Decompression Theory

[Lost Yooper]

Thanks Doc, that's what I thought.

Liquid, based on some of my readings, it isn't uncommon for convulsions to occur virtually without warning, which can in turn result in imminent drowning and death. I've read reports where CCR guys have had this happen in very shallow depths (less than 30') and died. I sure as heck wouldn't want it to happen to me at 160'+ -- good buddy or not.

Now, I'm a risk taker -- more so than most -- but super high PPO2 diving isn't worth it to me, especially when there's a much safer alternatives (trimix, various deco procedures, etc.). I would personnally rate that activity as much more dangerous than deep air. Liquid, I really believe you're playing with fire by doing that type of diving, and if 'ole Murphy rears his ugly side you may find out the hard way.

Take care.

Mike

 

[padiscubapro]

Not to flame anyone but....
If you don't know ANDI standards you should not guess.. ANDI's extended range is not about deep air diving the recommended depth limit is 165 fsw (same as their technical diver TSD class that limits dives to a mandatory 30ft 9 minute stop) , 190 is only alowed under the best conditions(on the last training dive), and should only be used if the proper support is available so a diver can experience heavy narcosis that might happen on a switch to a bail out gass that wasn't an optimum mix, this must be agreed upon by both the instructor and student. The goal of the extended range class is to introduce UNLIMITED deco and unlimited gas switches for mission oriented diving (ANDI also has a normoxic trimix).

BTW ANDI has been around since 1988 and has a PERFECT training record no insurance claims and none currently pending!
This includes both CCR and OC training dive to 100m.

ANDI's stance if its deeper than 165 fsw you should be using helium, and recommends the use shallower to lower the END.

the normal progression from ANDI''s standpoint for OC
CSU complete safe air user - nitrox 50%
TSD technical safe air diver - nitrox 100% deco dive max 165, mex deco obligation mandatory 30ft stop for 9 minutes, minimum class depth 130 fsw, 1 gas switch
ERD extended range dive, max 165 unlimited gas switches and deco obligations
TMD trimix diver max 100 meters any mix any deco

for CCR diver there is no extended range, the progression is
CCR user (eqpt specific)
TRD tech rebreather diver
ERE - exploration rebreather diver (Helium)

with andi I am currently technical oc instructor (ext range with TDI - I limit depth to 165), I will be teaching technical inspiration (CCR) in the near future...

All ANDI classes deal extensively with knowledge development, even the csu program is 12- 14 hours of class work
From TRD and beyond a student can only take 2 classes in a row without a break for experience... TSd and ERD, or ERD and TMD (trimix).. ALL tech students (TSD and ABove)gets a questionere from ANDI Hq to make sure an instructor is not taking any shortcuts, and that all materials are covered.

I am certified through user Trimix.
personally I usually switch to helium deeper than 150, though when I was much younger I dove MUCH deeper on air.

http://www.geocities.com/padiscubapro/index.htm
ANDI, PADI, SDI, TDI
Technical and Recreational instruction

 

[roakey]

Originally posted by padiscubapro
ANDI's extended range is not about deep air diving the recommended depth limit is 165 fsw...

165 feet IS deep air. GUE for sure, TDI for sure and I think IANTD all recommend an END of 130 feet maximum. GUE actually recommends a 100 foot END.

165 feet on air is, well, a 165' END, exceeding the well thought out maximums of several agencies.

Roak

 

[CheeseWhiz]

With the database of good practical and experimental knowledge that has been built up in the diving sport (and industry) over the past 20 years of so, it astounds me that anyone would want to risk oxygen toxicity or severe nitrogen narcosis by "pushing the limits." The number of deaths caused by these "cowboy" practices is well documented (read "The Last Dive" or "Deep Descent" for some well-written descriptions of a few).

Oh well...keep it up. After all, where will all the good books about diving accidents come from, if no one dies? (The last comment should be interpreted as sarcastic irony...or maybe ironic sarcasm...not as a true statement of the author's feelings.)

But my philosophy is: The best thing you can bring back from a dive is your life.

CW

 

[Lost Yooper]

Padiscubapro, thanks for your support. I just didn't feel like writing all that myself.

Any agency that advocates (allows, teaches, supports, etc) an END of 130' + isn't looking out for the welfare of their students.

BTW, ANDI advocates 190' not 180' according to their web site:

http://www.andihq.com/ANDIHQ/train.htm

TDI still advocates 180' on air according to their web site:

http://www.tdisdi.com/tdi/sandp/doc/erdc.pdf

It appears that IANTD has changed their policy to 130' END for which they should be commended as an agency, but many of their "leaders" still, albeit quietly, endorse deep air. IANTD seems to be coming around, but CCR's seem to be a big problem as well -- which they (and others except GUE) still endorse.

Mike

 

[roakey]

Originally posted by Lost Yooper
TDI still advocates 180' on air according to their web site:

Interesting. In TDI's advanced Nitrox text they talk about not exceeding a dose of 4 ATA of N2, which is 130 feet.

Left hand not knowing what the right is doing, perhaps?

Roak

 

[padiscubapro]

Originally posted by Lost Yooper
Padiscubapro, thanks for your support. I just didn't feel like writing all that myself.

