La valutazione del livello di integrità dei sistemi di protezione delle macchine, dall'analisi dei rischi ai dati affidabilistici.

Through the application of several different methods of analysis it was showed definitely that a risk analysis conducted on an industrial machine, taking into account the human factor from the beginning, has a significant impact in the assignment of SIL to all Safety Integrity Function (SIF). The same phenomenon occurs in the verification and computation of the performance level for each device of the press. Comparing these methods and the results obtained through the development of a further case study carried out during the Spring at Trinity College of Dublin it was possible to define a useful logical model of analysis to describe and assess the risks related to human-interface and usable to verify and calculate the safety integrity level of the safety functions of the machine. This methodology is a combination between the Integrated Dynamic Decision Analysis (IDDA) and the Technique for Human Error Rate Prediction (THERP). The application of the Decision Analysis has been made possible through a careful reconstruction of the operating procedure regarding the use of the press applying an using an ad hoc Failure Mode and Effects Analysis (FMEA) template. The system of the study was described by IDDA in a random sequence of events where the given values of probability derived from the THERP model for human error and from the method of calculation set out by the standard technique (EN IEC 62061) for dangerous failures of safety devices. This integrated approach has allowed to take into account human factors with greater detail and in a quantitative way describing where and why the operator can cheat or by-pass the safety system, unlike other methods of risk assessment where you could only identify where the man-machine interface should be analyzed in depth.