2 Examples of Why You Should Always Anaylse Your Gas

[wreckweasel]

Originally Posted by Fiona

I have always had my own analyser, I wouldn't rely on anyone else to do it.

....and that quite simply, is it. Trust no-one, always analyse.

[Paul Brookes]

In the original post, there was the following quote:

"Oddly enough in Croatia, the same valve fitting (threads) is used for all gases, facilitating confusion for those that are not properly vigilant."

Now, I am not a trained gas blender so I might be missing something really obvious, but surely we all use DIN 25mm threads here in the UK on our cylinders? Why is having the same thread size unique to Croatia?

On the subject of gas analysis, not analysing your gas after dropping off for a fill is stupid and asking for trouble - you must KNOW what you are breathing. However, if a commerical filling station managed to mix up the He and O2 in my fill and presented the cylinders to me without checking themselves, then that (IMO) would be neglegence of the highest order - easily fatal as was nearly the case here and could easily end up in the hands of solicitors.

The only exception I can think of is, if you see you cylinder being filled directly from a compressor, you can pretty reasonably certain that there is only air in there.
Personally, I dive a rebreather and I analyse the air diluent cylinder to calibrate the analyser before analysing the O2 - everytime I put the unit together.

[GLOC]

Originally Posted by Paul Brookes

In the original post, there was the following quote:

"Oddly enough in Croatia, the same valve fitting (threads) is used for all gases, facilitating confusion for those that are not properly vigilant."

Now, I am not a trained gas blender so I might be missing something really obvious, but surely we all use DIN 25mm threads here in the UK on our cylinders? Why is having the same thread size unique to Croatia?

AIUI there are M26 valves in most of Europe for O2 and M25 for the air, hence the comment.

If this is wrong, I am sure someone will clarify it quickly enough.

Regards

[Janos]

Originally Posted by GLOC

AIUI there are M26 valves in most of Europe for O2 and M25 for the air, hence the comment.

If this is wrong, I am sure someone will clarify it quickly enough.

Reading the original post, I took it to mean that they use the same valve threads on the supply tanks. Which I think we do here as well (ie Bullnose).

Janos

[Nick_lincoln]

Originally Posted by Scubee

Not a personal dig at all, and there was no comment about anybody's financial situation. If your buddy is happy with the situation, then fair enough. I have heard people say they will get one, but it isn't needed at the moment coz they can always use the one belonging to X. Who knows what financial hardship X may have gone through to protect him/herself from oxtox?

Definately plan to get one, only qualified as BSAC Advanced Nitrox diver this january so its on the list to get. Using buddies analysers is ok for now, but there will be situations where their analysers aren't there to be used.

[David Pye]

Originally Posted by Scubee

Nope. i would agree with Nigel to a point, however, my (limited) knowledge of physics is that gas is a gas because the molecules are further apart than if it were a liquid or solid. This allows the molecules to move. jiggling the cylinder around gives the molecules a bit more momentum, allowing them to mix up a bit.

Logically, gas is squished into a cylinder so there isn't a great deal of room for movement. However, the amount of gas that's in the debris tube & valve is minimal, and, quite honestly, I doubt it makes that much of a difference as it will be the first out when the valve is opened before the analyser is introduced.

I think there's a not completely irrelevant amount of gas in the debris tube and valve stem - while the volume isn't MASSIVE, don't forget it is under 232 bar of pressure, so would be at least a few lungfuls I think.

One of the characteristics of gas molecules is that they are more mobile than molecules in a liquid, and even more so than molecules in a solid. This means that diffusion occurs fastest of all in a gas, slower in a liquid and pretty much not at all in most solids, which is why I have to admit I still can't quite convince myself to believe that rolling the cylinder did anything to accelerate the process. By way of an example, consider how quickly a little smoke in the corner of a room will quickly diffuse by Brownian motion to give you a room full of smoke

[Fiona]

Originally Posted by Garf

test all your gas on the day you dive it.

No problem.

That would have been my first problem

I read some of these threads and thought silly buggers, analysing your gas is easy and obvious

I am diving tomorrow so yesterday I received a call from Howard, I was in the dive shop (where else) Howard is checking I have a 50%, yes no problem it has been sat in the garage for months, I hadn't used it as it is now out of O2 clean and needs to go in.

I get home and decide to change the stage kit to a Halcyon one I bought, so I check the mix and it's only 33%. OK no problem drain some off and go for a top up. I know it isn't O2 clean but only by about a month, I had already stripped the labels off before I took it in, OK now I have another problem not only is it not clean it is also out of test I wonder if I could bluff my shop and just put it in but decide this is not a good policy.

There isn't a problem Brett lends me a cylinder so I have my 50% again

Moral of the story - don't wait to analyse your mix, do it in good time