Retsch Cryomill - Manual (Page 54)

Safety and occupational health instructions
54
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9.2 Safety instructions on the handling of liquid nitrogen
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9.3 Oxygen deficiency
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The main components of air according to volumes are as follows:
– Oxygen O2 21 %
– Nitrogen N2 78 %
– Argon Ar 1 %
The gases contained in the atmosphere are not toxic. However, a change in
concentration (in particular changes to the oxygen concentration) may have effects
on life and burns. It is therefore essential for the air breathed in to contain sufficient
oxygen (> 19 %).
Humans cannot detect changes in the composition of air within the time that will
actually be necessary because the components are colourless and odourless.
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9.3.1 Dangers
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A danger of suffocation exists as a result of the normal evaporation of the liquid
nitrogen that pushes out the oxygen in the air. An oxygen deficiency is dangerous
and can cause death through suffocation. The reaction of the organism to oxygen
deficiency will differ greatly depending on the individual. It is not possible to provide
precise and generally applicable information on the symptoms of an oxygen
deficiency.
Example: under normal conditions (20° C; 1013 mbars) 1 l liquid nitrogen
evaporates to produce 680 l nitrogen gas.
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9.3.2 Causes
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An oxygen deficiency may arise during the following work or in the following
conditions:
– Nitrogen as liquid or gas
– Natural evaporation of liquid nitrogen
– Refilling of liquid nitrogen
– Leaks in containers for liquid or gaseous nitrogen
– Defect in the air feed or outlet
– Tipping over of the container
This list is not complete.
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9.3.3 Recommendations
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In order to prevent the danger of an oxygen deficiency, the following measures
must be taken.
The vessel:
• must be kept in a vertical position.
• must be provided with a suitable insulating lid.
• must be protected from direct sunlight and may not be set up near heat
sources.