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I thought I'd share an interesting little incident that happened to me this weekend. I've got to admit it taught me a couple of things (or should I say 'reminded'). Some background - my kit has been described as "ADIR", or "Almost DIR". Ie long hose, isolating manifold etc etc. Think DIR with enough tweaks in just the right places to infuriate the purists
I was diving mid-channel on a wreck in 63m. I wasn't with my usual buddy and managed to lose my replacement. I finished the dive, blew the blob, got to around 33m for the first stop and was sitting there waiting for the minute to tick over when there was this almighty BANG and shockwave - enough to scare the cr*p out of me. "Thunderflash", thinks I. "Must be a problem topside and the skipper's calling the dive but I do wish he hadn't dropped it quite so close to my DSMB!"
Then all hell seemed to break loose. I disappeared in bubbles. Lots of them. They were collecting underneath me, and were all around so I couldn't really see what was going on. Suit inflation? Cylinder O-ring? Burst LP hose? By the time I had collected enough of my wits to do something I was at 19m. I managed to dump enough buoyancy to get back in control while closing the centre manifold to at least save some gas. Then shutdown the spare reg which I thought was freeflowing after the supposed thunderflash shockwave. After what seemed like an age I seemed to stop it and get fully back in control.
Finished the rest of the deco without problems, and got back on the boat. Apparently it was quite impressive on the surface! Oh, and no thunderflash.....
Kit post mortem revealed the over pressure valve had gone on the main (right hand, long hose) reg - the opposite one to the one I shutdown to fix the problem(!).
Most likely explanation - the main 1st stage went TU for reasons as yet unknown and blew the OPV before overpressuring the main reg putting it into massive freeflow. I was so witless after having the damned thing explode next to my ear I didn't realise that it was a main reg freeflow(!) and just carried on breathing, more concerned about buoyancy and shutdowns than hamster cheeks. I was horizontal in the water which meant I collected a nice raft of bubbles that very quickly lifted me to 19m before I could fix things.
As the cylinder pressure dropped the 1st stage sorted itself out, which happened to coincide with the left hand shutdown. Main reg was breathing OK so no problems.
Things I discovered -So would I do anything different? No. I keep on thinking it through and I can't see anything that might have made things happen differently. This was exactly the sort of scenario that I froze half to death in Dorothea in February practising for when I did my mix course, and the emergency responses worked a treat. Maybe I could have recognised the freeflow 'hamstercheeks' feeling quicker? But I do think next time I hear a loud bang underwater I'll be reaching for the manifold much faster!
- OPVs go with one helluva bang. Especially when it's right next to your ear. It's enough to stun you.
- It's surprisingly difficult to work out where bubbles are coming from when you are surrounded by them, even if it's a freeflow. Especially after (1).
- A freeflow bubbles underneath you when horizontal in the water, and you rise surprisingly quickly!
- Isolating manifolds rock. (Cue manifold vs indies Holy War....
)
- Isolating drills rock even more.
- Never underestimate the importance of self-rescue. It can happen to you. And because of the initial unexpected loss of buoyancy and deco schedule I wouldn't have expected my buddy to have been available even if they were with me on the ascent. There's no point in potting two divers.
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Originally Posted by stillbubbling 
