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I've been lurking on this great forum long enough - and it's now time to come out into the open and ask for advice on a gas mixing problem peculiar to tek diving in Japan. Sorry for the long introduction, but without it, the Q's won't make sense!

I'm a UK diver living in Japan and am active in the emerging tech diving community in Tokyo. Here in Japan, diving is popular - but very very different to the UK. The dive sites are stunning (really stunning but that's a separate subject) but the organisational constraints are restrictive.

As a result of lack of diver education, legislation and conservatism diving in Japan is about 10 years behind diving techniques and practices in the UK. Nitrox is only just becoming available, twin-tank manifolds are rare and deco-diving is frowned upon. Almost all the mainstream diving is done with dive-operators and most is PADI "crowd-control" style diving with DM shepherds.

This is not my idea of fun and, luckily, there is a small and independently minded group of Japanese and foreign divers doing things differently and doing some great diving - if you want to dive on virgin WWII wrecks or see some really rare deep reef fish come to Japan. However we need some help on mixing sensible deco gases.....

Problem - we need to mix EAN50 or EAN80 for accelerated deco - but without an air compressor!

Background - Here in Japan we have the "Japan High Pressure Gas Law" which includes restrictions such as the one that says that to operate a breathing air compressor you have to have a license and a concrete bunker to put it in. This means that you can only buy gas from gas companies or very large dive operators and nobody owns their own tanks - full tanks are rented for every dive. This is a pain but there isn't really any way to get round it.

But the real problem is that the gas companies will only supply air, EAN32 or 100%O2 and, personally, I am a bit leary about diving deep air and then using 100%O2 as a deco gas. So we are looking for a solution to allow us to mix EAN50 and EAN80 based on what's available.

We can buy bulk O2 and we have 5L AL cylinders and one possible solution to our problem would be to buy a Haskel or KISS booster pump and then to decant O2 into the cylinders and then to use rented tanks of EAN32 and a booster pump to do partial pressure blending.

Has anybody done this and does anyone have any opinions on whether this is a daft idea.

Thanks, in advance, for any help. And if any YD divers want to dive in Japan, let me know.
 

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Grumbler-chief in Residence
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Hi,

No problem as long as you can scavenge the gas, I can't for the life of me remember the formula, I will post it from home when I get back. The only reason it is not done more often is the reay availability of air over here.

Andrew

As a thought, look at the 32%, most of my dives in the UK are 60M ish, we tend to use 32% as it gives a better bailout option than the 50%. Agree with you about the 100 versus 80% arguament though.
 

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more weaselly than a weaselly thing
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Why not get an O2 fill, decant it to get the required O2 pressure, then use a nanobooster (gordons) to air top it.

Its doable, although it might chew through a bit of drive gas.
 

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Andy / Zak

Thanks for the input. The reason we are not using EAN32 for the deco gas is simply to try and reduce the hang times. EAN32 in 10L AL's is what we use at the moment and we're trying to optimise things. There is no shortage of drive gas - all the PADI crowds put their used tanks in one place for the "air lorry" (same idea as a milk float) and we can easily utilise what they have left.

Formulas - are you just talking about normal PPblending ones?

Drive air consumption - any ideas of the requirements for drive gas - I guess it's a function of the piston volume on the drive side and compressor side of the booster pump plus the gas compressibility .... mmm ... that might not be trivial to work out.

Hugh
 

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PADI Internet Specialty Diver
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The little KISS gas booster will not quite give you a full 232 bar to top up the tank from an air cylinder.  However, the electric motor booster from the same company will and doesn't require any drive gas (being electric).

With a Haskel you need drive gas.  Any LP industrial compressor will do.

With a gas booster that gives 232 bar or higher output there is no need for a breathing air HP compressor as you can top off from a cylinder of air from the dive shop.

Sounds really good out there - I do some work for a Tokyo company but I've never been.  What I know of the Japanese they tend to follow the rules without question so I guess its hard to circumvent the situation you describe.  Very jealous - hope it goes well for you.
Chris.
 

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Grumbler-chief in Residence
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[b said:
Quote[/b] ]Formulas - are you just talking about normal PPblending ones?
Yes.

As for 32%, from 60M+ using 32% and 80% can and does give shorter deco times than 50 and 80. Also a much better gas for bail out as you can get onto it earlier than the 50.

Andrew

p.s.
Just checked it, more to be honest out of my own curiosity than anything else.

60M using 18/35, profiled on DDPlan with 20 / 80 gradient factors. The deco was 4 minutes longer with 50% then for the 32%

See, knew I was clever, honest guv.
 
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