Oxygen Toxicity risk with Nitrox?

[Eric802]

The materials consistently referred to1.6. I thought that odd enough that I mentioned it to the instructor during the classroom portion. I’ll see if I can access the materials tomorrow.

 

[tursiops]

The materials refer to 1.6 as the maximum, and 1.4 as what expereinced dives use...the "normal' operating depth as opposed to the maximum operating depth.

 

[MrVegas]

I have only been an avid ScubaBoard participant since 2004. I don't recall any during that period. Perhaps you could link to one.

That would be very surprising. Can you find a direct quotation?

It's been years since I read the book. I don't recall anything like that, but my memory is far from perfect. Perhaps you could find a quote on that for me? (I could try to contact Bernie to see if he remembers writing about it, but I really don't want to bother him.)

This thread contains references (though no specifics) to people dying at 1.4 and 1.3 (though cave diving, so maybe not directly on point): PO2 Max - Why 1.4/1.6? I think that is what I was remembering, but I guess you're right, not really standard NDL recreational diving. (I think there were some other threads mentioning incidents too -- but again, possibly technical diving and/or rebreathers.)

The "Last Dive" reference was to a specific diver -- see page 242 of the hardcover copy. According to the book, that diver regularly dived with a higher percentage of oxygen in his breathing gas than the Navy considered safe. The next page says he was found dead at 135 feet with 39%. The book guesses the probable cause of death as oxygen toxicity. (I did like the book and would recommend it.)

I cannot find my SDI materials right now, so I will have to get back to you on that one.

 

[Eric802]

The following are all from the TDI/SDI Computer Nitrox course materials. They continually reference a MOD of 130ft for EAN32, which is PPO2 of 1.6.

“You may find that the simplest and most versatile Nitrox mixture to use is one with an MOD that works with the sort of dive you regularly do, for example an EAN32 has an MOD of about 40 m/130 ft and therefore is an excellent choice as a common mix for deeper dives within the sport-diving limits.”

“For example, if using a Limiting PO2 value of 1.6:

• The MOD for EAN36 is 34 m/113 ft.
• The MOD for EAN38 is 32 m/105 ftt.
• The MOD for EAN40 is 30 m/99 ft.”

“For sport diving purposes, we can use EAN32 down to 40 m/132 ft where the pressure of the oxygen in the mixture is equal to 1.6 atmospheres.”

“To get the maximum depth capability from EAN32 you need to program your computer for a partial pressure of oxygen of 1.6. If you want to be more conservative, you can set your dive computer for a PO2 of 1.5 or 1.4.”

• “What partial pressure of oxygen is right for your conditions? Many experienced Nitrox divers use a PO2 of 1.6 in warm, calm water but reduce the PO2 to 1.4 in colder more challenging conditions.”

So yes, they do refer to different values for use in more challenging conditions or for more conservatism, but the “default” in the materials is 1.6.

 

[Kimela]

I'm sorry if this was addressed in the last 9 pages but ... a friend was saying they choose not to dive nitrox in Cozumel because of the occasional down-current that can happen unpredictably and spit you out at 140 ft or so. If this were to happen, what is the most likely outcome - assuming I'm healthy, have at least half a tank of gas, and am able to get free of the down-current to do my safety stop (and deco obligation if I incur one)? Is this a guaranteed DCS hit? Are the symptoms and treatment similar to a DCS hit? We generally stay on top of the reef - occasionally go out to a wall, but not very often at all - so I'm thinking we aren't likely to hit a down-current but I could be wrong in my assessment and need to be prepared.

I picked this up from a website (liquisearch) but wanted to know if anyone has first or second-hand experience with oxygen toxicity.

"Divers trained to use nitrox may memorise the acronym VENTID-C or sometimes ConVENTID, (which stands for Vision (blurriness), Ears (ringing sound), Nausea, Twitching, Irritability, Dizziness, and Convulsions). However, evidence from non-fatal oxygen convulsions indicates that most convulsions are not preceded by any warning symptoms at all. Further, many of the suggested warning signs are also symptoms of nitrogen narcosis, and so may lead to misdiagnosis by a diver. A solution to either is to ascend to a shallower depth."

 

[boulderjohn]

I'm sorry if this was addressed in the last 9 pages but ... a friend was saying they choose not to dive nitrox in Cozumel because of the occasional down-current that can happen unpredictably and spit you out at 140 ft or so. If this were to happen, what is the most likely outcome - assuming I'm healthy, have at least half a tank of gas, and am able to get free of the down-current to do my safety stop (and deco obligation if I incur one)? Is this a guaranteed DCS hit? Are the symptoms and treatment similar to a DCS hit? We generally stay on top of the reef - occasionally go out to a wall, but not very often at all - so I'm thinking we aren't likely to hit a down-current but I could be wrong in my assessment and need to be prepared.

