Thermo Scientific Forma 8602 Operating And Maintenance Manual page 92

Appendix A
a. Handling Liquid Nitrogen
Contact of liquid nitrogen or cold gas
with the skin or eyes may cause seri-
ous freezing (frostbite) injury.
• Handle liquid nitrogen carefully.
The extremely low temperature can freeze human flesh
very rapidly. When spilled on a surface, the liquid tends to
cover it completely and intimately, cooling a large area.
The gas issuing from the liquid is also extremely cold.
Delicate tissue, such as that of the eyes, can be damaged by
an exposure to the cold gas which would be too brief to
affect the skin of the hands or face.
• Never allow any unprotected part of your body
to touch objects cooled by liquid nitrogen.
Such objects may stick fast to the skin and tear the flesh
when you attempt to free yourself. Use tongs to withdraw
objects immersed in the liquid, and handle the object care-
fully.
• Wear protective clothing.
Protect your eyes with a face shield or safety goggles (safe-
ty glasses without side shields do not give adequate protec-
tion). Always wear gloves when handling anything that is,
or may have been, in immediate contact with liquid nitro-
gen. Insulated gloves are recommended, but heavy leather
gloves may also be used. The gloves should fit loosely, so
that they can be thrown off quickly if liquid should splash
into them. When handling liquid in open containers, it is
advisable to wear high-top shoes. Trousers (which should
be cuffless if possible) should be worn outside the shoes.
Thermo Fisher Scientific
b. Introduction
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. (0.7 m3) of gas.
The safety precautions in this manual 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 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 vent-
ing can result in excessive gas pressure which could dam-
age or burst the container. Use only the loose-fitting neck-
tube 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 withdraw-
al 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 con-
tainers are used for filling, follow the instructions supplied
with those units and their accessories.
Model 8600 Series A-1