Safe storage of ammonium nitrate products –scientific framework for government regulations

Ammonium nitrate (AN) is a solid chemical compound of paramount significance in the field of agriculture, as a high-nitrogen fertilizer component, and in the formulation of blasting explosives having major civilian applications within mining, quarrying and infrastructure construction work. Global production of AN totals several tens of millions of tonnes per year. AN is both a principal source of plant nutrient nitrogen and the world’s main source of explosive power for heaving and shattering, making the material common in manifold parts of civil society. Although stable under normal conditions of transportation and storage, AN harbors significant energetic potential, even when uncontaminated and without sensitizing admixtures. It may decompose explosively under certain adverse conditions – fire scenarios in particular. Historically, accidental bulk explosions of AN materials have given occasion to several of the worst industrial disasters of the last hundred years, killing thousands of people and inflicting enormous material destruction. The grave accident record related to AN has been persistent. Serious accidents with AN involved, with some of these being of truly catastrophic proportions, have hit city and port areas in the USA, China and Lebanon in the course of the last decade. Preparation of government guidelines and regulations for AN products with regard to production, transportation and storage – as solid materials (granules, prills, etc.), as aqueous solutions or in the form of aqueous emulsions, suspensions or gels – have for many years now proven to be a regulatory challenge. AN’s many uses and the sheer volume of AN production, when combined with the rather unpredictable behavior of AN materials under the influence of heat and/or shock, have made existing regulations in most parts of the world a type of needed compromise. For all practical purposes, AN is regulated for transport and storage as an oxidizing substance, even though the compound clearly harbors fundamentally explosive properties when handled in all but pure form and in large quantities. The objective of the present report is the creation of an updated scientific framework that may be used by those whose assignment is the formulation of regulations and guidelines pertaining to storage of AN products – both solid and fluid ones. The work herein includes the categorization of AN products covered by the Seveso-III Directive into a simplified three-tier classification system and the formulation of specific recommendations on the subject of separation distances between facilities with AN products and protected places, as well as guidelines on internal arrangements of storage facilities holding critical AN products. The concepts of detonation and blast wave dynamics have been central to all work herein. Expectantly, this text may prove useful for those involved in handling or regulating AN products. Effective regulation of AN products must ultimately address the fundamental unpredictability of the nature of AN: it normally behaves as a conventional solid oxidizing substance, hazardous yet fairly controlled, but it can now and then suddenly take on violently explosive characteristics. Significantly, it has proven all but impossible to predict exactly under what conditions that is likely to happen. The prospect of detonation must therefore regularly be taken into account.