VWR 5600 Series Operating And Maintenance Manual page 89

Appendix
Introduction
A-2 Model 5600 Series
The safe handling and use of liquid nitrogen in cryogenic refrigerators and
dewar flasks is largely a matter of knowing the potential hazards and using
common-sense procedures based on that knowledge. There are two
important properties of liquid nitrogen that present potential hazards:
1. It is extremely cold. At atmospheric pressure, liquid nitrogen boils at
-320°F (-196°C).
2. Very small amounts of liquid vaporize into large amounts of gas. One
liter of liquid nitrogen becomes 24.6cu. ft. (700l) of gas.
The safety precautions in this booklet must be followed to avoid potential
injury or damage which could result from these two characteristics. Do
not attempt to handle liquid nitrogen until you read and fully understand
the potential hazards, their consequences, and the related safety
precautions. Keep this booklet handy for ready reference and review.
Note Argon is an inert gas whose physical properties are very similar to
those of nitrogen. The precautions and safe practices for the handling and
use of liquid argon are the same as those for liquid nitrogen.
Use only containers designed for low temperature liquids.
Cryogenic containers are specifically designed and made of materials that
can withstand the rapid changes and extreme temperature differences
encountered in working with liquid nitrogen. Even these special con-
tainers should be filled SLOWLY to minimize the internal stresses that
occur when any material is cooled. Excessive internal stresses can dam-
age the container.
Do not cover or plug the entrance opening of any liquid nitrogen refrig-
erator or dewar. Do not use any stopper or other device that would
interfere with venting of gas.
These cryogenic liquid containers are generally designed to operate with
little or no internal pressure. Inadequate venting can result in excessive
gas pressure which could damage or burst the container. Use only the
loose-fitting necktube core supplied or one of the approved accessories
for closing the necktube. Check the unit periodically to be sure that
venting is not restricted by accumulated ice or frost.
Use proper transfer equipment.
Use a phase separator or special filling funnel to prevent splashing and
spilling when transferring liquid nitrogen into or from a dewar or refrig-
erator. The top of the funnel should be partly covered to reduce splash-
ing. Use only small, easily-handled dewars for pouring liquid. For the
larger, heavier containers, use a cryogenic liquid withdrawal device to
transfer liquid from one container to another. Be sure to follow instruc-
tions supplied with the withdrawal device. When liquid cylinders or
other large storage containers are used for filling, follow the instructions
supplied with those units and their accessories.
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