Joule heating-driven thermal dissolution of conductive filament (CF) is a vastly explored mechanism for the reset process in resistive switching (RS) phenomena. Here, we studied the possibility of thermal avalanche by a simple model compatible with experimental data of a bipolar RS device of LaMnO₃ and Cu₂S composites. Different critical voltages (V_c) are found for all samples, after which the avalanche process begins. Calculated power loss at critical voltages is very similar, corresponding to a unique critical temperature (T_c). The trend of the coefficient of exponent and reset voltage (V_reset) with Cu₂S concentration shows a deep connection between them and with oxygen vacancy concentration.