Noise suppression and particle separation apparatus for flows of high pressure, high velocity, particle-laden, gaseous fluid, such as geothermal steam, comprises a gaseous fluid conduit that has axially installed around its discharge end a larger diameter, cylindrical inner expansion chamber having a number of flow-dividing fluid discharge openings at which fluid flow diffusing elements are connected for receiving and diffusing the flow of gaseous fluid from the apertures. A still-larger diameter, cylindrical noise suppression chamber is axially mounted around the inner chamber and flow diffusing elements. The diffusion elements increase the fluid flow noise frequency range and sound deadening material installed in the outer chamber absorbs noise in this higher frequency range so that the venting fluid noise level outside the apparatus is no more than about 95 dB. To enable fluid expansion, the fluid conduit diverges at its outlet end, the inner chamber has a diameter at least about twice that of the flow inlet conduit and the outer chamber has a diameter that is at least about twice that of the inner chamber. Flow direction and velocity changes in the apparatus cause the disengagement of particulates entrained in the fluid flow.