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Jai Ganesh

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Registered: 2005-06-28

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Liquid Oxygen

Liquid Oxygen

Gist

Oxygen is the second largest component of the atmosphere, comprising 20.8% by volume. Liquid 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 temperatures 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 pressures.

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

Because the temperature 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.

Summary:

Purpose

The use of liquid oxygen in health care facilities has increased dramatically in the past few years. This Information Bulletin outlines the basic requirements of National Fire Protection Association Standard 99 (NFPA 99) for the safe storage, transfer and use of liquid oxygen in a health care facility. The 1999 edition of NFPA 99 is adopted by reference in the 2000 edition of NFPA Standard 101 (Life Safety Code).

Background

Transferring (also referred to as transfilling) of liquid oxygen from one container to another presents several potential hazards, which include the:

* Strong oxidizing properties of oxygen,
* Very cold temperature of the liquid and vapor (it's classified as a cryogenic fluid), and
* Pressure producing potential of the vaporization and/or liquid expansion processes.

Here are some important elements to remember relating to the storage and use of liquid oxygen:

* The transfer of liquid oxygen from one container to another can create an oxygen-enriched atmosphere within the vicinity of the containers. When a liquid oxygen container is not used for a period of time, there is a small amount of oxygen vented into the vicinity of the container. If the container is tipped over or placed on its side, a larger amount of oxygen will be vented. This venting may create an oxygen-enriched atmosphere if the container is stored in a confined space.
* In an oxygen-enriched atmosphere, materials that are combustible and flammable in air ignite more easily, burn more vigorously and produce a higher temperature when burning. Materials not normally considered to be combustible may be so in an oxygen-enriched atmosphere. Examples of these types of materials that may be found on or near patients/residents in health care facilities can include hair oils, oil-based lubricants, skin lotions, facial tissues, clothing, bed linens, alcohols, acetone and some plastics. Absorbent materials such as clothing or bedding, for example, may become saturated with oxygen when exposed to oxygen or an oxygen-enriched atmosphere and more readily ignite in the presence of a source of ignition.
* A hazard can also exist if the oxygen equipment becomes contaminated with oil or grease. It is important to keep liquid oxygen separated from sources of ignition.
* Unfortunately, there are many items in a typical patient/resident room in health care occupancies that can create a source of ignition if introduced into an oxygen-enriched atmosphere. These can include electric wheelchairs, electric razors, electric bed controls, hair dryers, remote television controls, television sets, radio and stereo equipment, computers, air conditioners, telephone handsets and fans.

Here are two other points to be aware of relating to the temperature and vaporization hazards:

* Liquid oxygen boils at –297.3 degrees Fahrenheit and is extremely cold. If permitted to contact skin or non-protective clothing, cold surfaces present on liquid oxygen systems such as valves, lines or couplings can cause severe frostbite or cryogenic burns. Skin will stick to cold surfaces at cryogenic temperatures, causing additional injury.
* One volume of liquid oxygen at standard atmospheric pressure when warmed will expand significantly and when vaporized will produce approximately 860 volumes of gaseous oxygen at ambient temperatures. The large volume of gaseous oxygen resulting from the vaporization of liquid oxygen has the potential, if trapped in a closed circuit not adequately protected by pressure relief devices, to generate gas pressures high enough to cause explosive rupture of containers, transfer lines, piping, and other system components.

Details

Liquid oxygen, sometimes abbreviated as LOX or LOXygen, is the liquid form of molecular oxygen. It was used as the oxidizer in the first liquid-fueled rocket invented in 1926 by Robert H. Goddard, an application which has continued to the present.

Physical properties

Liquid oxygen has a light or pale cyan color and is strongly paramagnetic: it can be suspended between the poles of a powerful horseshoe magnet. Liquid oxygen has a density of 1.141 kg/L (1.141 g/ml), slightly denser than liquid water, and is cryogenic with a freezing point of 54.36 K (−218.79 °C; −361.82 °F) and a boiling point of 90.19 K (−182.96 °C; −297.33 °F) at 1 bar (15 psi). Liquid oxygen has an expansion ratio of 1:861 and because of this, it is used in some commercial and military aircraft as a transportable source of breathing oxygen.

Because of its cryogenic nature, liquid oxygen can cause the materials it touches to become extremely brittle. Liquid oxygen is also a very powerful oxidizing agent: organic materials will burn rapidly and energetically in liquid oxygen. Further, if soaked in liquid oxygen, some materials such as coal briquettes, carbon black, etc., can detonate unpredictably from sources of ignition such as flames, sparks or impact from light blows. Petrochemicals, including asphalt, often exhibit this behavior.

The tetraoxygen molecule (O4) was first predicted in 1924 by Gilbert N. Lewis, who proposed it to explain why liquid oxygen defied Curie's law. Modern computer simulations indicate that, although there are no stable O4 molecules in liquid oxygen, O2 molecules do tend to associate in pairs with antiparallel spins, forming transient O4 units.

Liquid nitrogen has a lower boiling point at −196 °C (77 K) than oxygen's −183 °C (90 K), and vessels containing liquid nitrogen can condense oxygen from air: when most of the nitrogen has evaporated from such a vessel, there is a risk that liquid oxygen remaining can react violently with organic material. Conversely, liquid nitrogen or liquid air can be oxygen-enriched by letting it stand in open air; atmospheric oxygen dissolves in it, while nitrogen evaporates preferentially.

The surface tension of liquid oxygen at its normal pressure boiling point is 13.2 dyn/cm.

Uses

In commerce, liquid oxygen is classified as an industrial gas and is widely used for industrial and medical purposes. Liquid oxygen is obtained from the oxygen found naturally in air by fractional distillation in a cryogenic air separation plant.

Air forces have long recognized the strategic importance of liquid oxygen, both as an oxidizer and as a supply of gaseous oxygen for breathing in hospitals and high-altitude aircraft flights. In 1985, the USAF started a program of building its own oxygen-generation facilities at all major consumption bases.

In rocket propellant

Liquid oxygen is the most common cryogenic liquid oxidizer propellant for spacecraft rocket applications, usually in combination with liquid hydrogen, kerosene or methane.

Liquid oxygen was used in the first liquid fueled rocket. The World War II V-2 missile also used liquid oxygen under the name A-Stoff and Sauerstoff. In the 1950s, during the Cold War both the United States' Redstone and Atlas rockets, and the Soviet R-7 Semyorka used liquid oxygen. Later, in the 1960s and 1970s, the ascent stages of the Apollo Saturn rockets, and the Space Shuttle main engines used liquid oxygen.

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