Barriers to OHS interventions are factors that hinder proper design, implementation and evaluation. An analysis of the barriers is crucial for understanding intervention effectiveness and improving the way in which design, implementation and evaluation of interventions are carried out. However, there is little consensus on how barriers should be understood, how important they are in different contexts, and how they can hinder OHS interventions. This exploratory study based on interviews with 58 safety officers of Small and Medium-sized Enterprises (SMEs) gave an overview of the most frequent barriers to OHS interventions, as well as of the effect of the intervention process phase, of the firm’s size and of the sector. The most frequent barriers underline three main issues: regulation, resources, and information. The barriers are mainly concentrated in the design and implementation phases, and the frequency of barriers grows with the size from micro enterprises to small enterprises, and then it decreases from Small to Medium-large enterprises. The industry sector of companies does not imply meaningful differences among frequencies.