You are close Mike. Although the handrails were hollow tubing, they didn't carry any air. The feet of the uprights were bolted to the concrete pavement, which was cast with a slot in the kerb face which connected to the fresh air duct below. If you were standing on the pavement, fresh air would be coming in just below your feet. Foul air drawn off from the roof at the various ventilation stations. Hope this helps.
