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Date: Mon, 23 Nov 1998 20:19:34 -0500
To: "Mike Langborg" <mslangborg@cl*.ne*>
From: Joel Silverstein <joelsilverstein@wo*.at*.ne*>
Subject: Re: 80% arrrgh!! was Re: On the left
Cc: techdiver@aquanaut.com
yup   -- wasnt that covered in you training program?




At 09:42 PM 11/23/1998 -0000, you wrote:
>Ok, so 100% oxygen is the way to go. What do you do about "airbrakes".
>
>When, i.e. after 20/25min?
>for how long, i.e. 5/10 min?
>And what gas do you use for "airbrakes" i.e your 50%, your 36% or your
>bottommix?
>
>Mike
>
>
>
>-----Original Message-----
>From: Joel Silverstein <joelsilverstein@wo*.at*.ne*>
>To: gwaw@ix*.ne*.co* <gwaw@ix*.ne*.co*>
>Cc: Techdiver@aquanaut.com <Techdiver@aquanaut.com>
>Date: 23 November 1998 16:23
>Subject: 80% arrrgh!! was Re: On the left
>
>
>>Dear Arnie,
>>
>>It is quite easy to pump 100% oxygen to 3000 psi -- the dive shop needs to
>>make the investment in a proper oxygen service rated Haskel Gas booster.
>>Most any reputable dive center who is mixing gas for the consumer should
>>have one, anyone that does not should step up pet the pony and buy one.
>>
>>80% EAN was not created from a decompression standpoint it was justified by
>>those who did not have a gas booster. Here's why. Oxygen gets delivered in
>>2400 psi bottles, (some major cities have gas suppliers who can supply at
>>3500 psi) however you can cascade into a 3000 psi rated cylinder about 2250
>>psi of oxygen top up to 3k with air and you have 80% oxygen content. Simple
>>enough.  However .......
>>
>>80% EAN limits you severely. 1. at 20 and 10 fsw its PPO2  is too low make
>>it useful, at 40 fsw its too high for maximum exposure limits.
>>
>>10 fsw 1.04 po2  too low
>>20 fsw 1.28 po2  too low
>>30 fsw 1.53 po2  borderline
>>40 fsw 1.77 po2  too high
>>
>>Where as 100% oxygen is
>>
>>10 fsw 1.30 po2
>>20 fsw 1.61 po2
>>
>>(with the 10 fsw stop normally being taken at 20 fsw
>>
>>Advocates of the EAN80 (a/k/a stroke mix) have come up with a variety of
>>reasons to justify not using 100% oxygen --- one of the great ones is "its
>>good for divers who have trouble holding buoyancy at 10 and 20 fsw"
>>frankly if a technical diver cant hold a 20 fsw stop --- they should go
>>bowling and get the hell out of the water.
>>
>>Most divers who are using accelerated decompression tables have
>>standardized on their decompression mixes.  (some are finding that
>>hyperoxginated heliox mixes are working well too though that is beyond the
>>scope of this email)
>>
>>EAN 36 from 110 fsw
>>EAN 50 from 70 fsw
>>100% oxygen from 20 fsw
>>
>>Granted when you run one of the consumer dive profiling softwares you may
>>see only a small decrease in decompression time -- maybe 5 minutes by using
>>100% over EAN80. and though you may belive that is not a significant enough
>>advantage to make sure you have 100% oxygen here are a few more
>>non-scientific reasons.  From a mixing standpoint unless you are using
>>exceptionally clean hyper filtrated air or air produced from an oil free
>>compressor there is risk of explosion when mixing high pressure air on top
>>of 100% oxygen. It probably has not happened yet --- but some day some
>>goober will blow up a building doing it. Even if you are using a 30 cuber
>>(small) just cascading 2400 psi oxygen in it will give you 24 cuft of
>>oxygen -- for deco thats easily 40 minutes worth, which is a lot of gas. No
>>need to goober around making EAN80 for the other 6 cuft, its just too much
>>work for it and I am sure it costs a bit more, besides if you are doing a
>>dive that requires much more than 40 minutes of oxygen decompression you
>>would want a bigger tank. The fact that a tank has a pressure rating of
>>3000 does not mean you have to fill it to that level. I have an excellent
>>tank chart for all currently available tanks in the US on our web site - go
>>look at it. Next; most consumer available oxygen analyzers using
>>electrochemical sensors can be off by as much as 2% in their readings, so
>>is your 80% really 80 or is it 78? Whereas pure oxygen is upwards of 99%
>>pure -- it's a known item.
>>
>>Arnie, as a techie in training you have an opportunity right in front of
>>you. It's two roads ... the left road is filled with exploration,
>>friendships, technology and long proven safety procedures. The right road
>>is bumpy, full of mis answered questions, body bags, and strokified
>>convolution. I get the feeling your want to take the high road and do it
>>right. In Judaic studies we are taught to ask why not to follow blindly.
>>So in this very long winding response (If I had more time it would have
>>been shorter) the answer is .... EAN80 buys you 6 cuft more gas, but buys
>>you nothing else. Take no shortcuts when it comes to technical diving.
>>
>>Good Luck
>>
>>
>>
>>
>>
>>
>>
>>At 10:21 PM 11/22/1998 -0800, you wrote:
>>>Joel,
>>>
>>>Another question for you.  It is prompted by your post on the bottle
>>>marking issue.
>>>
>>>What is the advantage of 100% O2 compared to 80% O2.  I've been using
>>>the latter for deco.  For one, it is somewhat easier to get at local
>>>dive shops because it is harder to pump the 100% to 3,000 psi, but that
>>>is merely convenience.  More importantly, I can get on the 80% at 30ft
>>>and have the advantage of breathing a higher gradient gas mix sooner
>>>than waiting to the 20ft stop.  The published tables I've seen give no
>>>time advantage to doing deco on 100% over 80%.
>>>
>>>What is your view and why?  TIA.
>>>
>>>Blow gentle bubbles,
>>>
>>>Arnie
>>>Tech Diver in Training
>>>
>>Joel Silverstein
>>Scuba Training + Travel Co.
>>http://www.NitroxDiver.com
>>--
>>Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'.
>>Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
>>
>>
>
>
>
Joel Silverstein
Scuba Training + Travel Co.
http://www.NitroxDiver.com
--
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