A few years ago we had the opportunity to help flow test 20+ fire hydrants in the 3rd Street Tunnel in Washington, DC. The fire hydrants were unique in their style and operation because they were recessed in the tunnel wall in order to be protected from passing traffic. The fire hydrants are an important safety feature in the tunnel, which runs underground near the United States Capitol Building.
Each wall hydrant was flushed and flow tested and the hydrant caps were spray-painted using the DCFD color-code system for flow.
One of the problems in a tunnel is the dirt and grime that accumulates from vehicle exhaust.
Each of the wall hydrants had a "steamer" outlet and a 2-1/2" outlet.