Information Technology Reference
In-Depth Information
- The development of a technical system starts with its system require-
ments specification and ends with its safety approval.
- Human operators and their actions are not included in a technical system.
- Maintenance is not included in the definition, but maintenance manuals.
- Technical systems can be subject to a generic type approval, for which a
stand-alone risk acceptance criterion is useful.
A function is a “specific purpose or objective to be accomplished that can
be specified or described without reference to the physical means of achieving
it.” A function level is defined in prEN 15380-4 (2010) as “level, to group func-
tions of equal purpose”. The distinction between levels is described informally
as follows:
- First-level function: functional domain that encompasses a set of func-
tions related to the same general focus or service for the considered
(rolling stock) system.
- Second-level function: related to a specific set of activities which con-
tributes to completion of the functional domain defined at the first level
(at this level, it is not said how a second-level function is to be imple-
mented).
- Third-level function: related to a specific activity out of the related set
of activities, it encompasses a set of tasks (a function at least at level 3
should be supported as much as possible by one single subsystem).
It is proposed to use prEN 15380-4 (2010) which contains up to five hier-
archical levels. Taking into account the definition of function level, level 3
seems to be the most appropriate for the application of RAC-TS. At least
it does not seem reasonable to go into more detailed levels such as level 4
or 5. Table 2 gives some examples of functions to which RAC-TS may be
applied. Although prEN 15380-4 (2010) relates to rolling stock only, it can
be extended to infrastructure functions quite easily, e.g. by identification of
all interfaces of other functions to rolling stock. Some functions (or at least
interfaces) are already included in group K. In Table 2, some examples of
level 3 functions related to signalling are proposed.
4
Severity Classification
The first step is to find a proper approach towards the classification of ac-
cident severities. Here, EC Regulation 352/2009 has already made the first
decision and has defined the severity in RAC-TS qualitatively. This seems
reasonable as the severity of an accident scenario contains a strong random
element. Two very similar scenarios, e.g. the derailment of a passenger train
at high speed, may in reality lead to very dissimilar outcomes: while one
accident may result in dozens of fatalities, the other may result only in a
few light injuries. Also, due to the high safety level of European railways,
such accidents occur very rarely, so that the basis for statistical estimation
Search WWH ::




Custom Search