X-Message-Number: 2241
Date: 12 May 1993 08:29:35 -0700 (MST)
From: 
Subject: CRYONICS Cold Room Problems

In Cryomsgs #2235 and #2236, Brian Wowk and Charles Platt mention some
potential problems with the idea of putting the present dewars in the cold
room. Charles points out that the dewars are quite tall (9 ft. or so) and
therefore the cold room ceiling would need to be higher than that in a
typical room. This is not a problem, since of course the room could be
built with such a ceiling height, and in fact this is probably desirable
for a room of reasonable size (say 12 ft. x 12 ft. or larger). To minimize
heat leakage into the room it should have a low surface-to-volume ratio,
meaning (for a room with flat walls) as near a cubical shape as practicable.
Charles also says that the added expense of duplicating the dewars (double
insulation) is not justified. But we already have purchased the dewars;
presumably once we got the cold room up and running we would no longer offer
the option of storage in LN2; therefore we would no longer be buying new
dewars. Finally, Brian brings up the most important potential problem: a
"loss of coolant accident" inside the room if one of the dewars was to lose
vacuum and dump its load of LN2 rapidly into the room. Presumably, the room
will be monitored by a live human, the patients would not be left unattended
on autopilot. If vacuum was lost, well before all the LN2 was lost, it could
be drained out of the room: I assume the floor of the room will have a drain.
What would happen now if one of our dewars was to lose vacuum? Patients would
certainly be at risk! At least if the dewar was in a 135K environment, no one
would be at risk of meltdown.  --Mark

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