Abstract: An enclosed workplace support for temporary, immovable installation below and on each side of a bridge or other existing structure while performing work on bridge substructure. Double rows of upper and lower outriggers are installed to extend outwardly from each lateral side of the bridge and cables are attached to the outer ends of each row of outriggers. Additional cables are attached at opposite ends to bearings or other bridge substructure and extend parallel to the bridge centerline for an entire span. The cables support a high-strength flooring, preferably or rubber-coated chain link fencing. A nylon tarp is laid over the fencing below the bridge and extends around each side, attached to the outrigger cables, and is sealed to the bridge curbs. An exhaust blower maintains the interior of the enclosed workplace at subatmospheric pressure.