Dive Computer No Deco Computations Question

[johndiver999]

^^This. There is not a single reported incident of CNS 02 toxicity in a diver diving a single tank with a nitrox mix of less than 50% within recreational depths.

The whole CNS 02 toxicity thing is so overblown it's not much more than a myth.

I suspect the validity of this statement.

Not too long ago, I screwed up big time and was diving 135 and was really having trouble with the acuity of my vision on the bottom. When I went to change tanks over for the next dive, I realized I had just used a tank with 36% instead of 32% for that dive.

I think I was almost certainly experiencing some level of oxygen toxicity from that dive. I was very disappointed in my own carelessness and stupidity, both on the boat (before the dive) and during the dive- when I failed to acknowledge the problem underwater and respond appropriately to symptoms. I think I was lucky that day.

 

[LI-er]

I suspect the validity of this statement.

Not too long ago, I screwed up big time and was diving 135 and was really having trouble with the acuity of my vision on the bottom.

I suspect a fogged mask.

 

[tursiops]

^^This. There is not a single reported incident of CNS 02 toxicity in a diver diving a single tank with a nitrox mix of less than 50% within recreational depths.

The whole CNS 02 toxicity thing is so overblown it's not much more than a myth.

It is worth pointing out that the PPO2 of 32% (by far the most common blend) does not reach 1.6 until 40m, so if one stays within recreational depths, one stays below the likelihood of O2 toxicity. Even then, it takes perhaps a few minutes of exceedance of 1.6 for the toxicity to occur. The commonly used PPO2 max of 1.4 (33m) is designed to give you a buffer. And a common dive-operator rule of not to exceed 30m gives even more of a buffer.
CNS O2 toxicity is not a myth; it is just highly unlikely if one stays within recreational depths, and especially if one stays within PPO2=1.4 guidelines.
It is dangerous to suggest that O2 toxicity is a myth. Just dive by the guidelines.

 

[tursiops]

I suspect a fogged mask.

I certainly hope this is a sarcastic statement, meant in jest. The PPO2 of 36% at 135 ft is 1.8, definitely dangerous territory.

 

[boulderjohn]

Even then, it takes perhaps a few minutes of exceedance of 1.6 for the toxicity to occur.

The confirmed oxygen toxicity cases I have looked at suggest it takes more than a few minutes. Here are some of the cases.

1. I talked to the buddy of a victim. They were diving the HydroAtlantic wreck off of Boca Raton--deck at 150 feet and sand at 170 feet. The hit happened after about 20 minutes. He thought his double tanks had air, but they turned out to have 36%. (PPO2 roughly 2.1)

2. The cave diver at Ginnie Springs started his dive on his AL80 stage bottle, which was clearly labeled oxygen. His friends had pointed that out, but he insisted that he had filled the tank himself, and it had air, not oxygen. He refused to test. It was pure oxygen. I don't know exactly how long he was at 100 feet before he toxed, but it was a while. (PPO2 roughly 4.0)

3. The WKPP diver was part of a group that planned to leave their 50% AL80s at 70 feet before going to the bottom at 200 feet. The diver took the wrong tank and was breathing 50% at 200 feet for a while before he toxed. (PPO2 roughly 3.5)

 

[LI-er]

The confirmed oxygen toxicity cases I have looked at suggest it takes more than a few minutes. Here are some of the cases.

1. I talked to the buddy of a victim. They were diving the HydroAtlantic wreck off of Boca Raton--deck at 150 feet and sand at 170 feet. The hit happened after about 20 minutes. He thought his double tanks had air, but they turned out to have 36%. (PPO2 roughly 2.1)

2. The cave diver at Ginnie Springs started his dive on his AL80 stage bottle, which was clearly labeled oxygen. His friends had pointed that out, but he insisted that he had filled the tank himself, and it had air, not oxygen. He refused to test. It was pure oxygen. I don't know exactly how long he was at 100 feet before he toxed, but it was a while. (PPO2 roughly 4.0)

3. The WKPP diver was part of a group that planned to leave their 50% AL80s at 70 feet before going to the bottom at 200 feet. The diver took the wrong tank and was breathing 50% at 200 feet for a while before he toxed. (PPO2 roughly 3.5)

As to my earlier point, all 3 of these examples occurred well beyond recreational diving limits and recreational Nitrox levels.

