Class 2

A gas is defined as "a substance which at 50°C (122°F) has a vapor pressure greater than 300 kPa (3.0 bar) or is completely gaseous at 20°C (68°F) at a standard pressure of 101.3 kPa (1.01 bar)."

When packaged under pressure for transport, a gas can take one of five physical states, described as follows:

Compressed gas is entirely gaseous at -50°C (-58°F). This includes all gases with a critical temperature less than or equal to -50°C (-58°F).

Liquefied gas is partially liquid at temperatures above -50°C (-58°F). High-pressure liquefied gases have a critical temperature between -50°C (-58°F) and +65°C (149°F). Low-pressure liquefied gases have a critical temperature above +65°C (149°F).

Refrigerated liquefied gas is made partially liquid because of its low temperature. This is also referred to as cryogenic liquid.

Dissolved gas is dissolved in a liquid phase solvent.

Absorbed gas is absorbed into a solid porous material that results in an internal receptacle pressure of less than 101.3 kPa at 20°C (68°F) and less than 300 kPa at 50°C (122°F).

Class 2 dangerous goods include compressed gases, liquefied gases, absorbed gases, dissolved gases, refrigerated liquefied gases, mixtures of one or more gases (even if one or more vapors is from a different class), articles charged with a gas, and aerosols.

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