There have been numerous international instances over the last several years in which pumping of an emulsion explosive has resulted in an accident. To address the sensitivity of emulsion explosives to various parameters including pressure, a study of a particular ammonium nitrate (AN) based emulsion explosive has been undertaken using the ARC (accelerating rate calorimeter) and a Tian-Calvet heat flux calorimeter (HFC). The effects of pressure and both inert and oxidizing atmospheres on thermal behaviour were determined and compared with similar results obtained for AN per se. All the results for the emulsion explosive suggest an increased thermal hazard when operating in air in contrast with the observations for the same measurements in Argon. No such difference in the results for AN in air and Argon was observed. Significantly lower onset temperatures are observed in air from both the ARC and HFC measurements on the emulsion explosive. This observation is believed to be the result of oxidation of the oil phase in the emulsion. Additionally, the ARC results show some dependence on the choice of the initial temperature; a lower initial temperature results in an elevated onset temperature. Sample size also appears to be a factor influencing the onset temperature for both the HFC and ARC results. At a heating rate of 0.1 degrees C min(-1), the HFC results show a complex exotherm pattern far the emulsion in both Argon and air, but the latter results give a decidedly earlier onset temperature and a slightly larger Delta H. A complex exotherm pattern is expected for the decomposition of AN but, for the emulsion in air, oxidation of the oil phase further complicates the result. Crown