Nitrox on boat with air refill

[stuartv]

Your comment is proof of my post. Who does 5 hours at depth on one day. Not the average joe recreational diver.

5 hours in a 24 hour period? From some of my friends that have done a lot of liveaboards, that doesn't sound that unusual at all. But, I do realize that is an "I heard from a friend" type of statement.

 

[scubadada]

Your comment is proof of my post. Who does 5 hours at depth on one day. Not the average joe recreational diver.

It's not proof of anything other than your diving habits. I do it routinely, many other is SE FL do too. Sorry your opportunities are so limited.

---------- Post added November 18th, 2015 at 04:28 PM ----------

5 hours in a 24 hour period? From some of my friends that have done a lot of liveaboards, that doesn't sound that unusual at all. But, I do realize that is an "I heard from a friend" type of statement.

Hi Stuart, I have disagreed with some of your posts, but not this one, you are right on. In SE FL, I often do 4 dives per day for several days running, it's not that unusual

 

[packrat12]

In SE FL, I often do 4 dives per day for several days running, it's not that unusual

I would call you an unusual diver, even in SE FL. Most divers I see down there get a couple of dives a day for a couple of days at best. You are definitely a hardcore diver. As a result, you do enter the realm where CNS/OTU matters. Most recreational divers are really just occasional tourists. You are not.

 

[Doppler]

I was reading Staying Alive, a most excellent book by Steve Lewis, today at lunch and I was reminded of this thread. From the book:



Steve Lewis is also a SB member, I believe. Shame he hasn't chimed in here.

Well, I was away diving... and boy, this thread has made some interesting twists and turns hasn't it.

A suggestion to those who are truly interested in this topic.

Foremost is to go to the 'font of all knowledge:' the NOAA Diving Manual. It will clearly explain the difference between CNS single dive limits, CNS daily or 24-hour limits, and OTUs, which are used to determine the statistical likelihood of a diver developing whole body or pulmonary toxicity... something very different to Central Nervous System toxicity.

The original NOAA manual made no mention of CNS toxicity having a half-like with the exception of exposures to oxygen partial pressures of 1.6 bar... AND ONLY THOSE. The new manual mentions that technical divers do use the half-life concept in their calculations. I tend to agree with Bill Hamilton when he suggested that practice was bull****.

There is a better, and perhaps more conservative method, one that is also backed up by some degree of science. And that is to use the 24-hour limits to calculate one's exposure to CNS oxygen stress.

And while impractical to suggest that a recreational/sport diver staying within NOAA's prescribed single-dive limits has an opportunity to exceed suggested oxygen times, it is possible for recreational/sport divers to approach and perhaps to exceed NOAA's daily/24-hour limits under certain conditions.

 

[Lorenzoid]

. . . It will clearly explain the difference between CNS single dive limits, CNS daily or 24-hour limits, and OTUs, which are used to determine the statistical likelihood of a diver developing whole body or pulmonary toxicity... something very different to Central Nervous System toxicity. . . .

Does the "or" between "whole body" and "pulmonary" mean that these terms are synonymous? Some things I have read seem to imply they are synonymous or at least conflate them.

I have read your blog post on this, referring to the NOAA tables. I'm still confused as to whether there are TWO types of oxygen exposure to consider or THREE types of oxygen exposure to consider.

 

[Centrals]

5 hours in a 24 hour period? From some of my friends that have done a lot of liveaboards, that doesn't sound that unusual at all. But, I do realize that is an "I heard from a friend" type of statement.

Done it plenty of times when I was slightly younger than 55. CNS toxicity and NDL were never an issue because I dived conservatively.

 

[NAM001]

Could it be that you are not the average diver, unless average is defined by YOUR diveing habits. The knife cuts both ways. And of course those I dive with can do 5 hours a day also but not at the depth that is the problem issue with cns and otu's as it is a combined result.

It's not proof of anything other than your diving habits. I do it routinely, many other is SE FL do too. Sorry your opportunities are so limited.

---------- Post added November 18th, 2015 at 04:28 PM ----------



Hi Stuart, I have disagreed with some of your posts, but not this one, you are right on. In SE FL, I often do 4 dives per day for several days running, it's not that unusual

 

[tursiops]

Scubadada, can you explain further? To get in 5h at PPO2=1.0 requires (using 32% for an example) (say) 70 ft for 60 mins....5 times. But to get an NDL of 60 mins requires a 6h surface interval. How do I fit all that bottom time and surface interval into 24h? I understand this stuff pretty well...I'm just looking for a concrete example.

