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Liquid Helium

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Liquid Helium Safetygram 22 Liquid helium Liquid helium is inert, colorless, odorless, noncorrosive, extremely cold, and nonflammable. Helium will not react with other elements or compounds under ordinary conditions. Since helium is noncorrosive, 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 must be selected and designed to withstand the pressure and temperatures involved and comply with applicable codes for transport and use. Manufacture Most of commercial helium is recovered from natural gas through a cryogenic separation process. Normally, helium is present in less than 1% by volume in natural gas. Helium is recovered, refined, and liquefied. Liquid helium is typically shipped from production sources to storage and transfill facilities. Tankers, ranging in size from 5,000 to 11,000 gallons, contain an annular space insulated with vacuum, nitrogen shielding, and multilayer insulation. This de- sign reduces heat leak and vaporization of liquid helium during transportation. Uses The extremely low temperature of liquid helium is utilized to maintain the superconducting properties of magnets in applications such as MRI, NMR spectroscopy, and particle physics research. The main application for gas- eous helium is for inert shielding gas in metal arc and laser welding. Helium provides a protective atmosphere in the production of reactive metals, such as titanium and zirconium. Gaseous helium is used as a coolant during the draw- ing of optical fibers, as a carrier gas for chromatography, and as a leak detection gas in a variety of industries. Being both lighter than air and nonflammable, helium is used to inflate balloons and airships. Health effects Table 1: Liquid Helium Physical and Chemical Properties Being odorless, colorless, tasteless, and Molecular Symbol He nonirritating, helium has no warning Molecular Weight 4.003 properties. Humans possess no senses Boiling Point @ 1 atm –452.1°F (–268.9°C) that can detect the presence of heli- Freezing Point @ 367 psia –459.7°F (–272.2°C) um. Although helium is nontoxic and Critical Temperature –450.3°F (–268.0°C) inert, it can act as a simple asphyxi- Critical Pressure 33.0 psia (2.26 atm) ant by displacing the oxygen in air to Density, Liquid @ B.P., 1 atm 7.802 lb/ft3 (124.98 kg/m3) levels below that required to support Density, Gas @ 70°F (21.1°C), 1 atm 0.0103 lb/ft3 (0.165 kg/m3) life. Inhalation of helium in excessive Specific Gravity, Gas (air=1) @ 32°F (0°C), 1 atm 0.138 amounts can cause dizziness, nausea, Specific Gravity, Liquid @ B.P., 1 atm 0.125 vomiting, loss of consciousness and Specific Volume @ 32°F (0°C), 1 atm 89.77 ft3/lb (5.604 m3/kg) death. Death may result from errors Specific Volume @ 68°F (20°C), 1 atm 96.67 ft3/lb (6.035 m3/kg) in judgment, confusion, or loss of Latent Heat of Vaporization 8.72 Btu/lb (20.28 kJ/kg) consciousness, that prevents self- Expansion Ratio, Liquid to Gas, B.P. to 32°F (0°C) 1 to 754 rescue. At low oxygen concentrations, unconsciousness and death may occur in seconds and without warning. Figure 1: Liquid Helium Container Design Features Personnel, including rescue work- ers, should not enter areas where the 3/8" Adapter Isolation Valve oxygen concentration is below 19.5% 1 (Green Handle) C-1 /2" Adapter unless provided with a self-contained C-2 5/8" Adapter breathing apparatus or air-line C-3 3/4" Adapter C-4 respirator. Liquid Access Valve (White Handle) V-3 V-1 For more information on oxygen- 1 psig Relief Valve 10 psig Relief Valve SV-1 deficient atmospheres, consult SV-3 Air Products’ Safetygram #17, “Dangers 30"–0–30 psig Gauge PI-1 8 psig Relief Valve of Oxygen-Deficient Atmospheres.” V-2 SV-2 Extensive tissue damage or burns can 1 /2" FNPT RD-1 result from exposure to liquid helium Annulus Rupture Disk or cold helium vapors. Vent Valve (Yellow Handle) Note: For 100, 250, and 500 liter Annular Space containers, four adapter sizes are provided as shown in Figure 1. Smaller containers, 30, 60, and 100 liter, are supplied with 3/8" and 1/2" adapters. 