Conservatism

[The Chairman]

We always ran our PO2 at 1.3 max for cold water

I run 1.3PPO₂ on the first day on a rebreather and 1.2PPO₂ for any subsequent days in a row, no matter the water temps.

For cold water conservancy, I choose not to dive below 68F. I despise exposure protection, and caves are about as cold as I want to dive without any. When you're built like a manatee, you get to dive like one. When it's winter time, you'll find us manatee wannabe in the springs with the real deal. Jus' sayin'.

 

[formernuke]

I run 1.3PPO₂ on the first day on a rebreather and 1.2PPO₂ for any subsequent days in a row, no matter the water temps.

For cold water conservancy, I choose not to dive below 68F. I despise exposure protection, and caves are about as cold as I want to dive without any. When you're built like a manatee, you get to dive like one. When it's winter time, you'll find us manatee wannabe in the springs with the real deal. Jus' sayin'.

Can you dive with them? I had heard that when the manatees where in no divers allowed.

 

[The Chairman]

Can you dive with them? I had heard that when the manatees where in no divers allowed.

I can't splash with them, but they're allowed to come visit me. A cow once t-boned me while I was in Blue Spring, near Orange City. She cracked a few ribs and surprised the heck out of me as I had no idea she was in the area. She was with the smallest calf I had ever seen, and obviously, she did not want me in the area harshing their mellow. I hid behind a palm tree that had partially fallen into the basin, and when she was looking elsewhere, I slipped down the fissure, which was probably deeper than she wanted to go.

Lesson? Gentle giants can still be overly protective mamacitas. Don't mess with mom!!!

Same spring, a few years later, I came across a mamacita and her older calf on a drift dive down the spring run. No problems, but a couple of swimmers were being overly aggressive towards them. I def interceded. I was called an a-hole, a junior ranger, and made sure to report them to the next ranger I saw, when I exited.

Like most marine creatures, bubbles upset manatee. Not completely, but it's also easy to make them feel threatened if you're blocking their normal escape route. Manatee are always allowed to approach you, on or off scuba. You're not always allowed to approach manatee. For the most part, they can initiate contact, but you can't. There are a few info videos that are a good thing to watch that will list the rules in the area you're swimming and/or diving.

 

[Tom_Ivan]

There is more to conservatism than the setting on a dive computer. Some things to include...

• Get a heated undergarment and turn it on for your ascent
• Perform light exercise during your safety stop.
• Do some decent cardio 12 hours before your dive.
• Set your computer to display GF99. If your still of gassing a lot after your safety stop then stay a little longer

 

[dmaziuk]

1. Do we have any evidence 35/75 is safer than any other setting?

Well... because it's generally agreed that 100/100 is "too aggressive", it's probably fair to say 35/75 is safer than 100/100.

1. In an NDL dive does it really matter?

Yes: it controls the no-stop time.

 

[L13]

Yes: it controls the no-stop time.

GF Low has no effect on no-stop time. But the GF High of 75 will produce shorter no-stop times and therefore be more conservative than pure Buhlmann 16C.

 

[Belzelbub]

Yes: it controls the no-stop time.

Pretty sure 100days' post was referring to the OPs question number 2 (See below) not the GF setting.

2) Setting ppO2 to 1,2 would reduce my max depth and thus my nitrogen and oxygen exposure. Is doing both appropriate or is it (far) too conservative?

The point being that it'd be really hard to get into excessive O2 territory on an NDL dive. Setting to 1.2 would really only potentially have an effect on MOD.

For example, MOD for EAN32 at 1.4 is 111 fsw. Most online calculators only give the option of 1.4-1.6, but if you were to update this to 1.2, the MOD is now about 90 fsw. If planned dive was less than 90, no issues. However, if the planned depth is 100 fsw, using EAN32 would exceed the MOD, which may lead to using a mix with a higher N2 content.

 

[inquis]

2) Setting ppO2 to 1,2 would reduce my max depth and thus my nitrogen and oxygen exposure. Is doing both appropriate or is it (far) too conservative?

Running a PO2 of 1.2 at a given depth is LESS conservative with respect to nitrogen uptake compared to a PO2 of 1.4. Usually you pick a depth because there's something to see there and pick the gas accordingly.

As others have said, for a couple NDL dives there's no practical difference with respect to CNS. Both are WELL within the accepted guidelines (max of 3 hrs vs 4 hrs). A single-tank dive to 110 ft on EAN32 will only consume some 15-20 minutes of that allotment.