A gas loss non-emergency

[PfcAJ]

I've ALMOST had this happen before (always caught pre-dive), and its almost always after moving hoses around and not tightening it, but at least once I've had a hose come loose on a fitting that I KNOW I tightened by wrench. Weird **** happens underwater that seems to defy the laws of the universe.

 

[TSandM]

flots, your questions about gas are good ones.

A .7 SAC rate would be a highly stressed SAC for both of us. We also did not turn the dive on gas -- If I remember, I had about 300 psi to go to turn, and Peter had a little less than that. We turned on deco.

The nice thing about cave dives is that (at least in MX) what you did going in, you do going out. There is seldom enough flow to notice, or change your gas consumption. So, if it took me 1700 psi to get where I am, it should take the same to get home. Of course, I have TWICE that much to get home (in this case, plus 300 psi), so if I am stressed, I still have lots of gas. In the almost inconceivable event of Peter losing ALL his gas, we would certainly have a brief period of higher consumption, but a gas-sharing exit is something which we have drilled so many times that, within a short time, we should be back to baseline consumption. We also build in some conservativism by going into the cave very slowly, so that it's quite easy to exit faster without working very hard at all.

Diving all the way to thirds with two divers is not terribly conservative, which is why we seldom do it. It takes quite a problem to render a person diving manifolded doubles unable to access any of his own gas, though.

AJ, this was a weird one. We don't use hose protectors and this hose had not been moved or changed. Peter breathed the stage for 30 minutes on the way in without seeing anything untoward. He had been on it for about five minutes on the way out when the leak happened, and he can't remember doing anything that torqued or twisted the hose. Just one of those things!

 

[Hatul]

It's a good point as the loose hose probably would show up in a pre-dive check, though it's not practically possible to check for every gear failure. This anecdote points out that we usually can overcome one mistake, but with each added mistake the risk of tragedy increases. Accidents tend to happen when mistakes pile up and it becomes impossible to recover.

 

[Akimbo]

…As long as there's no overhead and no deco, bad gas planning in OW is generally only cause for embarrassment, not a funeral...

Sadly, you had to use the word “generally” to remain accurate. I think the most important lesson here for the general recreational diving population is not gas planning, but emotional preparation to handle an emergency.

There is nothing wrong with running low on air and surfacing — as long as the diver can make it to sunshine without injury. It happens all the time and was normal procedure for decades before SPGs and BCs. Piling on backup systems is not without consequence. It requires the skill to use them, diagnose more complex systems, and pack all the extra gear.

I contend that backup systems and gas planning are useless without panic control. I would go farther to say that backup systems and gas planning are unnecessary in the vast majority of accidents IF panic was under control.

http://www.scubaboard.com/forums/advanced-scuba-discussions/378868-panic-experienced-diver.html

 

[Doppler]

That's why we train and practice... glad everything turned out fine... but not surprised at all.


Sidebar observation: I'd guess that four out of ten hoses have been overtightened, two out of ten are a little loose, and only 40 percent correctly installed. Hint: It's the oring that makes the seal, not the thread.

Given only the options of too tight or too loose, the latter can usually be corrected during a dive (as illustrated here). The former will often manifest itself as an extruded oring.

 

[Greenjuice]

As long as there's no overhead and no deco, bad gas planning in OW is generally only cause for embarrassment, not a funeral.

You are right, of course, in OW it is nearly always not a big deal. The rigour I was setting, was in how closely a diver should stick to a plan. If the agreement was to come back with at least 500 psi, then I would like to suggest that it should be more than just embarrassing to not dive that plan. Somehow, it should be considered a tad more seriously than that.

 

[Hatul]

That's why we train and practice... glad everything turned out fine... but not surprised at all.


Sidebar observation: I'd guess that four out of ten hoses have been overtightened, two out of ten are a little loose, and only 40 percent correctly installed. Hint: It's the oring that makes the seal, not the thread.

Given only the options of too tight or too loose, the latter can usually be corrected during a dive (as illustrated here). The former will often manifest itself as an extruded oring.

So what's the correct way to tighten a hose?

 

[Greenjuice]

IF panic was under control.

http://www.scubaboard.com/forums/advanced-scuba-discussions/378868-panic-experienced-diver.html

Indeed. I suggest considering a panic event as a near miss - just as important if not more than equipment failure. It is the coincidence of near misses that leads to serious consequences. A diver with a low threshold for panic carries an increased risk burden like one who repeated goes into deco.

