Equipment Rebreather incident with narration

[Wibble]

I was surprised that he would need to ask the captain to send down deco gas. Would not his buddy and other divers be able to supply him?

A sign of diving "alpinist", insufficient bailout. That's a killer.

Obviously any other CCR diver (or even OC) would be able to donate additional gas.

The standard reason for needing more bailout than you've carried is hypercapnia (CO2 hit) where you're breathing like a steam train and have a ridiculously high SAC. However, you're supposed to plan the dive to take into account a high SAC, although it's nigh-on impossible to carry sufficient gas for a full-on CO2 hit where your SAC could be 4x or more your normal rate.

 

[Wibble]

If the diver in the video is the person I think it is, then he has a bit of a reputation - for doing fairly big and cool dives (great) but also for a bit of ego and old-school safety approach, at least when not teaching (perhaps not great).

So that can explain why someone might not want to call a dive and instead try to debug the problem.

Task fixation can bollox up your logical thought processes when the "chimp brain" takes over from the logical brain.

This was the cause of my full-on bailout when I flooded my unit at 50m/165ft because I was utterly convinced that the "little drips" were just loose lips. Actually I'd knocked the DSV (the mouthpiece open & shut lever which was partly open and letting a small trickle of water in) as I had tripped stepping off the boat's dive lift when jumping in and landed face first, ouch.

I ultimately ended up with a caustic cocktail which finally woke the logical brain that kicked the chimp off the loop. I literally said to myself "Golly gosh, a caustic cocktail, bail out now", so I reached down, pulled the bailout reg and hose from the cylinder, purged it, breathed, rinsed my mouth with some nice salty water, threw up the SMB, then did a textbook bailout ascent with gas switches and 25 mins of deco, exactly as per my training and practice. Was just like the old open circuit deco days. On the boat, the rebreather had around 2 litres/4 pints of milky caustic liquid.

WITH HINDSIGHT... (or what I learned from this incident)

• I made a simple situation far worse by being distracted by task fixation (clearing the loop of a mouthful of water) and not looking at the bigger picture
• Be aware of the chimp taking over; that b'stard will kill you
• Do a sanity breath from the bailout to clear your head and start thinking logically; this is one advantage of a bailout valve, but you should ensure your configuration allows you to easily do a sanity breath as a matter of course. At the time I was diving with a DSV and standard bailout which required the regulator hose to be re-stowed, so being lazy, I didn't do the sanity breath. Now I dive with a necklaced bailout which is trivial to bail out and back on the loop.
• Had I have done a sanity breath at the beginning, the incident would never have ended in a flooded unit with a caustic cocktail as the DSV would have been closed.
• If those "few drips" won't go away... IT IS A LEAK. Now deal with it as a leak checking as far and as quickly as you can that the obvious things are closed: DSV, T-pieces, ADV (auto diluent valve), etc.
• Most serious issues won't get better; the dive is over, end it while you can and stop delaying the inevitable whilst making things worse.
• If you've been messing around for more than a couple of minutes, you are part of the problem and you need to get out of the water

The caustic cocktail was loop water getting into the inhale side. Caustic is immediately recognisable and you'll naturally spit it out as it's so obnoxious.

It took me a couple of weeks to assimilate all the lessons from that incident. I now look back on that incident not as a OMG I nearly died, but as a superb lesson that will stay with me -- what doesn't kill you makes you better!

 

[Chris-Wood]

A sign of diving "alpinist", insufficient bailout. That's a killer.

Obviously any other CCR diver (or even OC) would be able to donate additional gas.

He had deep bail out and 50% for deco.

Pretty standard on UK boats at least to have a cylinder or two on the boat that the skipper can send down for situations like this.

Worst case, more time on 50%.

He said, and he will have dived with these guys before, that no one else would have 100% to donate, as they are also carry gas to 6m and relying on the boat for the 100%.

