BMU or building maintenance units are designed to accommodate façade access where roof rigged or ground rigged systems using davit arms cannot be reached. Building maintenance units are fitted with booms that can span terraces and roofs at lower levels and minimize the need for additional units at lower levels. BMUs are installed on tracks that are installed on the roof during building construction and require power at the roof level. The permanent platform attached the BMUs are parked on the roof. Unlike motorized davit system, BMUs are designed as four point suspension units, which has a higher factor of safety and does not require additional roof anchors for the lifelines. A static life, also known as a dog line, is installed on the stage where workers use for their secondary or lifeline attachment and attach their lanyards.