Safe machinery, step-by-step

The directive 2006/42/EC, generally known as the Machinery Directive (MD), provides the legal framework for plant and machinery safety. It is the benchmark by which the functional safety of plant and machinery must be measured within the European Union. We talk of "functional safety" when the safe operation of plant and machinery depends on the correct functioning of the installed safety-related control systems.

The Machinery Directive is concerned with the standardisation of European safety requirements on machinery. The Machinery Directive has the status of law and has been incorporated into respective domestic law by EU member states. It specifies a standardised level of safety for machinery placed on the market within the European Economic Area, so guaranteeing the free movement of goods. Machine builders use the CE mark to document that the product complies with the applicable directives. That’s why the CE mark is also referred to as the "Passport to Europe”. Machines that are joined together, such as robot cells and production lines, are also subject to mandatory marking. However, operators are also responsible if "significant changes" made to a machine during a retrofit, for example, mean that the risks need to be re-assessed and the Performance Level (PL) determined.

Basically the Machinery Directive regulates the essential health and safety requirements, defines what a machine is and describes the applicable certification procedures, CE marking, declarations of conformity, plus the requirements of the notified bodies.

Step 1: Risk assessment as the key to machinery safety

Machine manufacturers have an obligation to supply only safe products to customers in the internal European market. For this reason, they must calculate all the hazards associated with the machine in advance and assess the resulting risks. That's why the first step to machinery safety under the terms of the Machinery Directive is always the risk assessment, which can be used to estimate the individual risks regarding the operation and functionality of machinery in accordance with the applicable standards.

The contents and scope of risk assessments are not specified in any directive, but EN ISO 12100 describes the general procedure. All relevant hazards must be identified, based on the intended use – taking into consideration all the lifecycle phases prior to the machine being placed on the market. All the various groups who come into contact with the machine, such as operating, cleaning or maintenance staff are also considered. The risk is estimated and evaluated for each hazard. Risk-reducing measures are established in accordance with the "state of the art” guidance.

For example, there is a risk of crushing and shearing when operating a mechanical press. The risk is described in detail and the severity of injury and frequency of exposure is estimated and assessed, for example. Afterwards the risk reduction measures are presented, if possible using fixed guards. One technical protective measure could be for set-up and start of single stroke operating mode only to be possible using a two-hand control.

Following on from these considerations, the potential reduced risk is presented as part of the risk assessment.

The quantitative approach of Pilz's "Hazard rating numbers” (PHR) makes sense when it comes to also determining those risks that cannot be reduced through control measures, but only by using covers or fences for example. The PHR procedure introduced by Pilz, with its corresponding assessment figures, is used for a strictly objective and practicable estimation of a plant's risk.

The machine manufacturer must then design and construct the machine to take account of his assessment. Risks are calculated from the frequency and severity of potential injury and damage to health or material damage, combined with the possibility or otherwise of technical, organisational or personal measures to avert or protect against the hazard. The residual risk is calculated at the same time: if it is too high, additional measures are required. This iterative process is continued until the necessary safety is achieved.

The result of the risk assessment ultimately determines the requirements of the technical protective measures. It also refers to the reliable performance of the guard function, for example. The challenge on projects such as these is to examine and assess the overall process as well as estimate the individual risks correctly.