 

[justinthedeeps]

Great credit to this diver for sharing this real life scenario

First sign (?) @ 7m40s loop volume keeps decreasing--despite level depth--resulting in unexpected ADV supplementation of lost loop volume. Though this went mostly unnoticed

Rare but possible, this could not only be a sign of a leak, but also can be a sign of frozen sensors and a decreasing -real- ppO2, regardless of what possibly blocked sensors read. Shrinking loop volume can be caused by oxygen being consumed without replacement, with sensors 'stuck' on high values (wet membranes or old sensors can do this)

In fact, when repeated bubble check discovered no leak, despite unexplained shrinking loop volume, I would be strongly suspecting sensor block. And this can even be caused by leaks. Eventually inert gas builds up in the loop to the point of being nearly hypoxic, or rapidly hypoxic during ascent.

At the very least, this might call for a dilPO₂ sensor check, followed by manual (or solenoid) return to setpoint to verify accurate sensor range (including mVs) and responsiveness. But why though... when bail out is easy?

 

[justinthedeeps]

In higher level courses we are taught skills to stay on the loop longer, if necessary, but we are also taught to bail out from up to ~100 metres deep.

Unfortunately, I think the advanced philosophy can encourage people to stay on the bottom and solve the problem the 'advanced' way (e.g. 'bubble checks' etc), rather than choosing the simplest fix (BO and go up)

68 metres is an easily managed bailout for someone who hasn't lost control yet--best chosen early!

 

[steinbil]

I was surprised that he would need to ask the captain to send down deco gas. Would not his buddy and other divers be able to supply him.

This is a method used by RB divers with surface support. Colour coded SMBs are used to let the surface know what they need. Reduces the amount of cylinders a diver needs to carry.

A sign of diving "alpinist", insufficient bailout. That's a killer.

He had deep bail out and 50% for deco.

Pretty standard on UK boats at least to have a cylinder or two on the boat that the skipper can send down for situations like this.

Worst case, more time on 50%.

He said, and he will have dived with these guys before, that no one else would have 100% to donate, as they are also carry gas to 6m and relying on the boat for the 100%.

I'm no CCR diver, but this sounds super scary to me. Not even team bailout, which already sounds sketchy, but boat bailout? I got the impression from the video that he's not carrying enough 50% to complete the deco by himself. I guess you could say that he could complete his deco on 50% if he got gas from a buddy, but team bailout with improper deco gases doesn't sound very appealing. And how many teams are in the water? He states the boat can only drop gas once - so a single 100% bottle for all the divers on the boat. All this in open unprotected water with currents? And none of the divers in the water has an O2-bottle. Is this really common practice in the UK?

 

[Wibble]

A sign of diving "alpinist", insufficient bailout. That's a killer.

He had deep bail out and 50% for deco.

Pretty standard on UK boats at least to have a cylinder or two on the boat that the skipper can send down for situations like this.

Worst case, more time on 50%.

He said, and he will have dived with these guys before, that no one else would have 100% to donate, as they are also carry gas to 6m and relying on the boat for the 100%.

AIUI, the dive was only to 67m/220ft. This is pretty easy for every diver to have sufficient bailout for the planned depth for all but the worst CO2 hit. We lost a UK diver last summer for diving with insufficient bailout; quite the community wake up call.

Have watched the video again and I appreciate that the need for the drop bottle was the poor deco gas of 50%.

My alpinist point was that all CCR divers should be carrying sufficient bailout gas to get themselves out of the water unaided, with the caveat of the bad CO2 hit. On a MOD2 dive, it's normal to dive with two bailouts; the bottom bailout and one deco bailout, typically around 50%, which you can get on to at 21m/70ft. 50% isn't a great gas for accelerated decompression and will extend the dive a fair bit, which must be taken into account in the bailout planning.

A flooded unit is a very legitimate reason for bailing out!

As there was a drop-bottle available on the dive boat AND had been agreed with the skipper in advance with the correct signal, then it makes sense for the diver to request that better gas from above to shorten the dive time. I assume this was why the drop bottle was requested, not because the bailed out diver had insufficient 50% available to complete the extended dive (which would be a failure in planning).


