8 1.1 What are gases? What is a gas? A “gas” or “gaseous substance” is one of the three states of matter, the other two being “solid” and “liquid”. Gases, general definition Gases are materials or material mixtures/preparations that • have a vapour pressure of over 300 kPa (3 bar) at 50°C or • are completely gaseous at 20°C and a standard pressure of 101.3 kPa (1 bar). Pressurised gases Pressurised gases are gases that • are contained in a vessel under at least 200 kPa pressure (overpressure) or more, • are liquefied or • are liquefied and frozen. This includes compressed, liquefied, dissolved and frozen liquefied gases. Density of gases Gases have the following properties, depending on their state, e.g. Based on the temperature of the gas and pressure in the ambient atmosphere. Gases are • heavier than air if their density is > 1.3 kg/m3, • just as heavy as air if their density is ≤ 1.3 kg/m3 and ≥ 1.2 kg/m3 and • lighter than air if their density is < 1.2 kg/m3. Liquefied gases are at low temperatures after extraction, and therefore are generally heavier than air in this state. 1 COMPRESSED GASES | Terms and definitions N O T E The term critical temperature is important in this context. The critical temperature is the temperature above which a pure gas can no longer be liquefied depending on its pressure, or can no longer change its state of matter. Sample
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