Companies increasingly operate as parts of regional or international networks. This trend in business has resulted in work sites where several employers’ staffs operate simultaneously. To improve mutual occupational safety at shared industrial work sites, a nation-wide procedure called occupational safety card (OSC) training has been developed in Finland. All interested groups have been actively involved in the development of this model. This article describes the process throughout which the OSC model was developed. Research and development (R & D) at a university and within industry started 10 years ago, and was based on both practical and experiential needs and literature. This document presents the first analysis of how the frequency of accidents at work varied during the years of implementation at the work sites of the early adopters of the OSC. This article also contains an evaluation of the effects of OSC implementation on the safety management system.