Experiments were performed to compare intermediate-scale (I m(3)) and laboratory-scale (20 L) inerting results. In general, laboratory-scale inerting levels were higher than intermediate-scale values. This can be attributed to the use of a strong ignition source to initiate the test, which may have overdriven the explosions in the smaller test vessel. Previously reported agreement between the smaller test vessel and full-scale experiments may be due to overdriving in the 20 L chamber, leading to high inerting levels similar to those encountered in full-scale tests due to flame acceleration. Use of weaker ignition sources in the laboratory-scale chamber did produce inerting levels similar to those observed in the intermediate-scale vessel. A new flammability limit parameter has been defined as the minimum inerting concentration (MIC; in units of mass concentration, i.e., g m(-3)). This is the concentration of inertant required to prevent a dust explosion regardless of fuel concentration. Previous experimental work in a 1-m(3) spherical chamber has shown this flammability limit to exist for some fuels. In the current work, inerting experiments were performed in a 20-L Siwek chamber using identical materials to those used in the 1-m(3) chamber. The results show that an MIC can be determined in the smaller test chamber; however, there is a strong dependence on ignition energy strength used to initiate the explosion. In the 20-L tests, as in the 1-m(3) tests, not all combustible dust and inertant mixtures showed a definitive MIC, although they did show a strong dependence between inerting level and suspended fuel concentration. As the fuel concentration increased, the amount of inertant required to prevent an explosion decreased. Even though a definitive MIC was not found for all of the dusts, an effective MIC can be estimated from the data. The use of MIC data can aid in the design of explosion suppression schemes.