Directive 1999/92/EC is to be implemented within a year. It requires the determination of hazardous zones where an explosive atmosphere (ATEX) may occur. This zoning is expected to be accurate. So is to be the evaluation of effects associated with an ignition of the so defined ATEX zones. Hence, Physical phenomena which are involved in the formation of ATEX must be taken into account and quantified : leak and vaporization of a flammable liquid, leak of a flammable gas, dispersion of a layer of combustible dust. It is not recommended to oversize a zone, nor to design a zone having such a small volume that the effects of an ignition would be negligible.
