In the recent years the growing interest for cleaner and low carbon content energy sources has addressed the development of several industrial and civil applications based on methane, hydrogen, and their mixtures. The use of these gases rises, however, several technological issues for the storage and the transportation systems. Among others, cryogenic liquefaction (as liquified natural gas, LNG and liquified hydrogen, LH2) and cryo-compressed gases are considered among the most promising potential solution. On the other hand, when low and ultra-low temperature are considered, several questions regarding the safe use of such gases are raised, including the behaviour of the cold vapour phase in air after the release of liquid or cryo-compressed gas from containment system. In this work, the flammability limits of hydrogen, methane and their blends at low and ultra-low temperatures were estimated by using the laminar burning velocity obtained by means of detailed kinetic mechanism. Numerical results were compared with experimental data and empirical correlations commonly adopted for this purpose. The data agreement demonstrates the applicability of the developed procedure for the estimation of safety parameters at low and ultra-low temperature and for future technological applications, even at cryogenic conditions.