X-Message-Number: 2244
Date: Thu, 13 May 93 11:31:41 CDT
From: Brian Wowk <>
Subject: CRYONICS Dewar Hazard

Mark Voelker:
 
> 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.
 
        Putting fragile dewars in the coldroom, with the associated 
requisite of constant human monitoring, is not in keeping with the 
design philosophy of a room that would otherwise be failsafe.
 
        More to the point, the problem is not "loss of coolant."  The 
problem is *loss of heat*.  A vacuum-failed dewar would suck heat from 
the room at the ferocious rate of 10kW without spilling a drop of LN2.  
Of course, spilled LN2 would only make the problem worse.  The room 
will not have or need a drain, and even if it had one, vaporizing LN2 
in pipes under the room would be an explosion hazard.
 
        The question of human supervision is almost academic.  If a 
Bigfoot failed inside the room, you would have all of *five minutes* 
to lift a three ton -196'C metal object out of the room before 
adjacent patients cooled dangerously.
 
        Putting dewars (even neuro dewars) inside the room, while 
conceptually elegant, is in practice too complicated and dangerous to 
consider.
 
                                                --- Brian Wowk

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