Most of what appears below was taken from the Air Products’ website with its permission.
Information Specific to Liquid Helium
Liquid helium is inert, colorless, odorless, non-corrosive, extremely cold, and nonflammable. Helium will not react with other elements or compounds under ordinary conditions. Since helium is non-corrosive, special materials of construction are not required. However, materials must be suitable for use at the extremely low temperatures of liquid helium. Vessels and piping should be designed to American Society of Mechanical Engineers (ASME) specifications or the Department of Transportation (DOT) codes for the anticipated pressures and temperatures.
Being odorless, colorless, tasteless, and nonirritating, helium has no warning properties. Humans possess no senses that can detect the presence of helium. Although helium 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 helium 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.
- Molecular Symbol: He
- Molecular Weight: 4.003
- Boiling Point @ 1 atm: -452.1°F (-268.9°C, 4oK)
- Freezing Point @ 367 psia: -459.7°F (-272.2°C, 0oK)
- Critical Temperature: -450.3°F (-268.0°C)
- Critical Pressure 33.0 psia: (2.26 atm)
- Density, Liquid @ B.P., 1 atm: 7.798 lb./cu.ft.
- Density, Gas @ 32°F (0°C), 1 atm: 0.0103 lb./cu.ft.
- Specific Gravity, Gas (Air = 1) @ 32°F (0°C), 1 atm: 0.138
- Specific c Gravity, Liquid @ B.P., 1 atm: 0.125
- Specific c Volume @ 32°F (0°C), 1 atm: 89.77 cu.ft./lb.
- Specific c Volume @ 68°F (20°C), 1 atm: 96.67 cu.ft./lb.
- Latent Heat of Vaporization: 34.9 Btu/lb. mole
- Expansion Ratio, Liquid to Gas, B.P. to 32°F (0°C): 1 to 754
Liquid helium is most frequently provided to customers in a liquid container. The below image depicts a typical liquid container design. The liquid container consists of two cylindrical vessels, one within the other. The annular space is evacuated and contains multiplayer insulation. Helium is typically withdrawn as a liquid but may be withdrawn as a gas at low flow rates and pressure. Multiple pressure relief devices are installed on these liquid containers to protect against overpressure. A 1 psig relief valve SV-3 protects the vessel from overpressure during shipment and storage. When the container is placed in service, an isolation valve V-3 is closed to isolate this pressure relief valve. An 8 psig relief valve SV-2 now limits the vessel pressure. This permits the vessel to be pressurized to just under 8 psig to enhance the removal of liquid helium. The transfer tube has a 10 psig relief valve SV-1 to protect the container from any back pressure from the filling operation. A rupture disk, RD-1, protects the outer vessel.
The user of any cryogenic liquid container should be thoroughly familiar with the product and the mechanical workings of the container before using the product. The appropriate liquid helium valve positions are presented below. Valve handles on the container are color coded green, yellow, and white. During transportation and storage, the liquid transfer valve V-1 (white) and the vent valve V-2 (yellow) are closed, while the isolation valve V-3 (green) is open to the auxiliary relief device. To transfer liquid helium, a vacuum jacketed withdrawal stinger (dip tube) is first inserted through V-1 (white); V-3 (green) is closed and V-2 (yellow) is opened and used to pressurize the liquid container with clean dry helium gas. When the container is pressurized to the desired level, the transfer of liquid helium can begin. Excess pressure in the container can be relieved before, during, and after the liquid helium is transferred. To vent gas, V-2 (yellow) can be opened. Prior to placing the liquid container in storage or shipment, V1 (white) and V-2 (yellow) should be placed in the closed position, and V-3 (green) should be placed in the open position. Failure to close V-1 (white) and V-2 (yellow) may cause an ice plug in the neck of the liquid container, creating a potential hazard.
Handling and Storage
Helium equipment includes liquid containers, vacuum jacketed transfer lines, process equipment, and accessories needed to safely handle and use the product.
Store liquid containers, when not in use or connected to a closed system, in a well ventilated storage area.
When moving, never tip, slide or roll liquid containers on their side. Liquid or gaseous containers must be secured during transport. Keep the liquid containers vertical at all times. Avoid mechanical or thermal shock. Always move liquid helium containers by pushing, not pulling.
Liquid helium container valves should never be left open to atmosphere for extended periods. Keep the fill/withdrawal vent outlets closed to prevent contamination. Check the system regularly for frost accumulation. If restrictions resulting from freezing moisture or air, or foreign material is present in openings or vents, immediately contact the vendor for instructions; blockage or restriction of openings or vents may lead to excessive vessel pressure and subsequent rupture. Do not attempt to remove restrictions without proper instructions from the liquid helium supplier. If possible, move the liquid helium container to a remote location. Reference Figure 1 and Figure 2 for proper valve orientation.
Provide a safety relief valve on any part of the system where liquid can be trapped between closed valves in lines or vessels.
Transfer liquid from containers by using the product vapor pressure or external gaseous product pressure. Use pressure reducing valves and pressure relief devices, as necessary, if the pressure source is high. The pressure source should be dry, gaseous helium. In addition, dry helium gas should be used to purge the transfer lines and receiving vessel prior to liquid helium transfer. Transfer lines for liquid helium should be well insulated and vacuum jacketed. Never pour liquid helium out of the container.
Provide protection for liquid helium containers against extremes of weather, where outside storage areas are 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.
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.