Cold storage may involve:
(1) refrigerator temperature (4°C or 40°F)
(2) standard freezer (just below 0°C)
(3) deep freeze (-20°C, -40°C, etc)
Some items such as red blood cells and vaccines must be maintained at refrigerator temperatures and may deteriorate if allowed to freeze or to reach room temperature.
Temperature monitoring may involve:
(1) a surrogate marker
(2) a thermometer
(3) a thermocouple with analogue to digital data storage
(4) an alarm or alerting system
Surrogate markers include:
(1) a tube with fluid frozen at an angle that is placed vertically in a freezer. If the freezer has warmed above freezing and dropped back down, then the fluid in the tube will freeze horizontally.
(2) a temperature indicator that changes color when a certain color has been reached
Thermometers may involve:
(1) a bare thermometer: this is sensitive to variation in temperature associated with entering the storage unit
(2) a thermometer with the bulb in fluid: this is less sensitive to immediate variation in temperature caused by opening a door
Electronic thermocouple:
(1) high-low temperature reading (mini-max)
(2) analogue recording of ink onto paper
(3) digital recording into a computer
The decision on how to monitor cold storage depends on:
(1) what is being stored
(2) how crtical it is that storage be within certain parameters
(3) how critical it is to document
(4) whether transport is involved
