X-Message-Number: 2030
Date: Fri, 26 Mar 93 01:38:42 CST
From: Brian Wowk <>
Subject: CRYONICS: Fog Problem

John Hagerman:
 
> Will there be any problems with fog?  How hard will it be to see down
> into the room when lowering something into it?  How will condensation
> be prevented on the faceplate of a worker being lowered into it?  And
> will it rain into the room?  (Sorry if this is way too naive....)
 
        Fog is always a problem, even when trying to see patients in LN2 
dewars.  The problem is caused by the big inrush of warm, humid air that 
replaces the volume of the thick dewar lid as you remove it.  In a few 
minutes the fog settles, the vapor stratifies, and things become pretty 
clear.  If you're in a hurry you can also insert a warm object into the 
LN2 causing it to boil vigorously and quickly displace the fog with dry 
nitrogen.
 
        Fog problems with the Cold Room are potentially worse than with 
dewars.  Removing the cubic-meter foam sections on top will cause an 
enormous inrush of room air, and fog like crazy.  I suggest connecting 
the room gas vent to a cylinder of dry nitrogen, and putting the room 
under positive pressure as a cube is lifted off.  That should solve the 
problem quite nicely.  (An air compressor with a cryogenic dehumidifier 
could be used in lieu of the gas cylinder.  As a rule, you want to 
always push dry gas into the room or else rime ice will buildup on 
everything.)  Also, the room vapor circulation system will have to be 
shut down during during these operations.  This could probably be done 
for a maximum of about one hour.  I will be discussing this issue 
further in other postings.
 
        Condensation on the faceplate of cryosuits is a concern of mine 
also.  Mike Darwin of Biopreservation is doing R&D on these suits, and 
he believes that keeping the helmet filled with dry oxygen will prevent 
the problem.  Bear in mind that this must be a solvable problem, or 
we'll never know the personal pleasure of one day walking on moons in 
the outer solar system. :)
 
        Concerning cryosuits: I am now thinking that cryosuits are a 
convenience, not a necessity for operating my Room.  Cryosuits 
will not be needed for work in patient storage cells for the same 
reasons we do not currently need scuba divers in liquid nitrogen.  The 
only serviceable equipment will be in the central "utility cell."  The 
utility cell, which holds the circulating fans and insulated LN2 
reservoir, will itself be thermally insulated from the rest of the room.  
(I'll give various reasons for this in another posting.)  Thus for short 
(one hour, approx.) time periods the utility cell can be warmed by 
internal space heaters so that a worker in winter clothing and an oxygen 
mask can replace fans, etc.  Remember that patient storage cells remain 
covered by their cubes, and insulated from the utility cell while this 
work goes on.
 
        And no, it won't rain into the room.
 
                                                --- Brian Wowk

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