Fume cupboards or fume hoods were originally manufactured from timber, but in these more modern times, fume cupboards are made from mild steel that are epoxy coated. Fume cupboards or fume hoods are large pieces of scientific equipment, commonly found in chemistry laboratories, and are designed to contain and extract unpleasant fumes and from limiting a persons exposure to them. There are two main types of fume cupboards, ducted and recirculation. With the ducted types of fume cupboards, old asbestos vent pipes have been replaced on health grounds, by polypropylene or PVC. All fume cupboards work on the same principle; air is drawn into the front of the unit and either filtered or fed back into the room, or expelled to the outside of the building by a fan. Fume cupboards are available in a wide range of widths, and can accommodate from one to three operators. Fume cupboards are usually dim inside, and many will have internal lights, and on educational fume cupboards, the sides are usually glass, allowing viewing for several pupils at once.