Liquid nitrogen is nitrogen that is cold enough to condense to a liquid state. It can range from negative 196 to negative 210 degrees Celsius, and it is this extremely cold temperature that makes it suitable for cryogenic uses.
Liquid nitrogen is one of the most common cryogenic liquids. It is odorless, colorless, and non-flammable. It is used in the cryopreservation of biological specimens, the removal of skin abnormalities, and even sometimes during cryosurgery to remove dead or damaged tissue. The most notable of these applications is cryopreservation, in which biological material is frozen and thus preserved. When stored under these extreme conditions, cellular activity stops (such as the biochemical reactions leading to cell death), and biological samples are able to be cryogenically stored for a long time, and later thawed for use.
In medical settings, liquid nitrogen can be used for tissue removal. Dermatologists utilize the extreme temperatures as an acne treatment. Warts can be frozen off of the body. In some cases liquid nitrogen may be used in surgery to help remove abnormal tissue. Additionally, liquid nitrogen may be used to store tissue samples that have yet to undergo testing.
Although non-flammable, the use of liquid nitrogen can pose some health issues. Freeze burns can occur if one comes into contact with liquid nitrogen, causing surface injuries and tissue damage. The use of protective gear (such as safety goggles, cryogloves, and cryoaprons) can prevent such injuries. Additionally, proper ventilation is crucial to have when working with liquid nitrogen. The evaporation of nitrogen into an enclosed space can build up and displace any available oxygen, causing asphyxiation. Inhalation of nitrogen can cause dizziness, confusion, nausea, loss of consciousness, and death. Death can occur quickly, within just seconds of inhalation. As liquid nitrogen is non-detectable by human senses, proper ventilation is quite literally a matter of life and death.
Explosion is another possible concern when working with liquid nitrogen.
Liquid nitrogen has a 1:694 liquid-to-gas expansion rate. If tightly sealed in a container, the build up of gaseous nitrogen as it warms from the liquid state can cause a rapid pressure increase. Containers containing liquid nitrogen should never be completely sealed and should have some way to relieve pressure.