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.
Those parts of the house that are on a level with the ground may have exits leading at once into the street, but others must make use of staircases. It is important that no part of the house shall be at any great height above the pavement Probably the best arrangement will be obtained if the lowest parts of the house are at least as far below street level as the top tier is above it. To go upstairs to the streets is considerably more desirable, in case of panic, than to descend. The press of people in descending a staircase is very liable to cause someone to stumble, and the consequent crushing will ensue.
In order to avoid the danger just mentioned, exit stairs must be as easy in the going as possible, with risers not more than 6 inches high; while winding steps must not be allowed. The stairs should be enclosed with walls, and should in no case be of open construction; they should have hand-rails on either side, while if they are 6 feet or more in width they should be divided in two by a central hand-rail. These hand-rails are of great assistance in preventing persons from stumbling. All unexpected steps are strictly to be avoided, while, on passing through a door, a landing should be met before the staircase begins. There should be no doors leading into the stairs other than that from the auditorium at the top or bottom, and that into the open air at street level. The stairs should be of solid description, and at least sufficiently fire resisting to remain unaffected until every one can be got out of the building. The width of a staircase must naturally be governed by the number of people it has to serve. The London County Council's regulations lay down that, to accommodate not more than 300 people, staircases shall be at least 4 feet wide, while if more than 300 people are to use the staircase it must be 5 feet wide.