Purpose The purpose of this paper is to unpack the shared understandings of safety held by workers on large UK construction sites using a complexity lens, and so provide empirical support for the inclusion of situational self-organising within construction site safety management systems (SMS). Design/methodology/approach A social constructionist epistemology supports the discourse analysis of talk (semi-structured interview and conversational), text (SMS and documentation) and visual (safety related signage) data collection from five large (+20 pound m) UK construction sites. Findings Construction workers readily understand safety to be an emergent phenomenon with the complex system that is the construction site. Contemporary safety management approaches struggle with this complexity, yet there is the potential to mobilise situational self-organising on sites to improve safety in practice. Research limitations/implications - Epistemological foundations mean no claim is made to generalisability as perceived by traditional positivistic parameters. The data are limited to large (+20m) pound UK construction sites; however, underlying construction management systems are common to the industry as a whole and can find fit with practitioner experiences and other empirical academic work from both the UK and other countries. Practical implications - Situational self-organising of safety management within the construction workforce is proposed as a key contribution to a relevant, dynamic and effective SMS. Originality/value Data are analysed from a social constructionist perspective and considered through a complexity lens. This approach unpacks these data in an original way to seek synergy with existing adaptive safety approaches, specifically situational self-organising and make recommendations for practice.