Page 16 Leica EM TIC 3X Operating Manual 07/17
Fig.1.1: When working with LN
2
for refilling the Dewar avoid protective glasses
(a), boots (c), walking shoes (e) and protective gloves (g) out of which the LN
2
cannot easily escape if entered. LN
2
splashing into the closed protective
glasses (a), open boots (c), shoes (e) or protective gloves (g) evaporates
suddenly and can cause serious burns.
Always use protective glasses (b) with side protection which are open at the
top and at the bottom. Only use boots if you have loose (not narrow) trousers
coming outside the boots (d) and completely covering the gap. Wear only open
slip-on sandals (f) in the lab, no walking shoes or court shoes. Always wear
cuffless trousers if you wear slip-on sandals. Never wear protective gloves
when pouring LN
2
or when putting the Dewar head on the Dewar vessel. Just
use an open flannel cloth (h) to protect your hands from the cold. Gloves
should be used only to grasp dry cold parts. They are unsuitable for LN
2
work.
Only use metal Dewars specifically designated for storage of LN
2
, since only
containers of this kind exclude risks during storage. For routine cryo-preparation
metal troughs (1 cm Styrofoam insulation), Styrofoam containers or plastic troughs
are eminently suitable and ensure low risk cryo-preparation.
Check the evaporation rate of your metal Dewar regularly every three months and
compare these rates with the rate given by the manufacturer. The evaporation rate of
an undamaged metal Dewar should be well below 1 litre of LN
2
per day. Defective
Dewar vessels with higher evaporation rates are a safety risk, and should be taken
out of work or repaired.
Do not leave LN
2
standing in open vessels where it can exchange with the room
atmosphere. The boiling point of LN
2
(-
196 °C) is lower than liquid oxygen’s boiling
point (-183 °C). When the exchange surfaces are extensive enough, oxygen from the
