Gives advice for the technique of using the pressure of a protective gas to prevent the ingress of an external atmosphere to a space which may contain an ignition source, when (in a hazardous area) selecting, installing and maintaining electrical apparatus. Also gives recommendations for the continuous dilution technique to a concentration below the lower explosive limit (LEL) of the atmosphere within a space containing a gas emission source that may result in an explosive gas/air mixture. Gives descriptions of techniques and definitions.