What is Liquid Oxygen?

What is Liquid Oxygen?

As is evident by its name, liquid oxygen is oxygen in its liquid form. Liquid oxygen is derived by distilling liquid air, which consists of about 19 percent oxygen, 80 percent nitrogen, and small amounts of inert gases like argon, krypton, and xenon. Liquid air, in turn, is derived by rapidly expanding pressurized gaseous air, which has been first purified in order to remove the carbon dioxide and other substances that have high points, such as hydrocarbons, which may hamper the expansion process. The liquid oxygen obtained from this is pale blue in color and has paramagnetic as well as cryogenic properties.

As far as commerce is concerned, liquid oxygen is categorized as an industrial gas and is used widely for medical and industrial purposes. Since the expansion ratio of liquid oxygen is 860:1, it is used in military and commercial aircraft these days. Liquid oxygen is also commonly used as a liquid oxidizer propellant in rockets, generally in combination with kerosene or hydrogen.

Because of its cryogenic characteristic, if liquid oxygen comes in contact with anything it becomes very brittle. Liquid oxygen is also a powerful oxidizer, so organic matter burns rapidly and energetically in liquid oxygen. Moreover, when soaked in liquid oxygen they can explode unpredictably if they come into contact subsequently. Petrochemicals often exhibit this kind of trait.

How is Liquid Oxygen Made?

Oxygen and nitrogen are the two gases that the air we breathe is mostly made up of. Therefore, in order to get liquid oxygen, both these gases have to be cooled to a certain temperature. To change nitrogen into liquid, it has to be cooled to -321 degrees F, or -196 degrees C. Oxygen can be turned into liquid at -183 degrees C. The air has to be first compressed and then cooled in order lower the temperature of these two gases to such an extent. The temperature becomes even lower once the air is expanded again. This process is repeated several times, until eventually the temperature of the air drops down to -312 degrees F, at which point it turns into liquid. This liquid, however, consists of both oxygen as well as nitrogen. In order to isolate the oxygen, the liquefied air is heated just enough so that nitrogen turns into gas again, thus leaving just the liquid oxygen.

Liquid Oxygen Safety Considerations

Some of the dangers of liquid oxygen are: severe burns caused by being exposed to cold temperatures; over-pressurization because of the expansion of some amounts of the gas into large amounts of the gas in equipment that is inadequately vented; the surrounding area being saturated by oxygen; and the high chances of combustion occurring in the event of the oxygen coming into contact with a material that it is non-compatible with.

Liquid oxygen’s low temperature and the vapors released from it can be dangerous to human tissue because it can burn it, plus, it can make many kinds of construction material it comes into contact with so brittle that they can shatter. Due to the large ratio of expansion from liquid to gas, it has the ability to build pressure rapidly in places where there are chances of liquid being trapped. Therefore, these areas need to be first identified and then protected by providing pressure relief. This ratio of expansion also can cause areas where the air gets saturated by too much oxygen. It is an important fact to know that the fire chemistry begins changing when the oxygen level increases by just 23 percent.

Hence, there are high chances of materials, such as hair and clothing, which ignite easily in air catching fire and can burn more violently because of the extra oxygen. 23 percent oxygen levels can be reached quite swiftly and anybody handling liquid oxygen should be aware of this danger. If clothing should come into contact with liquid oxygen, they should be taken off at once and aired for about an hour at least. The handlers should go to an area that is well ventilated and avoid all sources of fire until their clothing gets free of oxygen completely.

Open flames and smoking should not be permitted in any area where liquid oxygen is kept or handled. Liquid oxygen should not be allowed to come into contact with any combustible material or organic material of any kind. Asphalt, tar, cloth, kerosene, grease, and oil are some of the organic material that can have a violent reaction with oxygen when a spark ignites it.