[Histonet] liquid nitrogen

[Smith, Allen]

    Before trying to handle liquid nitrogen, get someone who uses it to show
you how to handle it! Liquid nitrogen is very dangerous when improperly
handled. I know of 2 deaths from the abuse of liquid nitrogen. 
    Liquid nitrogen comes in a high pressure cylinder holding anything from
200 ml to 50 liters of liquid nitrogen (which will expand to 0.025 to 6
cubic meters of nitrogen gas).  The high pressure cylinder itself is
dangerous.  If it falls and the valve breaks, escaping gas will turn the
cylinder into a missile.  The escaping gas can cause severe frostbite if you
are near it.  Even at a distance, large amounts of escaping nitrogen can
displace enough air to suffocate you.  
    Small amounts of liquid nitrogen spilled on yourself will cause severe
frostbite.  Large amounts can freeze a limb solid and make it as prone to
shattering as an ice cube.  
    If you must learn by yourself, buy one of the small bottles sold for
dermatological or lecture demonstration use.  They usually contain about 50
liters of nitrogen gas compressed down to about 400 ml at 120 Atm.  Wear
nitrile gloves over leather gloves.  Make sure your work area is well
ventilated. Clamp a Dewar flask in place and release the nitrogen quickly
into the Dewar flask.  Half of the nitrogen will escape as a very cold gas.
The other half will run into the Dewar flask as a liquid.  When the Dewar
flask is half full, shut off the nitrogen.  Drop the tissue into the liquid
nitrogen in the bottom of the Dewar flask.  After a few minutes retrieve the
tissue with long forceps and put it in your cryostat.  Let the liquid
nitrogen evaporate.
    Personally, I don't like liquid nitrogen.  The layer of nitrogen gas
that forms between the tissue and the liquid nitrogen prevents efficient
freezing. If the piece of tissue is large, the outside freezes first; then
the freezing of the inside of the tissue cracks the frozen outside.  	

Allen A. Smith, Ph.D.
Professor of Anatomy
Barry University School of Graduate Medical Sciences
    Podiatric Medicine and Surgery
Miami Shores, Florida  33161


-----Original Message-----
From: histonet-bounces <@t> lists.utsouthwestern.edu
[mailto:histonet-bounces <@t> lists.utsouthwestern.edu] On Behalf Of manal galal
Sent: Saturday, July 16, 2005 8:07 AM
To: Histonet <@t> Pathology.swmed.edu
Subject: [Histonet] liquid nitrogen

Hi all, 
 
  I wanted to ask about how to use liquid nitogen in freezing muscle
biopsies. I mean what does it come in? How much do I use? Do I discard it
after I use it? What kind of container do I use? How long do I put the
biopsy in it? How do I store it? 
  By the way I freeze muscle in the quick freezing chamber of the cryostat,
and am getting very little to no artifacts. But anyone that learns of how I
freeeze biopsies says that it will give me disasterous resuls. Do you think
liquid nitrogen will be superior to my old method.
 
Thanks in advance
manal

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