A safety curtain (or fire curtain in America) is a fire safety precaution used in large proscenium theatres. It is usually a heavy fiberglass or iron curtain located immediately behind the proscenium arch. Asbestos-based materials were originally used to manufacture the curtain, before the dangers of asbestos were discovered. The safety curtain is sometimes referred to as an iron in British theatres, regardless of the actual construction material.
Occupational safety and health regulations state that the safety curtain must be able to resist fire and thereby prevent (or at least hinder) fires starting on stage from spreading to the auditorium and the rest of the theatre, reducing injuries to audience members and members of staff.
The curtain is extremely heavy and therefore requires its own dedicated operating mechanisms. In an emergency, the stage manager can usually pull a lever backstage which will cause the curtain to fall rapidly into position. Alternatively, heat-sensitive components can be built into the rigging to automatically close this curtain in case of fire and finally it may be released electronically by a buildings fire control system if any alarm box is pulled. It can also be flown in and out, as some regulations often state that it must be shown to the audience, to prove its effective operation, for a certain amount of time during every performance. This usually occurs during the intermission.
In smaller theatres, a safety curtain is not usually required. Specifically, most building codes only require a fire curtain in theatres with a stage height of more than 50 feet. . The heavy, flame-retardant house tabs, can provide some degree of fire separation.
In the UK, it is a requirement that a safety curtain must be fully down within the proscenium opening within 30 seconds of being released. The introduction of such features was prompted by several serious fires, notably that at the Theatre Royal, Exeter in 1887.
The safety curtain can be combined with other safety devices, such as:
Note: due to use of Smoke Doors, and Fire curtains - in the event of a fire, the stage area is effectively turned into a chimney of sorts. The heated air rises and leaves through the smoke doors; this puts the building into negative pressure. This in turn draws fresh air in through any open exit doors. If you are waiting to exit in the audience you will have fresh air to breathe until the exit doors close. The exit doors which open out will be drawn closed tightly by this draft once they are no longer held open by evacuees. However, once the doors are closed, the fire loses its oxygen source. If the doors are then opened again, a backdraft can occur.