Hazard Characterization of Mixtures of Ammonium Nitrate with Swimming Pool Chemicals

摘要

There has been recent interest in the hazard properties of mixtures of ammonium nitratern(AN) and swimming pool chemicals containing chlorine due to the possible involvement of suchrnmixtures in the tragic accident in Toulouse, France, in September 2001. This paper describes thernresults from hazard studies of 50:50 mixtures of AN with SDIC, where SDIC is the sodium saltrnof dichloroisocyanuric acid, a swimming pool disinfectant chemical. The hazard properties ofrnthe mixture are compared with the properties of both pure components.rnThe thermal hazards of the mixture were investigated using a variety of techniquesrnincluding differential scanning calorimetry (DSC), accelerating rate calorimetry (ARC), andrnsimultaneous TGA-DTA-FTIR-MS. The sensitiveness of the mixtures to electrostatic discharge,rnimpact, and friction was also investigated.rnThe DSC traces of dry mixtures show relatively mild exothermic activity at about 60 - 90rn℃ and much stronger exothermic behaviour at about 110 - 125℃. In contrast, the DSC tracesrnfor the pure components do not show any exothermic activity below about 150 ℃. Thus, thernDSC results show that the mixture of AN and SDIC is less thermally stable than the purerncomponents. TGA results show mass loss steps that coincide with the exotherms observed in thernDSC.rnARC experiments were performed in sealed sample vessels initially at ambient pressurernof dry air. A heat-wait-search ARC experiment on a 0.5 g mass of dry mixture revealed an onsetrntemperature as low as 61℃ in a first, relatively weak step followed by a second step where rapidrnthermal decomposition occurred in less than an hour. When the experiment was repeated inrnmoist air, the onset temperature was reduced to 52 ℃.rnThe reaction products were determined using simultaneous TGA-DTA with FTIR andrnMS detectors. The products include CO_2, HCl, N2_O, and Cl_2.rnThe sensitiveness of the mixture to impact was assessed using the BAM Fallhammerrnmethod. The mixture exhibited a positive response (i.e., it produced a loud report) at limitingrnimpact energy of 7.5 J. The mixture exhibited a positive response to the BAM friction test at arnlimiting load of 360 N. The mixture did not exhibit any positive responses to electrostaticrndischarges at energies up to 156 mJ.rnThe results from this study suggest that accidental mixing of bulk quantities of thesernmaterials would pose a considerable hazard and should be avoided.