In The Netherlands, there are six large (petro)chemical clusters. Companies in these clusters are located next or close to each other. The policy of the Dutch government is to invest in these clusters, and to stimulate their growth. However, there is little scientific evidence that a cluster of (petro)chemical companies is safer than stand-alone (petro)chemical companies. This research, with an exploratory design, investigates parameters influencing safety of (petro)chemical clusters and stand-alone (petro)chemical companies. Insight into these parameters can lead to targeted initiatives (e.g. by government and companies) to improve safety in both clusters and stand-alone companies. Stimulating cooperation and sharing of knowledge is an important parameter, both in clusters and between clusters, and with non-clustered companies. Information exchange on accident scenarios between adjacent (petro)chemical companies with and without domino-designation requires extra attention. An overarching cluster body can contribute to a more safe, proactive and strategic cooperation. Furthermore, it is important that cluster policies include more than only spatial planning and external safety. Also after the establishment of clusters, companies should not be treated as individual companies, but as companies being part of a cluster, for instance when inspections are performed. Attention is needed for both domino- and escalation-effects, and possible domino-effects with (petro)chemical companies in clusters (just) below the Seveso-threshold. Integrated plants falling under the management of different companies require an adjusted approach to optimise safety.