Risk Reduction; Residual Risk - Siemens SINAMICS G120 Function Manual

Appendix
A.1 Standards and specifications
A.1.2.8

Risk reduction

Risk reduction measures for a machine can be implemented by means of safety-related
control functions in addition to structural measures. To implement these control functions,
special requirements must be taken into account, graded according to the magnitude of the
risk. These are described in EN ISO 13849-1 or, in the case of electrical controllers
(particularly programmable electronics), in EN 61508 or EN 62061. The requirements
regarding safety-related controller components are graded according to the magnitude of the
risk and the level to which the risk needs to be reduced.
EN ISO 13849-1 defines a risk graph, which can be used instead of the categories to create
hierarchical performance levels (PL).
IEC/EN 62061 uses "Safety Integrity Level" (SIL) for classification purposes. This is a
quantified measure of the safety-related performance of a controller. The required SIL is also
determined in accordance with the risk assessment principle to ISO 14121 (EN 1050). Annex
A of the standard describes a method for determining the required Safety Integrity Level
(SIL).
Regardless of which standard is applied, steps must be taken to ensure that all the machine
controller components required for executing the safety-related functions fulfill these
requirements.
A.1.2.9

Residual risk

In today's technologically advanced world, the concept of safety is relative. In practice, the
ability to ensure safety to the extent that risk is permanently excluded – "zero-risk guarantee"
– is impossible. The residual risk is the risk that remains once all the relevant protective
measures have been implemented in accordance with the latest state of the art.
Machine/plant documentation must always refer to the residual risk (user information to EN
ISO 12100-2).
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Safety Integrated Function Manual, SINAMICS G120 and G120C
Function Manual, 01/2011, FW 4.4, A5E03052391B AB