Handling Hypoxic Bailouts with a BOV

dunny

dunny

Member
Hi All,

I'm doing my MOD3 in 4 weeks and really looking forward to it. I intend to discuss this with my instructor but wanted to ask the CCR community how they currently handle hypoxic bailout mixes especially when using a BOV. I also use drager gag strap.

My current config is a BOV connected via QC6 to offboard bailout (deep mix). I'm planning to "standardise" my gases so that I do not need to be changing my bailouts for different types of diving. As such my deep mix will probably be 10/70 for dives up to 100m.

From my own thinking I've made the following conclusions
  • The most likely place to have an incident is probably on the surface straight after jumping in. E.g. freeflow / flood.
  • The second most likely place to have an incident is on my shallow deco stops since this is where the majority of the dive time is spent.
My concern is that on jumping in for example if the unit flooded it would be so easy to flick the switch and breathe a hypoxic mix on the surface. Especially since I use a gag strap.

As such my current thought process is as follows.

  1. Dive with the ADV shut until 6m. I don't want to be taking huge breaths from the ADV and trusting the solenoid to keep up.
  2. Dive with the BOV plumbed into the deep bailout, if anything goes wrong just press the up button on the wing.
  3. On ascent when I reach my 12/9/6m stops unplug the BOV from the deep mix and connect to shallow deco gas normally 50%.
I thought long and hard about jumping in with the BOV connected to the shallow mix but decided it isn't workable since there is generally a lot to do on descent and likewise stopping on the shotline at 6m to screw about with QC with potentially another 11 divers behind me is just asking for trouble.

What does everyone else do? I read on RBW about this but it was 7 years old and wondered if people have changed there approach.

Cheers
 
I don't do too many dives at those kinds of depths... But I plug in my bottom mix (whatever it is) and then keep the 2nd stage on my 50% relatively handy. Its up front and deployable - right near my suit power inflator on my chest. I have switched QC6s before and its not a huge deal, but forgetting to do this would be potentially disastrous at depth since I am not following gas switching protocols with the BOV. I accept the risk of the hypoxic mix in the BOV for the first 5-10m since I can either hit the power inflator and go straight up fairly quickly, or switch to the 50% in a pinch.

Prepare for an onslaught of "this is why a BOV is bad" posts :p
 
Dunny, I am in a similar position to you and have had similar thoughts. I dive a rEvo and have my on board and off board gas plumbed into my bov via a y block with the off board having a QC6 on it, on the Y block I can switch between off board an on board gas. The idea is to have two gas plumbed in one breathable on the surface and the deeper gas. The issue I have found with the rEvo is that I am not able to isolate the ADV which is only fed by on board gas.
 
Semaj said:
Dunny, I am in a similar position to you and have had similar thoughts. I dive a rEvo and have my on board and off board gas plumbed into my bov via a y block with the off board having a QC6 on it, on the Y block I can switch between off board an on board gas. The idea is to have two gas plumbed in one breathable on the surface and the deeper gas. The issue I have found with the rEvo is that I am not able to isolate the ADV which is only fed by on board gas.
Click to expand...
I think I know what you mean but do you have any photos you could share?
 
dunny said:
I think I know what you mean but do you have any photos you could share?
Click to expand...

"Every time we sell a manifold or switch block, we shudder a little bit. The gas switch block is used in primarily by surface supply divers to switch from surface supply to emergency bailout gas. Manfolds are primarily used in gas distribution systems. But the key here is that there are not different gas mixtures involved. Unfortunately divers sometimes get the idea to match these products up with multiple cylinders and/or or quick disconnects to create some type of elaborate system for rapid switching between different gas mixtures and/or cylinders. Gas switching errors are very often involved in technical diving accidents. Over the years we've learned about several near misses and fatalities that were directly attributable to mistakes with switch blocks that were connected to different gas mixtures. No matter how careful the diver, or how many safeguards, we think using switch blocks with different mixtures is a very bad idea." https://www.divegearexpress.com/manifolds-switch-blocks
 