@Chris-Wood - welcome to ScubaBoard

 

[davehicks]

Just one other thought and suggested outcome of this scenario. Can we all agree that putting a bucket over the top of your CCR is NOT a good design? There were no bubbles being produced by this leaking unit because the manufacturer placed a bubble trap over the whole thing. This severely limits the utility of a bubble check at the beginning of the dive, something that all CCR divers should be doing. Of course, this guy skipped all the normal and expected safety checks when building his unit and diving it, so it likely would not have helped in this case.

I would be expecting a Service/Recall notice from the vendor to all owners. If you need to protect the unit, please do so with a fully vented cage and not an airtight bucket that slowly fills up with lost gas.

If you own one of these units (AP Inspiration?) then bust out a drill and start making some holes in that bucket.

 

[Wibble]

I'm no CCR diver, but this sounds super scary to me. Not even team bailout, which already sounds sketchy, but boat bailout? I got the impression from the video that he's not carrying enough 50% to complete the deco by himself. I guess you could say that he could complete his deco on 50% if he got gas from a buddy, but team bailout with improper deco gases doesn't sound very appealing. And how many teams are in the water? He states the boat can only drop gas once - so a single 100% bottle for all the divers on the boat. All this in open unprotected water with currents? And none of the divers in the water has an O2-bottle. Is this really common practice in the UK?

For these types of dives to the MOD2 depths around 60m/200ft to 70m/230ft, it's very common in the UK for the boat to run a "lazy shot" line with trapeze.

Lazy shot:
This is where the primary shot line with the grapnel and buoy is used to "shot" the wreck (the grapnel hooks into the wreck). A lazy shot is a buoy with a secondary line about @40m/130ft long that attaches with a quick release snap shackle to the main shot line; this has a weight attached 2m/6ft from the end to give a catenary sag. Close to the snap shackle is a small bungee loop where your tag is attached. A 3m/10ft or 4m pole is attached to a ~6m/20ft line with a buoy and the other end attached to the lazy shot at 6m/20ft forming a trapeze for the decompressing divers to hold on to.

Everyone goes down the lazy shot and attaches their "tag" to the bungee loop, then continues down the main shot line, attaching their strobe above the wreck. They do their dive and MUST come up the shot line, collecting their strobe on the way to their first stop. The tide will be running so it's quite common to have to hold onto the shot line, or just gently fin towards it. As the ascent proceeds, the diver will eventually get to the snap shackle from the lazy shot which is attached to the main shot line. The diver collects their tag and, if there's no more tags on the loop, will unclip the lazy shot from the main shot line. Everybody then drifts in the current with the now vertical lazy shot line, proceeding through their stops and all hanging around the 6m/20ft trapeze. Some will ascend higher if they prefer shallower final stops.
/Lazy shot


The benefit of a lazy shot is that ALL divers are on the shot line, so if there's any problems there's plenty of gas and experience to help resolve the issue. Also, the boat will follow the two buoys of the shot line as it drifts away from the primary shot line.

The drop cylinder should, in theory, never be required. In this case I surmise that the flooded loop diver was using the drop bottle as he should have had sufficient gas to complete the dive, but wanted to shorten the dive with a better gas. (Maybe there were good biscuits on the boat ;-) )

The plan would never be to rely upon the drop tank for bailing out. OK, maybe if it's a very deep MOD3+ dive, but this is all part of the overall dive plan along with team bailout - well out of scope here. For MOD2 dives a single diver can carry sufficient bailout gas from the worst possible point, i.e. at the end of the bottom time.

Should several divers decide to bailout on the same dive, they should all be self-sufficient with their own gas, but also have backup gas supplies carried by the with other non-bailed out divers deco gas if required -- as they're all together on the lazy shot.

 

[LFMarm]

I have been trained to carry all my bailout gas also on MOD3+ dives. Team is there to help but you needed to be able to get out on your own in case of separation or multiple people bailing out at the same time. For serious dives it means carrying 5+ AL80s which is the least fun part of these dives. I personally never do dives where I don’t have enough bailout gas to get out on my own.