Experimental and theoretical approach to the assessment of stability criteria for safe transport of ammonium nitrate based emulsions

The safety issues connected to storage and transportation of ammonium nitrate and ammonium nitrate emulsions are to be considered of primary importance, as demonstrated by the Tolouse explosion and various handling and storage accidents in different countries. This paper is focused on the assessment of the self-heating behaviour of ammonium nitrate emulsions (ANE) and the establishment of stability criteria for transport or storage conditions. The influence of low level contaminants on ANE reactivity is experimentally explored as well. The reaction patterns of ANE were studied by miniautoclave and Dewar experiments. An assessment of the experimental results against the Frank-Kamenetskii model for self-heating showed that small levels of heat production will already lead to self-heating. In principle, a Dewar test can be not sensitive enough to detect this level of heat production in the relevant temperature range. However, extrapolation in the downward direction of the results obtained at higher temperatures appears to provide a way to assess the safety of large-scale transport or storage. The results of such an evaluation are most likely conservative, as self-heating is also suppressed by evaporation of small amounts of water from the emulsion under "open" conditions. Key words: Ammonium nitrate, emulsion, explosion hazard, impurities, transport