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

Abstract

Fertilizers containing ammonium nitrate have caused several accidents over time, including toxic clouds, fires and explosions. Therefore, in this work we have studied the accident produced in Escombreras (Spain) related to the decomposition of fertilizer NPK 15-15-15 composed basically of monoammonium phosphate, ammonium nitrate and potassium chloride. The fertilizer was stored in a silo and its decomposition produced a toxic cloud formed by 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. The fault tree has revealed several weak points in the storage conditions. The dispersion of the gases produced has been simulated to evaluate the distance to which dangerous concentrations of gases would reach. The consequences of the accident are met with almost 4000 people affected although most of them only with minor irritations and episodes of confinement of the nearby population. To conclude, a series of lessons have been extracted that can help avoid similar accidents in the future.