Legal basis / information The following apply to the storage of compressed gases, among others: ››› Dangerous Substances and Explosive Atmospheres Regulations 2002 (DSEAR) ››› Health and Safety Executive (HSE) ››› HSE – Drum and Cylinder Handling Guidelines ››› UKLPG – Storage of Full and Empty LPG Cylinders and Cartridges – Code of Practice No. 7 ››› NERC – Guidance to Safe Storage and Installation of Gas Cylinders Definition 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. Compressed gas A gas that is gaseous when filled under pressure at 50°C, including all gases with a critical temperature ≤ -50 °C. Liquefied gas A gas that is partially liquefied when filled under pressure at temperatures above -50 °C. We can differentiate between: • Gas liquefied under high pressure – a gas whose critical temperature is between -50 °C and +65 °C • Gas liquefied under low pressure – a gas whose critical temperature is over +65 °C Frozen, liquefied gas A gas that is partially liquefied when filled upon gas extraction due to its low temperature Dissolved gas A gas that is dissolved under pressure in a liquid solvent when packaged Properties Examples Flammable gases Hydrogen, Methane, Ethane, Acetylene, Propane, Butane, Special forming and Test gases Oxidising gases Oxygen /Air nitrogen oxide mixtures (laughing gas) Toxic and corrosive gases Arsenic, Phosphine, Carbon monoxide, Ammonia, Hydrogen sulphide, Sulphur dioxide, Chlorine Inert gases Nitrogen , Inert gases, Shielding gases (welding) 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. Gases are divided into four major groups according to their properties: Gases under pressure are divided into four groups according to the GHS/CLP Regulation Annex 1, taking into account the state of aggregation and the critical temperature Tk (critical temperature Tk above which a pure gas can no longer be liquefied). Please observe local legislation and regulations. 263
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