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.
Not only must the actual exits and exit passages and staircases be considered in respect to rapid flight; but every part of the theatre that must be traversed in order to leave it must be arranged on the same principles. The distance between seats must be such that people can pass readily, and the automatic tipping seat is of great service in this respect. On leaving the seats the gangways must be of ample proportions and should, if possible, be constructed with slopes instead of steps; for the latter, as before pointed out, may lead to much confusion and loss of life. In order that people may quickly reach these gangways from their seats, the number of seats in a single row between gangways should be limited, and in this respect the London County Council's regulations specify that " no seat shall be more than 10 feet from a gangway measured in a line of the seating."
No temporary obstruction must be allowed in any passage or staircase. If a chair or other article of furniture be used in any part which the audience have to traverse on their way out, it should be fixed to the floor, for the danger of any such article loose among a panic-stricken crowd is obvious. In certain cases, as those in which halls are only occasionally used for the purpose of performances, it is difficult to attain the latter requirement; but in any case, rows of chairs must be rigidly battened together.