Leica Biosystems LN22 - Manual (Page 12)

12 Instructions for Use V1.2, RevB – 10/2012
• Never leave LN
2
in open containers where it can exchange with the
room atmosphere. The boiling point of LN
2
(-196°C) is lower than that
of liquid oxygen (-183°C). If a large LN
2
-surface is exposed to the air,
oxygen from the air is absorbed by the LN
2
while nitrogen is released
into the air. LN
2
with a high content of liquid oxygen has a bluish color.
In that case, caution is advised, since concentrated liquid oxygen is a
fire hazard.
• Make sure that your Dewar vessel is filled with no other substances
than LN
2
. If at the filling location also other gases are refilled, install a
warning sign there that clearly states: “Liquid nitrogen only”. Check
the color of the cryogen! Bluish color indicates a high oxygen con-
tent (see previous paragraph). If LN
2
is stored during a prolonged
period of time, liquid oxygen will accumulate in the LN2 vessel, since
liquid oxygen has a higher boiling point (-183°C) than liquid LN2
(-196°C).
• Never fill a Dewar vessel up to the neck with LN
2
(Fig. 6). In case of a
boiling delay, there is danger that the rapidly expanding gas bubbles
will force the LN
2
in the neck upwards causing it to splash (Fig. 7). For
this reason, always make sure that the LN
2
surface level is below the
neck of the vessel (Fig. 8). Also bear in mind, that in most cases the
length ‘l’ of the outer insulation differs from the length ‘L’ of the actual
Dewar neck.
GN
2
LN
2
LN
2
level
Fig. 6 Fig. 7 Fig. 8
2. Safety
LN
2
level