Current Views on Hypoxic bailout/BOV Configurations

[Gareth J]

Do the benefits really outweigh the complexities and limitations? Compared with the manual alternatives?

I dived fro a long time using the original AP Valve, and relying on my independent regulator on a necklace.

In many ways it simplified things as @Wibble says. On my MOD3, I had a slightly hot bottom mix and a decompression mix. We planned various bailout protocols. The final deep dive did rely on us running the bailout as a team if it had all gone to rat **** at the the end of the dive.

Despite my comfort with the off board bailout, I was very ware that for a CO2 hit it may be impossible to make the exchange between the mouthpiece and regulator.
From all of the research I read, and talking to a few people who had had CO2 hits. The feedback I got was although people knew they had a problem. The instinctive (blood chemistry) drive to take another breath stopped them making an exchange. Those that had resolved the problem and only managed by aggressively flushing the loop with clean gas, until they could hold their breath for a few seconds to make the exchange, initially they had been unable to do this.

This was the final driver for me to get a BOV. Currently it is plugged into the onboard DIL for the vast majority of my diving. Because I have been doing very little MOD3 type diving.
When I have had problems, I have flipped the BOV, for 'safe / sanity gas', and flushed the loop with the off board Bailout. My preference is to flush the loop, and stay on the loop if possible, as I was taught on my MOD3, but the BOV is very reassuring.

Also, for my OC buddies, it reassures them that they can safely switch me to clean gas --- although if plumbed into the onboard 3 litre cylinder, that may not last long!

One of the big points at the moment, is I do currently do quite a lot of unhitching my side slung bailout during and after a dive. This is problematic if plumbed in, unless it can be easily unplugged.

Gareth

 

[Wibble]

Thank you for those points. Very informative.

Connecting the BOV to the 3litre dil seems just plain wrong. With any depth it would be rapidly depleted and would probably not give anywhere near enough time in the case of a CO2 hit to curb the breathing for the switch to a larger cylinder. In any case the wing's connected to the diluent making empty dil doubly problematic.

One would expect the BOV to be connected to the primary (deep) bailout using some form of high-flow connector such as a QC6, as opposed to a standard Schrader valve (BCD, drysuit) which would not have sufficient flow for a deep bailout especially CO2 induced? Would you have both QC6 and a Schrader tail on the deep bailout such that you could offboard plumb in some diluent?

Would you have other QC6 connectors on the other deco bailout cylinders? Along with the Schrader valves for offboard / drysuit / buoyancy backup? What size tails would you have on the QC6's? I normally use 50cm/19" Schrader tails for offboarding -- same size?

What's the "standard" for QC6s? Males on the cylinders, female on the long BOV LP hose?

 

[Tracy]

Would you have both QC6 and a Schrader tail on the deep bailout such that you could offboard plumb in some diluent?

Would you have other QC6 connectors on the other deco bailout cylinders? Along with the Schrader valves for offboard / drysuit / buoyancy backup? What size tails would you have on the QC6's? I normally use 50cm/19" Schrader tails for offboarding -- same size?

What's the "standard" for QC6s? Males on the cylinders, female on the long BOV LP hose?

I don't know that there is an actual standard. But they way I and most others run involve a female QC6 on the unit and male stems on the bailouts.
I run QC6s on all of my bailouts. My 50/20 also has a standard bc qc for backup suit inflation if needed. It is my lowest helium gas should my on board tank become un-usable or depleted.
My BO QCs are on 22" hoses, I find that gives plenty of length for plugging in from either side but doesn't come near the bottom of the tank when standing to prevent damaging the fittings.

 

[grantctobin]

Males on the bottle allow cleaning of the nipple before being plumbed in. E.g stage sits in a cave for a few weeks, has crud around rim. Pressurize, push the nipple against cylinder to clear it, then plumb in. Iirc, the manufacture intended it to flow the other way (female to male), but 1/100 in the dive community does that.

