Abstract: An air curtain (14) is used to dynamically separate a zone (10) to be protected and a contaminating zone (12) communicating with each other through at least one separation zone (11), the air curtain being formed by simultaneously injecting at least two adjacent clean air jets into the same direction in the separation zone (11). More precisely, the air curtain (14) comprises a slow jet, in which the tongue (16) covers the entire separation zone (11) and a fast jet inserted between the slow jet and the zone (10) to be protected and for which the injection flow is such that it induces an air flow equal to approximately half the injection flow of the slow jet, on its surface in contact with the slow jet. Preferably, clean ventilation air is also injected into the zone (10) to be protected at a flow equal to at least the air flow induced by the surface of the air curtain in contact with the ventilation air, and in any case at a speed not less than 0.1 m/s.