Risk Reduction; Residual Risk; Machine Safety In The Usa; A.1.2.8 Risk Reduction - Siemens SINAMICS G120 Function Manual

Risks must be reduced by designing and implementing the machine accordingly (e.g. by
means of controllers or protective measures suitable for the safety-related functions).
If the protective measures involve the use of interlocking or control functions, these must be
designed in accordance with EN ISO 13849-1:2006. For electrical and electronic controllers,
EN 62061 can be used as an alternative to EN ISO 13849-1:2006. Electronic controls and
bus systems must also comply with IEC/EN 61508.
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 graded according to the magnitude of the risk must be taken into
account. These are described in EN ISO 13849-1:2006 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 13849-1:2006 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).
A.1.3

Machine safety in the USA

A key difference in the legal requirements regarding safety at work between the USA and
Europe is that, in the USA, no legislation exists regarding machinery safety that is applicable
in all of the states and that defines the responsibility of the manufacturers/supplier. A general
requirement exists stating that employers must ensure a safe workplace.
Safety Integrated Function Manual, SINAMICS G120
Function Manual, 07/2010, FW 4.3.2, A5E03052391B AA
Appendix
A.1 Standards and regulations
163