Oxygen Toxicity risk with Nitrox?

[grf88]

I know N2 helps for HPNS, but hadn't heard that for oxtox. Any links to further details I could explore?

Unfortunately I am at an age where I can remember what I read but not necessarily where I read it.

 

[davehicks]

If you hit PPO2 1.6 for a few minutes you are going to be fine. It's not like you are going to instantly have an issue when your cross these best-practice limits. The effects are cumulative and take time.

The real issue here is that you had a dive plan with a known MOD and you exceeded it. That is only going to lead to problems the more times you deviate from your planned safety limits. Next time it will be dropping below your minimum tank pressure, or the planned dive time limit, etc. Make a plan and do you best to stick to it.

 

[inquis]

DAN held a conference back in 2000 where agency representatives talked about the incidences each knew about. No one could report a case at 1.6 atm for an NDL dive. PADI backed off to 1.4 for margin. Time and exertion (CO2 actually) plays a huge role. I wouldn't hesitate to rescue a buddy below 1.6. I would chase a flashlight down to 1.6. I plan dives to not exceed 1.4 and ACCIDENTALLY busting that is a problem.

These two posts may be useful for further details:

Is my approach to diving with Nitrox logical?

except if your nitrox computer malfunctions then what? :) best to have both computers set for the gas you use and just cut some time off your dive. Same thing but more accuracy if you lose a computer on a dive then It would be abort the dive, but that is a good point

scubaboard.com

EAN32 diver below you at 40-odd meters?

http://www.rubicon-foundation.org:8080/dspace/bitstream/123456789/3991/1/15233161.pdf Page 5 (67) has a little chart labeled "Day to day variations in time duration until onset of CNS oxygen toxicity symptoms of a single diver. From Donald, 1947 (16)." Interesting (and a little scary) to say...

scubaboard.com

 

[tursiops]

If you hit PPO2 1.6 for a few minutes you are going to be fine. It's not like you are going to instantly have an issue when your cross these best-practice limits. The effects are cumulative and take time.

The real issue here is that you had a dive plan with a known MOD and you exceeded it. That is only going to lead to problems the more times you deviate from your planned safety limits. Next time it will be dropping below your minimum tank pressure, or the planned dive time limit, etc. Make a plan and do you best to stick to it.

I mostly agree with this, but note that increased CO2 is reported to exacerbate OxTox onset.
OP: Chasing hammerheads at depth in blue water is a recipe for increased CO2. Stick with PPO2<1.4, and don't do something just because you see others doing it.

 

[L13]

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.

The recreational limit is 40m. Again it concerns me that people exceed their planned limits in recreational dives (or any dives), on a regular basis. An occasional deviation can sometimes be the right judgement call, but it shouldn't be a routine.

Plan you dive. Dive your plan.

 

[Lriemann]

First rule of diving nitrox is to know your MOD and obey it. Distractions of sharks and everyone else going below their MOD are no reason to ignore MOD.

How long were you below your MOD?

I would say one to four minutes every dive.

 

[Kimela]

In regards to the insurance comment, I would guess your computer would be what would get you busted as it will go the hospital with you if there's an 'event'. Nobody will trust the dive log (I wouldn't anyway).

 

[scubadada]

Hi @Lriemann

Does your computer calculate your CNS O2 exposure? What did it say after your dives? Here is a DAN article on oxygen toxicity and the NOAA CNS O2 exposure table. See comments under the table regarding recommended PO2 exposures

Oxygen Toxicity

Oxygen toxicity happens with partial pressures overwhelm the body. Severe cases of oxygen toxicity could cause cell damage or other symptoms.

dan.org

 

[Lriemann]

Hi @Lriemann

Does your computer calculate your CNS O2 exposure? What did it say after your dives? Here is a DAN article on oxygen toxicity and the NOAA CNS O2 exposure table. See comments under the table regarding recommended PO2 exposures

Oxygen Toxicity

Oxygen toxicity happens with partial pressures overwhelm the body. Severe cases of oxygen toxicity could cause cell damage or other symptoms.

dan.org

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View attachment 752520

Thank you.
My computer does not contain this information.

I'll add that we were told by the guide to not go below 40 meters, but 35 to 40 is okay.
All the dives were guided, unless one (two) chose to go without a guide.

 

[scubadada]

Thank you.
My computer does not contain this information.

I'll add that we were told by the guide to not go below 40 meters, but 35 to 40 is okay.
All the dives were guided, unless one (two) chose to go without a guide.

The NOAA table is very useful. You increase your CNS O2 exposure by 3% for every 5 min at a PO2 of 1.4. It is 4% every 5 min at a PO2 of 1.5 and 11% for every 5 min at a PO2 of 1.6.

Not that you should routinely break your MOD, but 1-4 minutes below your MOD of 1.4 will not add much to your CNS exposure.

I'm sure it is already clear to you that it is best to learn dive physiology and to not necessarily rely on your dive guide or others.