Risk Reduction; Residual Risk; Machine Safety In The Usa - Siemens Sinamics S110 Function Manual

Safety Integrated Functions
8.1 Standards and regulations
8.1.2.8

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 954-1 or EN ISO 13849-1 (previously EN 954-1) or, in
the case of electrical controllers (in particular, 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 954-1 defines "categories" for this purpose. Annex B describes a method of selecting the
required category for designing and implementing the safety-related controller components.
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.
8.1.2.9

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).
8.1.3

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.
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