Nitrox question?

[TMHeimer]

13:1.....? But the rest of the statement is obvious and the same for DCS. Tissues (density, etc.) vary from person to person. The condition of these tissues varies in the same person day to day (your tired, sick, hungover, etc.).

 

[Rich Keller]

From my book:

"In terms of susceptibility to O2 toxicity, the actual variation among individuals, or from one day to the next, may be as great as 13:1."

What does it mean?

TIA

What they are saying is that everyone reacts differently to oxygen toxicity just like people react differently to nitrogen narcoses and the bends. The closer you push to the oxygen tolerance limits the more these differences come into play. One of the basic tests for someone to qualify to be a navy or commercial diver is an oxygen tolerance test to weed out those who are more susceptible to oxygen toxicity. I have no idea why the sport diving industry does not do this other then if you fail the test they can not sell you nitrox equipment. I have no idea what the 13 to1 refers to.

 

[jar546]

I always thought it was 14:1

 

[diverrex]

I always thought it was 14:1

It's actually 14.28653:1

 

[agilis]

Thirteen to one is a huge, enormous ratio for something of this nature, whatever it is they are measuring. The lack of any kind of explanation makes the numbers meaningless.

I think most divers understand that there is a very wide range of susceptibility to DCS and O2 toxicity, a substantial variability among people and for each individual depending on all kinds things, most of which can't be predicted or measured with any accuracy. That's why 'pushing the tables' has always been a very bad thing to do.

I'm not sure how many people still use the tables, but even those trusting souls who think a battery powered device is an infallible authority probably know that you should never approach the limits set by a computer. Extra safety stop time and other hedges are, I hope, seen as an absolute necessity. Of course, there is no shortage of fools in evey kind of activity.

There are also different algorithms used by computer manufacturers, so a substantial safety buffer is set by any sane diver, except in emergency situations. But thirteen to one? Maybe somebody forgot a decimal, misplacing it along with the name(s) of what was being measured.

 

[Rich Keller]

SSI's EAN Chapter 2 page 14

Here's the whole paragraph:

"In terms of susceptibility to O2 toxicity, the actual variation among individuals, or from one day to the next, may be as great as 13:1. Fortunately, NOAA's working-diver limits are conservative and - while they cannot guarantee 100 percent safety - they nonetheless substantially increase one's safety margin."

Could they be saying that 1 in 13 people do not have what would be considered normal oxygen tolerance?

 

[Bob DBF]

Ya got to love out of context numbers.

I could see an experiment using a set ppo (2?) for a set time with a group of subjects tested over several days. If the avrage was 1 hit out of 13 (or 12.blablabla) and there was no predicting who would take the hit, someone might express it this way.

Authors sometimes forget their readers may not have access to all their research when they drop in a fact that makes no sense without the background material. I say we track him down, I've got the feathers if anyone can find the tar and a rail.



Bob
------------------------------
I may be old, but I’m not dead yet.

 

[Rich Keller]

Ya got to love out of context numbers.

I could see an experiment using a set ppo (2?) for a set time with a group of subjects tested over several days. If the avrage was 1 hit out of 13 (or 12.blablabla) and there was no predicting who would take the hit, someone might express it this way.

Authors sometimes forget their readers may not have access to all their research when they drop in a fact that makes no sense without the background material. I say we track him down, I've got the feathers if anyone can find the tar and a rail.



Bob
------------------------------
I may be old, but I’m not dead yet.

I could see it if this was coming from a research paper but this came out of some sort of SSI training manual. People should be able to understand what they are saying. This looks more like some lawyer wrote the thing.

 

[Tigerman]

Training manuals tends to come out of research though...

I love the tar idea tho, if not for anything else, nothing beats a good mob (as long as youre part of it)