KANBrief 4/12

Machine safety: reducing the incentive for the defeating of safety devices is all-important

A study (Defeating of safety devices on machinery (in German only), HVBG, 2006) has shown that around 37% of protective devices on machinery are defeated, temporarily or permanently. This affects not only obsolete machinery, as might perhaps be expected, but also, and on a large scale, machinery of more recent manufacture. The key to solving this problem lies in giving greater consideration to the needs of users and thereby reducing as far as possible the incentive to defeat safety devices.

Defeating of safety devices can frequently be attributed to machinery not possessing safe solutions for commissioning, setup and adjustment operations or for troubleshooting. It is therefore – in contravention of the requirements of the EU Machinery Directive – not prepared for all necessary operating modes and cannot be operated without safety devices being defeated.

Astonishingly however, defeating occurs even on machines that do possess safe solutions. The reasons for this are generally ergonomic deficits in their safety and operating concepts. In particular, constraints upon visibility and the possible pace of work are a hindrance to the user and present a continual incentive to disable the protective devices.

A duty for manufacturers

In Germany, Section 15(2) of the Occupational health and safety act states that workers must observe the intended use of machinery and protective devices. The manufacturer however must not rely solely upon the operator being able to ensure this in all cases. The measures taken by the operator will be ineffective should the machine not possess a well conceived safety concept.

Annex I (1) of the EU Machinery Directive requires manufacturers to consider not only the intended use of a machine, but also its reasonably foreseeable misuse. Where protective devices obstruct operation of machinery, it is foreseeable that they will be defeated.

The EN ISO 12100 (Safety of machinery – General principles for design – Risk assessment and risk reduction) basic machinery safety standard also requires consideration to be given to foreseeable misuse. However, few product standards to date have included specific information on how defeating can be prevented. It would be advantageous for such provisions and requirements to be included in further product standards. In addition, missing operating modes must be added to standards if necessary.

The primary objective: reduction of incentives for the defeating of safety devices

Manufacturers can take effective measures against defeating by observing the following three principles at the design stage:

1. Prevention of defeating, by designing machinery such as to provide as little incentive as possible for it.

2. Obstructing defeating, for example by the use of position switches with coded actuators or RFID.

3. Detection of defeating, for example by plausibility tests performed by intelligent machine controls (PLCs).

The most important approach for the prevention of defeating is therefore the conceptual design of a machine. Should a thorough safety and operating concept that considers the needs of the operator not be in place at this (early) stage, any subsequent measures can be only corrective in nature.

Improving the safety culture in companies

At the same time, companies must also take action. A study by the DGUV has shown that defeating is tolerated and in some cases even encouraged in the companies of many of the operators studied. Nevertheless, many machine operators see no urgent need for action, despite the fact that the defeating of safety devices constitutes a violation of the German Ordinance on industrial safety and health (Annex 2, 2.3).

Workers often considerably underestimate the hazards presented by a defeated safety device. Operators must therefore ensure a safety culture that addresses the subject of defeating proactively. This includes raising workers' awareness of the subject of defeating by drawing attention clearly to hazards, by providing training, and by penalizing abuse.

Manufacturers, dealers and operators can find useful information, such as a table for identifying the incentive to defeat safety devices, model design solutions and checklists.

Ralf Apfeld