Deco penalties

[Rec Diver]

Deco with 40% from 28% bottom mix is totaly unefficient.

This may appear to be so. However, the 28% oxygen at depth made a noticeable reduction to the narcosis. I guess this would be why trimix is becoming so popular, the more you can lower the nitrogen content of your gas the less the effect of the narcosis. Also, breathing a higher concentration of oxygen at your deco stops as compared to the air your breath at depth greatly increases the speed at which the nitrogen in your system is transformed. Deco stops with 100% oxygen can cut your deco time in half as compared to deco stops on air. This is very, very efficient.

 

[MonkSeal]

This may appear to be so. However, the 28% oxygen at depth made a noticeable reduction to the narcosis. I guess this would be why trimix is becoming so popular, the more you can lower the nitrogen content of your gas the less the effect of the narcosis. Also, breathing a higher concentration of oxygen at your deco stops as compared to the air your breath at depth greatly increases the speed at which the nitrogen in your system is transformed. Deco stops with 100% oxygen can cut your deco time in half as compared to deco stops on air. This is very, very efficient.

Increasing oxygen percent in mix does not decrease narcosis. Quite the oposit. Oxygen has higher narcotic potential then nitrogen, meaning 28% is probably more (or at least as same as) narcotic at given depth then 21%. The only way to reduce narcosis is to replace nitrogen with helium.

 

[Rec Diver]

Just for the record (not to critique your methoid of diving, Rec Diver, to each his own), I just finished IANTD's Adv. Rec Trimix, and am currently in Full Trimix, and this is not any kind of diving I'm being taught. 28% bottom mix and 40 % deco using navy air tabes... Nope, can't recall that lesson.

When I took the IANTD deep air class the instructor supplied us with a copy of the Navy air tables. I would guess that your instructor did not feel that this would be an important piece of information for you to know. I think that if you check the source of most of the dive tables and software available today, I think you will find there origin is with the Navy dive tables. Also, some computer manufactures, mine included; Aeris, use the Navy dive tables as there source for performing there decompression obligation software. Since this dive was planned to use our computers for decompression measurement obligation, we decided, because of our age, to use 40% oxygen mix for the deco gas. This allowed for a very good safety margin. The 28% at depth was for comparing the narcosis felt on the second dive as compared to air, or 21% oxygen, on the first dive. Since we carry multiple computers on our dives we were comparing decompression obligations of each one to a base line, namely the Navy air tables.

I appreciate the training you have taken and are now into the realm of trimix usage. I however, do not think that just because my instructor says I should use a certain mix of gas that this would the best route for me to go. I would much rather calculate my own gas mix.

 

[Rec Diver]

Increasing oxygen percent in mix does not decrease narcosis. Quite the oposit. Oxygen has higher narcotic potential then nitrogen, meaning 28% is probably more (or at least as same as) narcotic at given depth then 21%. The only way to reduce narcosis is to replace nitrogen with helium.

The only way to reduce narcosis is to reduce the amount of nitrogen. Trimix makes up for this reduction in nitrogen by adding helium to the mix. However, the first dive was done on air, 21% oxygen, and the second was done on 28% oxygen. There was in fact a noticebale difference, less, of a narcotic effect of the nitrogen on the second dive for me and those in our party. Oxygen is claimed to have a higher narcotic effect than nitrogen, however, the effects of neither nitrogen or oxygen are truly understood as a narcotic.

 

[MonkSeal]

The only way to reduce narcosis is to reduce the amount of nitrogen.

No, the only way to reduce narcosis is to reduce the amount (percent) of narcotic gas in the mix. Beeing both (at least equaly) narcotic, changing oxygen and nitrogen ratio in mix (i.e. diving nitrox) nothing will be achieved regarding less narcosis.

Oxygen is claimed to have a higher narcotic effect than nitrogen, however, the effects of neither nitrogen or oxygen are truly understood as a narcotic.

Some things do not have to be truly understood, sometimes it's enough to be measurable.

 

[Rec Diver]

No, the only way to reduce narcosis is to reduce the amount (percent) of narcotic gas in the mix. Beeing both (at least equaly) narcotic, changing oxygen and nitrogen ratio in mix (i.e. diving nitrox) nothing will be achieved regarding less narcosis.

