1,3,7,9-tetranitrodibenzo-1,3a,4,6a-tetraazapentalen (z-TACOT) is a thermostable compound which exhibits low-sensitivity to external stimuli. At elevated temperature it undergoes thermal decomposition. Thermal properties and safety of z-TACOT use in terms of the heat-explosion hazard were examined. The obtained kinetic parameters of the decomposition reaction and thermal capacity of z-TACOT were used to determine the maximum safe temperature of technological processes which involve z-TACOT. The temperature is 266 degrees C. Based on the attained safety parameters z-TACOT can be classified as a non-reactive, stable compound which does not exhibit dangerous behaviour in the Koenen test.