Nitrox Question

[vladimir]

I use the Suunto Cobra and the Sunnto Gekko wrist, when my computer is set to 32% o2 it says I have MOD of 127 with the po2 of 1.6. My SSI dive tables say the MOD for 32% is 135 with a po2 of 1.6. I know its just a few feet but I want to know what I can really do safely. Can I go to 130 or not. If I do what will my computers do at that depth.

The risk of a brief incursion beyond your MOD is minimal. There seems to be widespread agreement that a maximum PO2 of 1.4 is prudent. It used to be 1.6. The shift was not accompanied by a rash of ox-tox cases. You will have to decide what level of risk is appropriate for you--if you are comfortable with the risk at 127', there is nothing dramatically different about 137'; there is no MOD Rubicon, it's more of a continuum.

 

[DiveNav]

The risk of a brief incursion beyond your MOD is minimal..........

It depends ..... how long and how far .....

.....there is no MOD Rubicon, it's more of a continuum....

I agree on that.
According to NOAA table

You could stay several minutes with a ppO2 of 1.6ATA .... before CNS kills you ..... but you should also keep in mind the O2 you have accumulated in previous dives.

Also, if by mistake you go over 1.6ATA, those "several minutes" become very very short. :shocked2:

Bottom line? Dive conservative and stick to 1.4ATA

Alberto (aka eDiver)

 

[vladimir]

Bottom line? Dive conservative and stick to 1.4ATA

Or 1.3. To be really safe, stick to 1.3. Wait, why not 1.2? That would be really safe. If 1.3 is safe, 1.2 is really safe. New guideline guys: 1.2. Why take unnecessary risks?

 

[DiveNav]

....Why take unnecessary risks?

stay in bed

 

[seaworm]

at 1.6 is pushing it what ever happens stay at 1.4!!!!!!!!!!

 

[vladimir]

what ever happens stay at 1.4!!!!!!!!!!

That's going to pose a problem for the ascent, unless you're a seasoned diver.

Nine exclamation points--that's pretty emphatic. What do you base your conviction that 1.6 is "pushing it" on? Is there data to support it? A statistically significant number of ox-tox cases at, say, 1.7? I have no doubt that 1.6 is riskier than 1.4, but why is one "unsafe" and the other "safe"?

 

[ajduplessis]

vladimir: It is about being safe. People react differently to CNS and PO2 related conditions. There is no stats or data pointing to a “magical number”. The message here is to stay safe as you already highlighted. It is the little things that put you in danger. The difference between 127 and 137 is little, but could have a big impact on you as a diver.

It is brief incursions beyond the dive plan/tables/dive computers that gets divers into trouble.

 

[H2O 70]

The risk of a brief incursion beyond your MOD is minimal. There seems to be widespread agreement that a maximum PO2 of 1.4 is prudent. It used to be 1.6. The shift was not accompanied by a rash of ox-tox cases. You will have to decide what level of risk is appropriate for you--if you are comfortable with the risk at 127', there is nothing dramatically different about 137'; there is no MOD Rubicon, it's more of a continuum.

My understanding of 1.6 vs. 1.4 was that 1.6 was what the Navy had settled upon and their basis was on their soldiers, who tended to me younger and in better shape than most recreational divers. NOAA, whose divers tended to be more like recreational divers, thought it was be better to not push the envelope and settled upon the more conservative 1.4 ppO₂.

I thought the current research out there could make no positive correlation to age, fitness and oxtox except to stay in the conservative 1.4-1.2 ppO₂ and the incidences of oxtox became nil and there is where we came up with the current 1.6 for deco and 1.4 for working.

 

[DiveNav]

That's going to pose a problem for the ascent, unless you're a seasoned diver.

THAT was hilarious

 

[Van Isle]

Just to clarify for the OP:

From Lang, M.A. (ed.). 2001. Proceedings of the DANNitrox Workshop, November 3-4, 2000.
Divers Alert Network, Durham, NC. 197 p.

"The conclusion then is that there are no documented oxygen seizures
from recreational nitrox diving at 1.6 atm or less on single exposures."

Time at exposure is a contributing factor to cases where oxygen toxicity has occurred. Hard work, CO2 retention, large amounts of Advil, pseudoephedrine ("Sudafed"), and prescription drugs also may have had an effect in reported toxicity cases.

Summary: if you reach 1.6 PPO2 you will not die, spontaneously combust, or otherwise be injured under safe, normal, recreational diving circumstances. Oxtox risk decreases as PPO2 decreases as N2 exposure and DCS risk increases. That's why there's special training!

Recommendation: Given the amount that I can sometimes dive, the cold water in which I dive, and my overall level of conservatism, I would not plan a bottom of 130' on 32% EAN. In a "contingency" I would without hesitation dive to 130' on 32% EAN. YMMV.

VI