A Dangerous gas mixture

[pwl]

ALWAYS watch somebody fill your doubles[...]

this isn't always practical; ensuring your isolator is open before doing your own test would catch the problem that occurred here, however.

I knew there was a reason that even though I'm sure it's open I always take a sample from both valves.

this sounds like an even better standard procedure.

 

[battles2a5]

I've read so many horror stories about closed isolators that I am almost superstituous about getting fills. I only let 2 guys at my LDS fill my doubles and I always make sure the iso is open when I drop them off and pick them up. I always check pressure and mix at the shop after I've ensures the iso is open before I'll accept them. When I am in cave country I'm standing right there during my fills (and most of the guys down there are pretty good, anyway), but I still do the same routine when analyzing at the dive site.

Anyway, glad you caught it in time and the worst that came of this was a thread on Scubaboard

 

[wedivebc]

Use independant doubles, you'll never have this problem.

 

[Rick Inman]

While there had the tanks analized and it came up 42% oxygen!

At least you came out nice and clean.

I once watched a tank monk- ah, a dive shop employee hook a fill hose to my right post (isolator was already open), fill the tanks, take the hose off and hook it to my left post, turn on the pressure and then say with surprise, "Hey. This side is already full."

 

[MXGratefulDiver]

... and the moral of the story is to always get in the habit of doing a basic flow check before analyzing or pressure-checking your cylinders. Never assume the valve is open, and if it's closed, never assume that the gas in one side matches that in the other.

Back in the days before I knew anything about doubles, I was diving on the Cape Breton at a depth a bit in excess of 100 fsw, when a fellow in doubles swam up to me, pointed back behind his head, and gave me a little twisty motion with his hand. It took me a while to figure out that he wanted me to open his isolator valve ... and being the accommodating sort, I did.

Fortunately, nothing bad happened, because I found out later that the two of us had broken several basic safety protocols regarding the proper use of an isolation manifold. Number one among them is that whenever anybody but you is in a position to mess with your valves, you should ALWAYS do a flow check before breathing off of the cylinders.

In your case, I would also recommend getting an analyzer ...

... Bob (Grateful Diver)

 

[RJP]

Boy, I really misread the title of this post. When I saw "A Dangerous Gas Mixture" I had assumed it was going to be a post about a dangerous gas mixture. A better title for this post would have been "Careless diver get's lucky - gives Darwin a miss for another day!"

he *did* check in the store. the isolator being shut off then opened changed the final reading.

AT THE STORE: not only did he only check the O2 at just one post, he must not have checked the pressure at all. If he HAD checked the pressure at the store he would have found the problem; either by 50/50 dumb luck in checking the pressure on the tank that wasn't filled completely, or by being reminded by the presence of a pressure gauge in one of his hands to check the isolator to make sure he knew whether he was reading the pressure in one tank or two.

AT THE DIVE SITE: he seemed confounded by the low reading on his SPG until his BUDDY suggested checking the isolator...his BUDDY had to suggest he check the isolator? Following any proper gear set-up protocol/checklist would have had the OP checking that both posts and the isolator were fully open well before the point that he was standing there with his hands on his hips, looking at his SPG thinking "huh?"

Also, I'm a bit concerned about what come across as the lack of a well thought-out dive plan: "...the PSI went up to 1840 and my buddy and I figured that would be sufficient for one dive so we entered the water." At a minimum I would have liked to have read "We compared this to our planned dive and determined that 1840psi was well within the limits..." or even that "...we modified our plan to accomodate available gas." However I'm reading the OP as saying "we were planning on 'winging it' with full tanks, so we figured that 'winging it' with 1840psi was fine too."

Ultimately the diver and the diver alone is responsible for knowing exactly what is in his tanks - both mix and quantity. Yeah, some dope at the fill station was innattentive, but there were at least 6 or 7 specific points along the way where the OP would have caught the problem if he had followed a fairly simple, yet rigorous approach. However, even when he finally DID catch the problem he still ended up entering the water with an unknown mix. It could have just as easily ended up being a drastically hypoxic trimix if somehow the other cylinder was topped off with helium instead of air. Unlikely, of course, but no way to know for sure without analyzing.

