Richard,

I've done quite a bit of work with LN2 in the past at the TEM and SEM
level.  The following are from my notes taken during one of Prof. H.
Sitte's work shop on Cryo-TEM which he used to hold in Seefeld, Austria
(old friend and mentor, he is now retired, where does the time go?). 
These are some safety pointers.

1 liter or liquid nitrogen equals 1 cubic meter of nitrogen gas

N2 is heavier than atmospheric gas and builds from the floor up

nitrogen gas unlike carbon monoxide will give no physical signs (ie:
headache)

N2 will not normally support combustion  (the opposite in fact) HOWEVER
'blue' nitrogen will, the blue color is liquid oxygen condensed from the
atmosphere

I do not know of any legal requirements but during the late 70's and
early 80's there were some reports of near misses in basement EM labs
where cryosectiong took place in poorly ventilated rooms.  Cryo-TEM
units (at that time and maybe even today) used more LN2 cutting at
higher temperatures eg: 7 liters per hour at -80 oC as opposed to 3.5
liters per hour at -165 oC.  So sectioning at -80 for 2 hours would have
generated 14 cubic meters of N2, enough to fill a small room.

probably more then anyone needed to know.........




Richard.Pitman@wri-tr.wmids.nhs.uk wrote:
> 
> Hi All,
> 
> We have stored tissues in liquid nitrogen for many years. We have two 35 litre dewars actually in the lab, replenished from a 250 litre store located outside the department. The hospitals Occ Health and Safety dept. have received a mail shot from a company which supplies oxygen depletion monitors. We both agree that we should install one of these gadgets in the lab, even though we've had no problems to date.
> 
> (We did once have a vacuum failure in one of the Dewars, and 35 litres of N2 boiled off. Luckily, our lab is well ventilated (draughty).)
> 
> Does anyone else have experience of these monitors -  are they a legal requirement in some areas ?
> 
> Anyone know how many cubic metres of N2 gas  is evolved from 1 litre of liquid ?
> 
> The reasoning is that N2 displaces oxygen, thus entry to a room with a faulty N2 store could have fatal consequences - I have a vague recollection that this happened recently in a lab in Scotland, any info on this ?
> 
> Richard.Pitman@wri-tr.wmids.nhs.uk
> 
> Richard Pitman FIBMS,
> Head MLSO,
> Dept of Histology, Cytology & Immunology,
> Worcester Royal Infirmary NHS Trust

-- 
best regards,
Bob
Robert Schoonhoven
Laboratory of Molecular Carcinogenesis and Mutagenesis
Dept. of Environmental Sciences and Engineering
University of North Carolina
CB#7400
Chapel Hill, NC 27599
Phone 
office 919-966-6343
   Lab 919-966-6140
   Fax 919-966-6123 

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