In this paper an accident caused by the loss of control of a chemical reaction is analysed. Though the loss of control did not generate an extreme temperature and pressure increase, the reaction produced Hydrogen Chloride, which was released at a high rate from the reaction mass and finally released to the atmosphere. The aim of this study is to describe the triggering causes, to assess the consequences of the toxic dispersion and to propose the safety measures that should have been in place to prevent the accident. The reaction of interest had been studied during its development stage and carried out in the past in another production site of the same company with no incidents. Despite the knowledge available, the accident took place. These facts show the importance of the process design and the Management of Change (MOC) procedures.
