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Home , Liquid, Liquid oxygen

Safetygram 6

Liquid

Oxygen is the second largest component of the , comprising 20.8% by . oxygen is pale blue and extremely cold. Although nonflammable, oxygen is a strong oxidizer. Oxygen is necessary to support life.

Oxygen will react with nearly all organic materials and metals, usually forming an oxide. Materials that burn in air will burn more vigorously in oxygen. Equipment used in oxygen service must meet stringent cleaning requirements, and systems must be constructed of materials that have high ignition and that are nonreactive with oxygen under the service conditions. Vessels should be manufactured to American Society of Mechanical Engineers (ASME) codes and designed to withstand the process temperatures and .

Liquid oxygen is a cryogenic liquid. Cryogenic are liquefied that have a normal point below –130°F (–90°C). has a of –297°F (–183°C).

Because the difference between the product and the surrounding environment is substantial—even in the winter—keeping liquid oxygen insulated from the surrounding heat is essential. The product also requires special equipment for handling and storage.

Oxygen is often stored as a liquid, although it is used primarily as a . Liquid storage is less bulky and less costly than the equivalent capacity of high- gaseous storage. A typical storage system consists of a cryogenic , one or more vaporizers and a pressure control system. The cryogenic tank is constructed, in principle, like a . There is an inner vessel surrounded by an outer vessel. Between the vessels is an annular space that contains an insulating medium from which all the air has been removed. This space keeps heat away from the liquid oxygen held in the inner vessel. Vaporizers convert the liquid oxygen into a gaseous state. A pressure control manifold then controls the gas pressure that is fed to the process or application.

Vessels used in liquid oxygen service should be designed for the pressure and temperatures involved. design should follow similar design and conform to national standards and codes.

Manufacture Oxygen is produced by an unit (ASU) through of atmospheric air and separation of the oxygen by continuous cryogenic distil- lation. The oxygen is then removed and stored as a cryogenic liquid. Oxygen can also be produced noncryogenically using selective adsorption processes to produce gaseous product.

The ASU manufacturing process begins with a main air and ends at the output of the product storage tanks. Air is compressed and sent through a cleanup system where moisture, , and are removed. The air then passes through heat exchangers where it is cooled to cryogenic temperature. Next, the air enters a high pressure column where it is physically separated into a vaporous form of at the top of

the column and a liquid form of “crude” oxygen (~90% O2) at the bottom. This crude oxygen liquid is with- Table 1: Liquid Oxygen Physical and Chemical Properties drawn from the column and sent to Molecular Formula O2 a low-pressure column, where it is Molecular Weight 31.999 distilled until it meets commercial Boiling Point @ 1 atm –297.4°F (–183.0°C) specifications. The liquid oxygen is Point @ 1 atm –361.9°F (–218.8°C) sent to a cryogenic storage tank. Critical Temperature –181.8°F (–118.4°C) Critical Pressure 729.1 psia (49.6 atm) Uses , Liquid @ BP, 1 atm 71.23 lb/scf (1141 kg/m3) Oxygen is generally liquefied so that Density, Gas @ 68°F (20°C), 1 atm 0.0831 lb/scf (1.33 kg/m3) it can be more effectively transported Specific , Gas (air=1) @ 68°F (20°C), 1 atm 1.11 and stored in large . However, Specific Gravity, Liquid (=1) @ 68°F (20°C), 1 atm 1.14 most applications use oxygen after it Specific Volume @ 68°F (20°C), 1 atm 12.08 scf/lb (0.754 m3/Kg) is vaporized to the gaseous form. The of at BP 91.7 Btu/lb (213 Kj/Kg) primary uses of oxygen relate to its , Liquid to Gas, BP to 68°F (20°C) 1 to 860 strong oxidizing and life-sustaining in Water @ 77°F (25°C), 1 atm 3.16% by volume properties. Oxygen is commonly relied upon in health and medical applica- tions. Liquid oxygen is used as an oxi- In the chemical and Similarly, oxygen enhances the dant for liquid fuels in the industries, oxygen is used as a feed combustion process in industries systems of missiles and . component to react with that manufacture , aluminum, building blocks to produce chemicals copper, gold, lead, and cement, or that Oxygen is widely applied in the metal such as alcohols and aldehydes. In are involved in waste incineration or industries in conjunction with acety- many processes, the oxygen for reac- remediation. There are corresponding lene and other fuel gases for metal tion can be obtained from the use of productivity, energy, maintenance, cutting, welding, scarfing, hardening, air. However, direct use of oxygen, or and emissions benefits end users may cleaning and . Steel and iron enrichment of the air with oxygen, is realize. manufacturers also extensively use necessary for some processes. There oxygen or oxygen-enriched air to are several major petrochemical inter- plants suc- affect chemical and heating mediates that are presently manufac- cessfully employ oxygen to enhance associated with carbon removal and tured with high-purity oxygen, includ- their chemical process efficiency. other oxidation reactions. Benefits ing ethylene and propylene oxide Aquaculturists such as fish farmers such as fuel and energy savings plus (), vinyl chloride (for PVC), also see benefits in the health or size lower total emission volumes are and caprolactam (for nylon). of their livestock when the host envi- often achieved when air is enriched or ronment is oxygenated. replaced with higher-purity oxygen. The pulp and paper industry uses oxygen as a bleaching and oxidizing agent. A variety of process (liquor) streams show enhanced physi- cal properties after treatment with oxygen; plant operating costs also improve.

