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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.
The Dangerous Goods Regulations currently do not include limit leakage rates or sensitivity requirements for industrial leak testing procedures that are equivalent to the bubble test, which is the prescribed test method for design type testing of dangerous goods packagings. During series production of such packagings, various methods are used which often do not reach the sensitivity of the bubble test. Based on a suitable pragmatic approach, its sensitivity under industrial conditions can be considered 10-4 Pa m³/s (SLR).
For the selection of a suitable industrial leak testing method, however, factors other than the sensitivity are also important, for example flow direction, pressure level and automatability. The following methods are in principal suitable and equally effective as the bubble test: pressure rise test (vacuum chamber), ultrasonic bubble leak detection and gas detection methods (pressure technique by accumulation and vacuum chamber technique).
To ensure a uniform test level during design type testing and production line leak testing and therefore a comparable safety level as required by the Dangerous Goods Regulations, it is necessary to include a more precise specification in these regulations. On the one hand, this requires an information about the sensitivity of the bubble test, on the other hand, the inclusion of a list of suitable, equally effective industrial test methods with their specific boundary conditions