Question Why would Peregrine TX give me PPO2 alarm?

[PeterRabbit]

I just completed my open water training with my local SSI training facility and used my Peregrine TX on the open water dive at Homestead Crater which is at elevation 6,000 feet. It only goes down about 65 ft max, and I'd say my average depth was about 30 ft. This was my very first "real" dive with my dive computer, that wasn't in a 15 ft swimming pool. We did 4 dives total over the course of two days. When I surfaced, I noticed my dive computer had an alarm I had to acknowledge, it was a PPO2 alarm. I remembered reading about partial pressures, so I kinda understood what it meant, but at the same time, kinda didn't. I asked my dive instructor about it, and he said it was an alarm of partial pressure (which I already understood from the reading material). I will admit I don't fully understand partial pressures, other than they increase with depth. Since our dives were less than an hour each, and never went deeper than 60 ft., why would my Peregrine TX have given me a PPO2 alarm? I looked back at the data on the Shearwater app when I got home, and don't really see anything glaringly obvious of why I would get a PPO2 alarm after syncing everything. Also, since we were so shallow and the dives were brief, the computer counted my dive at two dives instead of one. I went into the settings to fix this, so that the end of dive delay was set to the MAX at 600 seconds to prevent this in the future.

Why would I have gotten a PPO2 alarm? Sorry for the seemingly stupid, and ignorant question from a new SSI student. I don't feel I was in any real danger at any time during the multiple dives, and can only assume it was a "false alarm." Can someone please dumb it down for me, and "ELI5", why the dive computer would give me a PPO2 alarm on such shallow dives, short in length of time? I acknowledged the alarm and it went away, but it still leaves me wondering why it gave me that alarm? It's also frustrating because even after syncing the dive computer to the app, I don't show any data that indicates that it gave me a PPO2 alarm, which leaves me wondering even further, WTF am I missing? Sorry in advance, I am new and still trying to understand everything. ALSO, my dive instructor is not very patient!!! If I don't get something, he moves on to the next thing. And just in case he is a member of this online board and reads this in the future, I mean that as constructive criticism, I am absolutely not bashing you and I am very thankful that you have gotten me this far!!!

 

[macado]

Is it possible it's giving you an alarm for surface ppO2? I believe your Shearwater will give a warning below .18

At ~6000 feet you're at 0.80 atm

.80 atm x .21 = .168 ppO2

 

[VsubT]

What % O2 was set? 100% O2 would have this alarm by 25', almost immediately upon hitting that depth.

Lance

 

[Zef]

The default dive mode for the Peregrine-TX is "Air" mode, but if you or someone else purposely or inadvertently set it to "Nitrox" mode then the depth you hit during your dive coupled with the gas mixture imputed either purposely or accidentaly, could have triggered the PPO2 alarm. To better understand and advise, we would need to see your computer's settings for the dive(s) in question along with your actual dive profile.

-Z

 

[PeterRabbit]

My dive computer was 100% set to AIR, not Nitrox. My gas O2, was set to 21%. My MOD PPO2 was set to 1.40, and MOD set to 188ft. I never went deeper than 64 feet.

 

[PeterRabbit]

Is it possible it's giving you an alarm for surface ppO2? I believe your Shearwater will give a warning below .18
View attachment 875341
View attachment 875342

At ~6000 feet you're at 0.80 atm

.80 atm x .21 = .168 ppO2

I found my ADV Config 2 screen, and it looks exactly like the picture you just posted. If you understand why I got the PPO2 alarm that being said, can you explain it like I'm five years old for my stupid pea-sized brain. And also, was it considered a "false alarm".?

 

[PeterRabbit]

I found my ADV Config 2 screen, and it looks exactly like the picture you just posted. If you understand why I got the PPO2 alarm that being said, can you explain it like I'm five years old for my stupid pea-sized brain. And also, was it considered a "false alarm".?

Oh and YES, I noticed the alarm was at the surface. Why would that be, and is it because I was at high altitude???

 

[macado]

I found my ADV Config 2 screen, and it looks exactly like the picture you just posted. If you understand why I got the PPO2 alarm that being said, can you explain it like I'm five years old for my stupid pea-sized brain. And also, was it considered a "false alarm".?

Sure. It's actually pretty simple. I just looked up the place where you were diving. 94 degree water sounds pretty warm! I bet you weren't cold. Someone can probably explain this better than me but here is the gist of it. I would mostly consider it a "false alarm" in the sense that you weren't in any immediate danger but it's definitely something you want to understand.

So you're basically doing what they refer to as an altitude dive. Homestead Crater is at 6000 feet. That is approximately .80 atm (atmospheres). The atmospheric pressure is less the higher above sea-level you are. I am surprised they didn't brief you about that but Altitude Diving is not really part of Open Water. Still, it probably deserved a quick explanation. Not a big deal but it's very good to know if you do more altitude diving.

