Nitrox as CCR diluent

[teksimple]

So I am headed to Galapagos with my Mk 15.5, and would like to make sure that my single K-bottle of O2 will last the entire two weeks on the liveaboard, or at least as long as my $1255 kegs of Sodasorb.

I have a bit of muscle as I lift weights almost every day. More muscle burns more O2, right? I am new to rebreathing, and with the hella strong currents expected around these islands, as well as my camera and lights, I am thinking I will blow through some O2. My diluent sphere holds approx 21cf, which is supposed to last approx six hours. Four dives a day, maybe 4-6 hours underwater per day...that would definitely put an impact on the 188 cf of O2 in the K-bottle. I only have one.

One way I thought to save O2 is use the nitrox off the M/V Sky Dancer and fill my diluent bottle with that. My max depth would rarely (if ever) exceed 100' anyway. This sounds a little more risky as far as increased chance of hyperoxia, but what do you think?

 

[Scubaroo]

Do you have a baby booster to get the O2 out of the K bottle? Jetsam make a pneumatic one you can run off scavenged air from used scuba tanks.

 

[teksimple]

Do you have a baby booster to get the O2 out of the K bottle? Jetsam make a pneumatic one you can run off scavenged air from used scuba tanks.

Yes, I am supposed to get mine next month, as per Kim. I have seen one of those Jetsam baby boosters run non-stop in a dive shop in Hawaii for months without failing.

The issue is, total quantity of O2. If I use 20 cubic feet of O2 a day, my K bottle would run out after 9 days. But if I flushed from my diluent bottle at depth, I would obviously use less than that.

 

[BigJetDriver]

One way I thought to save O2 is use the nitrox off the M/V Sky Dancer and fill my diluent bottle with that. My max depth would rarely (if ever) exceed 100' anyway. This sounds a little more risky as far as increased chance of hyperoxia, but what do you think?

Tek,

You will be doing yourself a favor if you run nitrox in your dil bottle. As you know, oxygen injection only occurs as necessary to make up oxygen loss from metabolic consumption. You will start with more O2 in your loop, so initially the solenoid will fire less often, and, of course, you have less nitrogen. Then, any time you inject some diluent you will "freshen" the loop. Your system will work to maintain set-point regardless.

The down side is, of course, your MOD, which with NN32 is 130 fsw, and you say this is not a problem. Your CNS clock, and OTU tracking will still run normally.

 

[teksimple]

Tek,

You will be doing yourself a favor .....

Thanks for the feedback. I am just not sure why it was not specifically mentioned in my class or what I have read, but maybe because it doesn't make economic sense since air is cheaper.

 

[caveseeker7]

Kent, Kim Meineche uses nitrox as diluent in his KISS-valved Dolphin CCR. He is the only person I know of who usually does so. You might want to contact him for some pointers.

 

[nigelvh]

You will be doing yourself a favor if you run nitrox in your dil bottle. As you know, oxygen injection only occurs as necessary to make up oxygen loss from metabolic consumption. You will start with more O2 in your loop, so initially the solenoid will fire less often, and, of course, you have less nitrogen. Then, any time you inject some diluent you will "freshen" the loop. Your system will work to maintain set-point regardless.

I'm having trouble with this.

Trying to work it out in I just don't see an advantage unless you virtually go full semi-closed. If you 'freshen' the loop surely you can't increase the O2 content or you raise the ppO2 so you must be loosing O2 which the solenoid will have to replace.

What am I missing?

 

[BigJetDriver]

I'm having trouble with this.

Trying to work it out in I just don't see an advantage unless you virtually go full semi-closed. If you 'freshen' the loop surely you can't increase the O2 content or you raise the ppO2 so you must be loosing O2 which the solenoid will have to replace.

What am I missing?

Nigel,

Glad to see you over here as well!! The remark is meant in only the most general way. As you know better than most folks, the oxygen replacement rate is based soley on metabolic use rate. If the useage rate remains stable, and the loop remains completely closed (i.e. no venting), the injection solenoid only fires when the PPO2 is drawn down to its trigger point. Given the conditions stated, there is only a small benefit for the first few breaths, since you started with more O2 in the mix. After that, the only benefit it is that it contains less nitrogen than air.

If you do have to bail-out to OC due to some problem, the benfit will be that you will be bailing out to nitrox, rather than air.

As I say, given his stated conditions, it cannot hurt, and (in general) will help the situation.

Cheers!

 

[hornetplt]

I have used NITROX 32 for diluent on my modified constant manual CCR Azimuth. I don't see any real benefit for NITROX diluent on rigs that control ppO2 via electronics. Because of MOD bail-out considerations, I have sense gone back to strait-up air.

Nigel,

Glad to see you over here as well!! The remark is meant in only the most general way. As you know better than most folks, the oxygen replacement rate is based soley on metabolic use rate. If the useage rate remains stable, and the loop remains completely closed (i.e. no venting), the injection solenoid only fires when the PPO2 is drawn down to its trigger point. Given the conditions stated, there is only a small benefit for the first few breaths, since you started with more O2 in the mix. After that, the only benefit it is that it contains less nitrogen than air.

If you do have to bail-out to OC due to some problem, the benfit will be that you will be bailing out to nitrox, rather than air.

As I say, given his stated conditions, it cannot hurt, and (in general) will help the situation.

Cheers!

 

[O2BBubbleFree]

Hi all,

Please help this rb wannabe in his continuing education...

If I’m understanding all this right, the hyperoxia concerns stem from the fact that adding diluent with a higher FO2 (relative to air) will cause a larger positive swing in the loop PO2. Please correct me if I’m worng.

I have used NITROX 32 for diluent on my modified constant manual CCR Azimuth. I don't see any real benefit for NITROX diluent on rigs that control ppO2 via electronics.

Your above statement implies (by it’s converse) that there is some benefit to using NITROX 32 for manually-controlled RBs. The only benefit I can see would be not having to manually inject O2 as often. Are there other benefits?

I guess, in the middle of a dive, if you hit your low PO2 limit just before an anticipated decent (where diluent will be added) you could refrain from adding O2. In contrast, an eCCR would add O2 solely based on the current state of the loop, not being able to anticipate.

Also, by ‘constant manual’ CCR, you are talking about a constant mass flow, manual add (KISS-style) O2 feed, correct?

With a constant flow of O2 it seems to me that the positive PO2 swing (relative to setpoint) would have a longer duration due to the fact that it’s being constantly ‘fed’ O2. Wouldn’t this increased time above the setpoint additionally increase your risk of hyperoxia? Is there some way to easily increase the duration of your loop’s low PO2 state to counterbalance the high PO2 state? Or is this slight deviation trivial when talking about the OxTox timeframe?

Thanks, again.