Bail Out and BOV

Osiris said:
I'm puzzled how a BOV that uses the same components as a standard reg, with WOB tests to the same standard could be worse that a standard reg?
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The issue is that BOV's even though some may use all the same components of a standard reg - are modified by combining a reg and DSV. Their WOB is not held to the same standards as a standard reg, and it is well known that the WOB on BOV's is not as good as a standard reg.

So I am happy with a BOV being a transitional tool to a reg I know works really well when I want it to, making my WOB as low as possible to blow off as much CO2 as quick as I can.

Also in the case of a caustic cocktail situation, your BOV may be rendered useless.
 
Osiris said:
I'm puzzled how a BOV that uses the same components as a standard reg, with WOB tests to the same standard could be worse that a standard reg?

A hypercapnia episode as one of the worst things that could happen to a diver (OC or CC), in the case of the CC diver being able to stay on a BOV for the entire recovery phase with access to all our b/out would surely be the nirvana we all seek?
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Here's something I posted elsewhere, scant data I'm afraid:

Old thread resurrection. I was reading this: Knock Yourself Out (Carbon Dioxide ? The Diver?s Nemesis) John Clarke Online and realised I didn't know the difference in WOB between OC and CCR, and given its so important to PCO2 I googled it. This thread came up, and here is what I found:

0.41-0.96 J/L (50m, 62.5lpm, Apeks XTX range: http://www.apeks.co.uk/downloads/XTX_Brochure.pdf)
2.0 J/L (40m, 62.5lpm, Inspiration: http://www.apdiving.com/downloads/downloads/Inspiration_WOB_08_06.pdf)
0.92 J/L (40m, 62.5lpm, iCCR - section 8.3.7 pp81: http://www.deeplife.co.uk/or_files/DV_OR_WOB_Respiratory_C1_101111.pdf)

...

The OC performance of the ALVBOV is also available.

0.87J/L (50m, 62.5lpm, OC ALVBOV: http://www.deeplife.co.uk/or_files/DV_DL_ALVBOV_Breathing_Params_A3_100318.pdf)

...

Matt.
 
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Osiris said:
I'm puzzled how a BOV that uses the same components as a standard reg, with WOB tests to the same standard could be worse that a standard reg?

A hypercapnia episode as one of the worst things that could happen to a diver (OC or CC), in the case of the CC diver being able to stay on a BOV for the entire recovery phase with access to all our b/out would surely be the nirvana we all seek?
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The Shrimp BOV on OC works VERY well, I have seen it tested and it falls within the 1.6 J/L. It works much better than most OW OC regs coming in that I have seen as a reg tech. I have used it to practice bail from 2200' back in Jackson Blue (when the flow was nonexistent). I breathed off it the whole way out.
 
Regardless of WOB of the regs, who thinks they could switch from CC to OC in under 2mins when sufferering a CO2 hit?
 
Sorry to resurrect an old thread, but I finally have the first version of my offboard gas connection setup. It wasn't particularly user friendly on its first outing, but that was because the hose lengths weren't ideal to allow me to connect the QC6's together when kitting up on the boat. I'm gonna mess about again and try to make it better.

All I've done here is add a Y block at the bottom of the stock JJ 3-1 diluent manifold. I then have 2 hoses feeding the 3-1 manifold. 1 comes from the on board diluent first stage, the other hose has a female QC6 connector, and hooks in to a male QC6 coming from the off board first stage.

My plan was to run the offboard hose through the bottom L) hole on the JJ wing and connect up near my L) hip, however this made it very difficult to manipulate when kitted up. By increasing that hose length and finding a neat way to stow it after it's connected, I think the system will be more user friendly.
 

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Are you going to have different IPs on the first stages or just feed from both and have the off board switched off?

I'm trying to decide how to have on board access to my off board. Just can't decide between all the pros and cons. Especially with whether or not to use a gas switch block.
 
Tiptopperoo said:
Regardless of WOB of the regs, who thinks they could switch from CC to OC in under 2mins when sufferering a CO2 hit?
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in my own experience, not a hope in hell unless you do it within seconds of starting to feel breathless, wait 10 or 20 seconds to be sure you have an issue and your screwed. Having a CO2 hit at 20m scared the shit out of me. First sign of feeling breathless these days and I'm off the loop for sanity breaths.
 
I had co2 issues at 18 meters depth. I noticed it due to an increased rate of breathing, about 30% higher than normal. I stopped and it didn't go away. Since direct ascent was an option and there were plenty of buddies around I decided to see how it would develop. I signalled to my buddies and moved to the deco station (open water area of the mine at six meters) where I stayed on the loop for five more minutes, just to see what would happen. In the end I went from my normal rate of breathing (12/min) to 16/min which was the point where I noticed it up to 18/min when I bailed out 7 minutes after noticing (stop and wait included). I had no real sense of breathlessness. Rate of breathing started to normalize after about two minutes on OC. Only remaining symptom after ascent was a slight headache which I strongly associate with post-CO2 retention (I've had it a couple of times on OC in high current/deep as well as in CO2 experiments in medical training). Scrubber use was a total of 180 minutes and it had settled considerably, it rattled like a pair of maracas when I disassembled it. All my fault but that's a separate post.

