Ammonium nitrate (AN) reactive hazards have been widely investigated for several years; however, incidents continue to occur. One of the most recent incidents occurred on April 17, 2013, where a fire led to an explosion at the West Fertilizer Company in West, Texas, USA. These incidents highlight the dire need for continuous research on AN hazards and alternatives to make its use safer. AN can thermally decompose and further detonate under certain conditions, e.g., in the presence of impurities which act as promoters. However, certain additives can act as inhibitors and reduce the risk of its runaway. The main objective of the research presented here focuses on the synergistic effect of an inhibitor and a promoter on AN decomposition. The Reactive Systems Screening Tool (RSST) has been used in the study of the runaway behavior of AN in the presence of a promoter (KCl) and an inhibitor (Na2SO4), and it is compared with the behavior of AN with each additive separately. It was found that when both additives are mixed, Na2SO4 induces a rise in the decomposition "onset" temperature. The presence of KCl, however, induces a more violent decomposition worsening all other parameters. Potential decomposition mechanisms are also discussed. (C) 2015 Elsevier B.V. All rights reserved.