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The planned conversion of Seattle Metro Transit's bus operation to LNG necessitated modifying bus maintenance garages in order to assure fire-safety in the event of a leak from a vehicular LNG fuel system. The modification approach developed involved characterizing the probable worst-case leak from the bus' on-board LNG fuel system, and assuring that the building's ventilating system would keep the leak diluted to a concentration below the lower flammability limit. Leak dispersion behavior was modeled using computational fluid dynamics (CFD), and by a simple volumetric model suitable for PC spreadsheet. Comparison between the two models indicated that the volumetric model is a reasonably accurate means for estimating ventilation requirements.