TechArchive

Original article date: April 1999

Many machine builders were horrified at the additional paperwork that seemed to be required when the Machinery Directive came into force. Now that the dust has settled, it seems that a pragmatic approach can be taken. PHILIPPE CRISPIN of Huxley Bertram Engineering explains.

The official literature for the Machinery Directive looked like it would be heavy going when it started to be published five or six years ago. At first sight, it seemed that CE marking would add significantly to the time and costs associated with building automation and special-purpose machines. The only sources of practical advice were a trade magazine, Industrial Technology, and Pilz’s guide to the Machinery Safety Standards; the DTI, BSI and HSE produced little advice that could be described as ‘practical’.

At Huxley Bertram Engineering we realised that it would be inefficient for all of the engineers to try and work through the growing pile of documents relating to CE marking, so one engineer was tasked with distilling it all into an in-house guide. When this was complete, it became apparent that CE marking was really just a case of following a logical sequence of actions and there was nothing that we would not be able to do if we applied ourselves.

In addition to the in-house guide, one of the most useful tools was the Pilz Interactive Guide to Machinery Safety. This was educational, helped us with the risk assessments and, lastly, made documentation far simpler than it otherwise would have been. And let’s face it, documentation is one of the biggest elements in CE marking!

At that time, several consultancies were springing up, all of them offering assistance with the CE marking process. However, we found that we could work it all out for ourselves or, if there was something out of the ordinary, we could get telephone advice from the staff at Pilz or Lacs (the Longlands Advisory and Consultancy Service, which had assisted Pilz in the preparation of its literature and software). Similarly, there were various software packages becoming available to aid the preparation of the Technical Construction File, but we found that these were not necessary so long as a methodical approach was taken.

Initially CE marking involved additional effort for the formal risk assessment and documentation and an allowance had to be made for this in proposals for new projects. Design practices, however, were already rigorous enough that there was usually only minor additional safety-related hardware to be included in the cost estimation.

Many of the machines that Huxley Bertram designs and builds are for automatically assembling and testing products, though the company also develops research equipment and smaller jigs and fixtures used during manual assembly. The large assembly cells will typically be built around an indexing table, perhaps with bowl feeders supplying components via conveyors or vibratory linear feeders. For these, the philosophy is to house the entire machine within guarding as far as possible, leaving non-hazardous equipment (such as bowl feeders) outside. At an early stage in the design the decision is taken whether to use fixed guards, hinged doors with interlocks, or light curtains as a means of protecting the operator(s) from the machinery.

The safety of any machine is considered during the initial design phase, almost as a continuous process, using past experience, relevant standards and good practice as appropriate. Leaning heavily on experience during the design phase means that the formal risk assessment can be used as a confirmatory exercise to ensure that the hazards have been eliminated or minimised as appropriate once the equipment is approaching design completion. Approaching the risk assessment in this way reduces the reworking of the formal risk assessment should the design change as the equipment is developed.

When new staff are taken on, they have access to what is now a significant bank of information on the machines that have already been built and documented. New employees can therefore quickly gain from the experience of the existing staff.

The situation now is that CE marking is no longer viewed as too much of a burden; it is an integral part of the project administration and, as time passes and experience builds, it becomes ever quicker and easier. The application of experience during the design process ensures that the formal risk assessment can be undertaken at a relatively late stage in the machine build. Very rarely are changes necessary and, if so, it is usually only a question of making minor additions to the guarding.

A balance has to be struck when carrying out the risk assessment. For a start, it must be assumed that the machine operator will make mistakes and that if an accident can happen, it will. But on the other hand, you have to draw the line somewhere and decide at what point the operators are being unreasonable in trying to bypass guard switches or otherwise injure themselves.

The whole process of CE marking should result in safer machines by elevating the importance of safety in the design and build process. But this statement should be put into context. It does not mean that older, non-CE marked machines were necessarily unsafe. The difference now is that the chance that a machine will cause an accident has been reduced, which is undeniably a good thing!

One contentious issue that is given careful consideration for every machine built by Huxley Bertram is whether a guard override switch should be fitted. Maintenance staff can certainly benefit from having closer access to the machine to do their job, but a machine is significantly more hazardous if it operates with the guards open. If a guard override switch is not fitted, however, a maintenance operator may bypass the safety circuits in order to run the machine with the guards open. If an accident subsequently occurs, it might be argued that the machine supplier had encouraged this bad practice by not providing a guard override switch. Clearly there is no simple answer to this problem, which is why every machine is considered on a case-by-case basis. Furthermore, if an override switch is fitted, the machine is usually not allowed to operate fully automatically, only to run in single-cycle mode and at a reduced speed or lower force (if this is practical), whenever the override is used.

CE marking can be approached in a pragmatic way by using experience to build machines that are, as far as possible, safe-first-time. Looking at some other machines, it makes you wonder how the machine builders have concluded that the equipment can satisfy the requirements of the Machinery Directive and hence be CE marked. Either they are not undertaking a risk assessment correctly or there are some fundamental misunderstandings. Sure, the machine may never cause an accident if the operators are careful or if a particular set of circumstances never arises, but that is an unsatisfactory situation. Apart from the serious injuries that could occur, employers could be taken to court under the Health and Safety at Work Act for failing to provide a safe machine. The only prudent course of action is to purchase from a reputable supplier that follows the correct procedures to CE mark the machine.

Huxley Bertram Engineering specialises in designing and building automation, special-purpose machinery and research equipment. Philippe Crispin and his colleagues can be contacted on 01954 250809.

April 1999