Your Questions Answered

Design Engineering and Robert Bosch address some of the pressing issues of the day in this monthly feature

Q: I need to upgrade and redesign the protective fencing within a manufacturing plant. I am aware that the EC guidelines on this topic have changed but I am not sure which apply and what systems are now available.

A: (Steve Yardley – Bosch Product Manager for aluminium extrusion products)

In recent years EC laws on the protection of employees in the workplace have become more stringent. These changes primarily concern noise, pollution and safety fencing. Legislation in this area is quite complex and full details can be obtained from the Health & Safety Executive or British Standards.

The EC guidelines which protect workers from the accessibility of danger zones count as binding in all member countries. One of the problems with revising guidelines is ensuring that everyone understands and is aware of them, particularly in sensitive situations where a person’s safety can be in question.

Within the safety laws for protective fencing there are three main standards: EN292, EN294, and EN811.

EN292 covers machine and equipment safety, and contains information regarding separating safety devices. These are physical barriers that hinder the entrance to a source of danger and offer protection against parts that may fly out, or leaking liquid materials, and so on.

Although the barrier may be a housing, fence or shell, it must be constructed in a way which ensures that it cannot be removed without tools or force.

EN294 refers to safety distances against reaching danger zones with upper limbs. These distances are dependent upon the protective barrier height and the openings within the protective mesh. For example, when using a 40 by 40mm mesh the guard needs to be a minimum of 200mm from the danger zone.

EN811 governs the safety distances against the reaching of danger zones with lower limbs. It allows greater flexibility than EN294 providing that:

a) All people to be taken into consideration are at least 14 years old.

and

b) It can be demonstrated that only the lower limbs could be used to reach danger zones.

There are also certain restrictions on the size of openings permitted on such restrictive fencing. For example, a 180mm opening constitutes a hole large enough to allow whole body entry and therefore would not pass the standards.

Although this appears to be a complicated topic, there are a few simple steps you can take to help plan the construction of safety systems.

The exact choice of safeguard for a particular machine should be made on the basis of a proper risk assessment.

When designing a safeguard, the types of guard and their methods of construction should be selected to take account of the mechanical and other hazards involved. Guards and safety devices should also be compatible with the working environment of the machine and designed so that they cannot easily be overcome. They should also provide the minimum possible interference with the machine operation in order to reduce the incentive to get around the guard.

With your final choice, make sure you look out for systems that provide a versatile and economical safety guard. Some can be assembled by one person and are simple to extend or modify should manufacturing requirements change.

There are also alternatives to the conventional non-variable steel structures; mainly systems designed using aluminium extrusions (like Bosch’s EcoSafe). These systems are easy to plan and have fully prefabricated elements including frame elements, suspension brackets, locks and latches and coloured trim profiles. One of the main benefits of using a modular aluminium construction is that the system can easily be adapted to future requirements.

If your requirements are more complex, some companies offer a software planning package that represents the entire layout in the form of clear CAD drawings.