New accidents or incidents due to human error do not "just happen" and in most of the cases the cause relies not only on human incompetence or negligence [1]. In scientific literature the Human Error Probability (HEP) is defined, in case of discrete tasks, as the number of errors divided by the number of opportunities for making errors. The HEP is a key element in system accidents and disasters, especially in high-risk fields, such as industrial plants, nuclear plants, and aerospace. According to Health and Safety Executive agency (HSE), the errors can be classified in two categories. The first category includes the so-called "slips or lapses" errors: they are considered "actions that were not as planned" or unintended actions. These kinds of errors occur during the completion of a familiar task and include slips (e.g. pressing the wrong button or reading the wrong gauge) and lapses (e.g. forgetting to carry out a step in a known procedure). Therefore, they cannot be avoided by means of training, but an improved workplace design can reduce their likelihood and provide a more error tolerant system. The second category of errors includes the errors of judgement or decision-making, so-called "mistakes". They occur when the worker accomplishes the wrong action believing it to be right. In most cases, a mistake occurs in situations where Human Error Probability (HEP) is a key element in the chain of events that could lead up to system accidents and despite the efforts of recently studies to evaluate the human reliability, many of the limitations and problems have not yet been solved. The model proposed tries to overcome these limitations by means of a method that combines the advantages of a dual-phase learning approach with that of a multi-attribute utility analysis, in accordance with Dar-El' s theory. Results of numerical simulations show the effectiveness of the model in quantifying, over time, the HEP and in evaluating the human task error proneness by varying the work breaks schedule.