Incident reporting is usually considered as an effective means to improve the safety of ‘‘at risk” socio- technical systems, as it allows implicated actors to learn from past incidents. Safety could thus be enhanced via the use of an institutionalized Incident Reporting System (IRS), enabling organizations to improve the quality of actions and reactions in case of a deviation from normality, or to prevent such deviations from happening in the ﬁrst place. Yet, there is a lack of inductive analyses of actual, on-site uses of IRS. In this paper, we address this gap, using the results of 28 semi-structured interviews conducted with agents from SCK-CEN. The study relies on a vulnerability-oriented Science and Technology Studies approach. Our results show that practices of incident reporting are more varied than the institutionalized ones. Indeed, actual reporting practices are to be related to speciﬁc expressions of solidarity between colleagues within a negotiated drift – a pragmatic interpretation of the reporting procedure. Overall, the paper displays a grounded analysis of incident reporting practices which may contribute to a better understanding of how safety is co-constructed by workers, and provides opportunities for further research and concrete path of actions for practitioners.