The narcotic effect in the gas is the nitrogen; hence the term narcosis. The reduction of nitrogen in a trimix mixture is the reason why trimix is becoming more popular. Lets take a look at Ric Inman's trimix mixture of 35/25. This mixture has 35% oxygen, 25% helium, and 40% nitrogen. This mix can be safely dove to 108' and will have the narcosis effect of a dive at lees than 40'. If what you say is true about the oxygen content having an equal narcotic effect, then why would you dive this mixture? According to what you have written the oxygen level should have Ric just a narcked as if he was using straight air. I think if you conatc Ric you will find that his narcosis level was none exsistent.

Some things do not have to be truly understood, sometimes it's enough to be measurable.

They do if you do not know what you are measuring.

 

[miketsp]

Increasing oxygen percent in mix does not decrease narcosis. Quite the oposit. Oxygen has higher narcotic potential then nitrogen, meaning 28% is probably more (or at least as same as) narcotic at given depth then 21%. The only way to reduce narcosis is to replace nitrogen with helium.

AFAIK this is a pretty dated opinion based on research back in the 80s & early 90s and all recent papers I have read indicate that O2 is NOT narcotic as it is metabolized too fast.

Edit:
So is oxygen narcosis fact or fiction? The scientific data available do NOT support the conclusion that oxygen is narcotic.
From
http://www.divermag.com/archives/dec96/divedoctor_Dec96.html

 

[MonkSeal]

The narcotic effect in the gas is the nitrogen; hence the term narcosis.

Not only.

Lets take a look at Ric Inman's trimix mixture of 35/25. This mixture has 35% oxygen, 25% helium, and 40% nitrogen. This mix can be safely dove to 108' and will have the narcosis effect of a dive at lees than 40'.

Having in mind that's deep deco mix it can be safely dove to 120'. At that depth it has narcotic effect of diving air at 80'.

If what you say is true about the oxygen content having an equal narcotic effect, then why would you dive this mixture?

It's not bottom mix it's deep deco mix. It's used for deco from depths when it gives better results in transition to EAN50 lowering nitrogen spike. BTW Bottom mix for depth 120' is 21/35.

They do if you do not know what you are measuring.

The level of narcosis is subjective feeling and it can be measured by comparing ones ability to perform certain tasks with and without narcotic influence.

 

[MonkSeal]

AFAIK this is a pretty dated opinion based on research back in the 80s & early 90s and all recent papers I have read indicate that O2 is NOT narcotic as it is metabolized too fast.

Edit:
So is oxygen narcosis fact or fiction? The scientific data available do NOT support the conclusion that oxygen is narcotic.
From
http://www.divermag.com/archives/dec96/divedoctor_Dec96.html

Oh, you quoted very recent research

 

[OWSI176288]

The narcotic effect in the gas is the nitrogen; hence the term narcosis. The reduction of nitrogen in a trimix mixture is the reason why trimix is becoming more popular. Lets take a look at Ric Inman's trimix mixture of 35/25. This mixture has 35% oxygen, 25% helium, and 40% nitrogen. This mix can be safely dove to 108' and will have the narcosis effect of a dive at lees than 40'. If what you say is true about the oxygen content having an equal narcotic effect, then why would you dive this mixture? According to what you have written the oxygen level should have Ric just a narcked as if he was using straight air.

Dude.....you have things way mixed up. The presence of helium in a trimix is the reason why it is less narcotic. This is why END calculations only use the Helium concentration and do not include the O2 concentration.

(1) Counting on Nitrox to reduce narcosis is not a good idea IMHO

(2) The term "narcosis" is derived from the word "narcotic and is defined as the unconsciousness induced by a narcotic drug. It is no way derived fron the word "Nitorgen."

(3) Oxygen is just as narcodic as nitrogen. I've felt sudden narcosis from switching from Trimix to an EAN deco. This is also one reason (of several) why I put some He in my deep deco mix. 21/35 for my 190 MOD bottle, and 35/25 in my 120 MOD bottle.

(4) 21/35 mix has an MOD of 185 ft (1.4 pO2 ata) and would have an END of ~110. I usually limit 21/35 to 165 ft so my END <100 ft.