Self-accelerating decomposition temperature (SADT) is determined generally by one of four testing methods recommended by the UN orange book, and can be analytically and numerically evaluated by using the calorimetric results of ARC, Setaram C80D and other instruments. The SADTs evaluated by ARC must be under the assumption of zero order reaction kinetics, and require extrapolation to lower temperatures. Using the C80D, however, the reaction can easily be detected in the vicinity of the SADT for many reactive materials due to its higher sensitivity. Therefore, the SADTs evaluated are more accurate, especially for those reactive materials whose reaction mechanism, phase and so on change near the SADT. In the present study, the Setaram C80D and the ARC were used to investigate the decomposition of an asphalt-salts mixture, which had caused a fire in a nuclear fuel facility. The decomposition mechanism of this mixture was complex but the high sensitivity of the C80D enabled it to be elucidated, and a reasonable estimate of SADT was obtained. The estimated SADT from the ARC was about 70 K higher, due to the first two steps of the decomposition being undetected. In the estimation of SADT, the value of acquiring kinetic data close to the SADT can hardly be overstated.