Machine guards combine innovation with regulation

Terry Hayward, MD of machine safety specialist Schmersal, discusses machine perimeter guarding and says combining innovation with regulation can provide a much more effective and productive solution.

Terry Hayward, MD of machine safety specialist Schmersal, discusses machine perimeter guarding and says combining innovation with regulation can provide a much more effective and productive solution.

At first glance, building a perimeter fence around a machine with hazardous operations is a simple affair - all it needs is a mechanical barrier that prevents access by humans simply by being in the way.

This is certainly the approach taken by some installers.

And such a simple structure could be easily constructed by fixing conventional steel mesh panels between vertical posts.

But is this good enough? Not according to the experts who wrote the standard BS EN95:1998 "Safety of Machinery - Guards- General requirements for the design and construction of fixed and moveable guards".

They believe that some important considerations should be included in the design, construction and erection of machine guards.

Clause 7.1 for example, refers to the ability of a guard to be climbed - an important point when assessing safety and protection as it takes into account the misuse or unintended use of machines, systems and structures.

The standard states that "Climbing on guards shall as far as practical be inhibited by design", and goes on to say that this could be achieved for example "by eliminating horizontal structural members and the horizontal component of mesh fabric from the outside surface of the guard, climbing is made more difficult".

It therefore follows that a well-designed guard system should use mesh that has the horizontal wire (the one used to gain a foothold) behind the front aspect of the guard.

Furthermore, the horizontal pitch between the vertical wires should be small enough to prevent the climber gaining a toehold.

Other benefits of this arrangement become clear when the standard discusses the issue of "viewing".

Clause 5.2.4 states: "To minimise the need to remove them, guards shall be designed and constructed to offer adequate viewing of the process".

Clause 5.10 also specifically refers to machine viewing and calls for the mesh to be "of adequate open area and suitable colour to permit viewing".

For practical purposes an arrangement where the pitch between the horizontal wire is greater than between the vertical provides optimum visibility, especially if the mesh is also finished in black.

Another little-known focus of the standard covers areas where access is required, and distinguishes between two different requirements.

For the first, where access is required during the working cycle of the machine, a moveable guard with an interlock, or an interlock with guard locking, should be used.

Here, innovative solutions include tamper-proof interlock switches with 15,000 individual key codes, AS-i compatible embedded-chip technology and hinge/switch and handle/switch combinations.

Where access is required only for machine setting, process correction or maintenance, a fixed guard can be used but only if the frequency of access is low and the removal and replacement of the guard panel is easy and is carried out under a safe system of work.

Perimeter guard structures that are firmly bolted or welded into position are not deemed suitable for these applications, as they are not easily removed and replaced.

The innovative solution is a modular system with mesh panels securely mounted to the fixing posts.

These can be removed easily and conveniently, but only with appropriate tools.

Support posts and guard frames should also provide a rigid structure as stipulated in clause 5.5.3 of the standard, which further states that the rigidity of the guard should be maintained, especially where deformation of the material could prevent the system from maintaining safe distances.

But how can an engineer assess the rigidity of a custom-made, one-off perimeter guard, or the material from which it is made, without destructive testing - especially if aluminium is used in the construction?.

Contrast this with modular systems, which are thoroughly tested to ensure that mounting posts and their ground fixings offer sufficient rigidity under many different mounting combinations.

Specifying a proven perimeter guard system will ensure the highest standards of protection as well as conformity to relevant regulations.

Innovative design of the system and its ancillaries will add further benefits such as ease of installation, a rigid structure, a clear view of the machine operation and safe access whenever required.

As Schmersal now offers two innovative solutions - the Satech perimeter guard system and an extensive range of machine safety products - the location and mechanical mounting arrangements, brackets and fixings are engineered to ensure that everything fits together as complete system.

This includes Schmersal's new STS range of emergency access and exit door handles and interlocks, which is suitable for all types of safety guards and offers six different switches, each with eight different mounting combinations.

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