mixing CCR and OC diving

[schwerve]

Quick bio: I have about 250 dives under my belt over about thirteen years. Got my AOW and EANx (up to 40%) certs. In May, I'll have an Inspiration "experience" through [ http://www.divetech.com ], and some rec OC dives as well.

I have my own dive computer (Suunto Solution Nitrox). It's a typical rec computer that stays at a fixed %O2 for an entire dive. Of course, when I dive with the Inspiration, my PPO2 will be "constant" instead.

What's the "best" way to figure my N2 loading, O2 exposure, surface intervals, etc., when switching back and forth between CCR and OC? If I need to use tables or a PC to figure this stuff out, that's just gonna suck.

 

[caveseeker7]

The only way to track that accurately is a computer that has the ability to calculate both fO2 and pO2 (HS Explorer, DeltaP VR2 and VR3, Buddy Nexus, Cochran something or other).

Or do a lot of math with fO2 and pO2 tables.

I'm pretty sure Seb at Divetech will take care of you and insure that you'll stay within safe limits.
A rebreather experience is usually a pretty short affair in the scheme of things, and limited to fairly shallow depths. Most places here do it in the pool.

You can use your OC computer and have a broad margin regarding N2 loading.
I doubt you'll rack up enough O2 saturation to become an issue (the daily limit at 1.0 ata pO2 is 5 hours, and there's a fair chance your diving will be at the shallow water setpoint of 0.7 ata). But again, ask the instructor you're doing the intro with.

 

[schwerve]

Or do a lot of math with fO2 and pO2 tables.

It isn't like I've forgotten how to use tables, but... crikey. The PADI Wheel was even more of a pain than tables when I used it (before I got smart and bought a 'puter).

A rebreather experience is usually a pretty short affair in the scheme of things, and limited to fairly shallow depths. Most places here do it in the pool.

No way am I "experiencing" a pool on Grand frickin' Cayman!!! (panic-skims divetech.com) Oh, OK, they'll take me for a spin at Turtle Reef. Crisis averted. Like to pull chains, dontcha? :smileysto:

 

[bubblefree]

No way am I "experiencing" a pool on Grand frickin' Cayman!!! (panic-skims divetech.com) Oh, OK, they'll take me for a spin at Turtle Reef. Crisis averted. Like to pull chains, dontcha? :smileysto:[/QUOTE]

Divetech offer a 1 to 2 Hour Rebreather Experience dive from one of their two locations to about 30 to 60 feet max. I did it this year before attending Innerspace to get my basic rebreather certification (Mod 1). It's useful to get a feel of what diving with a rebreather feels like but beware.....It is natural for your buoyancy to really suck on the first few rebreather dives. The main reason for me was that I was used to breathing in as I wanted to ascend and breathing out when I wanted to descend. Totally subconciously I found myself doing this and then running into a rock or something else hard and unforgiving! Hope you enjoy it.

 

[wedivebc]

Quick bio: I have about 250 dives under my belt over about thirteen years. Got my AOW and EANx (up to 40%) certs. In May, I'll have an Inspiration "experience" through [ http://www.divetech.com ], and some rec OC dives as well.

I have my own dive computer (Suunto Solution Nitrox). It's a typical rec computer that stays at a fixed %O2 for an entire dive. Of course, when I dive with the Inspiration, my PPO2 will be "constant" instead.

What's the "best" way to figure my N2 loading, O2 exposure, surface intervals, etc., when switching back and forth between CCR and OC? If I need to use tables or a PC to figure this stuff out, that's just gonna suck.

The most basic way is to calculate the fo2 for the setpoint (say 1.3) at the deepest point of the dive and then use the table or set your computer to that mix ie lets say you are doing a 100ft dive at 1.3 setpoint you would have the equivalent of 32.5% o2 in the mix. Treat it as a nitrox dive with tables and you will be well within limits. GAP or v-planner will also allow CCR dive planning if you are doing more advanced dives.

 

[Se7en]

Divetech offer a 1 to 2 Hour Rebreather Experience dive from one of their two locations to about 30 to 60 feet max.

60 feet depth on a 1.3 setpoint is the same as an air dive to about 25 feet. Your NDL is measured in days not hours... but you will hit the 100% cns limit at around 3 hours.

In short, don't worry about it.

I generally dive an air computer shallow, and tables deep

Se7en

 

[ZinnX]

60 feet depth on a 1.3 setpoint is the same as an air dive to about 25 feet. Your NDL is measured in days not hours... but you will hit the 100% cns limit at around 3 hours.

How do you calculate this?? I assume just take the 1.0 pp02 for 5 hours limit and divide in your setpoint. i.e. 5/1.3 = 3.8 hours

 

[caveseeker7]

You just read it off the NOAA tables.

NOAA Oxygen Exposure Chart
NOAA CNS Percentage Exposure Table

 

[Crazyduck]

Advanced Nitrox Class really helps here- topics are covered in the class.

You really need the NOAA Oxygen exposure chart.
Plus, if you want to get fancy you can use a multi gas computer and that way have multiple setpoints. Or am I getting ahead of the conversation.

I have to say that at the end of my “introduction” 2-1/2 hour pool dive I felt
FREAKING INCREDIBLE!
No dry mouth, enough O2 in the mix that I felt great, I was wide awake for the rest of the afternoon. I was ready to sell the farm after that! :uptosome:

 

[caveseeker7]

I was ready to sell the farm after that! :uptosome:

Problem is it was their farm.