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Proceedings of the Eighth International Conference on Probabilistic Safety Assessment & Management (PSAM)

Editor
Michael G. Stamatelatos
Michael G. Stamatelatos
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Harold S. Blackman
Harold S. Blackman
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ISBN-10:
0791802442
No. of Pages:
2576
Publisher:
ASME Press
Publication date:
2006

Since many years there is a worldwide discussion about the shortage of the oil reserves and the pollution of the cities by automotive exhaust emissions. For this reason the industry makes many efforts to develop alternative propulsions. Hydrogen economy plays an increasing role in economy since in some countries the efforts advanced. Besides the favourable characteristics such as energy source or energy storage, hydrogen also has some unfavourable characteristics. Analyses which identify possible risks and assess the users' acceptability are required. TÜV SÜD has completed different safety analyses for vehicles with hydrogen propulsion within the last years. The use of vehicles with hydrogen propulsion was both examined on public transportation and on vehicles for private transportation. Another differentiation was done according to the strategies of the storage of the hydrogen. The storage of cryogenic hydrogen has advantages and disadvantages compared with the storage of hydrogen in pressure vessel.

The work pursued different aims. The analysis of the public transportation was focused on a statement for the authorities with information about the overall risk. For these analyses the planned routes were taken into account. To analyse the damage not only the directly involved passengers, but also persons at the place of the accident were taking into consideration. This was quantified by the population density at the route. The frequency's evaluation of certain operating states was carried out using the existing resource scheduling of the transportation company. The operating states classification shows considerable influences on the results. The risks must be evaluated related to the acceptance of the customers and also related to the economical risk for private transportation vehicles. For the analysis it was necessary to create user profiles for private means of transportation. This is necessary for the evaluation of the frequency of operating states. The basic design and dimensioning of the hydrogen system is not in the focus of the probabilistic safety analysis because this is done deterministically according to the corresponding body of rules and regulations. Nevertheless it was noticeable, that weak points found by the interpretation of risk analysis results often agreed with deterministic deficits.

The definition of an acceptable risk for a new technology or a new development is a very difficult problem. The comparison of the results with the normal life risks was carried out for this purpose. Additionally we compared the results with the risks of conventional vehicles. Furthermore we did the same with cryogenic storage and storage in pressure vessels.

The assessment of the damage radius was one of the big efforts of the analysis. The calculation is very complex and extensive, especially because there are a high number of scenarios. These scenarios arise from the event tree analysis with many different sequences. Sequences with similar damage degree were therefore conservatively summarized and grouped in consequence classes. Another problem for the assessment of reliability data is the minor experience with such systems in the automotive area. An evaluation regarding this leads to conservative reliability data and therefore to conservative results. Nevertheless these results are qualified enough for the identification of weak points.

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