Strongly grounded in scientific knowledge, the instrument known as occupational exposure limits or threshold limit values has changed government modalities of exposure to hazardous chemicals in workplaces, transforming both the substance of the problem at hand and the power dynamics between the actors involved. Some of the characteristics of this instrument favor the interests of industries at the expense of employees, their representatives, and the authorities in charge of regulating these risks. First, this instrument can be analyzed as a boundary object that has very different uses in space and time. In particular, it is increasingly masking its industrial origins to appear as an instrument that is almost exclusively based on scientific rationale. In the case of asbestos and its substitutes, the use of an instrument relying on scientific expertise generates a specific temporality of implementation that allows manufacturers to take advantage of periods during which regulations are either nonexistent or very loose. Finally, the choice of a technoscientific definition of the issues contributes to shifting the negotiations to a field where companies are in a position of strength and their opponents are weakened.