Error Low PPo2 cause in OC Rec dive?

[00wabbit]

Today on a very short/shallow dive I go the error Low PP02 after surfacing. I wonder what could have caused it?

I did 2 dives today - My previous dives were 2 days ago so they should not have affected this dive.

I was diving with my wife in a low vis environment so the dives were short and shallow because she was not comfortable.

Computer settings: OC Rec Mode
Fresh Water
Med Conservatism

Dive 1 21ft for 19mins dive ended at 4:52
Dive 2 Start 5:14 30ft for 12 mins

These dives are at altitude approx 4500ft. I wonder if that may have affected it? On the first dive I made sure to turn on the computer before descending so that it can calibrate to the altitude. On the second dive, I didn't.

 

[BFRedrocks]

I'm thinking that having a relatively short SI (22 mins) along with the computer defaulting to a sea level barometric pressure for the second dive when you were actually diving at altitude is what caused the issue. Hopefully someone with more knowledge and experience with the computer than I (I've had my Petrel 2 for about 2 months now) can provide further clarification.

 

[Dhboner]

I would contact Shearwater directly...they have amazing customer service.

 

[crunchiespg]

I had the same issue today. Also a mountain lake. But i also had the issue after a good hour plus surface interval.
Did you get anywhere figuring this out?

 

[tcoen]

Hi,

The cause for the low PPO2 message is the altitude at which you are diving. The default low PPO2 warning limit is 0.19 ata [atmospheres absolute]. Since PPO2 is ambient pressure multiplied bythe FO2 (21% for air), the PPO2 near the surface can easily fall below 0.19 near the surface.

For example, at 4500ft elevation the ambient pressure is about 0.85 ata, resulting in a PPO2 breathing air of 0.1785 ata.

The low PPO2 warning level can be adjusted, but unfortunately not when in the OC Rec mode. But you can adjust it in the OC tec mode, then switch back to OC Rec mode and the value will stick. Steps:
- Switch to OC Tec mode.
- Go to "System Setup->Adv Config->Adv Config 2"
- Change the OC Low PPO2 setting to something lower like 0.17
- Swtich back to OC Rec mode.

I hope this helps answer your question.

Best regards,
Tyler Coen
Shearwater Research

 

[brsnow]

Hi,

The cause for the low PPO2 message is the altitude at which you are diving. The default low PPO2 warning limit is 0.19 ata [atmospheres absolute]. Since PPO2 is ambient pressure multiplied bythe FO2 (21% for air), the PPO2 near the surface can easily fall below 0.19 near the surface.

For example, at 4500ft elevation the ambient pressure is about 0.85 ata, resulting in a PPO2 breathing air of 0.1785 ata.

The low PPO2 warning level can be adjusted, but unfortunately not when in the OC Rec mode. But you can adjust it in the OC tec mode, then switch back to OC Rec mode and the value will stick. Steps:
- Switch to OC Tec mode.
- Go to "System Setup->Adv Config->Adv Config 2"
- Change the OC Low PPO2 setting to something lower like 0.17
- Swtich back to OC Rec mode.

I hope this helps answer your question.

Best regards,
Tyler Coen
Shearwater Research

Hi, into this today in the pool in Denver. This is helpful.

 

[brsnow]

Hi,

The cause for the low PPO2 message is the altitude at which you are diving. The default low PPO2 warning limit is 0.19 ata [atmospheres absolute]. Since PPO2 is ambient pressure multiplied bythe FO2 (21% for air), the PPO2 near the surface can easily fall below 0.19 near the surface.

For example, at 4500ft elevation the ambient pressure is about 0.85 ata, resulting in a PPO2 breathing air of 0.1785 ata.

The low PPO2 warning level can be adjusted, but unfortunately not when in the OC Rec mode. But you can adjust it in the OC tec mode, then switch back to OC Rec mode and the value will stick. Steps:
- Switch to OC Tec mode.
- Go to "System Setup->Adv Config->Adv Config 2"
- Change the OC Low PPO2 setting to something lower like 0.17
- Swtich back to OC Rec mode.

I hope this helps answer your question.

Best regards,
Tyler Coen
Shearwater Research

I was curious why it does not adjust the level or why it is absolute for the altitude? I have no doubt there is a reason Friend dives the SB G2 and it seems to take the change into consideration. I just want to make sure I don’t forget to change it back

 

[Tracy]

I was curious why it does not adjust the level or why it is absolute for the altitude? I have no doubt there is a reason Friend dives the SB G2 and it seems to take the change into consideration. I just want to make sure I don’t forget to change it back

No reason to change it back. .17 is an acceptable low limit at sea level as well.

 

[brsnow]

No reason to change it back. .17 is an acceptable low limit at sea level as well.

Thank you

 

[brsnow]

No reason to change it back. .17 is an acceptable low limit at sea level as well.

What would be considered not acceptable? I will be doing my dry suit classes around 9k, my guess is .17 will cause an error which is fine, but for diving from sea level to 9k is there a “safe” setting to leave it in?