Why not go to 100' ?

[Eric T Lewis]

I am a former commercial diver. I've done 130' air on scuba, and 200' air on surface supplied air. Deeper than that I was on mixed gas.

It comes down to how the narcosis is going to affect you. It affects everyone differently and at different depths. The same way two beers make my wife loopy and don't affect me.

If you are old enough (like me) to remember the days that dentists gave you nitrous oxide; being narced feels like that.

If you get easily drunk, or easily affected by certain prescription meds. You probably will get easily narced. Remember the biggest danger is that you lose your good judgment. That is what will kill you.

It is normal to feel a little buzzed, but if you feel yourself getting flat out stoned, get out of there. The narcosis quickly goes away as you go shallower.

 

[DevonDiver]

If you are old enough (like me) to remember the days that dentists gave you nitrous oxide; being narced feels like that.

On account of the fact that nitrogen narcosis is actually an anesthetic effect. Most inert gasses have an anesthetic effect at varying partial pressures. The severity of effect (partial pressure onset) is generally believed to be linked to the lipid solubility of the gas. This is charted as the 'relative narcotic potency' of a gas.

The onset and symptoms of that anesthetic effect can vary from gas to gas. Argon, I believe, brings about narcosis symptoms akin to an LSD type experience.

If you get easily drunk, or easily affected by certain prescription meds. You probably will get easily narced.

There are a number of known issues which vary narcosis susceptibility. A primary one is CO2 retention. CO2 is a very narcotic gas. Work of breathing and elevated respiration/workload at depth can bring on narcosis very quickly.

It is normal to feel a little buzzed, but if you feel yourself getting flat out stoned, get out of there. The narcosis quickly goes away as you go shallower.

A study, published in 2012, into this assumption provided some surprising results. Worth a read of this article....

Read: News on Nitrogen Narcosis . Stiefel. K.M. 14/9/2016.

"A recent scientific study by Costantino Balestra and colleagues suggests that inert gas narcosis does not subside immediately after ascending to shallower depths. The effect of narcosis was measured by recording the flicker fusion frequency of divers at the surface and underwater".​

Reference:

Balestra, C., Lafère, P., Germonpré, P., 2012. Persistence of critical flicker fusion frequency impairment after a 33 mfw SCUBA dive: evidence of prolonged nitrogen narcosis? Eur J Appl Physiol 112, 4063–4068.

"...the progressive reduction of the CFFF in the
course of the dive seems to suggest a competition between
the effect of oxygen and the effect of nitrogen. With time at
depth, brain nitrogen concentrations increase up to a sufficient
level within the effect-site and narcosis sets in, as
measured by the reduction of CFFF after 15 min into the
dive. Upon return to surface, blood nitrogen concentrations
return to baseline, but the persistent reduction of CFFF
shows that that the narcotic effects dissipate only slowly.
Breathing oxygen after surfacing again decreases the
inhibitory pathways, restoring CFFF to a supra-normal
level".​

 

[Freewillow]

@ Devondiver.


Hello Andy,.


Because I believe that what you are posting on the forum, generally makes sense, I decided to re-read with the help of friends, the whole discussion. The disagreement between us comes from the fact that I am thinking about RSE ( remontée de Secours en expiration ) that is a technique, pretty close to the CESA but done without a second stage in the mouth but from depth of 60 to 90 feet.


It was a reaction to the misunderstood recommendation from a contributor:“."If you are of the mind set that you can cesa from 100 feet like you did in OW class, then you don't belong at 100”. I erroneously tought that the recommendation was to convince this poor beginner in order to make a 100 feet CESA. MY MISTAKE, English is not my mother tongue.


If you re read my posts, I always said that training to CESA FROM DEEP DEPTH was potentially dangerous. My guess is that I did not understand that you were referring to CESA from shallow depth the way it is done with PADI and other international agencies. I have no problem with these, of course.


So sorry for the misunderstanding even if I do not think that it justified your “insults” ( made that up…)...


So here, I follow up on my promise:


When it comes to Agencies and Countries, I was referring to CMAS ( 100 + agencies and countries). But this referred to RSE and not shallow water CESA.


I checked for authors of papers/articles/open letters that are supporting the fact that there RSE is potentially dangerous.


The names of

Dr Bernard Stockman

Dr Sven Van Poucke

Unité de médecine hyperbare

Universitair Ziekenhuis

Antwerpen

And


Dr Mathieu Coulange

Chef de service, Médecine Hyperbare, Subaquatique et Maritime

Pôle Réanimation Urgence SAMU Hyperbarie (RUSH)

CHU Ste Marguerite

 

[Eric T Lewis]

I am unfamiliar with the study you just quoted regarding the lasting effects of narcosis. I suppose it's possible that a large reduction in narcosis as you go shallower makes you feel like it's gone completely when in fact according to the study you still have some lasting effects.

