Leica EM FC7, Operating Manual

Page: 7 / 56

Page 6 Operating Manual Leica EM FC7 01/10
1. Safety Introduction
Liquid Nitrogen (LN
2
)
When working with liquid nitrogen (LN
2
) please bear in mind LN
2
is extremely cold. It
boils at -196 °C. Nitrogen gas (GN
2
) escapes at very low temperature from the
boiling LN
2
. Both LN
2
and GN
2
as well as cooled elements (e.g. pipes, valves,
hoses, containers or stoppers) can cause severe frost bite and burns to the skin and
eyes.
When LN
2
evaporates, it expands in a ratio of 1:700. 1 litre LN
2
produces almost 1
m3 of GN
2
. Care should therefore be taken to ensure that when large quantities of
nitrogen evaporate (e.g. when transferring LN
2
), the room should always be well
ventilated.
Removing LN
2
waste: dump LN
2
into an outdoor pit or container filled with gravel,
where it will evaporate rapidly and safely.
GN
2
is odourless and tasteless and will be inhaled like air. GN
2
is non-toxic, but a
high GN
2
content in the air (> 78%) reduces the oxygen-content (< 21%) and
produces immediate fainting and deep unconsciousness without any previous
symptoms.
When there is doubt about the adequacy of ventilation, use an oxygen analyser (0
to 25% scale) to check for oxygen. The content of oxygen must not drop below
18%.
If an unconscious person stays in a low oxygen environment then death may occur.
If breathing stops, apply artificial respiration at once and notify doctor and
ambulance immediately.
For the reasons given above, never put LN
2
Dewars in a closed storage room or
chamber. The evaporation rate from Dewar vessels can rise to several litres a day if
they are defective due to improper handling or to natural wear over many years of
use.
Always keep the working area well ventilated.
Bring objects at room temperature carefully into contact with LN
2
. Initially an
insulating gas layer is formed preventing a large transfer of heat. During this initial
period little LN
2
evaporates. However, once the object has cooled down there may
occur unexpected strong boiling and spurting of LN
2
.
In the case of burns from LN
2
splashes, rinse the affected skin immediately with
plenty of water at hand temperature. For serious burns arrange for a skin specialist
to see them at once.
In the case of LN
2
affecting the eyes, rinse immediately with water at hand
temperature and arrange for an eye specialist to see it at once.
Never use glass Dewar vessels in the lab (especially glass Dewars larger than 2
litres capacity) without complete metal envelope: Glass Dewars often burst for no
obvious reason or due to unintentional mishandling (e.g. contact with metal
instruments etc.). Never work without open protective glasses when using LN
2
in a
glass Dewar.