# IoT-Aware Architecture to Guarantee Safety of Maintenance Operators in Industrial Plants
## 1 Introduction  
The positive effects on workers' mood and their well-being brought by the awareness of being in a safe working environment have been demonstrated by different works present in literature (e.g., [PERSON] et al. [1]) and actually acts as a good booster to the avoidance of accidents. Every working environment should guarantee safety to employees and operators both in normal operations and extraordinary duties (e.g., maintenance operations), however, the industrial domain is one of the fields in which it is more important due to the risk at which each worker is exposed. During the last decades, different solutions already contributed to the enhancement of the sector, and thanks to the introduction of new concepts like the \"Industry 4.0\" one has drastically changed how plants and factories are designed and operate all around the world. Nonetheless, based on the performed state of the art analysis reported in the related works section, at the moment of writing, the literature is still lacking an effective intervention in one of the most dangerous activities which is the maintenance of machinery in industrial plants. Based on the last statistical surveys, maintenance is still prone to a lot of accidents that have to be addressed in the future of safety engineering [2]. The workers' safety during maintenance activities, especially in huge plants, depends on the correct execution of complex procedures, the correct training of the operators, the effective supervision during the execution, etc. Furthermore, in addition to the inherent dangerousness of maintenance activities, nowadays such operations are often performed by third parties' employees, that, unfortunately, are not experts in the specific machinery they are going to maintain and usually have limited knowledge of the possible production problems and possible causes of severe injuries. Moreover, also from a legislative perspective, during maintenance activities of industrial environments generally workers are subjected to risk reduction necessity at the organizational level in accordance with the provisions of the legislation of health and safety of workplaces, Directive 89/391/EEC, 1989 [3]. One of the paradigms that, in our opinion, can play an important role in making maintenance activities safer is the Internet of Things (IoT). Although the machineries already integrate systems and solutions to guarantee safety during their normal operation, they cannot guarantee the same safety level during maintenance simply because such systems are usually off during maintenance. Instead, the IoT and its multitude of autonomous small devices can act as a promoter to monitor and intervene in the operations performed during maintenance activities. Although maintenance scenarios can be really complex and heterogeneous, the most important situations that are always present in almost all the maintenance procedures are summarized in the following list of actions that an operator has to sequentially perform during his/her duties: (a) de-energize systems before maintenance, (b) verify that there is not any other operator in the hazard zone in which he/she has to operate, (c) follow the procedures designed by the machine builders for correctly maintain the machinery, (d) verify that all the performed actions brought to the correct working of the machinery, and (e) re-energize the machinery itself. All these procedures are usually regulated by various directives and laws. E.g., the machinery-worker interaction is designed by the machine builder that has to fulfill the safety requirements of Machinery Directives 2006/42/CEE, annex I [4]. As a further example, the problem of the unexpected start-up of an axis of the machine during maintenance activities or the necessity of switching off the power before starting the maintenance are typically devised by the de-energization of dangerous devices as required by the safety requirements in the same Annex I (clause 1.6.3 \"Isolation of energy sources\").