Any reported cases of Ox Tox between 1.4 and 1.6?

[Seaweed Doc]

You can take air to 218 at 1.6, what are you talking about?

My bad: I didn't run the numbers and was relying on memory from what I was told 40 years ago. Maybe the instructor was getting at 1.5 in the 200' limit, and was separately mentioning ox tox at ppO2 of 2.0 atm. I'd filed those numbers in the back of my head and never checked them. .

Seems like 1.5 is right for 7 ATA at 200'?

 

[Seaweed Doc]

That depends on the symptoms and presentation. PFO is associated with severe, sudden-onset neurological DCS, inner ear DCS, and cutis marmorata. If @johndiver999 's bends were pain-only (I read "back hit" followed by pain relief with an attempt at IWR) then a PFO would be a red herring. It's more likely due to diving the computer to the edge of the no-stop limit, even if the computer says it's ok and clears deco. My old nurse manager used to say that we've never treated a bent computer.

Best regards,
DDM

Totally a side track, but this reminded me of the student of mine that got bent on the 100' dive of AOW. Very much an "undeserved" hit. We'd been diving several days in a row, but no more than 2 dives per day to less than 60' and this was the only dive of the last day.

She was diagnosed with a PFO (as I suspected). As you noted, she presented with sudden symptoms. However, it was "classic" pain in the elbows rather than neuro , skin, or inner ear issues. We had literally just stood up (after swimming to shallow water for the beach exit) and she immediately said "ow!" and said her elbow hurt. The victim did later develop some tingling in the feet, but only in the ER several hours later.

Would she be an exception to the rule?

 

[davehicks]

I have not had a cough but i have definitely experienced blurred vision for about one hour after a single 30 meter/60-70 minute square profile CCR dive at 1.4-1.6 PPO2.

 

[Jim Lapenta]

In 2007 I was doing my NAUI Intro to Tech and Helitrox. We had always used 1.4 for the working portion of the dive and 1.6 for deco.
Then one of the guys we used to dive Erie with was cave diving in Florida and toxed at 1.35. His buddy said he signaled to him that something was wrong and tried to get higher up in the cave. Started seizing and drowned.
We had a pretty good size group of people who regularly went to Erie and were doing dives that were in rec limits but with bottom times that resulted in deco obligations.
There was a large detailed discussion amongst the group and the instructors and CD overseeing the the shop and it was decided that since we were:
Diving in cold water (38 - 42 degrees)
Ages ran 40s to 60s
Drysuits with doubles and stages meaning a greater workload
Oxygen tolerance is not an exact number for each individual and
Different levels of fitness
As a group and for training purposes were going to exercise a little risk management and start mixing for a max PO2 of 1.3 for the working portion of the dives and still use 1.6 for deco. Some chose to use 1.5 and that was ok.
From then on for my personal dives and all tech training when I became an instructor, we mixed for 1.3. Since I was teaching in similar conditions. 40 degree bottom temps, heavy workloads, and ages of the students.
Over cautious? Maybe. But no one ever had an issue, and the effect on dive time and depth was negligible. No one ever complained about me being too safe of an instructor.

 

[BRT]

I have not had a cough but i have definitely experienced blurred vision for about one hour after a single 30 meter/60-70 minute square profile CCR dive at 1.4-1.6 PPO2.

Do you dive with contacts in your eyes?

 

[davehicks]

Do you dive with contacts in your eyes?

No. I use a prescription mask. I generally notice this diving at night, which I do frequently in Seattle this time of year. When I get in the car and drive off, I see a noticeable difference in my vision. Night dives are often followed by a post-dive dinner get together, and after dinner I don't notice the visual change anymore.

I always dive CCR at home, and if the dive is shallow, I don't notice this. My PPO2 will spend a lot of time in the .7-.9 range on shallow dives. If I spend 30-40 minutes in the 75-95 foot range with the PPO2 around 1.2-1.4, then I see the visual change.

 

[johndiver999]

My bad: I didn't run the numbers and was relying on memory from what I was told 40 years ago. Maybe the instructor was getting at 1.5 in the 200' limit, and was separately mentioning ox tox at ppO2 of 2.0 atm. I'd filed those numbers in the back of my head and never checked them. .

Seems like 1.5 is right for 7 ATA at 200'?

40 years ago, few people were considering oxygen exposure issues with air dives at 200. I personally think narcosis (on air) at 200 is a much bigger issue than oxygen exposure - for a short dive anyway.

 

[justinthedeeps]

Is this tongue in cheek or are you saying air breaks aren’t necessary

Yes definitely trolling. But is there really any science testing the air break heuristic?
It sounds like something someone just made up to 'fix' their hour+ deco on oxygen.

Like others in the thread, I am lucky enough that superiors inspect the 'always deco @ 1.6' mantra
ppO2 1.6 while demonstrably survivable for long durations seems almost never necessary

Probably better to:
accept ~1.4 on your mix / flush and do that extra 5 minutes
hang at 4.5 metres or 3 metres (10ft) instead of 6 (20) if you plan a long oxygen session--the ppO2 is lower AND the off-gassing gradients are better.
incorporate real 80% or even 50% blocks, if one of your main concerns is eliminating helium. Better CNS management than maximizing time at 1.6 with brief 'air breaks' on whatever other gas is available (trimix? lol)
run a higher GF-high, exit carefully, plan 'surface deco'
use a habitat or surface deco chamber for any deco plan above ~1-2hrs

The funniest part is divers who think their deco efficiency is directly a function of ppO2, which is an incomplete comprehension of decompression theory.

Some of these will start oxygen flushing at 30ft / 9m because "it's easier to hit 1.6" when in reality they will be off-gassing better at 10 ft / 3 metres at a ppO2 of ~1.3

 

[flymolo]

Yes definitely trolling. But is there really any science testing the air break heuristic?
It sounds like something someone just made up to 'fix' their hour+ deco on oxygen.

Scientific studies on air breaks

Post in thread 'Air Breaks: When & How Long do You do Them?' Air Breaks: When & How Long do You do Them? Gene posted a good summary of the literature. Additionally, TA 14-31, NEDU TR 17-13 Dec 2017 “MANIPULATING FREQUENCY OR DURATION OF AIR BREAKS DURING OXYGEN DECOMPRESSION DID NOT REVEAL...

scubaboard.com

 

[BRT]

No. I use a prescription mask. I generally notice this diving at night, which I do frequently in Seattle this time of year. When I get in the car and drive off, I see a noticeable difference in my vision. Night dives are often followed by a post-dive dinner get together, and after dinner I don't notice the visual change anymore.

I always dive CCR at home, and if the dive is shallow, I don't notice this. My PPO2 will spend a lot of time in the .7-.9 range on shallow dives. If I spend 30-40 minutes in the 75-95 foot range with the PPO2 around 1.2-1.4, then I see the visual change.

Interesting! We have noticed this in dives, air and nitrox, in that depth range and thought it had to do with contacts.