Cryopreservation is the process where cells or whole tissues are preserved by cooling to sub-zero temperatures. The point on the temperature scale where refrigeration ends and cryogenics begins is not well-defined, but most scientists assume it starts at or below -150 °C or 123 K (about -240 °F). Liquefied gases, such as liquid nitrogen and liquid helium, are used in many cryogenic applications. Liquid nitrogen is most commonly used although liquid helium allows for the lowest attainable temperatures to be reached. Cryogenics is used in applications such as cord blood preservation and livestock breeding. Look for uniform storage temperatures, cross contamination prevention, and safety features that protect users from liquid eruption.