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- Dangerous goods packagings (5)
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Organisationseinheit der BAM
The objective of this experiment was to verify that in regards to the leakproofness bubble test for packagings of dangerous goods, a reduction of the air overpressure from 0.2 to 0.1 bar can be compensated for by reducing the water surface tension to a value of approximately 33.2 mN/m by adding a wetting agent. It was experimentally proven that this method will yield the same leak diameters. This is important to avoid irreversible deformations during the leaktesting of intermediate bulk containers (IBCs) while using a test overpressure of 0.2 bar.
Bubble test experiments were carried out on artificial borehole-shaped leaks manufactured of two different materials high density polyethylene (HDPE) and stainless steel by ultrashort pulse laser technology and with two different immersion test liquids (deionized water and a 0.1% Lutensol FSA fabric softener active 10 solution). The characteristic diameters of the boreholes investigated were from 11.5 to 30.3 µm in length.
The objective of this work was to determine the maximum gauge pressure in the vapour phase above the liquid in different design types of dangerous goods packagings under normal conditions of carriage. The design types investigated were steel and plastic packagings with a volume of approximately 6 l.
Two different methods were applied. In method 1, the pressure inside the packaging filled with a certain filling substance (dichloromethane) was directly measured under simulated conditions of carriage (degree of filling: 90%; filling temperature: 15°C; temperature during storage: 31°C). The maximum measured gauge pressures were between 89 mbar for a light plastic jerrican and 336 mbar for a steel drum.
In method 2, the gauge pressure was calculated. The consideration of a rigid packaging combined with the assumption of a vapour pressure of zero during filling and sealing can serve as a worst case scenario. The calculated gauge pressure is approximately 1061 mbar. This procedure leads to the highest safety factor and does not require any experimental investigations.
For a more realistic approximation of the gauge pressure of a non-rigid packaging, a packaging-specific function of relative expansion can be used, which is determined by a hydraulic pressure test. The calculated values ranged from 105 to 347 mbar. Method 2 provides conservative results. No hazardous filling substance is needed, and it allows a prediction of gauge pressure for other temperatures, substances and filling degrees. Therefore, this method could serve as alternative to UN Model Regulations 6.1.5.5.4 (a).
Sift-proofness is a requirement for different types of dangerous goods packagings for solid substances according to the international Dangerous Goods Regulations. In these regulations, a sift-proof packaging is defined as a packaging that is completely impermeable to dry contents. This means indirectly that absolutely no mass transport of solid substances is allowed. Moreover, this requirement applies both to the original filling substance and to fine solid material generated during transport. Further specifications, test conditions or tolerable limit values are not given. This is in contrast to physical principles and the usual practice in other fields of technology in which sift-proofness is relevant. This paper shows the necessary steps for how the requirements for sift-proofness of dangerous goods packagings can be defined more precisely. Physical basics of the term ‘sift-proofness’ are explained. A qualitative as well as a quantitative approach is possible. In any case, it is essential to carry out appropriate vibration tests to assess the siftproofness. There is a need for systematical investigations of the sift-proofness of dangerous goods packagings.
The objective was to find out whether an explosive atmosphere can be created in a freight container by gaseous leakage flow of vapour-air-mixture through leaks in the closures of dangerous goods packagings filled with hazardous liquids. Because of high temperatures during intercontinental carriage, there is a gauge pressure in the free vapour phase inside the packagings which can cause a gaseous leakage flow. Two different methods were applied:
Helium limit leakage rates for 23 quantitatively important hazardous liquids concerning their lower explosion limit (LEL) were calculated for a worst case transport scenario (Method 1).
Helium leakage rates of five closure types of dangerous goods packagings with volumes of approximately 6 l were measured using the pressure technique by accumulation (Method 2).
All types of closures of steel packagings were uncritical. The maximum measured leakage was 33% of the limit leakage rate. The leakage rates of screw closures of plastic jerricans can exceed the LEL if there are production-related patterns such as non-concentricity of the closures and flashes on the neck. Especially for plastic packagings it is important to minimize gaseous leakage flow, because an explosive atmosphere can also be reached by permeation of the individual filling substance or by a combination of both effects. For the assessment of potentially explosive mixtures in freight containers, both mass transfer mechanisms have to be taken into account.
In practice, checks on dangerous goods transports often detect leaks of powdered dangerous goods from valved bags. In this work, the influence factors of a sudden release of powdery substances from the valves of valved bags were investigated.
Drop tests were performed on paper bags of UN design type 5M2 with internal sleeve valve using 2 different powdery substances (Esplas H130 and zinc oxide “Rotsiegel”).
The internal sleeve valves of all test samples were not sift‐proof with respect to both filling substances. For almost all test samples, the Esplas H130 powder already leaked out of pasted joints during manual filling. This is a contradiction to the requirement in UN 6.1.4.18.1, according to which closures and joints of paper bags 5M2 should be sift‐proof.
In the drop tests, longer valve lengths had a greater sealing effect for both filling substances (for filling degrees of at least 95% and for test samples which had already been mechanically loaded). As an extreme example, at the drop height of 1.20 m and a filling degree of 100%, the released amount of zinc oxide powder from a 10‐cm‐long valve was about 16 times higher than from a valve length of 12.5 cm.
The valve length is therefore a safety‐relevant parameter and should be specified by the manufacturer.
To ensure that only filling goods with similar physical properties in comparison with the test substance are used for valved bags, the user must be informed of the particle size of the test substance.
The dangerous goods regulations UN/ADR 6.1.5.5.4 (a) prescribe a maximum filling degree for determining the test pressure for the hydraulic pressure test by real measurements. The assumption is that the maximum filling degree of the liquid phase is the worst case concerning the gauge pressure. Therefore, the main objective of this study is to investigate the effect of the filling degree on the gauge pressure. Gauge pressure measurements and calculations for different substances were carried out at different filling degrees for a steel drum and a steel jerrican (heating up from 15°C to 55°C). The assumption that the maximum filling degree is the most critical is only valid for relatively rigid packagings: If the relative expansion of the packaging is smaller than the volume increase of the liquid phase due to heating up, the gauge pressure increases with increasing filling degree. But the opposite is true for relatively flexible packagings: If the relative expansion of the packaging exceeds the relative volume expansion of the liquid, the gauge pressure increases for decreasing filling degrees. The current regulations for the hydraulic test pressure determination at a maximum filing degree do not lead to the intended safety level. For a lower level than the maximum filling degree, the prescribed safety factor of 1.5 is not respected. Under transport conditions, it is possible that the inner gauge pressure exceeds the test pressure. This can result in a failure of the packaging. There is a need to reconsider the regulations.
This work focuses on the question if the bubble test prescribed in the Dangerous Goods Regulations has sufficient sensitivity to detect leakage rates, which could result in the formation of explosive atmospheres during transport. The sensitivity of the bubble test is not directly comparable with other leak testing methods because of its different flow conditions. Therefore, a normalized minimum detectable leakage rate under Helium test conditions is calculated for the bubble test. This sensitivity of the bubble test under reference conditions is compared with limit leakage rates for a worst‐case transport scenario. The sensitivity of the bubble test is not sufficient to prove the limit leakage rates for 6‐L packagings. The formation of explosive vapour‐air‐mixtures cannot be excluded. Therefore, more sensitive leak testing methods should be considered for smaller packaging design types.