How to clean the windows of the highest skyscrapers?

Skyscrapers are cleaned using brushes or mop applicators and squeegeed off to remove water and dirt. Skyscrapers under 300 feet can be accessed using a bosun chair. If there are insets, a cleaner may have to do a mid-air transfer to attach to anchorages located inside the inset. For buildings above 300 feet, a swing stage needs to be used per OSHA. Some high skyscrapers are equipped with a BMU (Building Maintenance Unit) which is like a boom lift permanently installed on the roof of the building.