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Organisationseinheit der BAM
One of the fundamental principles of the UN-GHS (Globally Harmonized System of Classification and Labelling of Chemicals) is that all hazards of a chemical should be assigned and communicated. There is no general prioritization of hazards in the sense that certain hazard classes are not applicable if another one has been assigned. In contrast to health and environmental hazards, there are physical or chemical factors which preclude certain combinations of physical hazard classes. So far, there is no common understanding as to which combinations are relevant and which not. For example, should a pyrophoric liquid be classified as flammable liquid in addition, or is this redundant and unnecessary? In the course of the implementation of the GHS by countries or sectors and the actual application by industry all over the world, such questions become more and more important.
This publication systematically discusses all combinations of the UN-GHS physical hazard classes and assesses them with regard to the relevance of possible simultaneous assignment to a chemical. For many of the combinations an unambiguous decision based on theGHS alone is not possible, thus confirming that the question which physical hazard classes might be assigned simultaneously to a chemical is not trivial. As one more milestone on the path to a globally harmonized system for the classification of hazardous chemicals, this should be discussed and ultimately solved on a global basis. It is the hope that this publication might serve as an impetus for such discussions.
Safe transport of cyanamide
(2009)
For many years cyanamide (CAS no. 420-04-2) was not commercially available due to its unstable nature. Since about 1965 the former "Süddeutsche Kalkstickstoffwerke AG" (current name: AlzChem Trostberg GmbH) developed a special stabilizing system. It was to be investigated to which Class (e.g. "Corrosive Substances", Class 8) or Division (e.g. "Self-reactive Substances", Division 4.1) of the International Regulations for the Transport of Dangerous Goods cyanamide (pure or as a 50% solution in water) should be assigned and based on this which maximum quantities are allowed to transport e.g. in tanks. Cyanamide is used for the synthesis of pharmaceutical and agrochemical actives, biocides, dyestuffs and fine chemicals.
During the last years cyanamide was tested at BAM and AQura. The results and an appraisal are presented in this paper. Thus, cyanamide should be classified according to the UN Recommendations on the Transport of Dangerous Goods in Class 8, UN number 2922 (50% solution in water) and UN number 2923 (pure substance) respectively, packaging group III, danger labels 8 + 6.1. Cyanamide, 50% solution in water, can be transported in portable tanks under specific conditions.
Tests according to the UN Recommendations on the Transport of Dangerous Goods for the determination of explosive properties of organic peroxides have been compared with screening criteria for explosivity based on measurements in a closed mini-autoclave (MCPVT). It will be shown that an additional screening test may be helpful but the information obtained from the UN tests are more important to characterise the specific properties of a substance under different conditions.
Many self-accelerating decomposition temperatures (SADTs) of solid organic peroxides and self-reactive substances have been determined with the UN test method H.4, which is a scaled down test in a small Dewar vessel. For solid organic peroxides and solid self-reactive substances Fierz has questioned this procedure in a recent paper. Fierz concluded that the Dewar test results should not be extrapolated to beyond 8 l packages, owing to the thermal insulation value of solids. On the other hand, long term experience with the test, with a great variety of solid organic peroxides and self-reactive substances show about equal critical temperatures in the small Dewar vessel and on 50 kg scale. In the present work, we first checked, by numerical simulations, the Dewar scale versus the larger scale, in a way comparable with Fierz method: both scales are simulated by spheres, consisting of a number of annular layers, for the large scale the usual external heat loss term is used but for the small scale the outside heat transfer is strongly limited. The outcome of these simulations, covering a variety of physical parameters, supports the concerns expressed by Fierz. After this, we performed accurate cooling and heating experiments with solid organic peroxide in the usual Dewar vessel, provided with a large set of thermocouples. The results of these experiments showed that the simulation model for the Dewar vessel has to be changed from a spherical analogue to a short cylinder of solid material with heat exchange mainly via its top (Utop 3.5 W/(m2 K), overall heat transfer coefficient) and some heat exchange (Uside 0.29 W/(m2 K)) through its cylindrical and bottom part. With this modified cylinder model (being neither an infinitely long cylinder nor a slab) of the Dewar vessel, we found that the UN method H.4 enables an accurate prediction of the SADT, with small deviations of 0 ± 2.5 °C. Further, by performing a truly three-dimensional (3D) finite element calculation in FEMLAB, the new heat characteristics of the Dewar vessel as well as a 50 kg package of dilauroyl peroxide, a solid organic peroxide, were checked. The outcome was compared with the critical ambient temperatures known for various package sizes, which agreed well.
Heat transfer to bodies engulfed in di-tert-butyl peroxide pool fires - Numerical simulations
(2016)
The thermal response of bodies engulfed in di-tert-butyl peroxide (DTBP) pool fires is studied numerically. High heat release rates, high velocities and high emissive powers portray the combustion of DTBP. This makes exceptionally hazard for bodies engulfed in DTBP fire accidents. The concept of adiabatic surface temperature (AST) is applied for DTBP pool fires to circumvent the difficulty of defining the fire exposure boundary condition at the solid surface. Adiabatic surface temperatures (AST) are computed for pool diameters 1.13 m and 3.4 m using the fire dynamics simulator. The thermal response of cask in a 1.13 m DTBP pool fire is studied to verify the concept of AST. It is found that a cask encounters twofold the heat fluxes in DTBP fires than in diesel pool fires. More than 30% of the net heat flux to the cask is a direct result of the convective heat exchange between the fire and the cask. This implies that the regular safety guidelines formulated for hydrocarbon pool fires are not adequate for the safety of the bodies engulfed in DTBP pool fires.
Computational fluid dynamics (CFD) simulation is used to predict transient and time-averaged glame temperatures and species concentrations of an n-hexane pool flame. Employing a combination of an assumed probability density function approach with laminar flamelets using detailed kinetic data and large-eddy simulation with Smagorinsky submodel is shown to be a promising way in modeling pool and tank fires. The measured species concentration and flame temperature profiles from gas chromatography, thermocouple measurements and holographic interferometry are used to validate the submodels for CFD simulation of pool flames.