The collapse properties of three kinds of fine particles (19, 30, and 59 mu m) are studied with a new type of bed-collapse technique, "isolated dilute-phase bed collapse," to determine the dense-phase properties under high superficial gas velocities. The properties of the emulsion and bubble phases are investigated by a video camera. The influence of particle size on particle collapse properties is also discussed When gas velocities are high the 30- mu m particles take the longest to collapse, have the smallest emulsion density, and have largest bubble volumetric fraction. These observations; indicate that the 30- mu m particles have a property that the others lack.