KANBrief 3/16

Openings in protective devices: confusion in practice

Machines such as palletizers, depalletizers, hood applicators and continuous handling equipment are used to package and transport goods in industrial manufacturing. These machines are closely integrated and present similar hazards. They are however governed by different standards containing different requirements for the openings in protective devices. Employers are faced with deciding what yardstick to apply for the purpose of risk assessment.

When danger zones on machines cannot be avoided by inherently safe design, preference is to be given to protective devices. In order for products to be inserted into and retrieved from the danger zones of machines, openings are required in the protective devices. Since the openings for pallets and large boxes are also sufficiently large for persons to pass through them, protective measures are required that are able to distinguish between persons and the loads being conveyed.

This presents users of the machines in the food industry with the problem that the Type C standards for palletizers and for continuous handling equipment for further transport within plants contain divergent requirements for the openings, and thus give rise to differences in the level of protection. This repeatedly results in questions from companies concerning adequate safety and the state of the art in the sense of the German Ordinance on industrial safety and health.

Numerous standards – little consistency

EN 415-10, Safety of packaging machines – Part 10: General requirements, which is applicable to palletizing machines, supports the requirements for the design of openings set out in the higher-level Type B standards as follows:

  • The distance between the fixed guard and the column for the light barrier must not exceed 180 mm
  • The distance between the light barrier and the outside edge of the load must not exceed 230 mm
  • The safety device is disabled during passage of the load (Muting in accordance with IEC 61496, Safety of machinery – Electro-sensitive protective equipment – Part 1: General requirements and tests or DIN EN ISO 13849-1: Safety of machinery – Safety-related parts of control systems – Part 1: General principles for design). For the duration of passage, the load must assume the safety function. If the duration of passage is substantially exceeded, the muting function must be cancelled and all hazardous movements halted
  • The muted area must not contain any operational holding positions for a product

Continuous handling equipment that accepts pallets and transports them further is governed by EN 619, Continuous handling equipment and systems – Safety and EMC requirements for equipment for mechanical handling of unit loads, which is currently being revised. Annex F of the standard contains typical design examples for preventing access to the danger areas. These "obstructions" are not derived from Type B standards. They primarily concern the "crush and shear hazards" between the load and the fixed parts of the protective devices at the point of load entry. In contrast to EN 415-10, EN 619 does not set out prevention of access or positive de-energization as a binding requirement. Instead, typical aspects of conveyor design (such as roller intervals, roller length, width of components) are listed as protective measures.

Confusion in practice

In companies in the food industry, the differences in requirements concerning the machines, particularly for comparable hazards, such as those presented by hoists, prompt considerable discussion. Crush or shear accidents on hoists have been shown to result in fatalities or irreversible injuries.

The state of the art is described in the German Ordinance on industrial safety and health as the state of development of advanced methods, equipment or modes of operation that justifies the assumption that a measure or procedure is suitable in practice for protecting the employees. During definition of the state of the art, reference is to be made to comparable methods, equipment or modes of operation that have been successfully proven in practice.

The objective must be that of defining uniform safety requirements for comparable hazards. In accordance with the ranking of safety objectives described in the Machinery Directive and all OSH regulations, priority is to be given to technical measures not dependent upon operator action. Since, in the course of the risk assessment, the employer is obliged to assess the measures taken in his installations, he is reliant upon an authoritative description of the state of the art for this purpose.

Markus Husemann