PO2 dive computer warning

[topher10]

EDIT: Typos in the original post have been corrected. My apologies. EDIT

I recently did a nitrox dive using 36% with the sand at 95ft. Therefore, no chance of going past PO2 = 1.4. However, right at the beginning of the dive, at around 85 ft, I realize my computer is beeping, and it says UP. I head up a few feet and the computer reverts to normal. A few minutes later, again around 85 ft, the computer alarms again, and again I go up and it reverts. Most of the dive is spent at 70 ft, but at times I go lower to see stuff. Over the course of the dive I decide that it is alarming somewhere around 80ft, and I assume this must be an early warning related to PO2, perhaps 1.2 or 1.3.

Now that I am home I know that with a 36% mix PO2 = 1.2 at 77ft, and that my computer (in NORM mode) gives a warning at 1.2 and then an alarm at 1.4. So every time I crossed 77 ft it was warning me, even though I was well away from 1.4.

My question is: Is this 1.2 warning appropriate, or something to be concerned about?

I feel that I have 3 options:
1. Always use a mix that stays above 1.2. For instance, I would have no alarms on this dive with 32% instead of 36%. However, I am losing some of the benefits of Nitrox by doing this, essentially adding an additional safety layer and never diving past 1.2.

2. Just deal with the alarm but avoid going to 1.4. I can silence it and it just says up, while still giving depth. But I am not sure this is ideal.

3. Swap to Tech mode and set the PO2 alarms myself. Perhaps the warning becomes 1.4 and the alarm becomes 1.5 or 1.6.

Thanks for any thoughts/advice.

 

[drk5036]

What computer? This should be a configurable option.

 

[northernone]

I'd set the warning to whichever ever level I am personally comfortable with. That's generally 1.4, some alarm at 1.3, that's what yours seem to be doing?

Otherwise, turning it off and monitoring depth responsibly in silence. I dislike noisy computers and would rather be attentive.

Cameron

 

[drk5036]

Also seems your math is off? 77 feet is 23 meters, which is about 3.35 atm. 0.36 x 3.35 is 1.2. Which would be a more reasonable place to see an alarm going off.

 

[caruso]

I set all my computers to P02 1.6 and advise all my dive buddies to do the same. (I also shut off all audible alarms that I can and advise my buddies to do it as well).

The whole 1.4 vs 1.6 risk is overrated.

There has never, ever been a reported incident of an 02 hit on a single tank recreational diver on Nitrox <40% at any depth.

 

[drk5036]

I set all my computes to P02 1.6 and advise all my dive buddies to do the same. (I also shut off all audible alarms that I can and advise my buddies to do it as well).

The whole 1.4 vs 1.6 risk is overrated.

There has never, ever been a reported incident of an 02 hit on a single tank recreational diver on Nitrox <40% at any depth.

is that really true? Never?

 

[ChuckP]

I set all my computes to P02 1.6 and advise all my dive buddies to do the same. (I also shut off all audible alarms that I can and advise my buddies to do it as well).

The whole 1.4 vs 1.6 risk is overrated.

There has never, ever been a reported incident of an 02 hit on a single tank recreational diver on Nitrox <40% at any depth.

I wouldn't advise a new diver to alter from the recommended PO of 1.4 - especially one that is asking questions about it and has their math slightly off.

Your computer may be set up to warn at a PO2 of 1.2 (not 1.02) with an audible alarm. For your safety, you may want to keep that audible alarm or as you gain confidence, turn it off. Generally speaking, if the hard bottom is above the MOD - you can't get deeper than the MOD, there'd be no need for an alarm.

Diving with nitrox means paying a bit more attention before and during the dive - as you gain experience, it becomes second nature but you should never become complacent in your diving.

 

[caruso]

is that really true? Never?

Let me rephrase. I've never seen or heard of it anywhere and any time this topic has come up on this board or elsewhere no one else can produce anything either. The closest I ever read about was where a double tank diver accidentally breathed a 50% Nitrox mix at a depth something greater than 150' and it took over 45 minutes for an 02 hit which to me at least means our recreational limits are not even close to anything dangerous at P02 1.6 even allowing for variation between divers.

 

[tursiops]

I recently did a nitrox dive using 36% with the sand at 95ft. Therefore, no chance of going past PO2 = 1.04. However, right at the beginning of the dive, at around 85 ft, I realize my computer is beeping, and it says UP. I head up a few feet and the computer reverts to normal. A few minutes later, again around 85 ft, the computer alarms again, and again I go up and it reverts. Most of the dive is spent at 70 ft, but at times I go lower to see stuff. Over the course of the dive I decide that it is alarming somewhere around 80ft, and I assume this must be an early warning related to PO2, perhaps 1.02 or 1.03.

Now that I am home I know that with a 36% mix PO2 = 1.02 at 77ft, and that my computer (in NORM mode) gives a warning at 1.02 and then an alarm at 1.04. So every time I crossed 77 ft it was warning me, even though I was well away from 1.04.

My question is: Is this 1.02 warning appropriate, or something to be concerned about?

I feel that I have 3 options:
1. Always use a mix that stays above 1.02. For instance, I would have no alarms on this dive with 32% instead of 36%. However, I am losing some of the benefits of Nitrox by doing this, essentially adding an additional safety layer and never diving past 1.02.

2. Just deal with the alarm but avoid going to 1.04. I can silence it and it just says up, while still giving depth. But I am not sure this is ideal.

3. Swap to Tech mode and set the PO2 alarms myself. Perhaps the warning becomes 1.04 and the alarm becomes 1.05 or 1.06.

Thanks for any thoughts/advice.

You are forgetting to add 1 atm to your calculation. The PPO2 at 95 ft is 1.4, not 1.04. Your alarm is probably going off at 1.3.

 

[caruso]

You are forgetting to add 1 atm to your calculation. The PPO2 at 95 ft is 1.4, not 1.04.

Is he neglecting an atm or inventing a zero? Inquiring minds want to know.