why NOT using OC/DSV?

CCR900

Simon

Whilst having the utmost respect for your comments on CO2 symptoms and the diver's inability to go OC, I must ask you a question. I have asked myself a number of times (I own the NEMO & owned the KISS OCDSVs); is the current quality of OCDSV available equal in quality to the OC regulators that we are so used to using at depth? Yes all is cool at 20m but what about at 100m?

I have heard negative comments on the single O ring on the NEMO and the below par breathing standard of the KISS OCDSV.

Rgds

Fil

Pelagian

I agree that CO2 can be too debilitating to faciliitate an offboard switch. But the last deep dive I did the 7% oxygen I used in my dil would have yielded a PO2 of .11 ATA at 20ft, so now I have lingering Hypercapnia symptoms compounded by Hypoxia, during the longest runtime section of the dive where I'm most likely to break my canister through.

I would chose to go open loop on an off board tank(which I rotate through as I ascend, too keep them appropriate for the depth) or on Oxygen if I was less than 20ft.

After my head had cleared I'd switch off board completely.

Cheers

Seb

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Simon Mitchell

Fil,

Excellent question. I think the answer is a definite no. My KISS OC DSV does not breathe as well as a dedicated OC second stage. I have tried switching at 100m and it works, but I do have to confess to having worried about the increased breathing resistance in a situation where you are short of breath. The option (which I tried and which works) that I resolved to use if ever in extremis in this setting is to more or less "ventilate myself" during inhalation using the purge button. This markedly reduces the inhalation resistance. I remain a little worried that this requires some thought, but its a fairly easy and intuitive manoeuvre when you are gasping for gas!

Seb,

A couple of points.

First, while your analysis of the most likely timing of scrubber failure makes superficial sense (ie, late in the dive), in practice, this is not when most events occur (at least in my experience of treated divers and accident analysis). Catastrophic CO2 events frequently occur early when the hard work of descent and swimming about coupled with work of breathing at the bottom unmasks some problem, such as defective scrubber material or an incorrect assembly of the unit. It follows that being plumbed into your hypoxic mix is exactly what you want. As I said earlier you can replumb into a more oxygen-rich bailout when shallower if it is appropriate to do so.

Second, I guess the point of my earlier post was to sound a warning that it is very easy to describe rational simple-sounding contingency plans for CO2 toxicity in internet posts. Managing the reality in-water has proved to be less than simple, even in expert hands. I'm not convinced you would be capable of "choosing" to do anything much more complicated than turning a knob (and as I said above, even pushing the purge button worries me). It follows that I remain to be convinced by your plan. I think it would be instructive for you to talk to a diver who has actually suffered a severe in water CO2 hit (if you know one).

Regards,

Simon M

Mdemon

My Bob H BOV has a cheap Dacor Viper on it. It works at 80m but WOB is nasty - funnily enough I did what Simon did and tried purging, which helped. Bob Howell also produced them with Poseidon regs on, which will blast as much gas as you need regardless of depth. I have also seen an ATX50 (IIRC) on the Polish BOV.

I just wish these things were made as standard. Even if it's the worst breathe in the world, that BOV will save your life if the alternative is a full-blown, incapacitating CO2 hit.

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ScubaDadMiami

How about using a high performance regulator from offboard gas that is placed on a neck strap? I realize that it would take up a fair amount of "real estate" on the neck area. However, it would perform well at depth, and it seems that it would not take a large effort to get to it (especially when compared to deploying a regulator from offboard gas otherwise).

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wizbang

Koputai/Jason M are you about.?
Have you fitted a BOV to your Mk yet.?
If so what one and how have you got it configured.?
If not, why not?
thanks Wiz

jradomski

I had a NEMO and sold it to Phi (I just decided I didnt like the DSV/OC combo, I prefer an off board reg), The Single ADDED O-ring just makes the loop 100% gas tight.. The dsv is manufactured to some pretty tight tolerances and without this new o-ring it BARELY leaks.. (its actually its 2 orings) one on the barrel and one on the attachment point for the reg.. The barrel o-irng was added on the updated version.

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All posts are personal opinions and DO NOT reflect any affiliated agency unless specifically stated.

ROB DAVIE

Try the BOV from Divematics USA, Inc. Works like a champ!

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Drmike

I have bailed to my BOV at 105m and it breathed reasonably well not as well as my Apeks thats bungeed on the bail-out tank thats feeding it - bit I can always bail off the BOV and switch to that if I really need to.


The concern here is KISS. I have been completely disabilitated by CO2 to the extent that I couldnt even move (or had any will to move, despite knowing I was being poisoned) Turning a handle is simple and in my experience the human mind does not wish/willingly do anything major that would in any way interupt breathing when in these situations.

Changing the status quo is not easy in this situation. Powerful basic survival instincts kick in and tell you 'hey I can breathe so what!' your less powerful intellect tells you that what your breathing is poisonous - but your basic instinct says 'im breathing - all is well - why the hell should I stop breathing - even for a moment - spit out the mouthpiece fumble for a 2nd stage' - etc etc yeh I know its bad but at least Im breathing'. 'Maybe Ill just sit here and rest for a while - I am feeling quite Ok about all this - cant really be bothered too much - feeling ok really - just need to rest a while....lights start to dim.....


The above was my experience and what prompted me in part to go for a BOV.


Having the 2nd stage on the bail tank is great. I have great doubts how useful it would be in a real hit.

If you have a BOV the only thing your changing is your turning a handle. Take any OW student and ask them to take their reg out of their mouth underwater and you can see that it is a stress raiser. Its not KISS. When we are taking a hit - no matter what experinece we are - we are all OW students.

If your buddy takes a hit - you try getting him to take a 2nd stage!! a lot easier if you just turn his handle for him.


Plumb it into your deepest off board trimix tank. Even if its not normoxic for the majority of dives as long as you dont breath it on the surface (why would you? - Would you breathe from your non normoxic OC 2nd stage on the surface too?) it will be suitable for instant bail at any depth at anytime. Take a few sanity breaths get your act together and then either bail to the offboard 2nd stage or plug in the optimum bail gas for the depth you are at.

Switch valves to feed OC gas to the BOV can lead to breathing the wrong gas (I think this makes the risk outweigh the benefit) at depth and adds complexity. I preffer to KISS. I know that I do not bretahe from my BOV above a few meters deep. Any other time as soon as I bail I ask myself what depth I am at and if I need to plumb in another mix or shall I just go to OC.


I dont see the BOV as a replacement of the bail out tanks 2nd stage. I see it as a first stage bail, and intermediate step between CC and OC. Although I can stay on the BOV buy plugging in different gasses I also have the option not to.

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nigelh

I had one in my hand but the CO2 in my brain said "Sorry. Removing the loop from your mouth is not an option."

I've posted it here before but my only solution was to start exhaling through my nose, which flooded my mask as it was a bit of a steam train breathing rate, and let the ADV kick in. This seemed to work where a 'normal' DIL flush hadn't. As soon as I could I just ripped out the loop and stuffed the reg in my mouth and then shut off the loop. My son, as buddy, has not forgiven me for that dive yet.

I now have strong views on how to pack a scrubber and a BOB DSV.

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nigelh