2 Health effects When pure oxygen is inhaled at Containers Normally, air contains 21% oxygen, pressures greater than 2 or 3 atmo- Liquid oxygen is stored, shipped, and and oxygen is essentially nontoxic. No spheres, a characteristic neurological handled in several types of containers, health effects have been observed in syndrome can be observed. Signs and depending upon the quantity required people exposed to concentrations up symptoms include nausea, dizziness, by the user. The types of containers to 50% at 1 atmosphere for 24 hours or vomiting, tiredness, light-headedness, in use include the dewar, cryogenic longer. mood changes, euphoria, confusion, liquid cylinder, and cryogenic storage incoordination, muscular twitching, tank. Storage quantities vary from a The at 1 atmosphere of burning/tingling sensations (par- few liters to many thousands of gal- 80% oxygen for more than 12 hours ticularly of the fingers and toes), and lons. Since heat is always present, can cause irritation of the respiratory loss of consciousness. Characteristic vaporization takes place continuously. tract, progressive decrease in vital epileptic-like convulsions, which may Rates of vaporization vary, depending capacity, coughing, nasal stuffiness, be preceded by visual disturbances on the design of the container and the sore throat, and chest pain, followed such as loss of peripheral vision, also volume of stored product. by tracheobronchitis and later by pul- occur. Continued exposure can cause monary congestion and/or edema. severe convulsions that can lead to Containers are designed and manu- death. The effects are reversible after factured according to the applicable Inhalation of pure oxygen at atmo- reduction of oxygen pressure. codes and specifications for the tem- spheric pressure or less can cause peratures and pressures involved. pulmonary irritation and edema Premature infants placed in incuba- after 24 hours. tors to breathe oxygen in concentra- Dewars tions greater than in air can develop Respiratory symptoms can occur in Figure 1 illustrates a typical vacuum- irreversible eye damage. Within six two to six hours at pressures above jacketed dewar. A loose-fitting dust hours after an infant is placed in a 1 atmosphere. One of the earliest cap over the outlet of the neck tubes high-oxygen atmosphere, vasocon- responses of the lung is accumulation prevents atmospheric moisture from striction of the immature vessels of of water in its interstitial spaces and plugging the neck and allows gas the retina occurs, which is reversible within the pulmonary cells. This can produced from vaporized liquid to if the child is immediately returned cause reduced lung function, which is escape. This type of container is non- to air, but irreversible if oxygen-rich the earliest measurable sign of toxic- pressurized. The most common unit of therapy is continued. Fully developed ity. Other symptoms include fever measure for the capacity of a dewar is blood vessels are not sensitive to and sinus and eye irritation. the liter. Five- to 200-liter dewars are oxygen toxicity. available. Product may be removed Extensive tissue damage or cryogenic from small dewars by pouring, while burns can result from exposure to larger sizes will require a transfer liquid oxygen or cold oxygen . tube. Cryogenic liquid cylinders that are pressurized vessels are sometimes incorrectly referred to as dewars.

