Safe machinery,
step-by-step
P
recise knowledge of what
is technically feasible and
what is permitted from
a legal perspective is a
prerequisite for designing safety
technology that will offer the greatest
possible potential for productive
machine operation.
The Machinery Directive is concerned
with the standardisation of European
safety requirements on machinery;
it has the status of law and has been
incorporated into respective domestic
law by EU member states. It specifies
a standardised level of safety for
machinery placed on the market
within the European Economic Area,
so guaranteeing the free movement
of goods. Machine builders use the CE
mark to document that the product
complies with the applicable directives.
Machines that are joined together,
such as robot cells and production
lines, are also subject to mandatory
marking. However, operators are also
responsible if “significant changes”
made to a machine during a retrofit,
for example, mean that the risks need
to be re-assessed and the Performance
Level (PL) determined.
Step 1: Risk assessment as the key
to machinery safety
Machine manufacturers have an
obligation to supply only safe products
to customers in the internal European
market. For this reason, they must
calculate all the hazards associated
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PECM Issue 20
with the machine in advance and
assess the resulting risks. That’s
why the first step to machinery
safety under the terms of the
Machinery Directive is always the risk
assessment.
The contents and scope of risk
assessments are not specified in any
directive, but EN ISO 12100 describes
the general procedure. All relevant
hazards must be identified, based
on the intended use – taking into
consideration all the lifecycle phases
prior to the machine being placed on
the market. All the various groups who
come into contact with the machine,
such as operating, cleaning or
maintenance staff are also considered.
The risk is estimated and evaluated for
each hazard. Risk-reducing measures
are established in accordance with the
“state of the art” guidance.
For example, there is a risk of crushing
and shearing when operating a
mechanical press. The risk is described
in detail and the severity of injury and
frequency of exposure is estimated and
assessed. Afterwards the risk reduction
measures are presented, if possible
using fixed guards. Following on from
these considerations, the potential
reduced risk is presented as part of the
risk assessment.
The quantitative approach of Pilz’s
“Hazard rating numbers” (PHR)
makes sense when it comes to
The quantitative approach of
Pilz’s “Hazard rating numbers”
(PHR) makes sense when it
comes to also determining
those risks that cannot be
reduced through control
measures, but only by using
covers or fences
also determining those risks that
cannot be reduced through control
measures, but only by using covers
or fences for example. The PHR
procedure introduced by Pilz, with its
corresponding assessment figures,
is used for a strictly objective and
practicable estimation of a plant’s risk.
The machine manufacturer must then
design and construct the machine
to take account of his assessment.
Risks are calculated from the
frequency and severity of potential
injury and damage to health or
material damage, combined with the
possibility or otherwise of technical,
organisational or personal measures
to avert or protect against the
hazard. The residual risk is calculated
at the same time: if it is too high,
additional measures are required. This
iterative process is continued until the
necessary safety is achieved.
The result of the risk assessment
ultimately determines the requirements
of the technical protective measures. It
also refers to the reliable performance
of the guard function. The challenge
is to examine and assess the overall
process as well as estimate the
individual risks correctly.
Pilz offers a wide range of safety
services including risk assessment, for
more information
contact [email protected]
or call 01536 460766