Isolation Manifold Question

[TSandM]

Actually, even behind you, you're more likely to have a leak from something involving a first stage, than a blown tank o-ring or manifold failure. Hoses come loose, o-rings fail, and if you are in an overhead environment, you can hit and dislodge the first stage (one of the reasons DIN regulators are preferred in those settings). If you aren't wearing a thick hood and thick gloves, it's surprising how often you can localize a leak, either by sound or touch. Of course, we have yet to have a massive one. I really think they are rare.

 

[mahjong]

Agree. Nice to know the massive failure is rare. Knock on wood, I've never seen one (I have seen a couple divers take the plunge without opening their valves on singles, and one solo diver doing so on doubles--he barely made it back to the surface!)

I've indeed seen more than a few rather leaky first-stages on divers underwater. There were very steady streams of bubbles--far more than could be mistaken for a bleeding Sherwood first-stage--but these still were not catastrophic leaks. In all but a couple cases the diver him/herself was unaware.

Actually, even behind you, you're more likely to have a leak from something involving a first stage, than a blown tank o-ring or manifold failure. Hoses come loose, o-rings fail, and if you are in an overhead environment, you can hit and dislodge the first stage (one of the reasons DIN regulators are preferred in those settings). If you aren't wearing a thick hood and thick gloves, it's surprising how often you can localize a leak, either by sound or touch. Of course, we have yet to have a massive one. I really think they are rare.

 

[DA Aquamaster]

Agree. Nice to know the massive failure is rare. Knock on wood, I've never seen one (I have seen a couple divers take the plunge without opening their valves on singles, and one solo diver doing so on doubles--he barely made it back to the surface!).

In general a diver, and in particular a technical diver, should be able to reach their valves.

Where it can get dicey is in a dry suit. If a dry suit diver is hot dropping in a current or dropping into a curerent and pulling their way up a current line, and in either case needs to be substantially negative on entry to begin an immediate descent, then if the valves are turned off, there is a potential for the suit to quickly squeeze and make it impossible for the diver to reach his or her valves. That results in the diver going all the way to the bottom with no gas to the suit, the wing or the regs. That generally ends really badly for the diver.

Obviously in that situation you want to be doubly sure the valves are open and the hoses properly attached before stepping off the boat. I had one incident where a very new and especially "helpful" mate on the boat checked my valves for me while standing behind me before I jumped off the boat. I felt a lot more going on than just the expected stabilizing hand in rough seas and decided to recheck to ensure both regs were delivering gas. Sure enough, the mate had gotten confused with the doubles manifold and had turned both posts off.

I turned around and communicated intensely with him. Something helpful yet educational to the effect of: "If you ever touch my ******* valves again I'll ******* kill you."

The captain then reiterated to him in a slightly more polite manner that you never touch a technical diver's valves as it tends to make them really cranky.

 

[Akimbo]

Akimbo do you have one pressure gauge for each post or one total.

No, but I check the pressure before and after equalizing before re-closing the isolation valve. I keep the gauge on the primary regulator/cylinder. I suppose if I were worried enough to have a gauge on both regulators I would wear a third independent pony… or switch to surface supplied.

 

[VooDooGasMan]

No worries just wondering, thanks for the input.

 

[Akimbo]

Agree. Nice to know the massive failure is rare. Knock on wood, I've never seen one (I have seen a couple divers take the plunge without opening their valves on singles, and one solo diver doing so on doubles--he barely made it back to the surface!)

I've indeed seen more than a few rather leaky first-stages on divers underwater. There were very steady streams of bubbles--far more than could be mistaken for a bleeding Sherwood first-stage--but these still were not catastrophic leaks. In all but a couple cases the diver him/herself was unaware.

I doubt reliable failure rate stats exist but this article in Advanced Diver Magazine provides a useful indication of flow rates for various failures: Life Ending Seconds, 3000 to Zero in 72 Seconds. A table based on this article is reprinted in the SDI Solo Diving Manual, Table 1, Page 38.

In the end it probably doesn’t matter what the stats are. People are satisfied to make some of their daily safety decisions based on probability, driving on a freeway for example. Yet other decisions necessitate, in their view, a backup or a backup to a backup. How different individuals respond to the self-preservation instinct is interesting.