The self-sustaining decomposition of ammonium nitrate fertiliser: Case study, Escombreras valley, Spain

Fertilisers containing ammonium nitrate have caused several accidents over the years, including toxic clouds, fires and explosions. For this reason, this work examines the accident that occurred in Escombreras valley (Cartagena, Spain) related to the decomposition of NPK 15-15-15 fertiliser, composed basically of monoammonium phosphate, ammonium nitrate and potassium chloride. The fertiliser was stored in a silo and its decomposition produced a toxic cloud formed of nitrogen oxides. Calculations have been made to determine the amount of heat released in the accident and the temperature gradient in the stored pile. The causes of the accident are not clear but could be related to the presence of decomposing organic matter. Fault tree analysis has revealed several weak points in the storage conditions. The dispersion of the gases produced has been simulated to evaluate the distance that dangerous concentrations of gases would reach. Almost 4000 people suffered the consequences of the accident, although most of them experienced only minor irritations and episodes of confinement due to their proximity to the site. To conclude, a series of lessons have been extracted that can help avoid similar accidents in the future.