Performance Level (PL)

EN ISO 13849-1 is a harmonized standard to the Machinery Directive 06/42/EC (and therefore applies to machines and plants) and introduces the concept of PL (Performance Level).

EN ISO 13849-1 provides the manufacturer with an iterative method to assess whether the risks of a machine can be limited to an acceptable residual level through the use of appropriate safety functions (machine behavior related to the operation of safety components such as interlocking microswitches, light curtains, emergency buttons, …). The method adopted foresees the evaluation of each risk, to which is associated a criticality value that then establishes design criteria for the associated safety function, imposing on the higher risks an increasing degree of reliability of the safety functions, diagnostic capacity against possible malfunctions, periodic control and maintenance requirements, etc…

Using the graphic scheme below (figure 1), as a starting point, the EN ISO 13849-1 standard foresees the risk assessment as using the “SxP” method, i.e. a function of the severity and probability of occurrence of a certain dangerous event.

Depending on the graphical path following the assessment, a certain “performance level” is then required of the safety functions associated with the risks that have been assessed: this “required” performance level is called PLr (Required Performance Level).
The manufacturer of the machine, during the design of the machine’s safety functions, must then apply the technical standards up to a sufficient level to achieve the PLr previously defined.
Upon completion, the machine’s technical file must contain documented verification (through calculations according to methods provided by the EN standards and through the use of appropriate tools) that the PL reached is at least equal to the one initially required.