Each of the circuits in the U.S. Court of Appeals is a semi-autonomous region of the federal judicial system. There is no requirement, constitutional or otherwise, that they agree on everything.
The Fifth Circuit, covering Texas, Louisiana, and Mississippi, has long been an outlier on the question of “controlling employer” (typically a general contractor or construction manager) responsibility for OSHA compliance with regard to employees of separate employers (typically subcontractors or trade contractors) at multi-employer construction sites. The Fifth Circuit has held that a contractor could not be cited for OSHA violations that affected only employees of other contractors.
There is a limit to the autonomy of the appellate circuits, however. A superseding ruling of the U.S. Supreme Court can mandate uniformity. On this subject, the Supreme Court now requires judicial deference to reasonable agency interpretation of ambiguous statutes, which compelled the Fifth Circuit to revisit its “separate employer” rule. It has now joined the mainstream and holds employers with control of the worksite responsible for OSHA violations affecting the employees of other employers at the worksite, not just its own employees.
This issue also covers a differing site conditions decision from the Armed Services Board. A design-build contract does not shift the risk of differing site conditions to the contractor. The same Differing Site Conditions clause is used on all fixed-price contracts. The effect is the same as with traditional design-bid-build contracting.