First, your Shearwater automatically adjusts for altitude. It has a depth sensor that reads milibars. It automatically handles any decompression adjustments for altitude.

Page 6 of Peregrine TX Mmanual

Consider 1 atm to be sea-level or 0ft (approximately 1013 millibars)

Air which is 20.9% oxygen / 78% nitrogen has a partial pressure of ~. 21 ppO2 at sea level however you were not at sea level, you were at high elevation.

.80 atm x .209 (ppo2 of air) = .167 ppO2.

In simple terms, At 6000ft it's the equivalent of breathing about 16.7% oxygen. Your Shearwaters is set to give a warning when ppO2 is lower than .18 ppO2 (18% oxygen) hence why you got a ppO2 warning on the surface.

Hope that helps.

 

[PeterRabbit]

Sure. It's actually pretty simple. I just looked up the place where you were diving. 94 degree water sounds pretty warm! I bet you weren't cold. Someone can probably explain this better than me but here is the gist of it. I would mostly consider it a "false alarm" in the sense that you weren't in any immediate danger but it's definitely something you want to understand.

So you're basically doing what they refer to as an altitude dive. Homestead Crater is at 6000 feet. That is approximately .80 atm (atmospheres). The atmospheric pressure is less the higher above sea-level you are. I am surprised they didn't brief you about that but Altitude Diving is not really part of Open Water. Still, it probably deserved a quick explanation. Not a big deal but it's very good to know if you do more altitude diving.

First, your Shearwater automatically adjusts for altitude. It has a depth sensor that reads milibars. It automatically handles any decompression adjustments for altitude.

Page 6 of Peregrine TX Mmanual
View attachment 875343

Consider 1 atm to be sea-level or 0ft (approximately 1013 millibars)

Air which is 20.9% oxygen / 78% nitrogen has a partial pressure of ~. 21 ppO2 at sea level however you were not at sea level, you were at high elevation.

.80 atm x .209 (ppo2 of air) = .167 ppO2.

In simple terms, At 6000ft it's the equivalent of breathing about 16.7% oxygen. Your Shearwaters is set to give a warning when ppO2 is lower than .18 ppO2 (18% oxygen) hence why you got a ppO2 warning on the surface.

Hope that helps.

Yes that makes perfect sense. I knew it would be an altitude dive, but I didn't think it would be enough to cause alarms on the computer unless perhaps I went diving the day before at sea level or something like that. But your explanation makes sense, and I also get the sense that I was never really in any danger. I did look up in the instructions that the altitude is automatically set and calculated by the Peregrine TX, so my initial thought was OK, so the dive computer KNOWS that I am at a higher altitude and will take this into account, thus eliminating any and all false alarms. Perhaps the alarm was not necessarily "false", but at the same time, I am going to assume the alarm was given in an effort to be "conservative", but at the same time, I was never in any real danger.

 

[PeterRabbit]

Al

Sure. It's actually pretty simple. I just looked up the place where you were diving. 94 degree water sounds pretty warm! I bet you weren't cold. Someone can probably explain this better than me but here is the gist of it. I would mostly consider it a "false alarm" in the sense that you weren't in any immediate danger but it's definitely something you want to understand.

So you're basically doing what they refer to as an altitude dive. Homestead Crater is at 6000 feet. That is approximately .80 atm (atmospheres). The atmospheric pressure is less the higher above sea-level you are. I am surprised they didn't brief you about that but Altitude Diving is not really part of Open Water. Still, it probably deserved a quick explanation. Not a big deal but it's very good to know if you do more altitude diving.

First, your Shearwater automatically adjusts for altitude. It has a depth sensor that reads milibars. It automatically handles any decompression adjustments for altitude.

Page 6 of Peregrine TX Mmanual
View attachment 875343

Consider 1 atm to be sea-level or 0ft (approximately 1013 millibars)

Air which is 20.9% oxygen / 78% nitrogen has a partial pressure of ~. 21 ppO2 at sea level however you were not at sea level, you were at high elevation.

.80 atm x .209 (ppo2 of air) = .167 ppO2.

In simple terms, At 6000ft it's the equivalent of breathing about 16.7% oxygen. Your Shearwaters is set to give a warning when ppO2 is lower than .18 ppO2 (18% oxygen) hence why you got a ppO2 warning on the surface.

Hope that helps.

Also, one other question I had was, does it matter at what altitude the cylinder was actually filled? For example, I know for a fact that the cylinders I was breathing off of, were filled at an altitude of 2800 sq ft, then transported up the the altitude we were diving at. Does that have absolutely anything to do at all with the percentage of oxygen inside the cylinder? What if the cylinder had been filled at the same altitude as the dive site, would anything have changed?