Special applications require special fume hoods. Radioisotope Hoods have stainless steel one-piece liners. Perchloric acid hoods have washdown systems and either stainless steel or PVC liners to withstand acid exposure. Acid digestion hoods have PVC liners and Lexan sashes to resist etching by hydrofluoric acid. Floor-mounted hoods accommodate oversize apparatus. Pass-through hoods allow access from both sides and may be installed in the wall between two rooms.