Best Nitrox Mix/ Profile at 100'

[scubadada]

I'm staying out of it less I be accused of being uncivil yet again.

Not inappropriate, one would generally assume that an experienced diver would easily be able to deal with this query, something is wrong here. The answer is not that everyone must pursue advanced decompression training

 

[Instructor_Tom]

got it, that's good stuff. Should have stopped and thought about the diffusion rates for He and N a bit more.

I went back and read on Mass Transport limits and that makes sense on the effect of the NDL

http://www.scubaboard.com/forums/as...es-quality-inert-gas-saturation-he-vs-n2.html

Mass transport of inert gases into biomass
depends on the product of gas solubility times
diffusivity. Helium has faster diffusivity,
and N2 has higher solubility relative to each
other (like 1/2.8 and 4.2 roughly). For short,
shallow exposures, the slower diffusivity
of N2 results in less total gas buildup in bulk
tissue, and hence shorter NDLs than He. For
longer and deeper exposures, He wins because
of its lower solubility. The point where
He and N2 NDLs meet, or cross over, is called
the "mass transport boundary".

bap & kevrumbo;

thanks for the clarification, my complete understanding of the advanced physiological aspects of diving are still developing. since the original question was about longer and deeper dives I was not considering bounce dives or shallow dives in relation to the question asked and miss-stated/over simplified my response.

the important thing is that the question is addressed with as much factual information.

it's too bad that some posters on this thread feel so insecure in their manhood that they have to resort to beaves and butt head types of remarks in order to feel better about themselves.

thanks

T.




Sent from my iPad using Tapatalk HD

 

[bada3003]

Let's see. Rec dive limit is considered around 130 ft. When I'm wreck diving at 80-130 depths, I make three safety stops during slow ascent. One at 60 (a couple of mins), one at 30 (3 mins), one at 15 (5 mins). That's for a bottom time of around 20 mins. It's not cave diving, but having 1000 PSI to perform these stops during ascent is what I do. Is it conservative? Hell yea. Prudent? Maybe.

Per DAN stats, OOA is a common cause of diving accidents, and OOA is often caused by not being conservative with air reserves. By definition, NDL does not require safety stops. But then again, smart folks say that all dives are decompression dives. Given the many unknowns of diving physiology, I tend to think the rule of thirds is useful, even for OW.

Why would anyone follow the rule of thirds on an OW dive? I have never understood that.

 

[dumpsterDiver]

Let's see. Rec dive limit is considered around 130 ft. When I'm wreck diving at 80-130 depths, I make three safety stops during slow ascent. One at 60 (a couple of mins), one at 30 (3 mins), one at 15 (5 mins). That's for a bottom time of around 20 mins. It's not cave diving, but having 1000 PSI to perform these stops during ascent is what I do. Is it conservative? Hell yea. Prudent? Maybe.

Per DAN stats, OOA is a common cause of diving accidents, and OOA is often caused by not being conservative with air reserves. By definition, NDL does not require safety stops. But then again, smart folks say that all dives are decompression dives. Given the many unknowns of diving physiology, I tend to think the rule of thirds is useful, even for OW.

I'm learning a ton on this thread.. the rule of thirds is: to leave 1/3 of your air for an ascent...

 

[eelnoraa]

Why deco diving require move from AL to Steel??? moving from single tank to double makes more sense regardless of tank material. And I don't think He is meant to extend NDL at all

1. you have 1200 PSI in your tanks and want to use more of your gas. you need to get some advanced training and learn decompression diving. this will require 2 things 1 moving from AL to Steel tank with increased capacity and the use of an AL30 or AL40 for accelerated deco.

..... 2 the addition of Helium will extend my NDL since Helium is not an absorbed gas like Nitrogen.

---------- Post added September 18th, 2013 at 04:28 PM ----------

Some instructors, rather than go through the whole "rock bottom" or "minimum gas" concept, simply get around it by teaching their students to dive thirds. It's not conservative enough for some dives, and wildly overconservative for others, but it is simple.

Or some instructors, maybe even majority of OW instructors do NOT understand the concept of rock bottom. I say "Not understand" not "not know". More than once, I got questioned by instrutor and DM on boat, for signaling ascent at 100ft with ~1500psi in my AL80.

 

[Tigerman]

I'm learning a ton on this thread.. the rule of thirds is: to leave 1/3 of your air for an ascent...

And here I have been thinking that it was 1/3rd in, 1/3rd out and 1/3rd in case the manure hits the spreader...

 

[eelnoraa]

Let's see. Rec dive limit is considered around 130 ft. When I'm wreck diving at 80-130 depths, I make three safety stops during slow ascent. One at 60 (a couple of mins), one at 30 (3 mins), one at 15 (5 mins). That's for a bottom time of around 20 mins. It's not cave diving, but having 1000 PSI to perform these stops during ascent is what I do. Is it conservative? Hell yea. Prudent? Maybe.

It really depends on what tank(s) are you using? Single AL80 or even HP100, not so conservative. LP108 or HP130, yes, it is ok conservative.

---------- Post added September 18th, 2013 at 05:12 PM ----------

And here I have been thinking that it was 1/3rd in, 1/3rd out and 1/3rd in case the manure hits the spreader...

and sometime not enough even on OW, depending on the tank size too

 

[Instructor_Tom]

Why deco diving require move from AL to Steel??? moving from single tank to double makes more sense regardless of tank material. And I don't think He is meant to extend NDL at all

an AL80 hold 77cft of gas, double AL80s holds 154. A single LP108 with a cave fill holds 130cft of gas. it's simpler to change 1 thing and extend your deep bottom time than to change your whole configuration. if you really like the longer dive time then you can step up to double steel tanks and really get into long dive times depending on Air consumption rates and deco schedules. my last dive to 90+ was 88min and I surfaced with 1200 psi on my back gas on dbl lp108s.

AL80s and Faber tanks make awful doubles sets ( I've tried them) because they will be ass light in a significant way over the course of the dive and be fighting to keep your butt down during your deco stop. I would only recommend using worthington tanks as a doubles rig; they tend to stay fairly level in trim over the course of the dive

my personal opinion.

Sent from my iPad using Tapatalk HD

 

[chrpai]

A single LP108 with a cave fill holds 130cft of gas.

That's not much of a cave fill... You can easily get that much gas in an LP95.

 

[bada3003]

Yea, but the question pertained to the rule of thirds in the context of OW where the claim was that it wasn't meaningful. The "1/3rd in the case the manure ..." is correct, and with a buddy I've not dived with that's what ends up happening oftentimes in OW (and NDL) dives to be super conservative.

And here I have been thinking that it was 1/3rd in, 1/3rd out and 1/3rd in case the manure hits the spreader...

---------- Post added September 20th, 2013 at 10:02 PM ----------

Yes, I agree on both counts.

I was going by my breathing rate, in colder water (down to mid-40s), where following the last 1/3 for ascent with ALU80 works out for me on average. A couple of weeks ago I was diving with a new buddy to around 80 feet but ended up ascending with 1400 PSI in my tank on account of my buddy reaching 1000 PSI. We did safety stops at 30 and 15 feet. That was the dive plan, we followed it, he had 700 PSI when reaching the surface, I had 1200 PSI.

It really depends on what tank(s) are you using? Single AL80 or even HP100, not so conservative. LP108 or HP130, yes, it is ok conservative.

---------- Post added September 18th, 2013 at 05:12 PM ----------



and sometime not enough even on OW, depending on the tank size too