| Buildings featuring projections
out from the vertical face, such as cornices, ledges, “eyebrows”
or fins, create difficulty for the stage to maintain contact with the
building. These sleeves act as the top side of the sleeve, prohibiting
the wire and its fitting to fall through. Drop thru sleeves, with a four
to one safety factor, must be designed by an engineer capable of analyzing
the sleeve, its attachment to the ledge, and identifying its overall effect
on the cornice. The drop thru concept only works for powered, ground rigged
equipment.
An alternative to the drop thru sleeve is a continuous
monorail track around the building, tucked under the ledge or cornice.
Its circular appearance around the top of the building structure has earned
the nick name of halo track. A pair of monorail trolleys rides the track,
hanging from the rail’s outside face, yet not interfering with the
support tubes. The track and trolley system may support a single manned cage, a powered platform, or occasionally, a non-powered chair. If a long stage is used, one trolley for each stage end is engaged on the monorail. |
