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. ---------------------- >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. Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=2198