This European Standard specifies minimum requirements for free flow surface supplied and free flow surface oriented diving apparatus to ensure a minimum level of safe operation of the apparatus. It applies to the following: a maximum depth of 50 m for apparatus using: 1) air or; 2) oxygen or; 3) oxygen in nitrogen mixtures (Nitrox) or; 4) oxygen in helium mixtures (Heliox) or; 5) oxygen, nitrogen and helium mixtures (Trimix); water temperatures between 4 °C and 34 °C or outside these temperatures as specified by the manufacturer; environmental temperatures between -20 °C and 50 °C or outside these temperatures as specified by the manufacturer. The requirements of this European Standard are intended to take account of the interaction between the wearer, the apparatus, and where possible the environment in which the apparatus is likely to be used. This European Standard does not cover saturation diving systems, mini bell systems or apparatus used for oxygen decompression only.