To make matters even worse, the "buddy separation" in area that the OP admits was "tight and silty every where I went" could have been a huge problem if the gas in the tanks was actual some way-out-of-bounds mix.

Now, before I get crucified for slamming the OP, I know I am being a bit overly harsh but doing so to prove a point. As we're taught in tec and overhead training, an error chain in this type of diving is much shorter and much more likely to end very badly than in recreational diving. There's a certain level of rigor you follow on every dive - whether it's dive 50 or 500 or 5,000. You cut any corner and you are playing with your life. This time it was merely an inconvenience, but that wasn't for lack of trying on Darwin's part! Hell, if Darwin hadn't screwed with the OP's buddy's computer they might have been deeper than the MOD for a 42% mix before realizing there was a problem.

All that said, a genuine "thanks" to the OP for taking the time to share the story with us. Kudos for caring enough about your fellow divers to bare yourself so that we could learn from your experience.

 

[MXGratefulDiver]

Now, before I get crucified for slamming the OP, I know I am being a bit overly harsh but doing so to prove a point. As we're taught in tec and overhead training, an error chain in this type of diving is much shorter and much more likely to end very badly than in recreational diving. There's a certain level of rigor you follow on every dive - whether it's dive 50 or 500 or 5,000. You cut any corner and you are playing with your life. This time it was merely an inconvenience, but that wasn't for lack of trying on Darwin's part! Hell, if Darwin hadn't screwed with the OP's buddy's computer they might have been deeper than the MOD for a 42% mix before realizing there was a problem.

All that said, a genuine "thanks" to the OP for taking the time to share the story with us. Kudos for caring enough about your fellow divers to bare yourself so that we could learn from your experience.

It's pretty evident from the OP that this is not a diver who has ever HAD tech training ... so holding him to tech training standards is pretty pointless.

This is also a perfect example of why dive instructors generally do not encourage the use of doubles for recreational-level divers ... since by its nature it introduces a few extra ways to get yourself into serious trouble, and therefore the risks will often outweigh any possible benefit to using them.

For those of you reading this who are wondering what object lesson to take away from the story, perhaps the best (and most obvious) one would be to get some training in the proper use of doubles, if you've decided to use them. That training can take many forms, and doesn't necessarily need to be a formal class. But at a minimum it should cover some basic protocols for making sure your valves are in the position you THINK they're in, that you can reach and manipulate your own valves easily, and that you have developed an understanding of why more gas doesn't necessarily imply a safer dive.

... Bob (Grateful Diver)

 

[texey]

I DID check it at the dive shop using their analyzer. But I didn't insure the isolator was open for the check.

 

[texey]

... and the moral of the story is to always get in the habit of doing a basic flow check before analyzing or pressure-checking your cylinders. Never assume the valve is open, and if it's closed, never assume that the gas in one side matches that in the other.

Back in the days before I knew anything about doubles, I was diving on the Cape Breton at a depth a bit in excess of 100 fsw, when a fellow in doubles swam up to me, pointed back behind his head, and gave me a little twisty motion with his hand. It took me a while to figure out that he wanted me to open his isolator valve ... and being the accommodating sort, I did.

Fortunately, nothing bad happened, because I found out later that the two of us had broken several basic safety protocols regarding the proper use of an isolation manifold. Number one among them is that whenever anybody but you is in a position to mess with your valves, you should ALWAYS do a flow check before breathing off of the cylinders.

In your case, I would also recommend getting an analyzer ...

... Bob (Grateful Diver)

Thanks, and yes I plan I buying my own analyzer.

 

[texey]

Suprised you did not do an independent check of your Nitrox mix, just took what the shop gave you in blind faith.

I DID do an independent check of the Nitrox mix myself using the same post the employee used to check the gas.