This is the whole conundrum that comes with using a BOV, how to run a system that has a breathable gas plumbed into the BOV at all times, I see three solutions they all have risks 1) switch to OC reg for shallow bailout scenarios, there is still the very real risk that you switch to the BOV that has a hypoxic mix, 2) plug in unplug gas for different stages of the dive, extra task loading during the dive could mix up plugging in the wrong gas, gets small amounts of salt water in the system, 3) use a switch block with gases for deep and shallower plugged in, in my case hypoxic and normoxic, need to develop a standard protocol for every dive ie at 6m switch from normoxic to hypoxic flush loop. I don't have shallow nitrox gases plugged in to my y block arrangement as described above, but in a full blown bailout scenario can plug in the shallow nitrox and oxygen bailouts to feed the BOV as needed, or I breath these from the OC reg.

I am not locked into the approach I described above and like the OP am interested to hear how others are dealing with this issue.
 
Last edited:
dunny said:
I think I know what you mean but do you have any photos you could share?
Click to expand...


here is a picture

full
​
 
dunny said:
Hi All,


From my own thinking I've made the following conclusions
  • The most likely place to have an incident is probably on the surface straight after jumping in. E.g. freeflow / flood.
  • The second most likely place to have an incident is on my shallow deco stops since this is where the majority of the dive time is spent.
M

Cheers
Click to expand...

You are making many assumptions here.
In my experience, BO has only ever been needed on descent (adv failure) or at the bottom, due to high work load. Both times I wanted my hypoxic BO. This is the stressful part of the dive. the shallow stuff other than jump should be slower and more relaxing.

My meg setup for deepies is as follows.

normoxix onboard 3l
hypoxic off board in 80 or steel.

everything is plumbed into the oboard reg for use, incld bov, wing bo etc.
the offboard has a qc to connect or disconnect it. mroe for convience than anything.
it is plumbed INTO the onboard first stage.

so... off board off or disconnected, you are on normoxic.
off board on and onboard off, you are on hypoxic.

for rich BOs, its a reg.

switch blocks are a horrendous idea.

also, if you breathe hypoxic for a few seconds at the wrong depth, you arent going to die instantly. better than water.
 
dunny said:
Hi All,

I'm doing my MOD3 in 4 weeks and really looking forward to it. I intend to discuss this with my instructor but wanted to ask the CCR community how they currently handle hypoxic bailout mixes especially when using a BOV. I also use drager gag strap.

My current config is a BOV connected via QC6 to offboard bailout (deep mix). I'm planning to "standardise" my gases so that I do not need to be changing my bailouts for different types of diving. As such my deep mix will probably be 10/70 for dives up to 100m.

From my own thinking I've made the following conclusions
  • The most likely place to have an incident is probably on the surface straight after jumping in. E.g. freeflow / flood.
  • The second most likely place to have an incident is on my shallow deco stops since this is where the majority of the dive time is spent.
My concern is that on jumping in for example if the unit flooded it would be so easy to flick the switch and breathe a hypoxic mix on the surface. Especially since I use a gag strap.

As such my current thought process is as follows.

  1. Dive with the ADV shut until 6m. I don't want to be taking huge breaths from the ADV and trusting the solenoid to keep up.
  2. Dive with the BOV plumbed into the deep bailout, if anything goes wrong just press the up button on the wing.
  3. On ascent when I reach my 12/9/6m stops unplug the BOV from the deep mix and connect to shallow deco gas normally 50%.
I thought long and hard about jumping in with the BOV connected to the shallow mix but decided it isn't workable since there is generally a lot to do on descent and likewise stopping on the shotline at 6m to screw about with QC with potentially another 11 divers behind me is just asking for trouble.

What does everyone else do? I read on RBW about this but it was 7 years old and wondered if people have changed there approach.

Cheers
Click to expand...

