Low temperature gas viscosity

Cryogenic Liquids
Most cryogenic liquids are colorless, odorless, and tasteless when vaporized to a gas. As liquids, most have no color (except liquid oxygen which is light blue). However, whenever the cold liquid and vapor are exposed to the atmosphere a warning appears. As the boil-off gases condense moisture in the air, a fog forms that extends over an area larger than the vaporizing gas. Many cryogenic liquids are inert gases, and may inert an enclosed space. Inert gases will not support life. Both the liquid and its boil-off vapor can rapidly freeze human tissue and can cause many common materials such as carbon steel, plastic, and rubber to become brittle or fracture under stress. Liquids in containers and piping at temperatures at or below the boiling point of liquified air (-318 F) can cause the surrounding air to condense to a liquid. Extremely cold liquified gases (helium, hydrogen, and neon) can even solidify air or other gases to which they are directly exposed.

Cryogen

Boiling point
(1 atm),°C (°F)

Critical pressure
psig^a

Liquid density, g/L

Gas density (27°C), g/L

Liquid-to-gas expansion ratio

Type of gas

-186(-303)

710

1402

1.63

860

Inert

-269(-452)

125

0.16

780

Inert

-253(-423)

188

0.082

865

Flammable

-196(-321)

492

808

2.25

710

Inert

-183(-297)

736

1410

1.4

875

Oxygen^b

CH4

-161 (-256)

673

425

0.72

650

Flammable

^a pound per square inch gauge; b Although oxygen does not burn, it will support combustion. Oxygen-enriched atmospheres may lead to violent reactions, such as rapid combustion or explosions, with incompatible materials.