Another (legit) nitrox ?

[ekewaka]

And those that post that diving Nitrox on an air table or computer is safer, does anyone have any facts about that statement. I don't need opinions, I'm looking for some properly documented studies that actually have proven the stated increase of safety.Do these exist??

That would depend on what you are comparing it to. If you are asking whether diving nitrox with air tables is safer than staying on the boat, then the answer is probably no. If you are asking whether diving nitrox with air tables is safer than diving some other gas with some other tables, then we need to know what gas and what tables before the question can be answered.

 

[Michael Schlink]

What NET DOC said, the op wants to know if he's(or she's) going to load up on the "pulmonary" side of the problem, which requires a bit of time and pressure. CNS does require the same just in reverse, higher pressures and a little bit of time can have you doing the U/W jitterbug in a few minutes. My opinion for whatever thats worth is that in typical recreational diving OTU's aren't a big concern, I'm not saying NO concern because it can crop up just not that often. MOD is a whole 'nother ball game.
If I were King I'd have everybody diving 32 right out of their first OW course.

 

[Michael Schlink]

ekewaka, I think my question was rather clear. Many say that diving Nitrox on an air table or puter makes them safer as in less likely to get hit, because of the THEORETICAL less N2 loading. Which imho hasn't been proven or documented hence when I teach Nitrox I say the best reason to dive Nitrox is longer BT's and shorter SI's and that it isn't safer. To go one step further I wouldn't ever dive Nitrox on an air table, I set my puter to the mix and go diving, I use the computer as it was designed, I take advantage of the longer BT's provided by BOTH "multi level tracking" and the Nitrox benefit. My dive lasts longer than had I started the dive with air and a linear table, call me crazy

 

[raymond phule]

CNS does require the same just in reverse, higher pressures and a little bit of time can have you doing the U/W jitterbug in a few minutes.

My understanding is as follows. It is taken from the link above and for example the gue tech compendium.

1. We have a problem if we dive at a very high ppO2. This result in CNS problems and is very dangerous. It can happen pretty fast when it happen and it can happen on a single dive. A safe ppO2 is considered to be 1.4 and is used as a rule for many agancies. Over 1.6 is very dangerous. We use MOD to avoid this.

2. We can also have problems with CNS due to high ppO2 (under 1.4) over a longer time. This is also very dangerous but it doesn't happen if you dont dive for a long time. CNS % and the daily NOAA limits is used to track this. Many posts in this thread seems to be about this.

3. You could get full body or pulmonary problems if you dive with high ppO2 over a long time. This is not that dangerous as the ones above and it also takes a lot of diving over several days to get problems. OTU is used to track this.

I got the impression that you kind of ignore the #2 problem . I believe Steve and most other people here talk about #2 problem.
edit:changed toxity to problem to try to clearer. edit once again. I am really sorry that I used the word toxity instead of problem before. I am sorry if anyone have been confused by my incorrect use of the term. Sorry. CNS toxity due to breaking the mod rule and cns % are actually the same.

We also have a problem with different names on things.

 

[Steve SDI/TDI HQ]

I believe Steve and most other people here talk about #2 toxity.

We also have a problem with different names on things.

No, I am talking about NOAA's 24 hour CNS toxicity limits... the naming conventions are pretty much set... You are confused and need to reevaluate the terms you use and what they describe.... for example: what's with this #1 and #2 toxicity.

Refer to them by the terms that have become accepted in the diving community: Central Nervous System and Pulmonary

Pulmonary toxicity is long-term low dose and is not an issue for OC recreational divers at all, even those conducting advanced trimix dives. CCR divers may need to be more cautious.

CNS toxicity IS AN ISSUE with all levels of nitrox diving and deep air diving. CNS limits published by NOAA (upon whose findings and limits ALL recreational nitrox tables are based as far as I know) have two distinct categories: single exposure and 24-hour exposure. These exposures -- doses -- are a function of oxygen depth and time.

The concerns expressed here are that many nitrox divers -- a statement that seems to be validated by the postings here -- do not fully understand the implications of the 24-hour limits on their nitrox diving.

