Thermo Scientific 7452 Operating And Maintenance Manual page 118

Handling Liquid Nitrogen
Thermo Scientific
Warning Contact of liquid nitrogen or cold gas with the skin or eyes may cause serious
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
carefully.
Wear protective clothing.
Protect your eyes with a face shield or safety goggles (safety glasses without side shields
do not give adequate protection). Always wear gloves when handling anything that is,
or may have been, in immediate contact with liquid nitrogen. Insulated gloves are rec-
ommended, 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.
The safe handling and use of liquid nitrogen in cryogenic refrigerators and dewar flasks is
Introduction
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 information 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 handling and use of liquid argon are the
same as those for liquid nitrogen. ▲
7007452 CryoMed Freezer AA-5