Regardless...my advice stands: If you feel too narced for your own good--better shallow up.

 

[DevonDiver]

I am unfamiliar with the study you just quoted regarding the lasting effects of narcosis.

I wrote about the study in my blog today. It's quite interesting:

Does Nitrogen Narcosis Impairment Persist?

I suppose it's possible that a large reduction in narcosis as you go shallower makes you feel like it's gone completely when in fact according to the study you still have some lasting effects.

The study mentioned didn't show a "large reduction in narcosis"... it showed virtually no reduction in narcosis impairment (even after 30 minutes post-dive).

There's a big discrepancy in the results achieved between subjective study and neurological studies using EEG and CFFF.

That discrepancy points to a situation where the diver might feel that narcosis impairment has ceased, but measurement of the brain function shows it most definitely has not.

In short, 'feeling' narcosis is an absolutely unreliable method of gauging your true state of mental impairment.

 

[halocline]

As far as the first stage failing and delivering too much gas to the second and causing a free flow, I agree, kinking the hose would probably just cause your alternate to begin to free flow. However, if you correctly identified the first stage internal pressure being too high as the culprit of a second stage free flow you could theoretically switch to your alternate and try to reduce the flow of gas exiting the primary by putting a more gentle bend in the hose. Releasing just enough gas to maintain the correct pressure in the first stage to keep your alternate happy.

I'm not sure what you're talking about here. A first stage failure due to IP spike will likely just overwhelm any obstruction depending on the amount of gas in the tank. There are some moderate IP spikes, I guess, that could somehow be partially contained, but generally, when a HP seat fails, you've got a huge pressure increase that can easily blow LP hoses. In any event, I wouldn't ever count on being able to control it while diving. The best thing would be to feather the tank valve, which is pretty tough as a single tank diver.

This just reinforces the importance of recreational divers always maintaining buddy contact so that assistance is available in the event of any problem, and immediate access to the surface. These are two of the most fundamental safety practices for recreational diving.

 

[Dan]

I'm not sure what you're talking about here. A first stage failure due to IP spike will likely just overwhelm any obstruction depending on the amount of gas in the tank. There are some moderate IP spikes, I guess, that could somehow be partially contained, but generally, when a HP seat fails, you've got a huge pressure increase that can easily blow LP hoses. In any event, I wouldn't ever count on being able to control it while diving. The best thing would be to feather the tank valve, which is pretty tough as a single tank diver.

This just reinforces the importance of recreational divers always maintaining buddy contact so that assistance is available in the event of any problem, and immediate access to the surface. These are two of the most fundamental safety practices for recreational diving.

Have you seen the low pressure hose blew up? I thought the reg would free flow first. I have seen the high pressure hose blew up.

 

[CuzzA]

I'm not sure what you're talking about here. A first stage failure due to IP spike will likely just overwhelm any obstruction depending on the amount of gas in the tank. There are some moderate IP spikes, I guess, that could somehow be partially contained, but generally, when a HP seat fails, you've got a huge pressure increase that can easily blow LP hoses. In any event, I wouldn't ever count on being able to control it while diving. The best thing would be to feather the tank valve, which is pretty tough as a single tank diver.

This just reinforces the importance of recreational divers always maintaining buddy contact so that assistance is available in the event of any problem, and immediate access to the surface. These are two of the most fundamental safety practices for recreational diving.

Well, like I said, theoretically you could reduce the flow of gas. Honestly, I was responding to Andy on the fly. What are LP hoses rated at, 400 psi? What is there failure rating? At what pressure would they fail?

I agree that if you had a complete failure of the first stage and the LP hose was receiving whatever the high pressure is in your tank (hopefully you still have some), completely kinking the hose may cause it to burst and fail. But, I don't see why you couldn't attempt to slow down the gas loss by slightly kinking it.

Nevertheless, I think hose kinking should be another tool in the mind shed if a situation presents itself and that would solve the immediate problem.

 

[halocline]

Have you seen the low pressure hose blew up? I thought the reg would free flow first. I have seen the high pressure hose blew up.

I've never seen a LP hose burst, but it does happen. You're right, any downstream 2nd stage would definitely start flowing first, but if there was something restricting it, with unabated pressure from a full tank building up, it would burst withing seconds. LP hoses are only rated to a few hundred PSI.

Fortunately catastrophic HP seat failure is very rare.

 

[KeithG]

I've never seen a LP hose burst, but it does happen. You're right, any downstream 2nd stage would definitely start flowing first, but if there was something restricting it, with unabated pressure from a full tank building up, it would burst withing seconds. LP hoses are only rated to a few hundred PSI.

Fortunately catastrophic HP seat failure is very rare.

Is there anything other than extreme abuse and neglect that would cause a complete HP seat failure?