I think in principle they COULD fall under the OSHA requirements, but they are exempt from the Executive Order because they also are not part of the executive, but it depends on the wording. USPS is a “business” because they are expected to operate on a revenue neutral basis and they provide a service. FDA, CDC are regulatory agencies that are clearly not businesses (they don’t produce anything or provide any service) so I doubt they would fall under OSHA, ditto for whitehouse, congress, senate. NIH is a gray area; they do perform research (a service) but they do many other purely governmental functions as well.