’re talking about, but that’s a hard disagree from me. Sacrificing safety and team integrity on possibly the most dangerous part of a dive - the ascent - for some weird notion of personal freedom that comes with no significant advantages of any kind, is mindblowing to me.

Doing tech decompression dives with different gases in the team is either solo diving or just wildly inefficient for no benefit - neither of which appeal to me.

PS.
This might belong to the pub, but this contorted idea of personal freedom makes no sense. Owning a weapon is not freedom. Sending your kids to school without worrying about school shootings is freedom. Diving different gases is not freedom. Having the same gas and deco schedule, and team redundancy and shared resources gives flexibility and freedom to focus on WHAT MATTERS. /rant

Please remember that we're not discussing advanced trimix here, but the rationale behind generally enforcing EAN32 on shallow dives, NDL or <30min deco. So the situation is that your insta buddy on the day trip boat filled only air to save $5, set his computer conservatively, and now tells you he's got 15min deco left while you're already done, a little low on gas and would like to get out. You will be certainly annoyed, but it's not a huge problem in open water. In a cave however it may become one.

 

[jadairiii]

Astronauts and U2 pilots do prebreathe oxygen prior to flights. It is not because the oxygen is doing them any special favors. They do that to eliminate nitrogen from their body. The rapid increase in altitude is still a problem. I spoke with someone who consults for both NASA and the Pentagon on DCS issues, and he is convinced pretty much every one of them is mildly bent on every flight.

There are a few stories out there from U2 Pilots flying around Afghanistan that are crazy (in print). During the height of the conflict the pilots were doing way more sorties then they ever did before and having some serious consequences, some have no recollection of even landing. All associated with DCS or O2 toxicity, cant remember, been awhile since I've read the articles.

 

[steinbil]

Please remember that we're not discussing advanced trimix here, but the rationale behind generally enforcing EAN32 on shallow dives, NDL or <30min deco. So the situation is that your insta buddy on the day trip boat filled only air to save $5, set his computer conservatively, and now tells you he's got 15min deco left while you're already done, a little low on gas and would like to get out. You will be certainly annoyed, but it's not a huge problem in open water. In a cave however it may become one.

Nope. I won't do deco dives with instabuddies. Sounds like normalization of deviance. A dive requiring deco stops is a technical dive in my opinion, and requires planning, a team and proper deco gases.

Also, if I'm not mistaken, a 30m dive requiring 30 minutes of deco might be just as risky as, or even more risky than, a 50m dive with the same deco obligation considering the longer exposure and higher load in the slow tissues.

 

[justinthedeeps]

Nope. That's not how Gradient Factors work.

Please amend/explain! You sound like you know how gradient factors work.

What is the surface GF for someone who is saturated on compressed air at 6 metres / 20 feet?

 

[inquis]

What is the surface GF (or GF/GF) for someone who is saturated on compressed air at 6 metres / 20 feet?

83%, though it takes 63 hrs to get there. 5 hrs only gets you to 37%. ETA: any good planner can give you this type of info; Subsurface is one that's easily available.

 

[steinbil]

Please amend/explain! You sound like you know how gradient factors work.

What is the surface GF for someone who is saturated on compressed air at 6 metres / 20 feet?

GF60 is 60% of the supersaturation indicated by the M-value. Meaning GF100 = M value. I don't know what the M values of the different tissue compartments are, but I'm sure you could look it up.

 

[boulderjohn]

We have had several threads in the past few years in which research was cited showing that divers fully saturated on air at 20 feet can ascend without violating M-values.