 

[optimator]

To answer the Ops question let’s create a dive plan. Let’s make the limiting factor in the dive plan OTU exposure. Let’s use some actual tables.

So the first question to answer is what is OTU exposure and what is the maximum daily OTU exposure.

An OTU is defined as 1 minute of breathing pure oxygen at 1 ATM.

The next question we must answer is how many OTU's can a person be exposed to in 1 day. In 1989 Dr. Bill Hamilton came out with the REPEX method specifying OTU's for multi-day exposure. However, since we’re recreationally diving let’s use the more conservative DSAT tables.

Using EAN36 the MOD is 90 fsw.

Using the DSAT Air tables the NDL for 90 fsw is 24 minutes

The maximum OTU exposure at 1.4 ATM is 150 minutes.

150 max OTU exposure per day / 24 minutes per dive = 6.25 dives. Or 6 dives on EAN36 at MOD using air tables to reach your daily oxygen toxicity limit.

If the OP wanted to dive the EAN36 table the NDL is 35 minutes at 90 fsw.

150 max OTU exposure per day / 35 minutes per dive = 4.28 dives. Or 4 dives on EAN36 at MOD using EAN36 tables to reach your daily oxygen toxicity limit.

 

[laughingman]

Many computers can be set for more conservative diving. If you use those settings then you can still use the correct nitrox settings and know the computer is adjusting the tables correctly to give you the additional safety your looking for. Check your computer user's manual.

 

[raymond phule]

No, I am talking about NOAA's 24 hour CNS toxicity limits... the naming conventions are pretty much set... You are confused and need to reevaluate the terms you use and what they describe.... for example: what's with this #1 and #2 toxicity.

Cant you try to read the whole post before quoting one sentence? I explained what I meant with those numbers. I also tried to be extremely clear about different problems because people seems to use different words and different meanings. I have also given references to one internet page and a training manual. So why do I seem to be confused? I have used almost the same names as you have in all my posts. I haven't used pulmonary but used OTU toxity in stead.

CNS toxicity IS AN ISSUE with all levels of nitrox diving and deep air diving. CNS limits published by NOAA (upon whose findings and limits ALL recreational nitrox tables are based as far as I know) have two distinct categories: single exposure and 24-hour exposure.

And this should clear up things? So CNS toxity in recretional NDL air diving is an issue? Do many people make NDL dives to 56 m? Is it possibly to make enough NDL dives on air over a 24 hour period to come close to the NOAA limits?

 

[ianr33]

My understanding is as follows. It is taken from the link above and for example the gue tech compendium.

1. We have a problem if we dive at a very high ppO2. This result in CNS problems and is very dangerous. It can happen pretty fast when it happen and it can happen on a single dive. A safe ppO2 is considered to be 1.4 and is used as a rule for many agancies. Over 1.6 is very dangerous. We use MOD to avoid this.

2. We can also have problems with CNS due to high ppO2 (under 1.4) over a longer time. This is also very dangerous but it doesn't happen if you dont dive for a long time. CNS % and the daily NOAA limits is used to track this. Many posts in this thread seems to be about this.

Your #1 and #2 are the same thing (CNS toxicity)

1.4 is only "safe" if kept within the time (dose) limits

1.6+ is only dangerous if the time(dose) is exceeded. Problem is that the time allowed is rather small and unpredictable.

1 minute at pO2 of 1.7 would not be dangerous (assuming you were not high on your CNS clock when you did it)
5 continuous hours at pO2 of 1.4 would be extremely dangerous.

Nothing magical about 1.4 and 1.6. Just sensible numbers to draw some guidelines at.

 

[raymond phule]

Your #1 and #2 are the same thing (CNS toxicity)

Agree but we still "solve" the problem in different ways. We set a mod (ppO2) and we calculate the total CNS %.

1.6+ is only dangerous if the time(dose) is exceeded. Problem is that the time allowed is rather small and unpredictable.

Yes, and it seems like it is very unpredictable. It is not safe to make any rules on something very unpredictable.