Most gases used in plants are also available as cryogenic liquids. Among the most common are oxygen, nitrogen, argon, helium and hydrogen.

Liquid oxygen is frequently delivered to a plant - and even to a construction site - and then vaporized for use in flame cutting, welding, metallizing, or heating. Other uses include oxygen injection into a foundry cupola and oxygen-based processes such as paper-pulp bleaching and steelmaking.

Liquid nitrogen is also very common. A variety of processes have been developed that use the liquid primarily because of its high refrigeration values. Examples include freezing food, stripping scrap rubber from tires and cables, and removing parting lines and risers from plastic injection-molded parts. It is even used as super-cold quenchant for high-alloy steels to transform retained austenite.

The availability of large volumes of liquid helium has made possible the rapid development of superconductivity. And these examples are only a few from some of the major industrial gases.

The key to the expanding use of cryogenic liquids is economics. The cost of delivering and storing the liquid is often lower than buying the gas in compressed gases cylinders. At room temperature (70°F / 21°C) and atmospheric pressure, nitrogen occupies 700 times as much space as the same amount of nitrogen in liquid form. The reduction in cost for containers, demurrage, shipping, and storage is enormous.

However, handling liquefied gases that are stored and used at very low temperatures requires some special knowledge and special precautions. To use these gases safely, the plant engineer and employees must know the specific properties of each liquefied gas and its compatibility with other materials, and must follow some common sense procedures.