A Safety Curtain would have most likely to have been a requirement under the conditions of licence issued under the Theatres Act. Although all fire safety provisions are now controlled by the Regulatory Reform Fire safety order it is understood the previously issued licensing conditions that where applied are still applicable.
The conditions of licence would also have stated that the safety curtain should be lowered at least once before or during every performance.
It would be worth checking if a copy of the Licensing Conditions is still available at the theatre.
The safety curtain was normally accompanied by a proscenium arch sprinkler or sparge pipe, to cool the safety curtain in the event of a fire and also an automatically opening stage vent know as a haystack lantern light would have been provided.
Again these were usually part of the conditions of licence and maintenance and testing were usually detailed.
Guidance on theatres can be found in the following documents.
Technical Standards for Places of Entertainment 2013
Produced by The association of British Theatre Technicians and others
5 free access of this guide can be viewed on line at the following link.
http://www.technical-standards-for-places-of-entertainment.co.uk/This guide states that a stage without a safety curtain is known as an Open Stage and the requirement would be that the stage is separated from the rest of the premises (e.g. dressing rooms, scenery stores etc by fire resisting construction.
A further guide entitled
Theatre Buildings: a design guide dated 2010 produced by the Association of British Theatre Technicians;
States that a safety curtain is not mandatory in the UK however this guide is mainly aimed at new theatres. It does state that a fire engineered solution as apposed to code based design may give a design advantages which may include the removal of the traditional safety curtain.
