Apparatus for separation of particles from a fluid stream entraining said particles comprises an inlet zone, a centrifugal separation zone, particles collection means and exhaust means, in which the inlet and separation zones are in communication via a transition zone for inducing vortical flow in the fluid stream, the transition zone having a diameter greater than the diameter of the inlet zone and comprising means defining an outlet port to the separation zone, an entry port being formed in the transition zone upstream of the baffle means, the entry and outlet ports being mutually arranged to minimise fluid perturbation in the fluid stream in use.