By Bert Stap BSc, Nick de With
BSc and Paul Hoogerkamp
Machine builders currently have
quite a few questions about how to deal with the requirements of the new
Machinery Directive 2006/42/EC as regards fixed guards, and in particular
safety fence systems. There are suppliers who take Article 1.4.2 of Annex I of
the Machinery Directive, ‘Special requirements for guards’, to mean that
fasteners must remain attached to the fixed guard and/or the machinery. Other
suppliers state that the legislator is not equating ‘fixed guards’ with ‘safety
fence systems’ as described above. The key questions are, of course, ‘how was
this legislation meant to be interpreted?’ and ‘who is right?’
What
exactly does it say in the new 2006/42/EC Machinery Directive? Two types of
guards are mentioned in the Machinery Directive. There mention of a fixed or a
movable guards with an interlocking device. Fixed guards can refer to the housing
of a machine, which might take the form of panels, which would require tools
for removal. The fixed guard should, where possible, not stay connected to the
machine. Movable guards, on the other hand, are associated with sliding doors,
hinged doors or inspection hatches. Movable guards, when open, should in fact
remain attached to the machine as much as possible.
Everyone
understands that a safety fence system consists of a combination of fixed and
movable guards (fixed panels with posts and hinged or sliding doors). No one
will disagree with anything that has been said so far.
In
the same requirement 1.4.2.1 of Annex I of the Machinery Directive, it is
further stated that the fastenings for fixed guards must remain attached to the
machine or to the guard (requirement 1.4.2.1. Fixed guards) ‘Their fixing
systems must remain attached to the guards or to the machinery when the guards
are removed.’ To be able to give a clear answer on what the legislature meant,
we must first consider how such security fence systems are applied to protect a
machine in practice. In most cases, security fence systems (Figure 1) are used
for larger machinery or installations where there is often a combination of
multiple machines (a ‘machine’ as defined in the Machinery Directive in Article
2, paragraph a, 4th dash). In many cases, the security fence is completely
detached from the machine(s) or, for example, only mechanically connected to
the machine in a few places. In addition, there are many variations on the
security fence systems mentioned above, such as, for example, an all-steel
casing around a welding robot. In many cases, this housing (see Figure 2) is
made of hardened sheeting and these panels are connected to each other by means
of bolted connections in the hardened flanges. Did the legislature have this
kind of a security fence system in mind when writing this requirement in
section 1.4.2.1?
They
were most likely thinking of the following, much more common situation. Many of
you will have seen or experienced part of a machine’s housing needing to be
removed for maintenance purposes. It is also not uncommon to discover that the
housing hasn’t been replaced a few weeks later. The housing ends up wandering
around the production area and is often not replaced. Various causes can be
given. In many cases, the manufacturer provides the machine housing with M6
bolts or screws (self-tapping) and fasteners. It is very easy for a serviceman
to lose a few of these small bolts or screws when disassembling the housing of
a machine for drive maintenance. He would then have to go to the warehouse to
get replacements in order to be able to put the housing back on again. However,
in situations such as this, the machine, plant or line will often be returned
to service without putting the housing back or putting it back properly in
order to get the plant running again as fast as possible. People often think
they will get around to it in the near future, but that near future soon
becomes never. In this way, maintenance work can end up resulting in part of
the guard system specified by the manufacturer going missing. This fixed guard
is part of the manufacturer’s risk analysis and risk reduction measures and its
absence can lead to a dangerous situation for the user of the system or machine.
The relevant requirement is easier to understand in this context. The
legislator is clearly asking the manufacturer/designer to devise other
fastening solutions.
It
would not be very hard to replace the bolts or screws with a different
fastening system. In the general requirements for guards (requirement 1.4.1),
there is also mention of removing fixed guards in connection with tool changes
or maintenance work. But when are security fences actually removed for
maintenance or tool change? Probably never. The panels of a security fence
protecting machinery or equipment are only very rarely removed during the
entire lifetime of the installation, for example, to replace a portion of the
machine/installation inside the security fence and only if the parts that need
to be replaced don’t fit through the doors in the security fence. Furthermore,
the fastenings of security fence panels are often of a totally different size
than the previously mentioned small bolts and screws. It is therefore much
harder to lose this type of fastenings. Certain types of security fence
systems, such as machine guards, require special fastening methods, which would
make it impossible to meet this requirement. Think of the well-known aluminium
safety fence system built from bolted together standard profiles filled with
Lexan, mesh or plate. Should these manufacturers also start thinking about new
attachment methods? We therefore suggest that it is not necessarily always
necessary to apply this part of requirement 1.4.2.1 to a security fence system
and that suppliers of security fence systems and machine builders who
themselves manufacture security fence systems or enclosures will in most cases
be able to stick with the attachment method they have been using thus far. A
standard solid bolt connection.
The
foregoing is underlined by the European interpretation of the new Machinery
Directive in the draft translation of the ‘Guide to application of Directive
2006/42/EC’. The explanation below relates to requirement 1.4.2.1:
...
1.4.2.1 requires fastening systems for fixed guards to remain attached to the
guards themselves or to the machinery when the guards are removed. This
requirement aims to reduce risks caused by guards not being replaced or being
only partially fastened due to loss of one or more of the fastenings when fixed
guards are removed, for example, for maintenance purposes. Application of this
requirement depends on the manufacturer’s assessment of the risk concerned. The
requirement applies to any fixed guards that are liable to be removed by the
user with a risk of loss of the fixings, for example, to fixed guards that are
liable to be removed during routine cleaning, setting or maintenance operations
carried out at the place of use. The requirement does not necessarily apply to
fixed guards that are only liable to be removed, for example, when the
machinery is completely overhauled, is subject to major repairs or is
dismantled for transfer to another site. The above explanation contains a
substantiation of our previous reading of requirement 1.4.2.1. It is very
clearly stated that the manufacturer may decide whether to use retained
fasteners for its fixed guards when performing its risk assessment. There is
talk of the risk of losing the fasteners and related replacement or incomplete
replacement of the fixed guards. In addition, it is indicated that, if fixed
guards need to be removed sporadically removed in connection with major repairs
to the machine or installation, this requirement does not necessarily apply. In our opinion, the latter clearly applies to
safety fence systems around machinery and installations.
Our
conclusion is therefore that in most cases standard bolted connections are
sufficient for use in safety fence systems. Don’t be fooled by the sales talk
of the safety fence suppliers and make sure to carefully assess whether you
really need to use retained screws and bolt connections. You have every legal
right to do so.
Bert Stap BSc is an independent, senior CE consultant at ESV Technisch Adviesbureau B.V. in Barneveld, in the Netherlands, with around 16 years of experience in the field of practical machine safety. He has previously been directly involved in the development of safety fence systems and fully-enclosed steel enclosures for welding robots.
Nick
de With BSc is a senior consultant at Fusacon B.V., teacher at NEN and member
of the NEC 44 and IEC TC44/WG7 standards committees.
Paul
Hoogerkamp is an independent CE consultant at Mecid B.V. in Vorden, in the
Netherlands.
