Medical Gas System Demand and Diversity (NFPA 99)

The first sizing step for an oxygen, medical-air, nitrous, or vacuum main.

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Checked against published worked examples from: Oregon Building Codes Division.

Details, formula, and sources

ScopeConnected 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 or tableconnected_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.

Source and editionNFPA 99 Health Care Facilities Code (medical gas and vacuum systems) demand and diversity, with ASSE 6010 for the installer qualification, by name.

Free accessThe connected-times-diversity demand relation is the NFPA 99 sizing method; the per-station flows and diversity factors are read from the adopted edition and the facility equipment list.

What governsEstimate. AHJ and licensed professional govern.

API field namesstations, per_station_scfm, diversity, connected_scfm, design_scfm

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