Abstract: The invention concerns a method for separating, by impaction, living particles and particles capable of being revived of a gas or a gas mixture under pressure, characterised in that it comprises a step (a) which consists in accelerating in a stage and along an axis (x) a single gas or gas mixture stream in a confined volume (V), to reach a speed not less than the speed of sound; a step (b) which consists in sudden deceleration of said single stream derived from step (a) in said volume, along substantially the same axis (x), at atmospheric pressure; a step (c) which consists in changing the direction of the gas or gas mixture flow at the output of the volume (V), which on average becomes radial; and a step (d) which consists in trapping said particles separated from the flow during step (c), on a target. In another embodiment, the method further comprises a step (e) which consists in counting the particles trapped during step (d).