Explosion of ammonium nitrate solutions, two case studies

Two ammonium nitrate solution explosion accidents are analyzed in terms of the boiling point and solubility data. Both accidents occurred following a prolonged stoppage. In both cases a local increase in concentration and/or crystallization of ammonium nitrate has been suspected. In the first case this has been due to loss of temperature control with consequent evaporation under vacuum. In the second case crystal formation was attributed to cooling crystallization owing to poor insulation. Other conditions increasing the likelihood of the explosion were also satisfied. These include lack of flow, increase in temperature, and catalysis by both increased solution acidity and the presence of stainless steel corrosion products.

► Basic events leading to solution explosion have been identified for two accidents.
► In the evaporator accident crystal formation was attributed to evaporation.
► In the neutralizer accident crystal formation was attributed to cooling crystallization.
► Accident conditions are followed on boiling point and temperature-solubility diagrams.
► Safe re-startup procedures and proper insulation maintenance training is emphasized.