Oxygen Toxicity risk with Nitrox?

[Belzelbub]

I pay attention to my computers.

Quoting for truth.

If more people did this, SB might be a lot quieter. Seems to be an unending supply of stories where divers either didn't follow their computer, or had no idea what it was trying to tell them. A lot of times we find that alarms were going off, but they had no clue and were just following the guide.

The "trust me" dives run counter to my training. I don't dive with DMs or Dive Guides in general, but if I did, I'd still be the one responsible for making decisions for me.

 

[BlueTrin]

I think a lot of people assume that others know better at first before you realise at some point that the only person who should take care of your safety is yourself.

Usually happens with a dodgy buddy/guide/instructor.

For me it happened very early: happened in AOW that was back to back with OW

 

[Centrals]

Some divers seem to ignore everything they had been told from the course.
Diving nitrox is easy and simple but there is ONE certain rule to remember.
Maximum operating depth(MOD) ie PPO2 at 1.6, this is the depth that you should not exceed because of potential O2 toxicity. Exceeding that for short period of time is probably safe but...... self-discipline. Chasing whatnot isn't the reason to ignore the rule.
I labelled my nitrox tank with MOD so as to remind me and others.
My computer is set at 1.4 and if the depth is exceeded, the alarm will come on to warn me. Have I ever exceeded it? Yes by deliberating dropping my arm to test the alarm.

 

[Fishdip]

Hi folks!

I recently came back from a one week Liveaboard in the red sea.

Everyone dived with Nitrox, usually at 30%.
According to procedure, maximum depth should be 36.6 meters to avoid oxygen toxicity.
This is also what we signed on in the log for every Nitrox tank.

However, in reality, many if not all divers went to 40 meters and slightly below on several dives.
My maximum depth was 42 meters, and I went below 36.6 on 5 dives.
This happened to me because of diving in the blue (lack of orientation) and seeing some nice hammerheads below, plus noticing other divers were doing the same.

A few days after returning, I met a Divemaster I'm friends with and mentioned it.
He told me I was very foolish to go below 36 meters for, and I quote, "a photo of a fish".
He said insurance won't cover me and he would not go to that depth with Nitrox to save a drowning diver.

Here are my questions:
Just how dangerous were my dives?
Was I taking a huge risk or are there already safety margins built in?
Is it true that there are no warning signs before toxicity kicks in and you experience the effects?
Is the signing of the log a way for the Liveaboard (and insurance company) to avoid responsibility in case of an accident at a restricted depth?
Where can I find statistics on oxygen poisoning from Nitrox?

Thanks a bunch.

On paper you are fine you where at 1.55PO. The only issue I see is not diving the dive plan and exceeding the limit you had set for the dive.

 

[Centrals]

Plan the dive and dive the plan with no exception.

 

[RobPNW]

Sounds like your divemasters on the boat didn't do their job. I've noticed that over time, in dangerous settings, people tend to let their guard down and get complacent because maybe they never have anyone get sick. Once, I was the Officer of the Deck on the bridge of an aircraft carrier and we were looking out over the flight deck. There was an aviation fuels worker taking a sample from a rotating helicopter. This is a task this person had done probably 1,000 times. But after about 500 hours of flight ops on that deployment, he literally turned and walked face first into the tail rotor splitting his head vertically in half. Do something about 1,000 without incident and you feel invincible.

 

[ABK]

Way too many people have died as a result of exceeding their gas's MOD. Plan your dive and dive your plan.

 

[tursiops]

On paper you are fine you where at 1.55PO. The only issue I see is not diving the dive plan and exceeding the limit you had set for the dive.

Well, maybe not really. His nitrox percentage was probably only within 1% at most, so his MOD was variable by at least 5 ft/1.5m.
PPO2=1.6 is not a magic boundary below which you are safe; it is quite physiologically dependent.
Also, PPO2=1.6 is "safe" without a CO2 buildup; he was swimming into the blue, looking for hammerheads, possibly a bit narced, perhaps a bit anxious. I would not assume zero CO2 buildup.
It was a dangerous activity, and we all hope he learned from it.

 

[BRT]

Way too many people have died as a result of exceeding their gas's MOD. Plan your dive and dive your plan.

What is your cut off for "way too many"?

 

[Fishdip]

Well, maybe not really. His nitrox percentage was probably only within 1% at most, so his MOD was variable by at least 5 ft/1.5m.
PPO2=1.6 is not a magic boundary below which you are safe; it is quite physiologically dependent.
Also, PPO2=1.6 is "safe" without a CO2 buildup; he was swimming into the blue, looking for hammerheads, possibly a bit narced, perhaps a bit anxious. I would not assume zero CO2 buildup.
It was a dangerous activity, and we all hope he learned from it.

Oh 100% its why I stated not following his dive plan is the big issue. And why I also said “on paper” because if you look at the numbers it can give you the idea that you can use it at that depth and still be in the “safe” zone. Now had the dive been “planned” and followed using the 1.4 safety factor we would not even be talking about this.