Thermal hazard analysis and initial decomposition mechanism of 5-(4-pyridyl)tetrazolate-methylene tetrazole

5-(4-Pyridyl)tetrazolate-methylene tetrazole (H4-PTZ-methylene tetrazole) was prepared. Thermokinetic characteristics of H4-PTZ-methylene tetrazole were described through differential scanning calorimetry (DSC). Ozawa method, Kissinger method, and isoconversional approach were used to calculate the kinetic parameters. Thermal safety parameters, such as self-accelerated decomposition temperature (SADT) and thermal ignition temperature (T_TIT), were evaluated from experimental results. The initial decomposition process was investigated using experimental and theoretical calculations. Geometric optimisation, Mulliken charges, electrostatic potentials, and decomposition pathways were explored using Gaussian 16. The simultaneous dissociation of C7–N8 and N9–N10 bonds (DM1) and of C13–N17 and N15–N16 bonds (DM2) had lower energy barriers. The theoretical apparent activation energy was higher than the experimental one. As a novel finding, the exothermic process observed through DSC was primarily because of the reaction that opened the tetrazole ring, which released nitrogen.