All scaffolds, hoists, cranes, stays, ladders, supports or other mechanical contrivances used in the erection, repairing, alteration, removal or painting of any house, building, bridge, viaduct or other structure, shall be erected and constructed in a safe, suitable and proper manner. Scaffolding or staging, swung or suspended from an overhead support and more than twenty feet from the ground floor, shall have, where practicable, a safety rail properly bolted, secured and braced, rising at least thirty-four inches above the floor or main portion of such scaffolding or staging, and extending along the entire length of the outside and ends thereof and properly attached thereto, and such scaffolding and staging shall be so fastened as to prevent the same from swaying from the building or structure.