cells in N2-safety hazards?

stebby at welchlink.welch.jhu.edu stebby at welchlink.welch.jhu.edu
Wed Jul 15 14:13:22 EST 1998


In article <35ac5447.5051507 at news.univie.ac.at>,
  a8803349.nospam at unet.univie.ac.at (Martin Offterdinger) wrote:
> Hi !
> Some years ago I wanted to thaw a cell line from liquid N2 storage;
> the fitting wasnt tight enough and the nunc-vial exploded during
> thawing in my hands. I was lucky and did not have been injured
> seriously. Some days ago I again wanted to thaw cells and saw liquid
> N2 inside the vial and did not thaw the cells for obvious reasons. I
> would like to know what is the worst case cenario if a vial explodes
> in your hands and what precautions should be taken.
> Do you know of any accidents that have occured? What about Cryoflex,
> do you use it, routinely and what are your experiences. This is of
> special importance to me because my boss is not convinced to spend
> money on htis safety precautions! I should also mention that N2(l)
> only very rarely enters the cryovial, but it still does happen!
> I am looking forward to a discussion!


Hello Martin.

You've picked a topic I have some experience in.  First, as you may have
guessed there have been incidents of exploding vials resulting in
injury.  Usually the traumatic ones are eye injuries--SO ALWAYS WEAR
SAFETY GLASSES OR A FACE SHIELD WHEN HANDLING VIALS THAT WERE HELD IN
LIQUID PHASE N2.  Other injuries range from minor to "dang...nasty gash"
cuts to exposed skin--arms, legs (shorts and skirts), etc.  I've never
used cryoflex so I can't tell you how it behaves during a catastrophic
tube failure (ok, ok...explosion..).  If it doesn't contain the sharp
shards, its not of much use.

Those who store vials in vapor phase have nothing to fear.  As you note,
the explosion occurs in vials where liquid nitrogen seeps into a vial.
Warming of the tube results in liquid to gas transition in a confined
space and...boom.  You can take steps to avoid this, however.  First,
quit warming in your hand!...at least initially.  My experience is that
if you remove a tube (hold it only by its very top) and you believe
liquid nitrogen is inside, set the thing down on the bench/what
ever--preferably behind something and wait a minute or so.  Usually the
gas is able to escape at room temp without detonating (you can hear it
hissing away).  Actually, in my experience, I've never had a tube
explode if you do this.  Holding it in your hand is too warm and creates
gas faster than it can escape past the O-ring of the tube.  This is by
the way an important point.  In the old days only the internally
threaded, O-ring equipped tubes were "certified" to be used in liquid
phase.  All others were vapor-phase only and guaranteed to leak if used
submerged.  In the past decade, even these tubes have been relegated to
vapor-phase only...unless used with cryo-flex tubing.  I have always
assumed this is due to fear of litigation.

You can take other steps to protect yourself. If you are REALLY worried,
have an ice bucket with dry ice in it, pull the tube, drop it into the
dry ice and let it sit for a few minutes. Alternatively, get one of the
plexiglas boxes you have in your lab for handling 32p.  Move the tube
directly from the nitrogen to the box, close the lid, and set it on the
bench to "degas".  If you don't have these boxes, go to a glass/plastics
supplier and buy 4--5 inches of 2 or 3 inch diameter plexiglas tubing.
This with a book on top will do a lot toward containing a tube failure.
Once the liquid is gone you can safely warm in your hand to your heart's
content.

Good luck,

Steve Dahl

My thoughts and not those of Johns Hopkins University

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