Bilco automatic smoke vent s-20sv, single leaf, galvanized steel, 30″l x 36″w automatic smoke vents aid firefighters in bringing a fire under control by removing smoke, heat and gasses from a burning building. Type sv single leaf smoke vents are ideal for applications requiring smaller vent areas, such as elevator shafts or stair wells ideal for venting small areas like stairwells or elevator shafts fusible link activated.