Don’t delay adopting

As the Machinery Directive EN 13949-1 standards better reflect advances in Machine Safety
System design, these standards should be adopted sooner rather than later, says Kevin Ives

The latest version of the Machinery
Directive has now been with us
for some time. 2006/42/EC was
introduced in 2006 and published in the
“Official Journal” (OJ) in September
2009. The publishing of any article,
directive or notification of a standard in
the OJ is the point at which the use of the
document becomes mandatory.

Ever since the first Machinery Directive,
the recommended method of meeting all
of the Essential Health and Safety
Requirements (EHSR’s) was to follow the
advice in the “Harmonised Standards”.

These are standards that have been
written in support of the directive. A list
of the standards applicable for use against
the directive is printed in the OJ following
the ratification of the directive.

As with the directives, the standards are
being improved/upgraded with new
versions being announced in the OJ as
being harmonised against the relevant
directive. In 2007, the long awaited
replacement for Safety of Machinery –
Design of safety related control systems EN
954-1 was printed. This standard, EN
13949-1, has the same title and seeks to
achieve the same ends but uses a risk-based
approach. The standard introduces new
criteria such as Diagnostic Coverage (DC)
and Mean Time To Dangerous Failure
(MTTFd), which need to be taken into
consideration when designing the system.

The normal situation, when a standard
is rewritten, is to allow a two-year
“change over” period. This is provided to
enable manufacturers to modify their
design and documentation to align with
the new requirements. Using this rule, EN
954-1 should have been revoked and
replaced by EN 13849-1 in late 2009. The
inclusion of EN 13849-1 as a harmonised
standard against 2006/42/EC was
announced in the OJ in September 2009.

At this point, the problems started to
emerge. There were a few complaints
made to the commission claiming that
two years did not allow sufficient time for
some manufacturers of components to
provide the information and data needed
to calculate failure rates, as required by
the latest standard. The commission
agreed and therefore delayed revoking
EN954-1 until the end of 2011. The latest
list of harmonised standards that can be
used to demonstrate compliance with the
directive, does not list EN 954-1. This list
was printed in the OJ dated 20th October,
2010. This clouds the issue further. In
theory, manufacturers cannot use
standards that are not harmonised to
claim compliance with the directive, but
EN954-1 will not be revoked until the end
of 2011.

All of the machine-specific standards
(C standards) that were written before the
introduction of EN 13849-1 list EN 954-1
as an appropriate standard to use for the
design of the safety-related controls. This
raises even more confusion.

The future is flexible
As the newer standards better reflect state
of the art in Machine Safety System
design, Pilz therefore recommends that
machine builders adopt these standards
sooner rather than wait until the end of
the transition period. Why? Because we
believe the future of automation and
machinery lies in flexible, modular
architectures, which will provide users
with the high level of availability and
adaptability required for agile, lean
manufacturing plants. Modern plant and
machinery will therefore require
intelligent safety systems.

The new standard reflects this increased
tendency to use electronic and
programmable systems for safety rather
than traditional electromechanical devices
that were used when EN 954 was
published. EN 13849-1 provides
requirements for the design and
integration of safety-related parts of
control systems, including software. It has
wide applicability as it applies to all
technologies, including electrical,
hydraulic, pneumatic and mechanical.

While acknowledging the decision of
the EU, we believe that the probabilistic
approach of the new standards provides
machinery designers and users with many
advantages when assessing the reliability
of safety systems. While there is an
increased complexity in requirements to
make design calculations, tools such as
Pilz’s PAScal Safety Calculator are
available to calculate the required
Performance Level (PL) and Safety
Integrity Level (SIL). This software also
evaluates a safety system designs and then
generates the necessary documents to be
included in the machine’s technical file.

Training courses are also available on the
new Machinery Directive 2006/42/EC,
including one, two and four-day City &
Guilds Machinery Safety Courses, Safety
Design and CE Marking.

Kevin Ives is a machinery safety consultant at
Pilz Automation Technology