My 2c fwiw
I dive a rEvo with a shrimp using QC6 connections. Like you its plugged into hypoxic bottom mix from the start. My thought process is that if something goes wrong when I jump in, I just push the inflate button and fix whats up at the surface.
If something goes wrong before the bottom mix is breathable I keep the 50% reg ready to go.
On the ascent once I get to 21M and i'm just decoing thats when i switch over to the 50% that has a QC6 plumbed into it. This involves me having to unplug the deep bailout and plugging in the 50%. A bit of a faff but I have nothing else going on at this stage of the dive.

Cathal
 
cathal said:
My 2c fwiw
I dive a rEvo with a shrimp using QC6 connections. Like you its plugged into hypoxic bottom mix from the start. My thought process is that if something goes wrong when I jump in, I just push the inflate button and fix whats up at the surface.
If something goes wrong before the bottom mix is breathable I keep the 50% reg ready to go.
On the ascent once I get to 21M and i'm just decoing thats when i switch over to the 50% that has a QC6 plumbed into it. This involves me having to unplug the deep bailout and plugging in the 50%. A bit of a faff but I have nothing else going on at this stage of the dive.

Cathal
Click to expand...
Great, same as what I'm planning. Have you noticed that you have to strip and clean the shrimp more since doing the QC swap i.e. salting up the barrel?
 
I have a QC6 on my 50% bottle, but I never use it. Mostly because if you leave the deep mix plugged in, you can take back gas breaks during long 6m stops by just switching to OC for ~5mins. Personally I get pretty snotty after a few hours and the drier OC air helps clear up my sinuses. They are still gross, just nice to blow my nose and clear my mask with impunity.
 
I have my BOV connected by an QC6 to one mix and that's my bottom mix. The bottom mix like all my BO cylinders has a second stage fitted, my thinking is that the BOV is only for the initial bail out and will soon be switched to the second stage. I wouldn't trust myself to be unplugging and plugging QC6's while holding my breath so don't see the point of having more than one cylinder connected. I like to keep things simple.
 
Careful planning and not rushing at start or end of dive and I don't worry about having hypoxic plumbed into my BOV. I pay particular attention to PO2 in shallows and try not to jump in with loop in (just like OC not jumping with hypoxic backgas). Its no different than OC diving with hypoxic backgas - just be prepared to bailout to an appropriate stage.
 
My BOV is always plugged into my onboard dil. I don't use a gas block and I never plug in off-board gas to my BOV. I dive my unit as an O2 rebreather down to 6 meters and if I had to bailout above 6 meters, I would bail to my off-board rich gas. My BOV is strictly used as a transitional bailout as I am moving to my off-board bailout. I've seen too many mistakes made with gas switching blocks and i find that having the off-board plumbed into my BOV limits my options in the event I need to hand off a tank to a member of my team.

I find this set up is more in line with the keeping it simple philosophy and makes for a cleaner, more streamlined configuration. Works equally as well in open water and in the overhead environment.

Just my $.02
 
All diluent/bailout is offboard and plugged into diluent MAV via QC6. Bypass on the MAV goes to BOV so whatever gas is plugged in goes to the unit and BOV. Keeps it simple with only one gas in use at a time. Onboard bottles are O2 and inflation. If there's a chance of getting hung up or delayed in the shallows I will plug in my deep deco, usually a 190 (18/45) bottle, for descent. On ascent, always have a breathable gas plugged in such as 50%.
 
Charlie Roberson said:
All diluent/bailout is offboard and plugged into diluent MAV via QC6. Bypass on the MAV goes to BOV so whatever gas is plugged in goes to the unit and BOV. Keeps it simple with only one gas in use at a time. Onboard bottles are O2 and inflation. If there's a chance of getting hung up or delayed in the shallows I will plug in my deep deco, usually a 190 (18/45) bottle, for descent. On ascent, always have a breathable gas plugged in such as 50%.
Click to expand...
Do you have a photo? What rebreather do you use?
 
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