Guidance for Use of CSM Recommendation - ERA - Europa

European Railway Agency
Collection of examples of risk assessments and of some possible tools
supporting the CSM Regulation
2.5.2. The acceptability of the estimated risks shall be evaluated using risk acceptance criteria
either derived from or based on legal requirements stated in Community legislation or in
notified national rules. Depending on the risk acceptance criteria, the acceptability of
the risk may be evaluated either individually for each associated hazard or globally for
the combination of all hazards considered in the explicit risk estimation.
If the estimated risk is not acceptable, additional safety measures shall be identified
and implemented in order to reduce the risk to an acceptable level.
[G 1] In order to evaluate whether the risks from the system under assessment are acceptable or
not, risk acceptance criteria are needed (see "risk evaluation" boxes in Figure 1). The risk
acceptance criteria can be either implicit or explicit:
(a) implicit risk acceptance criteria: according to sections 2.3.5 and 2.4.3, risks covered by
application of codes of practice and by comparison with reference systems are
considered implicitly as acceptable provided respectively that (see dotted circle in
Figure 1):
(1) the conditions of application of codes of practice in section 2.3.2 are met;
(2) the conditions for use of a reference system in section 2.4.2 are met;
(b) explicit risk acceptance criteria: in order to evaluate whether the risk(s) controlled by the
application of explicit risk estimation is acceptable or not, explicit risk acceptance criteria
are needed (see plain line circle in Figure 1 for third principle). These can be defined at
different levels of a railway system. They can be seen as a "pyramid of criteria" (see
Figure 9) starting from the high level risk acceptance criteria (expressed for instance as
societal or individual risk), going down to sub-systems and components (to cover technical
systems) and including the human operators during operation and maintenance
activities of the system and sub-systems. Although the risk acceptance criteria
contribute to the achievement of the system safety performance, and thus are linked to
CST and NRV, it is very difficult to build a mathematical model between them: see
{Ref. 12} for more details about that.
The level at which the explicit risk acceptance criteria are defined needs to match with
the importance and complexity of the significant change. For example, it is not
necessary to evaluate the overall railway system risk when modifying a type of axle in
rolling stocks. The definition of the risk acceptance criteria can focus on the rolling stock
safety. Reciprocally, large changes or additions to an existing railway system should not
be evaluated solely on the basis of the safety performance of individual functions or
changes that are added. It should also be verified at the railway system level that the
change is acceptable as a whole.
Reference: ERA/GUI/02-2008/SAF Version: 1.1 Page 45 of 105
File Name: Collection_of_RA_Ex_and_some_tools_for_CSM_V1.1.doc
European Railway Agency ● Boulevard Harpignies, 160 ● BP 20392 ● F-59307 Valenciennes Cedex ● France ● Tel. +33 (0)3 27 09 65 00 ● Fax +33 (0)3 27 33 40 65 ● http://www.era.europa.eu