Flow properties of powdery or granular filling substances of dangerous goods packagings—Comparison of the measurement of the angle of repose and the determination of the Hausner ratio

Abstract

To ensure safety when transporting dangerous goods, it is important to specify the flow properties of the respective solid filling substance of the packagings. For this purpose, the angle of repose is currently used for the UN approvals in Germany. Measurements were carried out on 12 powdery or granular substances applying the angle of repose measuring methods customary in the test centres. The results of the methods differ significantly from each other. In addition, some of the techniques cannot be applied for very cohesive or coarse‐grained materials. The results for the angle of repose show a strong scatter for some constellations (coefficient of variation more than 20%). Safety during transport of dangerous goods cannot be guaranteed with this currently practised system of measuring the angle of repose. As a consequence, an alternative parameter to characterize the flow properties of bulk materials should be used in the recognized test centers for dangerous goods packagings, such as the Hausner ratio. This approach leads to more precise test results for the substances examined (maximum coefficient of variation 2.8%). It also has advantages in terms of applicability and occupational safety. Since the flow properties are safety‐relevant, both in terms of mechanical safety and safety against the release of dangerous substances, the testing practice in the recognized test labs should be improved and standardized.

How to measure the angle of repose of hazardous substances in the test centres for dangerous goods packagings

“…The theoretical background of the flow properties of bulk solids has already been described in detail in the first part of the investigations. 1 At this point, therefore, only a summary of the most important correlations is given. The parameters presented below, angle of repose and Hausner ratio, are simple and quick methods of determining flowability to compare different materials.…”

“…The flow properties of bulk materials affect two aspects, namely both the mechanical safety of the packaging and the safety against the release of substances under normal conditions of carriage. [1][2][3] In the first case (mechanical safety), flow phenomena are responsible for the tearing of a bag due to impact. The poorer the flowability of the bulk material, the lower the damaging effect on the packaging wall.…”

“…3 There have been several reports of repeated leaks of dangerous goods from bags and FIBC that are actually intact in practice. 1,3,7,8 The following figures show releases that were detected by the German Police North Rhine-Westphalia Münster police during their controls in…”

“…In addition to the specification of other material parameters of the filling substance, the characterization of the flow properties is therefore particularly important in practice when transporting dangerous goods, both with regard to mechanical safety and sift-proofness. 1 The problem is that different methods are currently applied for measuring the angle of repose in the recognized test labs for dangerous goods packagings in Germany, as no specific method is prescribed. 3 The certificate of approval does not state which measurement method was used to determine the angle of repose and how the samples were preconditioned.…”

“…This was the motivation for part 1 of research on the subject. 1 In a first step, experimental investigations of the angle of repose were carried out using four methods commonly applied in the test centres The objective of this study is therefore to evaluate the applicability of the methods for measuring the angle of repose when testing substances with hazardous properties and to investigate the influence of different climatic preconditioning. For this, the resulting moisture content of the filling substance has to be determined.…”