In the 1980s, the accelerating rate calorimeter (ARC) made an advance in thermal hazard analysis, because it could record temperature and pressure data more accurately within the region of a self-decomposition reaction under approximately adiabatic conditions. Although, ways to keep adiabatic conditions may be similar, test cell (bomb) and sensitivity are not the same in ARC as in other adiabatic calorimeters, such as Vent Sizing Package2 (VSP2). However, the operating procedures-heat-wait-search (H-W-S)-are all the same. In this study, an improved operating procedure was used to find the slow first step catalytic reaction of hydrogen peroxide (H2O2) in the presence of hydrochloric acid (HCl). In these two reactions, the HCl concentration decreases with the activation energy of the first catalytic reaction and then increases with the activation energy of the second self-decomposition reaction. The temperature at which the catalytic and self-decomposition reactions intersect in the experiment operated by the improved method is the onset temperature of the experiment operated by the standard operating procedure. By the improved operating procedure, the duration of the first catalytic reaction increases with HCl concentration being decreased. Operating by the improved method, time to maximum heat rate (tmr) can be compensated at lower temperatures (40 degreesC to onset temperature), which cannot be accomplished by using the standard operating procedure, and the tmr can be modified at higher temperatures.