Comparative Safety Regulation and Testing of Ammonium-Nitrate-Based Fertilizers in Some Major Global Markets: Implications for Harmonization of Compositional, Thermal and Shock Hazard Testing

Abstract. Major fertilizer accidents over the past century demonstrate that ammonium-nitrate-based fertilizer incidents are triggered predominantly through two mechanisms: (i) self-accelerating thermal decomposition (SATD)-often initiated during storage via thermal or contaminant-based stimuli-and (ii) shock-initiated rapid decomposition resulting from accidents or explosive events, including detonation following fire. While both the United States and the European Union regulate ammonium nitrate extensively and share United Nations transport classification testing protocols, their regulatory philosophies differ. The United States emphasizes a bottom-up, facility- and storage-based regulatory system implemented through NFPA codes, state and local fire authority oversight, and OSHA-guided standards, whereas European Union regulations adopt a more top-down approach, principally via the Seveso framework and Regulation (EC) No 2003/2003, thereby imposing product-level compositional constraints and pre-market safety and performance testing as a prerequisite for CE marking prior to commercialization. This presentation examines how these distinct, yet complementary approaches could be strategically harmonized to better address both accident pathways. Although the United Nations framework already includes thermal stability, self-heating, and bonfire-type fire exposure tests, these assessments are primarily applied for transport classification rather than for systematic evaluation of fertilizer safety under storage conditions. For prevention of SATD, we recommend convergence toward a common set of compositional and product-level tests, coupled with thermal stability assessments selected to elucidate bulk self-heating behavior to the greatest extent practicable. These tests should include controlled thermal cycling that is quasi-representative of the dynamic environmental conditions known to exacerbate compositional instability in industrial storage scenarios. For shock- and confinement-driven hazards, we recommend broader adoption of detonation-resistance testing for high-nitrogen ammonium-nitrate fertilizers, such as the EU Regulation (EU) 2019/1009 Resistance to Detonation Test (RDT), UN gap-tests, or equivalent methodologies capable of assessing sensitivity to strong shock under realistic confinement conditions. While such testing is embedded in European market-access requirements-most notably through RDT-its absence from U.S. fertilizer product qualification, except where required for transport classification under the UN Manuel of Tests and Criteria, represents a gap in systematic hazard control. By aligning compositional testing and related product-level analyses with thermal stability, self-heating, and detonation-resistance assessments, this work proposes a pathway toward transatlantic harmonization of fertilizer safety testing. Such alignment would strengthen prevention across the full life cycle-from site-specific storage through transport-and thereby reduce the likelihood of catastrophic incidents arising from either thermal- or shock-driven failure modes.