3 Figure 1: Typical Dewar Figure 2a: Typical Cryogenic Liquid Cylinder, side view

Liquid Level Gauge Handling Ring Handling Post Annular Space Rupture Disk Inner Vessel Gas Use Vent Tube Vaporizer (Optional) Liquid Tube Outer Vessel Float Assembly

Cryogenic liquid cylinders Rubber Shock Mounts A typical cryogenic liquid cylinder is Foot Ring depicted in Figure 2. This is an insulat- ed, vacuum-jacketed pressure vessel. They are equipped with pressure relief valves and rupture disks to protect Figure 2b: Typical Cryogenic Liquid Cylinder, top view the cylinders from pressure buildup. Liquid containers operate at pres- Rupture Disk Pressure Gauge sures up to 350 psig (24 atm) and have Pressure Gauge Relief Valve Rupture Disk capacities between 80 and 450 liters Vent Valve Gas Valve of liquid. Oxygen may be withdrawn Vent Valve as a gas by passing liquid through an internal vaporizer or as a liquid under its own pressure. For more datails on the construction and op- eration of cryogenic liquid cylinders, consult Air Products’ Safetygram #27, “Cryogenic Liquid Containers.” Liquid Valve Pressure Pressure Liquid Valve Building Building Cryogenic storage tanks Regulator Valve Economizer Regulator Customer installations generally include a tank, vaporizer, and pressure control manifold (see Figure 3). Tanks Figure 3: A Typical Customer Station with a Cryogenic Storage Tank may be spherical or cylindrical in shape and are mounted in fixed locations as stationary vessels or on railcar or truck chassis for easy transportation. Sizes range from 500 to 420,000 gallons (1,893 – 1,589,873 Liters). All tanks are - and vacuum-insulated in the annular space and equipped with various circuits to control product fill, pressure buildup, pressure-relief, product withdrawal, and tank vacu- um. Tanks are designed to national specifications for the pressures and temperatures involved.

4 Transfer lines Shipment of liquid oxygen (40 psia) pressure are UN/DOT A liquid transfer line is used to safely All shipments of liquid oxygen must Authorized containers. These are remove liquid product from dewars comply with transportation regula- containers built to other than DOT or cryogenic liquid cylinders. A typical tions (DOT in U.S.). This applies to specifications, but ones authorized transfer line for dewars is connected motor freight, rail, air, and water ship- by DOT for use in the transport of ap- to a bayonet that provides a means of ments. For air shipments, all packages proved products. Containers used for using product vapor pressure buildup must also comply with International transporting liquid oxygen at pres- or an external pressure source to Air Transport Association/ sures greater than 25 psig (40 psia) remove the liquid. For cryogenic liquid International Civil Air Organization need to be designed, manufactured, cylinders, the transfer line is connect- (IATA/ICAO) and tested to DOT specifications. DOT ed to the cylinder’s liquid withdrawal Code of Federal Regulations, Title 49 valve. Dangerous Goods regulations: specifies these labeling and identifica- Water vessel shipments must also tion requirements: Liquid product is typically removed be prepared in accordance with the through insulated withdrawal lines to International Maritime Organization Hazard Class: 2.2 minimize the loss of liquid product to (IMO) regulations. In the U.S., all pack- Shipping Label: Nonflammable Gas gas. Insulated flexible or rigid lines are aging used to transport oxygen must and Oxidizer (For domestic shipments, used to withdraw product from stor- be either “UN/DOT Specification” or only the oxygen label may be used) age tanks. Connections on the lines “UN/DOT Authorized” and in proper Identification Number: UN1073 and tanks vary by manufacturer. condition for transport. Proper Shipping Name: Oxygen, NOTE: In the U.S., liquid cylinders Containers used for transporting Refrigerated Liquid designed to dispense gaseous oxygen liquid oxygen at less than 25 psig have valves equipped with standard Compressed Gas Association (CGA) outlets. Suitable pressure-regulating equipment may be attached. Valves provided for the withdrawal of liquid product are also equipped with stan- dard CGA outlets but differ from con- nections used for gaseous withdrawal. This prevents cross connections between processes using the liquid or gaseous product.

