X-Message-Number: 2198
From: 
Subject: CRYONICS: Measurement of contamination of LN2
Date: Mon,  3 May 93 04:24:33 PDT

>From *Cryonics*, Oct '81, in a report at the Lake Tahoe conference that 
year:


    One of the most interesting papers was one of the shortest.  Hugh Hixon 
reported on oxygen contamination in liquid nitrogen dewars which have been 
operated continuously over extended periods of time.  Hugh has found that 
one such container, an LR-40 operated by IABS for 3 years and subject to a 
good deal of traffic, contained 2% oxygen by volume.  This could be a 
serious long-range problem for both cryonicists and cryobiologists.  Even 
at -200xC, oxygen is active enough to oxidize both organic material and 
inorganic material such as carbon steel.  Hugh discussed several approaches 
to dealing with this problem such as the use of scavengers like sodium and 
potassium and more direct approaches such as draining the tanks and 
starting out fresh every few years.

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>From *Cryonics*, Oct '85, concerning dewar maintenance:

     We know from a study conducted in our laboratory several years ago 
that open mouth storage dewars steadily accumulate liquid oxygen (LOX) as 
a contaminant in the liquid nitrogen.  Even at -196oC LOX represents a 
potentially serious long-term hazard.  Not only will LOX act to degrade 
welds over long periods of time, it has the potential for damaging 
biologicals, including suspension patients.  In our experience, a 45 liter 
Linde LR-40 open mouth dewar accumulated 2% - 3% LOX over a 3 year period 
of operation. The lid was opened an average of twice a week for liquid 
level checks.  While there are no accepted standards for safe levels of 
LOX, it is ALCOR's policy to refill patient care dewars when the LOX level 
reaches the 2% - 3% range.  The use of our fill lid should reduce the LOX 
contamination which occurs during the filling of the A-2542.  Accumulation 
of water crystals (ice pumping) which occurs during filling operations 
should also be minimized by this device.  About 200 cc of water was 
removed from the A-2542 while it was empty and warmed up prior to being 
placed in the vault.

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