Common reasons for diving nitrox

[BHB ScubaTroll]

I just re-read the PADI Enriched Air Diver manual and it says nothing about a one hour minimum SI however all of the examples do use a one or two hour SI.

If you use the RGBM (Reduced Gradient Bubble Model) Tables there is a one hour minimum SI. These are "no calculation tables". But these were produced by NAUI and require one to follow certain rules:

• Minimum SI of one hour is required between dives
• If the actual dive depth is not listed, select the next greater depth
• The depth of each repetitive dive must be no greater than the depth shown on the row immediately to the right of the previous dive's depth, but can be shallower than the depth listed
• As the tables are designed, there can be no shallow dive followed by a deeper dive
• The maximum ascent rate is 9 meters (30 feet) per min.
• All dives require a 3-minute safety stop at 5 meters (+- 1 meter)/15 foot (+- 3 feet)
• On the sea level to 610 meters (2000 feet) tables, no more than three repetitive dives within a 12-hour period. In actual practice, the "third dive" may be a series of repetitive dives not exceeding the total maximum dive time of 150 minutes

The flying after diving rule is to wait at least 12 hours after a single dive within the prior 18-hour period, 15 hours after two dives, and 18 hours after 3 dives

In most cases, I find the RGBM too limiting (and too darned stupid) to use. But, this is where I believe some have determined the 1-hour SI from.

If this model was brought up in class, it could be what you remembered about a hon hour SI

 

[Tienuts]

In other words, sub-clinical bends make you tired. Nitrox means less N2 take up and thus lower incidence of sub-clinical bends - hence nitrox makes you less tired (if you regularly practice poor ascents).

This may be true if you dive Nitrox on air tables, however nitrox tables are adjusted based on nitrogen loading. You will end up with a similar amount of N2 in your system, because you have been down for a longer amount of time.

That being said, you are correct, the lethargy is caused by sub-clinical bends. This depends on your N2 loading of your respective tissue compartments. On deeper dives, your quick tissue compartmnents fill up quickly. Even a dive for just a few minutes at a deeper depth will cause microbuble formtion with a quick ascent and hence - lethargy.

O2 is narcotic in the sense that it affects you ability to think clearly just as much as N2 does.

Where is there litarature/studies supporting this? If O2 had such narcotic properties, why would deep divers try to keep their PO2's up around 1.2?

Narcosis starts from 1m - it's just not generally noticable until 20m or so and, for most people, not problematic until deeper.

Show me who gets the onset of narcosis symptoms at 20 meters. The earliest I have seen or heard of the onset narcosis is around 85 feet, or 28m for you.

 

[Freds@Aquanauts]

Show me who gets the onset of narcosis symptoms at 20 meters. The earliest I have seen or heard of the onset narcosis is around 85 feet, or 28m for you.

Well the all singing all dancing PADI manuals say it can happen anywhere after 18m or 60.2ft...So it must be true right???

But in all seriousness my badass buddy got narced at 22m, and i know a techie who had a customer who kept sending her reg in for repair because whenever she past 20m she said she started getting water in her mouth, in the end he went down with her, and all that was the matter was just after she hit 20m she started to smile...


Freds

 

[BarryNL]

Where is there litarature/studies supporting this? If O2 had such narcotic properties, why would deep divers try to keep their PO2's up around 1.2?

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=734806&dopt=Abstract

Show me who gets the onset of narcosis symptoms at 20 meters. The earliest I have seen or heard of the onset narcosis is around 85 feet, or 28m for you.

I can point to a number of divers I know, but I'll stick to pointing out that PADI standards (I don't know who you instruct for) teach the effects of N2 narcosis at often less than 25m on the AOW deep dive. Why would they do that if narcosis does not occur there?? I don't have the instructor manual but, I believe, I've heard narcosis only needs to be demonstrated at 18m+.

 

[jtivat]

There is a very good reason for having a one hour interval, which is that the brain and spinal tissues are "medium" tissues and usually modelled with a 12.5 minute half-time, which means that after a 1 hour interval these tissues are about 96% off-gassed. Considering these tissues cause some of the biggest problems if "bent" then off-gassing them almost completely between dives is a good idea.

It has nothing to do with nitrox though...

More info: http://www.diversalertnetwork.org/news/article.asp?newsid=514

I am not say you should not get an hour SI I am just pointing out that the PADI course dose not say this a requirement of Nitrox.

 

[Tienuts]

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=734806&dopt=Abstract

Barry thanks for the article, but it clearly says the decrement in mental function occured at a partial pressure of 1.65 or higher. The maximum partial pressure of O2 on enriched air dives is 1.4 to 1.6.

I can point to a number of divers I know, but I'll stick to pointing out that PADI standards (I don't know who you instruct for) teach the effects of N2 narcosis at often less than 25m on the AOW deep dive. Why would they do that if narcosis does not occur there?? I don't have the instructor manual but, I believe, I've heard narcosis only needs to be demonstrated at 18m+.

Nitrogen/oxygen have about same solubility - are somewhat narcotic at the deeper range of recreational diving. Using air or enriched air, narcosis is expected to be noticeable at about 30 metres/100 feet. - Cut and pasted right from the PADI instructor manual.

When breathing air, impairment due to narcosis starts at depths of about 30 metres/100 feet, or a nitrogen partial pressure of 3.2 bar. At depths of 90 metres/300 feet, or nitrogen partial pressure of 8 bar nitrogen narcosis leads to hallucinations and unconsciousness. - From the encyclopedia of recreational diving.

 

[Freds@Aquanauts]

Nitrogen/oxygen have about same solubility - are somewhat narcotic at the deeper range of recreational diving. Using air or enriched air, narcosis is expected to be noticeable at about 30 metres/100 feet. - Cut and pasted right from the PADI instructor manual.

Begging your pardon dude I went and checked when i went to bed and your right...Long day!!Whats 12m amongst friends??Oooh quite alot actually - my bad!


Freds

 

[BarryNL]

Nitrogen/oxygen have about same solubility - are somewhat narcotic at the deeper range of recreational diving. Using air or enriched air, narcosis is expected to be noticeable at about 30 metres/100 feet. - Cut and pasted right from the PADI instructor manual.

When breathing air, impairment due to narcosis starts at depths of about 30 metres/100 feet, or a nitrogen partial pressure of 3.2 bar. At depths of 90 metres/300 feet, or nitrogen partial pressure of 8 bar nitrogen narcosis leads to hallucinations and unconsciousness. - From the encyclopedia of recreational diving.

As I say, someone might want to ask PADI what, if this is their real opinion, the hell they think they're playing at with the AOW course. Why are they demonstrating narcosis to students at depths where narcosis, according to them, does not occur?

However, I suspect what PADI are saying here is actually that narcosis becomes problematic from about 30m - not that the first symptoms start there.

 

[laserdoc]

During my AOW course we went down 98 feet. Never felt a thing

 

[Toolbox-13]

Think you should have added one more option on the poll
All of the above...