 

[NAM001]

Lets hear from someone that dives 5 hours a day on 40% at 85' or 32% at 120 feet or 36% at 100. I doubt there are many if any. Any one can dive 32% at 40-50 ft and dive all day on it. If you are doing the first then you are not the normal rec diver. I will say that the dives I do that fall into the category of 5 dives a day have been flower gardens and that those dives are air dives. Those dives do not count for this conversation. I also realize that there are boats that do 4-6 dives a day on nitrox and that those dives are often very shallow dives 30-50 ft. Hence the ability to do that many dives a day. And also to add to this fire. It would be interesting to find those that dive that many dives a day,, day after day. Once again if there are those , they are not normal rec divers. which has to be considered when discussing what is and is not possible or should I say probable.

---------- Post added November 18th, 2015 at 07:26 PM ----------

I don't doubt that. I was with a shop that was considering doing a flower gardens trip on nitrox. Who ever did the work suspected that the 5 dive a day would have to be reduced to 3 or 4 dives a day, or change sites enough to provide shallower dives to prevent exceeding limits. The other option was to look at using lower content nitrox to maintain the 5 dives a day. The water depth at the gardens ranges from 65 to maybe 95'.

5 hours in a 24 hour period? From some of my friends that have done a lot of liveaboards, that doesn't sound that unusual at all. But, I do realize that is an "I heard from a friend" type of statement.

---------- Post added November 18th, 2015 at 11:26 PM ----------

I have some charts in front of me. This indicates to me that these 5 dives will max you out daily limit. This was done in a rush so there may be some errors. I hope I kept my tables straight. What is ironic is that most will say that nitrox may/most likely not be used at these depths. some of these dives pushed the NDL limit.
I am going to the 5 dives for 1 hour each day claim
I will assume 32% nitrox and 1 hour surface intervals
O2 factors figured at diver depth
NdL based on EAD

I will do the deepest depth for an Assumed 1 hour NDL per dive.
I know there are many other ways to do it but I choose this method.

1^st diveead 60 ftndl 55 minactual depth 75’apx 3.3 atmppo21.1
Cns 25otu70
1 hr si

Dive 2 45 ft eadactual depth 56 ftndl avalilable 89minapx 2.8PPO2 1.0
Cns 18out 55
Si 1 hr


Dive 3 45 ft eadactual depth 56 ftndl avalilable 92minapx 2.8PPO2 .9
Cns 18otu 55
Si 1 hr

Dive 4 50 ft eadactual depth 69 ftndl avalilable 55minapx 3.1PPO2 1.0
Cns 20otu 60
Si 1 hr

Dive 4 40 ft eadactual depth 51 ftndl avalilable 90minapx 2.7PPO2 .9
Cns 17otu 50

Daily totals cns=98%otu=290

Otu’s allowed per dive240-360.......daily limitavg based on ppo2 of 1.0 is 300.

 

[Doppler]

Does the "or" between "whole body" and "pulmonary" mean that these terms are synonymous? Some things I have read seem to imply they are synonymous or at least conflate them.

I have read your blog post on this, referring to the NOAA tables. I'm still confused as to whether there are TWO types of oxygen exposure to consider or THREE types of oxygen exposure to consider.

Whole body and Pulmonary are terms describing the same syndrome.

https://www.tdisdi.com/pulminary-oxygen-toxicity-with-technical-divers/


That said, I would suggest that as lay-persons and divers, we consider THREE branches of oxygen poisoning... the third being something only described by CCR divers to my knowledge (explanation below cribbed from Wikipedia):

The effects of oxygen toxicity may be classified by the organs affected, producing three principal forms:^[2][3][4]

• Central nervous system, characterised by convulsions followed by unconsciousness, occurring under hyperbaric conditions;
• Pulmonary (lungs), characterised by difficulty in breathing and pain within the chest, occurring when breathing increased pressures of oxygen for extended periods;
• Ocular (retinopathic conditions), characterised by alterations to the eyes, occurring when breathing increased pressures of oxygen for extended periods.