2.5.1.: Definition ►M4  Gases under pressure are gases which are contained in a receptacle at a pressure of 200 kPa (gauge) or more at 20 °C, or which are liquefied or liquefied and refrigerated. ◄

They comprise compressed gases, liquefied gases, dissolved gases and refrigerated liquefied gases. The critical temperature is the temperature above which a pure gas cannot be liquefied, regardless of the degree of compression.