This paper deals with the elaboration and the validation of a userfriendly numerical program (EOL) for the calculation of the ventilation patterns inside industrial premises. After the running-in. In period, "EOL" will be used by the technical staff in charge of ventilation projects. Here is set out the EOL unit devoted to the calculation of the mean flow inside the rooms. The structure of the software (presently restricted to two-dimensional mean flow configurations) is explained.