The minimum explosible concentration (MEC) is a crucial parameter in dust explosion evaluation and prevention. The standardized method currently used to determine the MEC relies on the measurement of explosion pressure P-m and the test results are strongly affected by dust dispersion behaviors. To investigate this effect, systematical experiments were performed for coal dust explosion in the Siwek 20-liter sphere. It is found that the measured values of P-m are apparently dependent on the ignition delay time t(ig) because of the time-dependence of dust dispersion behaviors. For the dust with a given mass concentration and size distribution, there always exists an optimal ignition delay time t(ig,opt) at which the P-m will reach its maximum value, P-max, and a slight deviation of t(ig) from the t(ig,opt), may cause the measured P-m to be obviously lower than the P-max. To reliably determine the MEC, the t(ig,opt) should be adopted in the test, rather than the fixed t(ig) of 60 ms as prescribed by IEC, otherwise, the resultant MEC may be overestimated. Based on the analysis of flame propagation in dust cloud, an alternative method by using combustion duration time t(com) is proposed to determine the MEC. Analysis for experimental data shows that the values of MEC determined by using torn are basically consistent with those obtained by using P-m at the t(ig,opt), but less affected by the t(ig), since the sensitivity of the t(com) to the t(ig) is much less than that of the P-m. (C) 2011 Elsevier B.V. All rights reserved.