Page 85 - The Veterinary Laboratory and Field Manual 3rd Edition

54 Willy Schauwers

Figure 2.10 Sure Chill open refrigerator.
Photo: Sure Chill® Company, Cardiff, UK. Figure 2.11 –80°C freezer. Photo: Dr Ziay Ghulam,
Dr Wahidullah Bahaer, Central Veterinary Diagnostic
and Research Laboratory, Kabul, Afghanistan.
Cooling units used in the laboratory

Cold storage units are an essential component refrigeration compartment. When power is sup-
of laboratory equipment. A standard domestic plied to the refrigerator, the water cools and
fridge unit (4±3°C) and a freezer unit (–20±3°C) ice is formed above the compartment, leaving
are adequate for most purposes. However, for only the denser water at 4°C cooling the con-
long-term storage of microbial organisms and tents. When the power is switched off, the water
some biological material (for example, serum) warms, becomes less dense and rises while the
a –80°C freezer unit is preferable. All refrigera- ice begins to melt and the cooler water descends.
tors and freezers (especially the –80°C freezers) This ensures water at a perfect 4°C remains
should be kept on a stabilizer in locations suf- cooling the contents of the compartment. The
fering from regular power cuts and poor-quality system can operate like this, without any power
electricity supply. whatsoever, for many days. Sure Chill® is a cool-
In cases where the power supply is regularly ing technology which is currently being used in
interrupted it may be worth considering the medical refrigerators. The refrigerator can stay
purchase of a solar-powered refrigerator/freezer, at 4°C for more than 10 days without power
gas-fired or paraffin-fuel cold storage units. (if not opened – it is important to keep cool-
Nowadays new technologies are available for ing devices closed as much as possible during
cooling. The patented Sure Chill® technology power breaks), and is used mainly in Africa to
works on the principle that water is at its densest store vaccines and other medical supplies. It can
at 4°C. Water, not ice, surrounds a Sure Chill® be powered by electricity or solar PV power and

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