Medical Gas System Demand and Diversity (NFPA 99)
The first sizing step for an oxygen, medical-air, nitrous, or vacuum main: connected flow = station (outlet/inlet) count x per-station design flow, and the system design flow = connected x a diversity (simultaneous-use) factor that falls as the station count rises. 20 oxygen outlets at 1.0 scfm with diversity 0.25 give a 5.0 scfm design flow; medical-surgical vacuum's higher simultaneous use (0.50) drives a larger design flow per inlet. The per-station flows and diversity factors are read from the adopted NFPA 99 edition and the facility's equipment list (user-supplied here); medical-gas piping is installed and certified by brazing-qualified plumbers and pipefitters (ASSE 6010), and a medical-gas verifier and the AHJ govern. This feeds pipe sizing, not the system design itself.
Formula and source
connected_scfm = stations x per_station_scfm; design_scfm = connected_scfm x diversity, the diversity (simultaneous-use) factor in (0, 1] falling as the station count rises.
NFPA 99 Health Care Facilities Code (medical gas and vacuum systems) demand and diversity, with ASSE 6010 for the installer qualification, by name.
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