5 Safety considerations Do not permit or open Storage The hazards associated with liquid flames in any areas where liquid oxy- • Store and use liquid containers with oxygen are exposure to cold tempera- gen is stored or handled. Do not per- adequate ventilation. Do not store tures that can cause severe burns; mit liquid oxygen or oxygen-enriched containers in a confined area or in overpressurization due to expansion air to come in contact with organic area unprotected from the extremes of small amounts of liquid into large materials or flammable or combus- of weather. volumes of gas in inadequately vented tible substances of any kind. Some of equipment; oxygen enrichment of the organic materials that can react • Cryogenic containers are equipped the surrounding atmosphere; and the violently with oxygen when ignited with pressure relief devices de- possibility of a combustion reaction if by a spark or even a mechanical shock signed to control the internal the oxygen is permitted to contact a are , grease, , kerosene, cloth, pressure. Under normal conditions noncompatible material. tar, and dirt that may contain oil or these containers will periodically grease. If liquid oxygen spills on as- vent product. Do not plug, remove The low temperature of liquid oxygen phalt or other surfaces contaminated or tamper with any pressure relief and the vapors it releases not only with combustibles, do not walk on or device. pose a serious burn hazard to hu- roll equipment over the area of the • Oxygen must be separated from man tissue, but can also cause many spill. Keep sources of ignition away for flammables and combustibles by at materials of construction to lose their 30 minutes after all or fog has least 20 feet or a half-hour fire wall. strength and become brittle enough disappeared. to shatter. Post “No Smoking” and “No Open Systems used in oxygen service must Flames” signs. It is important to note that fire meet stringent cleaning require- • Customer storage sites having a ca- starts to change when the ments to eliminate any incompatible pacity of more than 20,000 scf must concentration of oxygen increases. contaminants. The CGA’s Pamphlet be installed in accordance with the Materials easily ignited in air not only G-4.1, “Cleaning Equipment for Oxygen National Fire Protection Association become more susceptible to ignition Service,” describes cleaning methods (NFPA) Standard 55. but also burn with added violence in for equipment used in oxygen service. the presence of oxygen. These materi- CGA’s Pamphlet O2-DIR, “Directory of • Liquid containers should not be left als include clothing and hair, which Cleaning Agents for Oxygen Service,” open to the atmosphere for extend- have air spaces that readily trap the provides comparative information on ed periods. Keep all valves closed oxygen. Elevated oxygen levels can be cleaning agents used to clean oxygen and outlet caps in place when not reached very quickly, and all person- equipment. in use. If restriction results from nel must be aware of the hazard. freezing moisture or foreign mate- Also, review the Material Safety rial present in openings and vents, Any clothing that has been splashed Data Sheet (MSDS) and follow all contact the vendor for instructions. or soaked with liquid oxygen or ex- recommendations. posed to high oxygen concentrations Restrictions and blockages may should be removed immediately and result in dangerous over-pressuriza- aired for at least an hour. Personnel Buildings tion. Do not attempt to remove the should stay in a well-ventilated area Because of the large expansion ratio restriction without proper instruc- and avoid any source of ignition until of liquid-to-gas, it is very important to tions. If possible, move the cylinder their clothing is completely free of provide adequate ventilation in areas to a remote location. any excess oxygen. Clothing saturated where liquid oxygen is in use. A mini- with oxygen is readily ignitable and mum of six air changes per hour is will burn vigorously. suggested. U.S. OSHA has established the definition of an oxygen-enriched atmosphere as one containing more than 23.5% oxygen.

Remember, oxygen has no warning properties!