Again, there is not one single documented case of an 02 hit in a single tank recreational diver on Nitrox within recreational depth limits. And in these rather extreme examples it took quite a while for it to happen at levels FAR beyond PP02 1.4.

I certainly hope this is a sarcastic statement, meant in jest. The PPO2 of 36% at 135 ft is 1.8, definitely dangerous territory.

Why, because you believe that with no supporting evidence whatsoever?

 

[tursiops]

The confirmed oxygen toxicity cases I have looked at suggest it takes more than a few minutes. Here are some of the cases.

1. I talked to the buddy of a victim. They were diving the HydroAtlantic wreck off of Boca Raton--deck at 150 feet and sand at 170 feet. The hit happened after about 20 minutes. He thought his double tanks had air, but they turned out to have 36%. (PPO2 roughly 2.1)

2. The cave diver at Ginnie Springs started his dive on his AL80 stage bottle, which was clearly labeled oxygen. His friends had pointed that out, but he insisted that he had filled the tank himself, and it had air, not oxygen. He refused to test. It was pure oxygen. I don't know exactly how long he was at 100 feet before he toxed, but it was a while. (PPO2 roughly 4.0)

3. The WKPP diver was part of a group that planned to leave their 50% AL80s at 70 feet before going to the bottom at 200 feet. The diver took the wrong tank and was breathing 50% at 200 feet for a while before he toxed. (PPO2 roughly 3.5)

Calculated risk of pulmonary and central nervous system oxygen toxicity: a toxicity index derived from the power equation

The risk of oxygen toxicity has become a prominent issue due to the increasingly widespread administration of hyperbaric oxygen (HBO) therapy, as well as the expansion of diving techniques to include oxygen-enriched gas mixtures and technical diving. ...

www.ncbi.nlm.nih.gov

A few minutes at PPO2=1.8 is probably "safe." Less than 1% chance of toxing.
The like suggests that 15 mins at PPO2=2.0 is the limit for 1% risk of toxiing,. and goes up as the square of the time and the 6.8 [power of the PPO2. So PPO2-2.5 would suggest 7 mins as the limit.

 

[tursiops]

Calculated risk of pulmonary and central nervous system oxygen toxicity: a toxicity index derived from the power equation

The risk of oxygen toxicity has become a prominent issue due to the increasingly widespread administration of hyperbaric oxygen (HBO) therapy, as well as the expansion of diving techniques to include oxygen-enriched gas mixtures and technical diving. ...

www.ncbi.nlm.nih.gov

A few minutes at PPO2=1.8 is probably "safe." Less than 1% chance of toxing.
The like suggests that 15 mins at PPO2=2.0 is the limit for 1% risk of toxiing,. and goes up as the square of the time and the 6.8 [power of the PPO2. So PPO2-2.5 would suggest 7 mins as the limit.

One more citation supporting the Nitrox limits.

Vann RD, Hamilton RW. Central nervous system oxygen toxicity. In: Vann RD, Mitchell SJ, Denoble PJ, Anthony TG, editors. Technical Diving Conference Proceedings; 2008 Jan 18-19. Durham, NC: Divers Alert Network; 2009. p. 38--66.​

Attached.

 

[gordonscuba]

For the record, (and I hope there are dive computer companies listening), I hereby promise that I shall never spend a single dollar towards a dive computer that might lock out under any circumstances. The computer's job is to continuously calculate the Buhlmann model and present the output of those calculations to me in the form of calculated deco plans, NDL plans, SurfGF, GF99 whether on the surface or underwater. If, under certain circumstances, the computer can do that calculation, is functioning as designed, but by design willfully withholds the calculated result, then I shall ensure never to support said computer manufacturer with purchases.

 

[Belzelbub]

For the record, (and I hope there are dive computer companies listening), I hereby promise that I shall never spend a single dollar towards a dive computer that might lock out under any circumstances. The computer's job is to continuously calculate the Buhlmann model and present the output of those calculations to me in the form of calculated deco plans, NDL plans, SurfGF, GF99 whether on the surface or underwater.

Exactly. Same for me. Unfortunately, that really narrows the choices to a few manufacturers currently. Hopefully that will change.