The particle interception properties of metal filter elements with a hydraulic pore size of 20-98 mu m were investigated in order to evaluate their fail-safe functions. The fail-safe filter element is mounted alongside the main filter element and has to be rapidly plugged when a part of the main filter element is broken in order to prevent particle leakage. This study focused on how fast the filter element was plugged without serious particle penetration during the initial time. The particle leakage and the pressure drop change were measured in two modes in order to simulate a field situation. Mode one operated at a constant high-speed particle-stream flow rate and mode two involved rapid exposure of the filter element to the high-pressure high-speed dust stream. Particle leakage through the filter element increased semi-linearly and the pressure drop decreased exponentially as the hydraulic pore size of the filter element increased. A suitable hydraulic pore size for the metal filter elements lay between 50 and 60 mu m in order to intercept particles that were larger than 5 mu m within 2 min and without an additional pressure drop of more than 300 Pa under typical operation conditions of filter unit. A selected fail-safe filter element showed a stable base-line pressure drop of less than 3500 Pa for IGCC fly ash with a face velocity of 3 cm/s and 450 degrees C in a bench-scaled unit (BSU) using hot gas stream from an oil burner. (C) 2013 Elsevier B.V. All rights reserved.