2 Figure 2: Proper Valve Positions V-3 V-2 V-1 Green Yellow White Handle Handle Handle Valve Valve Valve Containers Liquid helium is stored, shipped, Vent and handled primarily in vacuum- Release excess pressure insulated liquid containers, which are before, during, and after product transfer as needed. sometimes mistakenly referred to as Closed Open Closed dewars. Liquid container capacities have been standardized to range from Transfer 30 liters to 500 liters. Larger quanti- Liquid in or out of liquid cylinder. ties of liquid helium are transported in tanks with capacities ranging from Closed Open* Open 5,000 to 11,000 gallons. Store or Ship Since heat leak is always present, va- Valve positions after excess pressure has been vented. porization takes place continuously in smaller containers. Rates of vaporiza- Open Closed** Closed** tion vary, depending upon the design of the container and the volume of Failure to close these two valves may result in a potential hazard. the stored product. Containers are de- * The yellow valve is used to presurrize the liquid container with clean, dry helium gas. signed and manufactured according ** Failure to close this valve may cause an ice plug in the neck of the liquid container, creating a potential hazard. to applicable codes and specifications for the pressures and temperatures encountered with liquid helium. Liquid cylinders A 1 psig relief valve SV-3 protects the The user of any cryogenic liquid con- Liquid helium is most frequently vessel from overpressure during ship- tainer should be thoroughly familiar provided to customers in a liquid ment and storage. When the container with the product and the mechanical cylinder. Figure 1 depicts a typical is placed in service, an isolation valve workings of the container before us- liquid container design. The liquid V-3 is closed to isolate this pressure ing the product. The appropriate liquid cylinder consists of two cylindrical relief valve. The vessel pressure is now helium valve positions are presented vessels, one within the other. The an- limited by an 8 psig relief valve SV-2. in Figure 2. Valve handles on the con- nular space is evacuated and contains This permits the vessel to be pressur- tainer are color-coded green, yellow, multilayer insulation. Helium is typi- ized to just under 8 psig to enhance and white. During transportation and cally withdrawn as a liquid but may the removal of liquid helium. The storage, the liquid transfer valve V-1 be withdrawn as a gas at low flow transfer tube has a 10 psig relief valve (white) and the vent valve V-2 (yellow) rates and pressure. Multiple pressure SV-1 to protect the container from any are closed, while the isolation valve relief devices are installed on these back-pressure from the filling opera- V-3 (green) is open to the auxiliary liquid containers to protect against tion. The outer vessel is protected by a relief device. overpressure. rupture disk RD-1. 3 To transfer liquid helium, a vacuum- Figure 3: Nonflammable Gas Shipping Label 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 Transfer lines Shipment of liquid helium Containers used for transporting be placed in the open position. Failure (vacuum-jacketed line) liquid helium at less than 25 psig to close V-1 (white) and V-2 (yellow) A vacuum-jacketed (VJ) transfer line (40 psia) pressure are UN/DOT autho- may cause an ice plug in the neck of should be used to remove liquid prod- rized containers. Containers used for the liquid container, creating a po- uct from the liquid containers. A typi- transporting liquid helium at pres- tential hazard. Air Products does not cal transfer line provides a means to sures greater than 25 psig (40 psia) recommend the removal or attempt to remove the liquid helium using either are required to be designed, manu- repair of any component of the liquid product vapor pressure buildup or an factured, and tested to national or container package. If in doubt about external pressure source to transfer international specifications. the functionality of any part of the product through this line. If an exter- container, please contact Air Products nal source is used to pressurize the For air shipments, all packages for assistance. liquid container, pressure regulators must be in compliance with Inter- and relief devices should be installed national Air Transport Association/ Customers must be aware of the as necessary to adequately protect the International Civil Air Organization importance of correct valve position- lines from the external high-pressure (IATA/ICAO) Dangerous Goods ing on liquid helium containers. Loss source. Regulators and relief devices Regulations, as well as national ground of product or potentially hazardous are intended to prevent overpres- transport regulations. conditions may result from improper surization of the liquid container. Dry valve configuration. helium is the only acceptable gas for Hazard Class: 2.2 external pressurization of the liquid Shipping Label: Nonflammable Gas container.
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