## 1 Introduction  
Rock falls threaten many communities in mountainous regions all over the world. In many countries, national authorities are making constant efforts to develop or improve hazard and risk management policies for effectively coping with this type of landslide, in order to prevent consequences which may possibly be severe [1, 2, 3]. The main principle behind the different strategies adopted can differ from one country to another: some hazard and/or risk management plans focus directly on the use of protection measures to reduce potential consequences [4], while others aim firstly at reducing exposure to rock falls hazards [5, 6, 7]. In spite of these differences, the use of protection measures (such as barrier fences, wire mesh/cable nets, anchors, embankments, walls, ditches, etc.) constitutes a common point to all approaches. On the one hand, these measures clearly represent the main solution to the problem of rock fall hazard and risk mitigation in those countries where the main goal is to act directly towards a reduction of potential consequences. On the other hand, even in those approaches oriented mainly to reducing the exposure of new assets, protections measures are still necessary to ensure the safety of those assets, which are already existing. Some of them (urban areas and/or infrastructures) might indeed be located in highly endangered areas, where land use planning alone would be not fully suitable/sufficient for managing the existing threat. Whichever the situation, therefore, it becomes crucial to ensure that the rock fall protections installed can perform in conditions as close to optimal as possible throughout their whole life span, in order for the protections to actually be capable of mitigating hazards. If this issue seems to be confidently manageable at the moment of designing new protection measures, thanks to current standards and guidelines available [8; 9; 10; 11; 12; 13; 14], it surely is more complex when protections already exist at a given site. Indeed, when the protections have been installed for some years or more (e.g. one or few decades), several conditions may be likely to have changed within this time frame - from environmental factors affecting the interaction with the protections, to lack of maintenance and changes in designing norms and guidelines to comply with [15]. All the factors and conditions which might negatively influence the operation of a protection measure can actually contribute to a degradation of its performance, down to the point that the protection might be not able to play its role any longer. This aspect raises the question of how to consider the presence of existing rock fall protections in hazard analysis and zoning. When the effects of rock fall protections are taken into account, this should be based on an assessment ensuring the performance of the protections as per design. If no assessment is made, professionals and decision makers working in this field might reconsider the hazard levels and the extent of the hazard zones defined and, depending on the degree of uncertainty affecting the problem, they might even be forced not to rely anymore on the behaviour of the protections. In turn, this could imply that hazard should be determined rather as if the protections were not present at all and, clearly, such an eventuality would strongly condition land use planning solutions at the areas concerned, as they are based on the severity of rock fall hazards. The problem of what the influence of protection measures is on hazard analyses, based on their actual conditions, needs therefore to be addressed specifically. However, despite some work having already been conducted in context [15; 16; 17], a structured methodology for taking all the relevant factors affecting the behaviour of protection measures into account and evaluating their effects on the protections' performances is still lacking.