All scaffolds, hoist cranes, stays, ladders, supports, or other mechanical contrivances erected by any person for use in the erection, repairing, alteration, removing, or painting of any building, bridge, viaduct, or other structure shall be constructed, placed, and operated so as to give proper and adequate protection to any person employed or engaged thereon or passing under or by it, and in such a manner as to prevent the falling of any material that may be used or deposited thereon.