This article examines the history of human exposure to silica, the second most common element on earth, to explore the problem of categorizing substances for regulatory purposes and the role interest groups play in developing policy. The regulatory history of silica teaches three important lessons: First, the most compelling account of the cycle of action and inaction on the part of regulators is the one based on interest groups. Second, knowledge about hazards is endogenous - it arises in response to outside events, to regulations, and to interest groups. Accepting particular states of knowledge as definitive is thus a mistake, as is failing to consider the incentives for knowledge production created by regulatory measures. Third, the rise of the trial bar as an interest group means that the problems of silica exposure and similar occupational hazards cannot simply be left to the legal system to resolve through individual tort actions. We suggest that by understanding market forces, regulators can harness the energy of interest groups to create better solutions to addressing the problems of silica exposure, as well as other workplace health and safety issues.