Thermo Scientific Cryo 740 Series, Operating And Maintenance Manual

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9-2 7000740r7 Cryo Series Thermo Scientific
Section 9
Appendix
The safety precautions in this appendix 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 information handy for ready reference and review.
Note Because argon is an inert gas whose physical properties are very
similar to those of nitrogen, 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 containers
should be filled SLOWLY to minimize the internal stresses that occur
when any material is cooled. Excessive internal stresses can damage the
container.
Warning Do not cover or plug the entrance opening of any liquid nitrogen
refrigerator 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
refrigerator. The top of the funnel should be partly covered to reduce
splashing. 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
instructions 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.
Introduction
(continued)