Evaluation of machines: apply the three-step rule to ensure their 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 it is known, the machine must be designed and constructed in such a way as to perform its function without endangering those who benefit from it. This principle must be considered valid both when its use is carried out under the foreseen conditions, but also taking into account possible improper uses (reasonably foreseeable) of the machine itself. The objective of the measures adopted in the design and production phase must be to eliminate any risk during the foreseeable life of the machine, including the transport phases, assembly, disassembly, decommissioning and scrapping.

Machine safety assessment

To assess 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 "Rule of three steps”Identifies a hierarchical scale of the 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 – Everyone information to be provided to users.

This order of priority is to be understood as "completing" a step, before moving on to the next. Accordingly, the manufacturer will have to exhaust all possible intrinsically safe design measures before resorting to protective measures. Similarly, it will have to exhaust possible protective 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 I am, clearly, more effective than protective measures or warnings. Some instances of inherently safe design measures are, for example, the replacement of a flammable hydraulic fluid with a non-flammable one; o the guarantee of the intrinsic stability of the machine through its shape and the distribution of the masses.

An intrinsically safe design measure is also considered to be the guarantee that the accessible parts of the machine have no sharp edges or rough surfaces and that there is a distance between the moving and fixed parts of the machine avoid the risk of crushing.

The manufacturer can, Furthermore, reduce noise emissions, vibrations, radiation or hazardous substances at the 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 the hazardous areas.

In all the cases just exemplified, safety for the user is produced by structural features, and therefore planning, of the machine itself, that – just – ensure the priority starting level and necessary to ensure the protection of users.

Second priority: Technical protection measures

When risks cannot be eliminated or mitigated by intrinsically safe design measures, the second priority is attributed to Technical protection measures. These are measures aimed at avoiding that people are exposed to the 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 they are fixed or mobile, the protection devices, Theinsulation of live electrical parts, the closure of noise sources and the damping of vibrations.

The manufacturer will be able to arrange containment or evacuation measures for hazardous substances, but also devices to compensate for the lack of direct visibility and facilities protection against the risk of overturning or falling objects. To ensure a satisfactory machine safety assessment, 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 given to exposed persons, in the form of warnings, signals and information about the machine, and to users in the instructions. It deals with, for example, of information or warnings on the machine with symbols or pictograms, acoustic or light signals, warnings against the use of machinery by certain people such as, for example, young people below a certain age or height.

The warnings belonging to this priority range also include those relating to assembly and installation in machine safety, information on complementary protective measures to be taken in the workplace, specifying the need to equip operators with adequate personal protective equipment and to 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 the machine safety assessment demonstrates how warnings and instructions should never replace intrinsically safe design measures and technical protective measures when these are possible, always taking into account the state of the art.

The safety assessment of a machine, indeed, it 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.