The use of liquefied natural gas (LNG) is constantly growing. However, safety issues regarding cryogenic storage and transportation systems are still to be fully resolved. In particular, the evaluation of the efficiency of inerting systems for low-temperature LNG vapour is essential. In this work, the variation of the flammability range (in terms of lower and upper flammability limits and minimum oxygen concentration) obtained by adding nitrogen to pure air for some representative LNG mixtures has been evaluated at ambient temperature and at temperatures below 0 degrees C by using a detailed kinetic model entitled KIBO, which has been proved to be reliable for the description of C-0-C-4 reactions in oxidative conditions, and by the limiting burning velocity theory. Strong differences are reported among pure methane and natural gas mixtures for all the investigated temperatures. The effect of composition is therefore relevant. Furthermore, the obtained results suggest that the lower flammability limit is determined by thermal aspects at high temperature only, whereas at low temperature, kinetic limitations are more relevant.