Reactive hazards have been a significant concern for the chemical process industries. Without sufficient control of chemical hazards and risks, reactive incidents have caused catastrophic consequences for humans and the environment worldwide. In order to help understand and evaluate reactive hazards, calorimetric investigations have been employed to characterize reactive chemical behavior. However, with the development of computer resources and computational chemistry, molecular simulation has become a powerful and reliable tool to complement and guide experimental testing. In this article, hydroxylamine ( HA) calculations demonstrate the application of molecular simulation for understanding and controlling reactive hazards. Using the quantum mechanical software Gaussian 03, HA bimolecular or water-catalyzed HA isomerization to ammonia oxide in aqueous solution was identified as the most likely decomposition pathways. Based on these molecular simulation results, recommendations are provided for safer handling of HA.