 

[JonG1]

I use Omni Swivel QD's (as does Jas) which seem a bit more common in the UK than QC6's although there are also a lot of the AP valves systems in use too.

Both are high flow especially as it will be mainly helium (trimix) in use as opposed to air (think AP's is rated to 40m on air at relevant flow rates).

Omni have a reputation for maintenance issues but no problems yet despite a lot of use in slate mines, and easy to self service, when needed. They don't have the purge fucntion that the QC6 have though.

I only have a QD on the deep bottle, on the basis that any further switch should be less stressful and can be planned and set up in advance like any other gas switch.

That said if you did add tails to other tins it gives you redundancy in the event of a 2nd stage issue on that bottle.

 

[kensuf]

A BOV provides:

Quick access to sanity breaths
Additional source of gas entry into the unit
And is easy enough to explain to other divers

The con that I see is it's a little more weight and there is some extra consideration on hose routing / gas source - if you're using a 3L bottle for DIL, inflation and the BOV, it's not going to be a lot of gas at any sort of depths. If I was using a 3L bottle for DIL I'd probably have the BOV plumbed into an external bailout source.

For my BOV I use a locking omniswivel QD at the mouthpiece. This is a slight deviation for me, I normally run QC6s to drive gas into units so that I can be compatible with my team. I've run into problems with QD's that wouldn't mate which is usually because the nipple on some is a bit too long, but my BOV is not something I would be sharing.

 

[JonG1]

Of relevance is the point that if you do choose to use a bov it's important not to lose sight of the potential need to switch out of it quickly if for instance its compromised by a caustic.

The alternate 2nd stage needs to be easily accessible and not buried under a stage, too far back in your arm pit, tangled in its keeper bungee etc.

I've been working with 3 bailouts in practice recently and noticed how easy it is to make the reg deployment hard.

Obviously it can be necklaced but that's another thread probably!

 

[Gareth J]

Of relevance is the point that if you do choose to use a bov it's important not to lose sight of the potential need to switch out of it quickly if for instance its compromised by a caustic.

The alternate 2nd stage needs to be easily accessible and not buried under a stage, too far back in your arm pit, tangled in its keeper bungee etc.

I've been working with 3 bailouts in practice recently and noticed how easy it is to make the reg deployment hard.

Obviously it can be necklaced but that's another thread probably!

That also highlights that bailout is a system that must be immediately available. Unlike a stage, which can be isolated after charging, it needs to be on and ready for use.
Those of us that dive with OC buddies are also aware that the bailout is our buddies AAS ( if they are not on a twinset or other redundant system.

 

[KevinNM]

From all of the research I read, and talking to a few people who had had CO2 hits. The feedback I got was although people knew they had a problem. The instinctive (blood chemistry) drive to take another breath stopped them making an exchange.

From the reports I’ve read and people I’ve talked too, that is the most common pattern. But a couple of people have reported just feeling more clumsy and and little bit off. And wondering why their teammates are shoving regulators at them. Not that a BOV isn’t perfectly usable is that situation, but a CO2 hit doesn’t always manifest in one way.

Both of the people involved were pretty confident that without their teammates intervention they wouldn’t have bailed out. While they were bouncing off the ceiling and floor of the cave, to the affected divers this wasn’t a big deal, while their their teammates knew something was horribly wrong with them.

 

[Wibble]

Those of us that dive with OC buddies are also aware that the bailout is our buddies AAS ( if they are not on a twinset or other redundant system.

Doesn't that violate the first principle: must be self sufficient?

Of course if you suddenly need it and there's a swimming bailout beside you, use it!

However, your first "muscle memory" reaction should be to grab your own bailout regulator. IMHO this should be practised on every dive, not least to confirm the thing's turned on and is in the right place, possibly with the secondary action to drag the cylinder forwards against the bungee (mine are sidemount bungeed) and pull out the reg.

I've been working with 3 bailouts in practice recently and noticed how easy it is to make the reg deployment hard.

That's a great point and supports the "check bailout on every dive" principle.