Machine evaluation: apply the three-step rule to ensure machine safety

Directive 2006/42/EC has the dual purpose of harmonizing the health and safety requirements applicable to machinery, while ensuring the free movement of the same within the EU market.

As is known, the machine must be designed and built in such a way as to carry out its function without endangering those who benefit from it. This principle must be considered valid both when its use is carried out in the foreseen conditions, but also taking into account possible improper uses (reasonably foreseeable) of the machine itself. The objective of the measures adopted during the design and production phase must be to eliminate any risk throughout the foreseeable life of the machine, including the transport, assembly, disassembly, disassembly and scrapping phases.

The evaluation of machine safety

To evaluate the safety of a machine there is a well-defined approach aimed at determining the measures to be taken to address the risks previously identified and assessed. This approach, often referred to as “Three step rule” identifies a hierarchical scale of measures to be adopted, in order of priority. At the top of this hierarchy we find the intrinsically safe design measures, followed by technical protection measures, to arrive – in last priority position – at information to provide to users.

This order of priority is to be understood as "completion" of a step, before moving on to the next. As a result, the manufacturer will need to exhaust all possible intrinsically safe design measures before resorting to protective measures. Likewise, you should exhaust possible protection measures before relying on warnings and instructions to users.

First priority: intrinsically safe design measures

The first priority is given to intrinsically safe design measures because they are clearly more effective than protective measures or warnings. Some cases of intrinsically safe design measures are, for example, replacing a flammable hydraulic fluid with a non-flammable one; or the guarantee of the intrinsic stability of the machine through its shape and mass distribution.

The guarantee that the accessible parts of the machine do not have sharp edges or rough surfaces and that there is a distance between the movable and fixed parts of the machine is also considered an intrinsically safe design measure avoid the risk of crushing.

The manufacturer can also reduce noise emissions, vibrations, radiation or hazardous substances at source; limit the speed and power of the moving parts or the translation speed of the machine itself; locate the dangerous parts of the machine in inaccessible places and adjustment and maintenance points outside dangerous areas.

In all the cases just exemplified, safety for the user is produced by structural, and therefore design, characteristics of the machine itself, which - precisely - ensure the priority starting level and necessary to ensure the protection of users.

Second priority: technical protection measures

When it is not possible to eliminate or mitigate risks through intrinsically safe design measures, the second priority is given to technical protection measures. These are measures aimed at preventing people from being exposed to dangers that it was impossible to contain thanks to the strategies applied in the previous phase.

Some examples of technical protection measures are i repairs, whether fixed or mobile, i protection devices, L'insulation of live electrical parts, the closure of noise sources and the dampening of vibrations.

The manufacturer will be able to prepare measures for the containment or evacuation of dangerous substances, but also devices to compensate for the lack of direct visibility and safety structures. protection against the risk of overturning or falling objects. To ensure a satisfactory evaluation of machine safety, information measures will then have to be added, where despite all the attention described in the first two phases it is not possible to guarantee the complete protection of users.

Third priority: warnings and information

For residual risks, therefore, information must be provided to exposed people, in the form of warnings, signs and information on the machine, and to users in the instructions. These are, for example, information or warnings about the machine with symbols or pictograms, acoustic or luminous signals, warnings against the use of machinery by certain people such as, for example, young people under a certain age or height.

Among the warnings belonging to this priority group are also those relating to assembly and installation in machine safety, information on the complementary protection measures to be adopted in the workplace, specifying the need to equip operators with adequate personal protective equipment and ensure their use.

Providing warnings and instructions for use is considered an integral part of the design and construction of the machine. However, this scale of priority in evaluation of machine safety demonstrates how warnings and instructions should never replace intrinsically safe design measures and technical protection measures when these are possible, always taking into account the state of the art.

The safety assessment of a machine, in fact, is not a static concept but evolves with the state of the art. The essential requirements of safety and health protection, therefore, necessarily take into account the state of the art at the time of construction and the technical and economic requirements.

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