I picked this up from a website (liquisearch) but wanted to know if anyone has first or second-hand experience with oxygen toxicity.

"Divers trained to use nitrox may memorise the acronym VENTID-C or sometimes ConVENTID, (which stands for Vision (blurriness), Ears (ringing sound), Nausea, Twitching, Irritability, Dizziness, and Convulsions). However, evidence from non-fatal oxygen convulsions indicates that most convulsions are not preceded by any warning symptoms at all. Further, many of the suggested warning signs are also symptoms of nitrogen narcosis, and so may lead to misdiagnosis by a diver. A solution to either is to ascend to a shallower depth."

Yes, you can get down currents in Cozumel, but they are rarely as bad as people think, and I think the myth of the Scuba Mau situation years ago might still be influencing thinking. I do know of some serious whirlpool effects that people don't want to talk about that were quite powerful, but in most cases, down currents can be handled easily by a competent diver.

So what if the worst case scenario you described happens? You wrote about a fear of a "down-current that can happen unpredictably and spit you out at 140 ft or so." You did not read the thread, but I suggest you do. In it you will find my comments on this sort of thing. With nitrox, there is, first of all, a pretty good safety margin in the standards. Second of all, problems don't happen seconds after exceeding MOD--there is a significant time factor involved with even some fairly major violations. If I were breathing 32% and hit a down current that took me to 140 feet before I was in control again, I would make a leisurely ascent without the slightest concern about oxygen toxicity.

 

[Cthippo]

I'm sorry if this was addressed in the last 9 pages but ... a friend was saying they choose not to dive nitrox in Cozumel because of the occasional down-current that can happen unpredictably and spit you out at 140 ft or so. If this were to happen, what is the most likely outcome - assuming I'm healthy, have at least half a tank of gas, and am able to get free of the down-current to do my safety stop (and deco obligation if I incur one)? Is this a guaranteed DCS hit? Are the symptoms and treatment similar to a DCS hit? We generally stay on top of the reef - occasionally go out to a wall, but not very often at all - so I'm thinking we aren't likely to hit a down-current but I could be wrong in my assessment and need to be prepared.

I'm a little out of my depth here (pun intended), but i can answer part of this. You are NOT guaranteed a DCS hit, especially if you come immediately back up and do whatever deco your computer recommends. A DCS hit occours when you come up too rapidly and so long as you have the gas to follopw your computer's deco plan, the risk of DCS in this scenario is very low.

What might kill you would be the oxygen toxicity, but I don't know how fast that comes on and if it can be avoided by getting off the elevator at 140 and immediately ascending above the MOD.

 

[boulderjohn]

The most serious case I know of in Cozumel came on Yucab Wall, and it happened to a friend of mine. They were near the end of the dive, and my friend and her spouse started to ascend a few minutes ahead of the rest of the group. Before they reached the surface, they found themselves spinning out of control. They eventually popped to the surface, followed by the rest of the group popping to the surface. Their computers showed they had descended to 100 feet and then sped to the surface. The DM took the whole group to the chamber for evaluation.

In that case, the most serious risk factor is a lung overexpansion injury caused by the rapid ascent. The second risk factor is the chance of DCS because of a rapid ascent. Oxygen toxicity, even if using a high oxygen mix, is a non-issue.

 

[michael-fisch]

Mr "Deep Stops",(Richard Pyle) was doing a Table 3 ride in a chamber, when the chamber operater became loudly insistant that he IMMEDIATELY stop breathing from the BIBS mask.
Because he was breathing pure oxygen at 6 Atmospheres and had been for some time.
High O2 levels won't kill you, but high O2 levels for long times will kill you without trained medical supervision.
As far as I remember the longest breathhold dive (O2 saturated with cramping at the start) was slightly over 27 minutes and the idiot that did it survived without any ill effects.

Michael

 

[Whitrzac]

Mr "Deep Stops",(Richard Pyle) was doing a Table 3 ride in a chamber, when the chamber operater became loudly insistant that he IMMEDIATELY stop breathing from the BIBS mask.
Because he was breathing pure oxygen at 6 Atmospheres and had been for some time.
High O2 levels won't kill you, but high O2 levels for long times will kill you without trained medical supervision.
As far as I remember the longest breathhold dive (O2 saturated with cramping at the start) was slightly over 27 minutes and the idiot that did it survived without any ill effects.

Michael

Dry vs wet makes a difference

Having a seizure in a chamber doesn't cause long term side affects like drowning and dieing.

The max pp02 had been continuously lowered since breathing oxygen under water started. I belive the early navy manuals speced a 2.0 max and have been also revised to 1.6.