Bubbles bursting at the surface of a bubbling gas fluidized bed (BFB) project particles into the freeboard. Coarser particles fall back, the solids loading declines with height in the freeboard, and fines are ultimately carried over. The height of declining solids loading is the transport disengagement height (TDH), measured in this research by positron emission particle tracking, and modelled from a balance of forces on ejected particles. Model predictions and PEPT-data are in good agreement. Almost all of the empirical equations overestimate the TDH. (C) 2010 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.