Liquid Nitrogen Facts

Liquid nitrogen immediately boils into its vapor at room temperature. The fog is a mixture of nitrogen gas and water vapor from the air.
Liquid nitrogen immediately boils into its vapor at room temperature. The fog is a mixture of nitrogen gas and water vapor from the air. Daniel Cattermole / EyeEm / Getty Images

Liquid nitrogen is nitrogen that is cold enough to exist in liquid form. It is used for many cooling and cryogenic applications. Here are some liquid nitrogen facts and information about handling liquid nitrogen safely.

Liquid Nitrogen Facts

  • Liquid nitrogen is the liquefied form of the element nitrogen that is commercially produced by fractional distillation of liquid air. Like nitrogen gas, it consists of two nitrogen atoms sharing covalent bonds (N2).
  • Sometimes liquid nitrogen is denoted as LN2, LN, or LIN.
  • Liquid nitrogen has the UN number 1977.
  • At normal pressure, liquid nitrogen boils at 77 K (−195.8°C or −320.4°F).
  • The liquid to gas expansion ratio of nitrogen is 1:694, which means liquid nitrogen boils to fill a volume with nitrogen gas very quickly.
  • Nitrogen is non-toxic, odorless, and colorless. It is relatively inert. It is not flammable.
  • Nitrogen gas is slightly lighter than air once it reaches room temperature. It is slightly soluble in water.
  • Nitrogen was first liquefied on April 15, 1883, by Polish physicists Zygmunt Wróblewski and Karol Olszewski.
  • Liquid nitrogen is stored in special insulated containers that are vented to prevent pressure build-up. Depending on the design of the dewar or flask, it can be stored for hours up to a few weeks.
  • LN2 displays the Leidenfrost effect, which means it boils so rapidly, it surrounds surfaces with an insulating layer of nitrogen gas. This is why spilled nitrogen droplets skitter across a floor.

Liquid Nitrogen Safety

  • Liquid nitrogen is cold enough to cause severe frostbite upon contact with living tissue. Wear proper safety gear when handling liquid nitrogen to prevent contact or inhalation of extremely cold vapor. Make sure exposed skin surfaces are covered and preferably insulated.
  • Because it boils so rapidly, the phase transition from liquid to gas can generate a lot of pressure very quickly. Do not enclose liquid nitrogen in a sealed container, as this may result in bursting or an explosion.
  • Adding a lot of nitrogen to the air reduces the relative amount of oxygen. This can result in an asphyxiation risk. Cold nitrogen gas is heavier than air, so the risk is greatest near the ground. Use liquid nitrogen in a well-ventilated area.
  • Liquid nitrogen containers may accumulate oxygen which is condensed from the air. As the nitrogen evaporates, there is a risk of violent oxidation of organic matter.

Liquid Nitrogen Uses

Liquid nitrogen has many uses, mainly based on its cold temperature and low reactivity. Examples of common applications include:

  • Freezing and transport of food products.
  • Cryopreservation of biological samples, such as sperm, eggs, and animal genetic samples.
  • Coolant for superconductors, vacuum pumps, and other materials and equipment.
  • Cryotherapy to remove skin abnormalities.
  • Shielding materials from oxygen exposure.
  • For quick freezing of water or pipes to allow work on them when valves aren't available.
  • As a source of extremely dry nitrogen gas.
  • For branding cattle.
  • For molecular gastronomy preparation of unusual foods and beverages.
  • Cooling materials for easier machining or fracturing.
  • Science projects, including liquid nitrogen ice cream, freezing flowers and then watching them shatter when tapped onto a hard surface, and making nitrogen fog.