This section is from the book "Modern Buildings, Their Planning, Construction And Equipment Vol6", by G. A. T. Middleton. Also available from Amazon: Modern Buildings.
Having provided ample and direct exits, it is then necessary that their whereabouts and the exact route to be taken in leaving the theatre should be clear and thoroughly indicated by large and well-lighted notices. The lights used for this purpose should form a system entirely distinct from that of the remainder of the theatre, in order to render them less liable to failure in case of fire. It is sometimes required that the exit notices should be illuminated with oil lamps, as these are independent of any one general source of supply. However, if either gas or oil be used for this purpose, the flame should be entirely shut off from the air in the auditorium, and the air supply should come from without by the use of inlet and exhaust pipes, otherwise the draught and smoke produced by a fire may in all probability render them useless.
All doors, not being exit doors, which are not labelled "Refreshment Room," "Cloak Room," etc. must be labelled " No Exit," in order that people may have no hesitation as to the route they are to take.
Separate systems of lights should exist for the stage, for the auditorium, and for the exits and passages, while there should be two complete installations throughout the whole theatre, in order that the theatre may not be left in darkness, which might possibly cause panic. The two installations may consist of electricity and gas, gas and oil, electricity and oil, or electricity supplied by two separate companies. Electricity (incandescent), properly installed, is infinitely the preferable form of lighting, on account of the absence of a naked flame, as well as from the fact that it is unaffected by draught and smoke.