Liquid Nitrogen

Most of what appears below was taken from the Air Products’ website with its permission.

Information Specific to Liquid Nitrogen

General

 Liquid nitrogen is inert, colorless, odorless, non-corrosive, nonflammable, and extremely cold. Nitrogen makes up the major portion of the atmosphere (78.03% by volume, 75.5% by weight). Nitrogen is inert and will not support combustion; however, it is not life supporting. Nitrogen is inert except when heated to very high temperatures where it combines with some of the more active metals, such as lithium and magnesium, to form nitrides. It will also combine with oxygen to form oxides of nitrogen and, when combined with hydrogen in the presence of catalysts, will form ammonia.

Health Effects

 Although nitrogen is nontoxic and inert, it can act as a simple asphyxiant by displacing the oxygen in air to levels below that required to support life. Inhalation of nitrogen in excessive amounts can cause dizziness, nausea, vomiting, loss of consciousness, and death. Death may result from errors in judgment, confusion, or loss of consciousness that prevents self-rescue. At low oxygen concentrations, unconsciousness and death may occur in seconds and without warning. Personnel, including rescue workers, should not enter areas where the oxygen concentration is below 19.5%, unless provided with a self-contained breathing apparatus or air-line respirator.

Physical Properties

  • Molecular Weight: 28.01
  • Boiling Point @ 1 atm: -320.5°F (-195.8°C, 77oK)
  • Freezing Point @ 1 atm: -346.0°F (-210.0°C, 63oK)
  • Critical Temperature: -232.5°F (-146.9°C)
  • Critical Pressure: 492.3 psia (33.5 atm)
  • Density, Liquid @ BP, 1 atm: 50.45 lb/scf
  • Density, Gas @ 68°F (20°C), 1 atm: 0.0725 lb/scf
  • Specific Gravity, Gas (air=1) @ 68°F (20°C), 1 atm: 0.967
  • Specific Gravity, Liquid (water=1) @ 68°F (20°C), 1 atm: 0.808
  • Specific Volume @ 68°F (20°C), 1 atm: 13.80 scf/lb
  • Latent Heat of Vaporization: 2399 BTU/lb mole
  • Expansion Ratio, Liquid to Gas, BP to 68°F (20°C): 1 to 694

Containers

The image below shows a typical cryogenic liquid cylinder. Cryogenic liquid cylinders are insulated, vacuum-jacketed pressure vessels. They come equipped with safety relief valves and rupture discs to protect the cylinders from pressure build-up. These containers operate at pressures up to 350 psig and have capacities between 80 and 450 liters of liquid. Product may be withdrawn as a gas by passing liquid through an internal vaporizer or as a liquid under its own vapor pressure.

Cryo_LN2

 

Handling and Storage

Store and use this product with adequate ventilation. Do not store in a confined space. Cryogenic containers are equipped with pressure relief devices to control internal pressure. Under normal conditions, these containers will periodically vent product. Do not plug, remove, or tamper with any pressure relief device. Never allow any unprotected part of the body to come in contact with uninsulated pipes or equipment that contains cryogenic product. The extremely cold metal will cause the flesh to stick fast and tear when one attempts to withdraw from it. Use a suitable hand truck for container movement. Containers should be handled and stored in an upright position. Do not drop, tip, or roll containers on their sides. Do not remove or interchange connections. Contact the vendor if you experience any difficulty operating the container valve or with the container connections. Discontinue use. Use the proper connection. DO NOT USE ADAPTERS!

Use piping and equipment designed to withstand the pressures to be encountered. On gas withdrawal systems, use a check valve or other protective apparatus in any line or piping from the container to prevent reverse flow. To prevent cryogenic liquids or cold gas from being trapped in piping between valves, the piping should be equipped with pressure relief devices. Only transfer lines designed for use with cryogenic liquids should be used. Some elastomers and metals such as carbon steel may become brittle at low temperatures and will easily fracture. These materials must be avoided in cryogenic service. It is recommended that all vents be piped to the exterior of the building or to a well ventilated indoor space.

Personal Protective Equipment (PPE)

One must be thoroughly familiar with the properties and safety considerations before handling a cryogenic liquid and its associated equipment. The eyes are the most sensitive body part to the extreme cold of the liquid and vapors of cryogenic liquids. The recommended personal protective equipment for handling cryogens includes a full face shield over safety glasses, loose-fitting thermal insulated or leather gloves, long sleeve shirts, and trousers without cuffs. In addition, safety shoes are recommended for people involved in the handling of containers. Depending on the application, special clothing suitable for that application may be advisable.

A special note on insulated gloves: Gloves should be loose-fitting so they are able to be quickly removed if cryogenic liquid is spilled on them. Insulated gloves are not made to permit the hands to be put into a cryogenic liquid. They will only provide short-term protection from accidental contact with the liquid. In emergency situations, self-contained breathing apparatus (SCBA) may be required.