STAND 12/07
Storage
Suitable nitrogen freezing containers
Chapter
[ 5 ]
[ 5 ]
| Description |
The chilled biological product is stored in high-quality insulated containers.
In order to facilitate easy access, the samples are located in rack systems.
Small quantities of samples are stored in dewars (mobile cans), more than a thousand
samples are stored in freezing containers. Liquid nitrogen is automatically poured up
to a predetermined level, vaporises there and keeps the storage temperature constant.
Integrated data storage equipment is able to record nitrogen levels,
temperatures and alarm situations.
By using freezing containers with racks standing down-side in the liquid phase of
the nitrogen the storage temperatures are between -196 °C below and -130 °C in the head area.
In this case freezing containers with big tip up lids are the best choice. The often offers
square shaped covers have no technical advantages. Racks made of stainless steel (inox) are
more stable. Having the better heat conductibility systems made of aluminium advances the
balance of temperature and create lower head area temperatures.
If the stored samples are intended to return to men the rules of the "Medical-Device-Directory" (MPG, Class IIa, 93/42/EWG) are to be observed. The safely storage of the samples at temperatures lower than -130 °C is part of the prescriptions. To avoid crosswise contamination of the samples by itself, only it is allowed to use the gas phase of nitrogen. Containers for this purpose needs a MPG / MDD-Admission and the isolation of the head area is more efficiently for minimising the gradient of temperature inside the containers. Head temperatures as low as -190 °C are possible using ingenious constructions. 
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