At low gas velocities, the standard deviation of pressure fluctuations measured in a fluidized bed decreases approximately linearly with decreasing gas velocity. Based on this fact, we propose a statistical method that can quickly determine whether a fluidized bed is moving towards the defluidized state or not. This short response time is typically only 15 s, which allows the method to be used as a safety measure. The method is illustrated by experiments with a fluidized bed of Geldart A particles. The influence of the purge flow through a pressure probe and secondary gas flow to the bed is addressed and a comparison with measuring the average pressure drop is made. (C) 2004 Elsevier B.V. All rights reserved.