Which agency is NOT involved in regulating radiation exposure of workers in the US?

The Federal Aviation Administration (FAA) is primarily focused on regulating civil aviation, including aspects like air traffic control, aircraft safety, and pilot certification. While the FAA does involve itself in issues related to radiation, particularly in the context of flight safety and radiation exposure for pilots and crew due to cosmic radiation, it is not directly responsible for regulating radiation exposure in the workplace.

In contrast, the Occupational Safety and Health Administration (OSHA) sets and enforces standards to ensure safe working conditions, including regulations around exposure to hazardous materials, multi-faceted including radiation. The Nuclear Regulatory Commission (NRC) oversees the use of radioactive materials and enforces regulations concerning radiation safety and exposure specifically within the nuclear industry. The Environmental Protection Agency (EPA) also plays a role in protecting human health and the environment by regulating pollutants, including those that involve radiation exposure.

Thus, the FAA's focus on aviation safety rather than direct regulation of workplace radiation exposure makes it the appropriate choice for an agency not involved in this specific area of regulation.