Hazardous area classification, as per EN 60079-10, is based on the explosive gas volume of the clouds in which the average gas concentration is related to the Low Explosion Limit (LEL) The higher Reynolds number, the less this approach is valid, because of the development of a concentration gradient due to the momentum driven flow. The resulting areas and volumes may be overestimated by two or three enders of magnitude, which is often critical in equipment design and selection. This paper proposes and technically justifies an overview of turbulent Jet flow modelling, with the aim at developing a more realistic calculation method of the hazardous areas, within the ATEX approach (C) 2009 Elsevier Ltd All rights reserved