A flammable gas could be ignited only if its concentration in air is over a threshold concentration, which is known as the lower flammability limit (LFL). Therefore, predicting LFLs of flammable gases is indispensable for safely handling such flammable gases. The Le Chatelier's mixing rule for the LFL is the prevailing method for estimating the LFLs of mixtures with multiple flammable components. In this work, a novel derivation for this rule is proposed based on the threshold temperature concept. It is found that the important assumption required to reach this mixing rule is that the adiabatic flame temperature rises at LFL are approximately the same for each flammable component. As the adiabatic flame temperature rise is in a sense the required energy gap to initiate a combustion, it should not change while adding/removing inert gas into/from the system. Therefore, it is also the required perquisite to predict the LFLs of mertized mixture or the LFLs in oxygen atmosphere. (C) 2018 Elsevier Ltd. All rights reserved.