Human factor analysis embedded in risk assessment of industrial machines: Effects on the safety integrity level

The study consists in devising a method to account qualitatively and quantitatively for the human factor in verifying the Safety Integrity Level (SIL) assigned to machinery. Two crucial aspects have to be taken into account modelling man-machine interaction in Quantitative Risk Analysis (QRA): 1. The need to include the human interaction in the logical model of QRAs techniques; 2. The quantification of the effect of human factors. The efforts were thus aimed at defining an improved methodological framework encompassing the integration of Human and Organisational Factors (H&OF) into safety analysis by means of quantitative risk assessment schemes. In the end, the Integrated Dynamic Decision Analysis (IDDA) was adopted, integrated to Task Analysis. This tool allows modelling the logic of a complex system; it provides a representation of all the possible alternative states into which the system could evolve as a real logical and temporal sequence of events. The proposed model is designed with the aim of transferring the IDDA philosophy to the in-depth study of the deviations that may occur during human implementation of operational procedures and to analyse their effects on system reliability.