A laboratory refrigerator or lab freezers have an obvious and essential function; these units are used to cool or freeze samples for preservation. Typically, refrigerators are used to store samples at a temperature between – 5 and 15 degrees Celsius, while freezers will normally store samples at a temperature between – 25 and – 15 degrees Celsius.
Some laboratory freezers are used to store biological samples such as vaccines at a significantly lower temperature. Cryogenic freezing is also used in some laboratories, but requires specialized equipment that is capable of generating and tolerating exceptionally low temperatures. Ultra low temperature freezers (usually -50 degrees C and below) commonly use a dual compressor cascade type of system to reach these low temperatures. The first compressor is used to obtain a temperature of around -40 degrees C, after which the second compressor kicks in to achieve the lower temperature that is needed. These lab freezers will be usually be noisier than a -20 degrees C freezer, create more heat output into the room and will use more energy. They are also more expensive to repair than a standard laboratory refrigerator or freezer if the compressor needs to be replaced, since this will require a repair technician who specializes in these somewhat exotic compressors.
Lab refrigerators and freezers include equipment for storing samples and special instrumentation used for conducting experiments requiring precise temperature control. For example, a lab refrigerator can be used to set up chromatography apparatus within the refrigerator chamber.
Refrigeration and freezing equipment is also used for the storage of medical or pharmaceutical supplies. A blood bank uses a lab refrigerator to preserve the quality of its blood supply. Laboratory refrigerators and lab freezers that store blood and blood products must meet a variety of regulatory and quality standards for obvious reasons. They normally come with an alarm system to warn laboratory personnel of an equipment failure. Plasma can be stored frozen in a plasma freezer for an extended time period. Since the typical expiration date is one year from the collection date, the problem of maintaining an adequate blood supply is greatly reduced. Pharmacies may also use a laboratory refrigerator to store vaccines, medications and other temperature sensitive compounds.
Laboratory refrigerators and laboratory freezers include equipment for freezing blood plasma or other blood products for future use. Some lab freezers are used to store enzymes or other biological reagents used to conduct tests. Laboratory refrigerators and laboratory freezers may be stand-alone, upright units or may fit under the lab counter. A lab freezer may also be fitted with locks to restrict entry, and may even be designed to safely insulate flammable materials from electrical sparks. Some laboratory refrigerators and laboratory freezers are also used as incubators that cycle between a heating period and a refrigeration period. These types of refrigerators are often used for culturing and monitoring the growth of bacteria.
Flammable chemicals that require refrigeration must only be stored in a laboratory refrigerator that is designed for the safe storage of flammables. A flammable liquid is defined as having a flash point of less than 100 degrees F (38 degrees C). Flammable storage laboratory refrigerators are UL approved for storage of flammable chemicals; lab freezers are often used for this purpose as well. Flammable storage refrigerators have no electrical sparking devices, relays, switches or thermostats that could ignite flammable vapors inside the cabinet. They may also incorporate design features such as thresholds, self-closing doors, magnetic door gaskets and special inner shell materials that control or limit the damage should a reaction occur within the storage compartment.
A label stating ‘Flammable Materials Refrigerator: Keep fire away’ should identify such refrigerators. Flammable storage units cannot be placed in a room containing explosive vapors, but chemicals that exude explosive vapors can be safely stored inside them. They are called lab-safe, fire-safe or explosion safe refrigerators. These refrigerators are more costly than the standard household or even laboratory refrigerator for that matter, but they must be used if flammables will be stored in the refrigerator.
Explosion proof laboratory refrigerators and lab freezers are rated UL explosion-proof and are similar in design to the flammable storage units, but they also have all operating components sealed against entrance of explosive vapors. Electrical junction boxes are also sealed after connections are made. These units are approved for storage of volatile materials in areas with explosive atmospheres and are the most costly of all types. This type of refrigerator is only required when storing flammable materials in an area with an explosive atmosphere such as a solvent dispensing room. An explosion proof laboratory refrigerator has very limited use on campus and require special hazardous location wiring rather than simple cord and plug connections.