To systematically reduce workplace safety risks and improve business performance, the principle of continuous improvement is usually used. It is based on the selection of objectives and subsequent monitoring of their fulfilment using key performance indicators in the given area, in the field of safety this means safety metrics. These, therefore, serve to constantly monitor the state of the organisation’s safety management system, i.e. to obtain information about the level of strategies, processes and activities used by the organisation to manage health and safety risks. Although the safety metrics applicable in a large organisation are already well described in the literature, thereis a problem with the use of these metrics in small or medium-sized enterprises. Here, the suggested metrics often appear to be ineffective, they cannot properly monitor the state of safety. This article aims to introduce a procedure for defining key performance indicators in the field of safety applicable in a small or medium-sized enterprise and to present this procedure in a case study.