Thermo Scientific Fisher Scientific 900 Series Operating And Maintenance Manual page 79

Appendix A Appendix A
Handling Liquid Nitrogen Handling Liquid Nitrogen
Introduction
A -2 Model 900 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 24.6 cu. 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 Because 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 containers
should be filled SLOWLY to minimize the internal stresses that occur when
any material is cooled. Excessive internal stresses can damage the container.
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.
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