Oxygen Toxicity risk with Nitrox?

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When I plan a nitrox blend I plan it to the sand even I don't plan to go that deep, just a extra margin of safety just in case.

Have I violated 1.6, yes.....

Planned the dive dove the plan. We knew that we had severe current close to the surface so ascent and descent on the line.

Did the dive while down surface surge came up so when we hit the 20 foot stop and switched to pure O2 all of sudden we were getting tossed up and down like rag dolls, 15 to 25 feet.

So switched back to backgas. Changed grip on line to maintain 20feet and back on O2 changed stop to account for that less than a minute of tossing and finished stop.

Wasn't over 1.6 for more than a few seconds.
In Cozumel, they tell me the sand is over 3000'
 
Nearly 20 years ago, I asked for nitrox 32 while diving in Cozumel, and the dive operator would only let me use it for one dive. The other dive had to be on air. That was pretty standard procedure when nitrox first stated to get used there. The DM would not let me use it on the first dive, planned to 80 feet. He gave the whole boat a lecture about why it was so dangerous to dive 32% nitrox on a dive planned to 80 feet--you might lose buoyancy control and suddenly plunge more than 30 feet and immediately die a horrible death. I could only use it on the dives planned for a max of 50-60 feet, with a hard sand bottom below us.

A few years later I was diving with a different operator, and they let me use it on both dives. Everyone on the boat was pretty experienced, and they noted that I was the only one allowed to use nitrox on the first dive. They deduced that I must be someone special. (I was an instructor by then, but I didn't think that was so special.)

It is completely different today. I was in Cozumel this past June, and everyone on our boat used 32% for both dives, including the Devil's Throat dive where we were briefly at about 125 feet. No big deal.

Thinking on nitrox has changed dramatically over the years. In the early 1990s, presentations on nitrox were not allowed at the annuual DEMA show--too dangerous even to talk about it. When I was first certified for it, my exam was 50 questions, with lots of math using a number of equations. It was one of the hardest exams I have ever done at any level in scuba. Today the exam is a piece of cake. The hardest part of the old exam was the calculations for pulmonary oxygen toxicity--it isn't even in the course today.

So the the thinking on the dangers of nitrox has changed dramatically, but some people are still deep into old school thinking.
 
Reference ?
Here's the reference.

In March 2000, six students and an instructor dived using open-circuit scuba in a narrow pass and were swept by a strong current to a depth of 90 metres' sea water. Three died and four were injured, which makes the incident the worst diving accident in New Zealand history. The group was on an officially-sanctioned course with many factors contributing to the final tragic events. The dive is described and the medical response examined. The legal consequences are reported and their implications for diver training and employment are discussed.


It's a tragic story, but not really relevant to this thread.
 
The number of people here defending the practice of exceeding MOD is appalling. Especially considering one of you is a "technical instructor". Shame on you.
 
The number of people here defending the practice of exceeding MOD is appalling. Especially considering one of you is a "technical instructor". Shame on you.
I assume you are including me.

Please don't speak in such sweeping generalities. Pray be specific. What did I (or anyone else) specifically say that was so shameful. Please explain why.
 
The number of people here defending the practice of exceeding MOD is appalling. Especially considering one of you is a "technical instructor". Shame on you.
What MOD and at what PPO2 are people defending the practice of exceeding? Can't see where @boulderjohn discussed anywhere that it was acceptable to exceed a MOD nor he has exceeded a MOD.
 
The number of people here defending the practice of exceeding MOD is appalling. Especially considering one of you is a "technical instructor". Shame on you.
Maybe you’re reading a different thread. Most people in this one have been very critical of the way the OP deviated from the dive plan and exceeded the MOD (at a PPO2 of 1.4) for his mix. Any posts saying otherwise are related to the fact that 1.4 is a conservative MOD and stating - factually - that the deviation (albeit thoughtless) was likely harmless.
 
I've enjoyed reading the full thread, and the various perspectives. Thanks to all. The general thrust of the discussion is how to appropriately avoid oxygen toxicity issues. The discussions seemed to start with the assumption that we know the correct oxygen percentage of the cylinder. I'd add that we need to be careful on that point.

Was recently in Bonaire and the dive operator had an O2 analyzer at the dock for people diving the house reef and one also at the compressor for people picking up tanks to take on shore dives. First morning there I got up early (before anyone had hit the water/ used the sensors) and looked at the dock analyzer and it was reading 19.8 %, then walked up to the one at the compressor which was reading 23%. When I asked about the sensors being calibrated got shrugs. Insisted they put a tank of plain air that was at ambient temp (minimize humidity and temperature variables, which also affect the sensor) on and recalibrate. They both were out by 1 - 2 percent. Then you also have the display accuracy of the analyzer, which can be +/-1%.

Important to remember how these work. The analyzers I'm familiar with use a calibration gas (usually air) to make a regression line that is then used to extrapolate what the analyzed tank O2 percentage is. If the calibration is off, so is the read out for your tank measurement. Some good comments in this thread were saying don't abdicate your safety to someone else. That goes for what the true O2 content of your tank is. This has been a longer note than I planned, so don't want to extend it, but if you're not sure how to properly measure your tank, find out. Analyzer manufacturers instructions for use are generally a good reference.
 
The recreational limit is 40m.
Not for every agency. Mine is at 60m.
 
Not for every agency. Mine is at 60m.
It was for the diver in question. But that wasn't the meat of that post. My point was the casual disregard for exceeding limits and dive plans. If your limit is 60m and you casually went to 62m, I would have the same statement.

Furthermore, I very much doubt that you casually dive to 60m. That is a dive requiring significant planning not casually deviated from, even if it is "recreational" for you.
 

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