 

[KeithG]

So what's the correct way to tighten a hose?

The technically correct method would be to use a torque wrench to tighten to manufacturer specs. But not the wrench you use on the lug nuts on your car tires. Hoses are torqued to inch lbs not foot lbs.

Not sure how many reg techs do this. I claim most tighten "by feel".

Under tighten eventually gets you a loose hose. Over tighten generally destroys your first stage by stripping the female threads. Your hose fitting is often made of stronger metal than the first stage body. An extruded o-ring "should" not happen as the fitting "should" bottom. At least that is how industrial hydraulic hose fittings are designed....

---------- Post added May 5th, 2014 at 01:09 PM ----------

Sadly, you had to use the word “generally” to remain accurate. I think the most important lesson here for the general recreational diving population is not gas planning, but emotional preparation to handle an emergency.

There is nothing wrong with running low on air and surfacing — as long as the diver can make it to sunshine without injury. It happens all the time and was normal procedure for decades before SPGs and BCs. Piling on backup systems is not without consequence. It requires the skill to use them, diagnose more complex systems, and pack all the extra gear.

I contend that backup systems and gas planning are useless without panic control. I would go farther to say that backup systems and gas planning are unnecessary in the vast majority of accidents IF panic was under control.

http://www.scubaboard.com/forums/advanced-scuba-discussions/378868-panic-experienced-diver.html

Panic is a strange thing that appears to be unpredictable.

I posted awhile ago about my divebuddy's equipment failure http://www.scubaboard.com/forums/near-misses-lessons-learned/444928-split-reg-hose.html and I am very impressed at how calm she remained (and I told her so after the dive!).

I think it has something to do with your training and experience with the "current conditions". We were in very benign conditions that we had lots of experience with. Not so sure what the result would have been if we were in more difficult conditions.

As an example, I witnessed a pair of divers panic at the surface when they realized they where being VERY SLOWLY swept away from the boat - in Bonaire! Ended up in a bad scene. Way too much blood and anguish. I should post about it....

 

[flots am]

You are right, of course, in OW it is nearly always not a big deal. The rigour I was setting, was in how closely a diver should stick to a plan. If the agreement was to come back with at least 500 psi, then I would like to suggest that it should be more than just embarrassing to not dive that plan. Somehow, it should be considered a tad more seriously than that.

A 1000' surface swim with everybody on the boat watching is usually an incentive to not do it too often, although some people just can't take a hint and do it again.

However I was mostly making the point that a lot of OW divers miss: If you're inside something and run out of gas and can't share, it's going to be fatal. If you're inside something and run out of gas and can share, but didn't do good gas planning, it's possible that both divers will die.

I wasn't bring this up to annoy TS&M, who AFAIK, does good gas planning, but to the OW divers who seem to think that it's OK to "go in just a little way" or rack up significant deco without understanding that the entire safety protocol for an OW dive is now useless.

And as long as I'm on a roll, one of the things I don't actually like about the OW curriculum is that it's infected with Horrible Positivism.

New divers are taught how safe SCUBA is, and what to do when various Bad Things happen, and almost without fail, if they do as taught, they actually will be safe. However it doesn't specifically cover what happens if they exceed the parameters of OW diving. New divers equate "a little beyond training" as "a little riskier than OW diving", when in reality it's like the difference between being ticked and being shot.

Sorry for the hijack.

---------- Post added May 5th, 2014 at 01:40 PM ----------

Sadly, you had to use the word “generally” to remain accurate.

I used "generally" because I've actually seen divers panic when not out of air, and come rocketing to the surface. Thankfully it's infrequent, with no injuries so far, but yes, it's absolutely possible to die underwater with a bad enough screwup.

---------- Post added May 5th, 2014 at 01:43 PM ----------

flots, your questions about gas are good ones.

A .7 SAC rate would be a highly stressed SAC for both of us. We also did not turn the dive on gas -- If I remember, I had about 300 psi to go to turn, and Peter had a little less than that. We turned on deco.

Thanks for the response. I wasn't trying to harass you; .7 is actually normal for me in the winter with thick drysuit underwear, a little current and a whole bunch of lead, so the dive plan looked a little scary for an overhead when I ran it in vPlanner.

flots.