Any agency that advocates (allows, teaches, supports, etc) an END of 130' + isn't looking out for the welfare of their students.

BTW, ANDI advocates 190' not 180' according to their web site:

>>>
The 180 was a typo you are right its 190 but as I said in reality its 165 (and listed as such in most description of coarse standards) and is strongly warned against in the instructor materials.
Narcosis evaluation does have its merits but as the description implied its not for everyone the instructor has to evaluate the student and the conditions, and the reason...

There are places this could be done at relative safety and others the instructor would have to be crazy.

If I was in the student's position I would like to know how I would function off my optimum mix and the level of functionality.
I know narcosis level will vary from exposure to exposure but at least its a benchmark under controlled conditions. In many offshore expeditions noone pumps helium they just top off with air so the first dives are done with a good END but as the dive days progress the END goes up..

About a decade ago I used to routinely go to 200 fsw on air, I don't do it anymore but I know If I had to I could manage at that narcosis level.

I have an even better benchmark, go down on trimix and then switch to air just for a short time, within a few breaths it hits you, then back to trimix to clear your head... This is even noticable at 100fsw but granted its minor and you really have to be intune with your body..

As I stated before ANDI's reason for extended range is not about depth per se its about technique, dive planning, and experience.. Especially since the trimix class is a 100M (328ft) max depth class..

 

[Lost Yooper]

I just don't understand why agencies continue to allow this when the option of trimix is so obviously better and safer. The agencies KNOW that deep air is dangerous (you even eluded to it yourself) and kills many divers every year, but rather than change their attitude and kill deep air entirely, they allow greed to enter the equation -- classes. They still convince their students that narcosis can be "managed" when, in fact, that is not always the case.

There is absolutely no good reason to dive deep on air. For every reason someone puts forth advocating deep air/END, there is a relatively simple solution to avoid it.

You should never have to function off your optimum mix, so that point is mute. If it's in your dive plan to have to function off a deep END mix, then you're doing something wrong.

I sure don't see how diving deep on air is going to improve one's technique, dive planning, or offer a pleasant experience. This couldn't be more backwards, IMO.

Mike

PS. If someone really wants to see what it's like to be narced, go for a chamber ride, but don't do it in a 170' of open water.

 

[aue-mike]

Hi Mike-
There is an easy explanation to why agencies continue to not take a stronger stand on deep air or better support trimix -- diving, in their mind (which is then reflected in their advertisement, rhetoric, etc.) is *not* dangerous. They don't want to admit that basic diving is dangerous or at least potentially harmful (except in their liability releases) and scare away customers. In fact, I have heard boasting that "you don't even need to know how to swim to scuba dive," just like Jackie Bissett in "The Deep." However, this is getting off the subject...

Instead of advocating optimal safety -- which would, in fact, be endorsing an END as close to 0 fsw as possible -- they turn a blind shoulder to preventing/eliminating impaired diving. They can not do this as it would appear to be hypocritcial based on past teachings. This is may not be necessarily accurate, but probably plays into it.

The only arguement that one could utilize to support deep air would be economics -- but then that arguement fails horrendously as you can not put an economic value on ones life.

In any case, to really get an eye-opening picture of the effect of narcosis, definitely take a chamber ride. However, you don't need to go to 170' -- 100' - 120' is plenty. I have also had past deep air experience in my past, as at the time there was no readily available alternative. As part of a training op, I took a chamber ride to 120' with a group of other divers. I thought it would be no big deal. At first it was no big deal and I had no *apparent* feeling of narcosis. However, once at "depth" and one of the guys spoke akin to Donald Duck, it set all of us off in a laughing fit. Pretty soon, I was trying to remember why I was laughing. One of the guys couldn't even figure out how to use the tender phone. When immersed, you have plenty of diversions to mask the true effects of narcosis, however, in a chamber the gloves come off and you get a real taste of reality...

In regard to PPO2, generally a 1.6 is considered the maximum for *resting* such as in decompression where there is little stress, and 1.4 maximum for the working stage. However, many are finding that a lower PPO2, such as a 1.2 max, provides better results than trying to max out your O2 the whole dive, especially when considering repetitive dives.

Commercial divers and the US Navy crank up a higher PPO2 on decompression (the US Navy was employing a PPO2 of 1.9 on the USS Monitor dives in 2001), however, it must be stressed that these divers have hats on and communication with the surface which helps to address any potential ox tox situations. On standard OC, you are foolish to push the envelope. When rolling the dice with physics, "increased safety" and accelerated decompression is *not* a benefit compared to death.

Cheers

 

[Dr Deco]

Dear Readers:

As Mike just pointed out, what commercial and military divers do is not to be compared to recreational diving. The former groups are always in communication with medical backup, very often, a recompression chamber is nearby, and divers have communication capability to the surface and full-face masks. They are always in water with capable help very close at hand.

This is not what recreational divers do. It has been possible to go diving as an amateur for almost two hundred years. However, it did require boats, compressors, and topside assistance. The cost was prohibitive, and it simple was not done. The Aqualung made one-man diving possible, but you cannot do the same diving that you do with full backup. High oxygen pressure for in-water decompression pushes one into this zone.

It is foolish to think that you can always get away with these practices! :boom:

Dr Deco