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the (qualitative) information given with the benchmark risk into parameter
classes. If there are no such information then it should be a decision made by
experts which accident scenario with which parameter classes describes best
the benchmark risk.
When based on the benchmark risk a parameter combination was chosen,
the resulting risk classes for other parameter combinations can be derived.
This should be done using the quantitative risk model and the factors used
for the description of the parameter classes.
4
Example of a Newly Constructed Risk Graph
Application sector:
The risk graph was developed as complement to an exist-
ing risk graph published in VDV 332 [3]. The VDV risk graph is actually used
in practice but upon a closer inspection a lot of flaws are obvious [4]. The
new risk graph was developed taking into account the special characteristics
of Nichtbundeseigene Eisenbahnen. These are e.g. a reduced maximum speed
and typical infrastructural limitations. It focuses on person trains only.
The
system model
(figure 2) was adapted from the system model given in
IEC 61508. The main function of a railway system is the transport of persons
and goods. Looking at e.g. a single person or a group of persons is dicult. In
some analyses the approach was used that by ensuring a safe passage of the
trains all persons or goods in the train are also safe. This approach was used
by the construction of the system model. The trains are guided by several
major functions. Both, the train and the major functions form the railway
system. This is enclosed by the environment.
Fig. 2. The system model
Analysis level:
According to the VDV-risk graph the risk assessment
method shall be used for safety functions. These are all functions which guide
a train safely through the railway net. There exist several possible functional
descriptions of the railway system which all have advantages and disadvan-
tages. It was defined that the analysis level consists of all functions performed
by the physical components which in cooperation with the interlocking or as
