The structure and organization of work are continually changing. Changes may be cyclical, reflecting economic and social conditions, including business cycles and labor market structures. Other changes, often resulting from new technologies, may be unidirectional. Whether or not the changes are temporary or permanent, employment arrangements affect worker exposures to workplace hazards and their ability to address them. In this paper, we focus on the effects on occupational safety and health (OSH) of relationships that have been described as fissured or market-mediated, including the staffing agency model, the franchised relationship, same site contracting, supply chain relationships, and contracting by a firm with many individuals. Worker safety may be affected by several factors, including economic pressures on contracted employers, the separation of control of the work environment from the employment relationship, and the short tenure of workers in some dangerous jobs. After summarizing the limited number of studies that attempt to measure the impact of these non-standard employment relationships on worker safety and health, we briefly discuss other changes in the labor market that affect OSH, and then turn to the policy and legal implications of these mediated relationships. Finally, we highlight the need for better data, safety and health surveillance, and research when employment relationships are fissured. The paper focuses on changes and strategies in the U.S. but provides some references to relevant international studies.