6 Handling • Use only transfer lines and equip- Personal protective • Cryogenic containers must be ment designed for use with cryo- genic liquids. Some elastomers equipment (PPE) stored, handled and transported in Personnel must be thoroughly and metals, such as carbon steel, the upright position. When moving, familiar with properties and safety may become brittle at extremely never tip, slide or roll containers considerations before being allowed low temperatures and may easily on their side. Use a suitable hand to handle liquid oxygen and its associ- fracture. These materials must be truck for moving smaller containers. ated equipment. Move larger containers by pushing, avoided in cryogenic service. not pulling. Avoid mechanical and The eyes are the most susceptible to • It is recommended that all vents be thermal shock. the extreme cold of the liquid and piped to the exterior of the building. vapors of liquid oxygen. The recom- • Never allow any unprotected part • On gas withdrawal systems, use mended PPE is a full faceshield over of the body to come in contact with check valves or other protective safety goggles; clean, loose-fitting uninsulated pipes or equipment apparatus to prevent reverse flow thermal-insulated or leather gloves; containing cryogenic product. The into the container. long-sleeved shirts; and pants without extreme cold will cause flesh to cuffs. Wear this PPE when handling or stick fast and potentially tear on • On liquid systems, pressure relief using liquid oxygen, or whenever the withdrawal. devices must be used in lines where possibility of exposure due to a spill there is the potential to trap liquid • Use only oxygen-compatible materi- exists. In addition, safety shoes are between valves. als and . recommended for those involved with the handling of containers. For additional information on the • If there is any difficulty in operat- storage and handling of cryogenic ing the container valve or container In emergency situations, self- liquids, refer to Air Products’ connections, discontinue use and contained breathing apparatus (SCBA) Safetygram-16, “Safe Handling of contact the vendor. Do not remove or must be used. Clothing that is fire- Cryogenic Liquids,” and CGA Pamphlet interchange connections. Use only resistant in air may be readily ignit- P-12, “The Safe Handling of Cryogenic the properly assigned connections. able in oxygen-enriched . Liquids.” Only trained and certified emergency Do not use adapters. responders should respond to emer- gency situations.

7 First aid Emergency Response System For skin contact with liquid oxygen, T 800-523-9374 (Continental U.S. and Puerto Rico) T +1-610-481-7711 (other locations) remove any clothing that may restrict 24 hours a day, 7 days a week for assistance involving Air Products and Chemicals, Inc. products to the frozen area. Do not rub frozen parts, as tissue damage Product Safety Information may result. As soon as practical, place For MSDS airproducts.com/MSDS the affected area in a warm water For safetygrams airproducts.com/safetygrams bath with a temperature not exceed- For product safety information airproducts.com/productsafety ing 105°F (40°C). Never use dry heat. Call a physician as soon as possible. Technical Information Center Frozen tissue is painless and appears T 800-752-1597 (U.S.) T +1-610-481-8565 (other locations) waxy with a possible yellow color. Monday–Friday, 8:00 a.m.–5:00 p.m. EST It will become swollen, painful, and F 610-481-8690 prone to infection when thawed. If [email protected] the frozen part of the body has been thawed, cover the area with a dry sterile Information Sources dressing with a large bulky protective Compressed Gas Association (CGA) www.cganet.com covering, pending medical care. In European Association (EIGA) www.eiga.org Asia Industrial Gas Association (AIGA) www.asiaiga.org case of massive exposure, remove American Chemistry Council (ACC) www.americanchemistry.com clothing while showering the victim with warm water. Call a physician immediately. For more information, please contact us at:

If the eyes are exposed to the extreme Corporate Headquarters cold of the liquid or vapors, immedi- Air Products and Chemicals, Inc. ately warm the frostbite area with 1940 Air Products Blvd. warm water not exceeding 105°F Allentown, PA 18106-5500 (40°C) and seek medical attention. T: 610-481-4911

Fighting fires Since oxygen is nonflammable but supports combustion, fire-fighting ac- tions require shutting off the source of oxygen, if possible, then fighting the fire according to the material involved.

Caution: Do not direct water streams toward venting oxygen. The water will freeze and plug the pressure-relief vent, which may result in container failure.

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