After showing credentials to whoever is in charge (owner, operator or agent), compliance officers may come in promptly, at reasonable hours, to any factory, plant, construction site or other workplace where an employer's employees work, and may inspect and investigate, within reasonable limits and manner and during working hours or other reasonable times, the premises and all relevant conditions, structures, machines, equipment and materials, and may privately question the employer, its agents and its employees. The Supreme Court (Marshall v. Barlow's, 1978) allows an employer to require a warrant; the Act also lets the Secretary compel witnesses and evidence under oath.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.