Question O2 sensor calibration

[justinthedeeps]

That sounds normal?

Reaching 1.5+ already shows that the sensors can read higher than typical diving setpoints 1.0-1.4--the main purpose of that cell check IMO. More so than trying to re-validate "100%"

A ppO2 ~1.5+ @ 6 metres would be ~94+% oxygen? ~5% inert gases are probably not going to impact deco in meaningful ways when that shallow.

Sitting at ~1.5 (or 5.5 metres) is probably not going to make or break one's deco. Many would also be comfortable at ~4 metres if it's the actual ceiling. Pure(ish) O2 doesn't care, the 'oxygen window' actually looks mathematically the same there when vetted (except for those believing 6 metres will keep their microbubbles smaller.)

A ~5% margin that shallow shouldn't be making much difference for typical deco or oxtox, compared to the already quite beneficial off-gassing gradients, and several other conditional/personal/situational factors

 

[SavageSeaCow]

1.55 is always my goal. Realistically as soon as you exhale after the flush you are introducing new inert gas so it won’t stay high for long and totally forcing 100% of your counter lung volume out in a flush isn’t likely. Sounds like you’re doing it right in summary.

 

[davehicks]

Does anyone have an experience where an O2 Flush at 20 feet resulted in the discovery of a significant issue with one or more oxygen sensors? In other words, has anybody gotten valuable from this exercise?

 

[Heat Miser]

I was taught to o2 flush, by tilting head and flushing o2 with the excess gas escaping through loose lips, I could never get to 1.6PPo2 at 6m using that method and it wasted lots of gas.

A second instructor teaches a more subtle method, full inhale through mouth, exhale through your nose ... do it in three to four smaller flushes ... this method works better for me.

if you really have problems try it at 7 meters (very briefly)

 

[Heat Miser]

Does anyone have an experience where an O2 Flush at 20 feet resulted in the discovery of a significant issue with one or more oxygen sensors? In other words, has anybody gotten valuable from this exercise?

Sure (5-6 times), it tells your if you cell is limited (i.e cant get to 1.6) and you replace it after you get out.

 

[rjack321]

That sounds normal?

Reaching 1.5+ already shows that the sensors can read higher than typical diving setpoints 1.0-1.4--the main purpose of that cell check IMO. More so than trying to re-validate "100%"

A ppO2 ~1.5+ @ 6 metres would be ~94+% oxygen? ~5% inert gases are probably not going to impact deco in meaningful ways when that shallow.

Sitting at ~1.5 (or 5.5 metres) is probably not going to make or break one's deco. Many would also be comfortable at ~4 metres if it's the actual ceiling. Pure(ish) O2 doesn't care, the 'oxygen window' actually looks mathematically the same there when vetted (except for those believing 6 metres will keep their microbubbles smaller.)

A ~5% margin that shallow shouldn't be making much difference for typical deco or oxtox, compared to the already quite beneficial off-gassing gradients, and several other conditional/personal/situational factors

Deco efficiency is not the purpose of the 20ft flushes

 

[justinthedeeps]

Sure (5-6 times), it tells you if you cell is limited (i.e cant get to 1.6) and you replace it after you get out.

But does it really matter whether this test happens at 1.6 vs. 1.5(+)? They are both values that should prompt a 'high O2' response.

Someone who calibrates at 1.0 and dives at 1.0 (totally reasonable for say a 3hr+ photography dive at ~≤15 metres) would only need to check for say 1.3(+) to verify that their sensors will alert them of a high O2 condition.

 

[justinthedeeps]

Deco efficiency is not the purpose of the 20ft flushes

I would partly agree, though going 100% loop O2 (vs say ~87% O2 @1.4 @6m) can shorten final stop lengths in a deco planner (small and unnecessary in many cases--especially when helium off-gassing is driving deco, unimpeded by 20 or 50% nitrogen in a nitrox deco gas)

So agreed the flush makes sure the sensors will register a high O2 condition, but there is actually nothing magical about the 1.6 number for that, anything between 1.4+ and 1.8 would do (latter for the hardcore 9 metre flush peeps who don't mind a lip tingle or rare catastrophic seizure.)

For that matter, a really easy way to check for 1.6+ might be to vent the loop, go onto open circuit, and blast oxygen through the loop at a deeper depth. It's not science, but that's what dry land oxygen pressure pot testers were made for.

 

[Heat Miser]

But does it really matter whether this test happens at 1.6 vs. 1.5(+)? They are both values that should prompt a 'high O2' response.

Someone who calibrates at 1.0 and dives at 1.0 (totally reasonable for say a 3hr+ photography dive at ~≤15 metres) would only need to check for say 1.3(+) to verify that their sensors will alert them of a high O2 condition.

yes the degree of non-linearity will show up to a greater extent at 1.6 ppo2 than at 1.5 ppo2 and therfore, you know to replace the cell, if it can't get to 1.6 at all, you know you really have a problem.

 

[Heat Miser]

Does anyone have an experience where an O2 Flush at 20 feet resulted in the discovery of a significant issue with one or more oxygen sensors? In other words, has anybody gotten valuable from this exercise?

I woud follow this up by saying that diving a rEvo, and using 5 cells, and using the suggested rEvo replcement strategy, its not unusual to find a limited cell occasionally (once a year)