In the end I do not believe that "hits" in the sense that you go from feeling fine and with a normal rate of breathing straight to all out panic exist outside of exposure to bad gas. It does not make physiological sense to me and it's contrary to my own experiences with CO2 from diving, experiments and from a clinical setting. What I am convinced of however is that much of the breathlessness will be suppressed if you're narced or exposed to high pO2 and that the bodys response can easily be missed. That it would totally eliminate the reflex leading to increased breathing with retained CO2 or acidosis seems unlikely though.

Just based on an informal experiment I've participated in myself we tested end-tidal CO2 during breathholds, with and without pre-breathing pure oxygen. The urge to breathe still appears but it is strongly suppressed (I did 12 minutes compared to my usual limit of about 3,5-4). The twitching of the diaphragm appears as well but this too is much weaker.


To summarize my personal belief is that the signs are there but that they are easily missed in our application. I also believe that my own ability to detect rising CO2 is pretty good, to the point where I'm confident that I can bail out before I am incapacitated. I run a DSV with an easy access bailout regulator instead of a BOV with that belief in mind. Hopefully it won't bite me in the ass one day. For those that have had bad experiences BOVs are the obvious solution and if you're on the fence a BOV is probably still the best idea.
 
I have heard form a couple of people who say they could get on to OC OK after getting what they suspected was a C02 hit. I have also herd from several who said taking the loop out of their mouth to go OC was about as easy as plucking out their own eye.

I dive a BOV because of the latter group.

If i get a C02 hit and its easy to go OC? Great. OK i wasted some money and suffered a bit of jaw ache but ho hum I can live with that.

On the other hand if i got a C02 hit and couldn't get on my OC gas because I didn't have a BOV? Id be dead and my family cant live with that.


QED i use a BOV

ATB

Mark
 
alexasigno said:
Are you going to have different IPs on the first stages or just feed from both and have the off board switched off?

I'm trying to decide how to have on board access to my off board. Just can't decide between all the pros and cons. Especially with whether or not to use a gas switch block.
Click to expand...

I'm gonna have a play with it, though I'm not actually confident that it will work. After all there is the venturi effect to take into account, and then you have to tune the bailout reg to a less ideal IP. I'm thinking the best way to do it is just dive with the onboard valve on, and the offboard off. If I need to bail to my BOV, then I bail and have to turn the offboard valve on.

I just had a play tuning the breathing on the the shrimp BOV last night and it breathes really well.
 
Tiptopperoo said:
I'm gonna have a play with it, though I'm not actually confident that it will work. After all there is the venturi effect to take into account, and then you have to tune the bailout reg to a less ideal IP. I'm thinking the best way to do it is just dive with the onboard valve on, and the offboard off. If I need to bail to my BOV, then I bail and have to turn the offboard valve on.
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Or dive with the offboard valve open and the onboard valve closed. Have a full Ali-80 of dil to bail out to. And if you lose the off-board open the onboard valve and use the 3l to run the unit, bouyancy in the wing, dill flushes etc, for the ascent.

If you have a very controlled rescue scenario you could take a diver on OC BOV from off-board, open on-board valve, close off-board valve, switch to a fresh off-board via swage lock, then open off-board valve and close on-board valve, new cylinder with no need to remove a reg until his breathing is under control.
 
Mark Chase said:
I have heard form a couple of people who say they could get on to OC OK after getting what they suspected was a C02 hit. I have also herd from several who said taking the loop out of their mouth to go OC was about as easy as plucking out their own eye.

I dive a BOV because of the latter group.

If i get a C02 hit and its easy to go OC? Great. OK i wasted some money and suffered a bit of jaw ache but ho hum I can live with that.

On the other hand if i got a C02 hit and couldn't get on my OC gas because I didn't have a BOV? Id be dead and my family cant live with that.


QED i use a BOV

ATB

Mark
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I currently run a BOV, but being relatively new I don't know that I have a great number of reasons why other than it seems like the safest/quickest approach to getting on OC. I also read somewhere of an account where a diver's buddy switched him to OC via the BOV and he swore it is what saved his life.

Never having a known CO2 hit, I'm wondering if it is, say, worse than after running hard for a couple of miles. I know I breath extremely heavily after my runs. At least it feels like I will never catch my breath. I never thought about whether I could hold my breath long enough to switch from a loop to a necklace (or other 2nd stage being offered). Is a CO2 hit similar, worse, different than heavy exertion?

Just wondering.

Thanks,
Chris
 
There is no faster way of getting bailout gas to a diver than a BOV, period.

Now, there may be some who think that speed is not critical, or that they would have no problem going to an offboard second stage during a CO2 hit. That is a matter of personal opinion that does not alter my initial statement. But my question to those who choose NOT to dive with a BOV is "why not?" What are the objections to a BOV? You may be correct that you don't NEED one, but what are the objections to having one just in case?

Here's what I've heard over the years, and I discounted all of them.
- The initial cost (miniscule compared to the cost of the rebreather)
- Additional dead space (also minimal and can be eliminated by switching to offboard second ASAP)
- Additional hose routing (please, get serious)
- Additional failure points and O-rings (have you counted the number of O-rings in your rig already?)
- Another item to have serviced (like servicing one extra second stage is going to kill you?)

Any of you naysayers want to add to the list? As far as I'm concerned, you don't need any reason to justify using a BOV, you need a damn good one to justify NOT using one.

Ken
 
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