This is a fire safety device that is installed in many proscenium theatres. Code requires a fire curtain if the stage house is greater than 50'-0" from finished floor to the underside of the roof or the next floor above the stage. Its major purpose is to create a flame retardant barrier between the audience and the stage that prevents smoke and fumes from entering the auditorium space. They take several hours to burn through their specialty fabrics, providing for a larger window of opportunity to evacuate patrons and staff, and for firefighters to extinguish / control a fire. Previously made of asbestos woven fibers, today are of a fiberglass material, the most popular of which is Zetex. Fire curtains may be manually or motor operated to raise and lower them for inspection / operation / maintenance. For emergency operation in the event of a fire, there are several methods of releasing the curtain. One required method is fusible links in the release line system. At a specific temperature, this link separates, allowing the curtain to lower itself. Other methods are the manual release of the line by release pins or rings, severing the rope with a knife or hatchet. Additional means of release can be activated by electro-mechanical means through the building alarm system. At no time is the path of a fire curtain to be obstructed by sets, lighting instruments, cables, etc. This would impede the proper operation of the device, causing great potential hazard. Code requires the curtain to be tested in the emergency mode every 90 days and record and document the test. This is to detect any possible malfunctions and ensure its proper functionality. In the UK, the fire curtain is made of metal, and thus is often referred to as "the iron." [Possible myth, but still a good story]: UK regulations state that the operation of the fire curtain be demonstrated to each audience. Therefore, the iron is down while the audience enters, and is raised just prior to the performance. See this thread http://www.controlbooth.com/forums/f...-question.html for discussion of proper procedures.