Oxygen Toxicity risk with Nitrox?

[boulderjohn]

Thanks for incident info!

I hope my point in describing them was not too subtle.

The standard MOD limits are very safe, and it takes time, often significant time, at the depth of the MOD violation to cause a toxic event. Toxicity is a real concern for technical divers because they are capable of making very serious mistakes leading to major violations for length periods of time.

In contrast, NDL divers are highly unlikely to have such serious violations. That does not give you permission to violate those norms. For NDL diving, I will normally stay within the 1.4 limit throughout the dive, but I will not hesitate to spend a few minutes of a dive within the 1.6 limits. In those cases, I know before the start of the dive that I am going to do that--it is not a result of not paying attention to my depth.

 

[Beau Holden]

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.

Pushing the the envelope is one thing, but going outside of it is all together different. Here pushing the envelope is knowing that 36.6 meters is the edge and trying to maintain that through out the dive. Going outside of it is anything below 36.6. If we want to bust the envelope just because one else is doing it, then instead of seeing hammerheads below, then we just might be seeing Jesus above. Its not that the MOD was exceeded for a short time, the the mental approach, if i did it once, I can do it again.

Here are my questions:
Just how dangerous were my dives?
Was I taking a huge risk or are there already safety margins built in?

Were your dives inherently dangerous? From an oxtox point of view, most likely not so much. Were you taking a huge risk? Yes. Its the mental aspect of this, they were doing it, so i can do it, that makes it a huge risk and wanting to depend on safety margins.

I work in construction and things like crane rigging have safety margins, like a cable has a rating of 15 tons and has a safety margin of 1.5 of 22.5 tons. I can go over 15 tons and up to 22.5 in theory, but sooner or later if I continue to do that, that cable is going to break. If we break the rules enough times, the rules will break us.

 

[Fishdip]

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

Can you supply some sort of an official estimate on this for NDL diving?

I know of many cases with technical diving, but I don't believe I have ever heard of a single one in NDL diving. I would like to see some examples the "way too many people" if you can find them.

In the technical diving cases I know, we are not talking about someone going to a PPO2 of 1.55 for 4-6 minutes. We are talking serious MOD violations, often caused by the diver thinking he or she had a different mix than reality. In those cases, the toxicity came after significant time. Here are some cases I know of. I am writing these from memory, and some of the details may be a tad--but only a tad--off.

• A diver broke his foot and could not dive for several months. When he was ready to dive again, he took his double tanks to a wreck (Hydro Atlantic) with a deck at 150 feet/45 meters and about 170 feet/52 meters to sand. He did not check the tanks because he was sure they had air, but they had 36%. His buddy told me it took about 20 minutes before he toxed.
• A cave diver used a tank that was clearly marked as having pure oxygen for a dive to 100 feet. He told his friends he had filled it himself, so he knew it had air instead of oxygen. He refused to test it. I am not sure how long he was diving on pure oxygen at 100 feet before he toxed.
• A cave diver was supposed to leave a decompression bottle with 50% at a 70 foot staging area and take a different one more appropriate for 200 feet. He left the deep bottle at the staging area and took the 50% to 200 feet. I don't know how long he was diving at 200 feet on 50% before he toxed.

Dont leave out the kids in FL breathing of HE in a pool.

 

[boulderjohn]

Dont leave out the kids in FL breathing of HE in a pool.

That was tragic, but it is not an example of oxygen toxicity.

 

[rob.mwpropane]

I think we can all agree that the dives themselves were benign.. it's the lack of knowledge that was dangerous.. that's it.

And I said it before, we all have these little dives early on where the "spidey sense" is going off but we don't find out until later why.. this is OP's "why".

The fact that he came here to find out the "why" as opposed to the other 20 people on the boat who could care less deserves some type of admiration.

 

[Belzelbub]

I think we can all agree that the dives themselves were benign.. it's the lack of knowledge that was dangerous.. that's it.

That and the blind, and in hindsight, unwarranted trust in the dive leader to keep the divers safe. While the dive operation should ensure that all dives are done safely, the ultimate responsibility for staying safe belongs to the individual diver.

The fact that he came here to find out the "why" as opposed to the other 20 people on the boat who could care less deserves some type of admiration.

Quite true. That is commendable. The OP realized the dive wasn’t within guidelines, and sought opinions. Now, I hope that next time better choices will be made. In this case, the risk was small, might not always be the case.

 

[Fishdip]

That was tragic, but it is not an example of oxygen toxicity.

What was it considered? I know it was not OT tho I was more just pointing out that no matter the depth breathing the wrong gas can kill.

 

[Belzelbub]

What was it considered? I know it was not OT tho I was more just pointing out that no matter the depth breathing the wrong gas can kill.

Extreme hypoxia. Ox tox is breathing too rich of an 02 mix. This was the opposite as the O2 content was zero.

 

[L13]

What was it considered? I know it was not OT tho I was more just pointing out that no matter the depth breathing the wrong gas can kill.

That was due to insufficient (none) oxygen, not due to to much.

 

[Marie13]

OP was a lemming. Following the others.