u201c w 3 u201d u201c w 3 u201d u03b4 u2033 upper and lower landings 330 and 340 get wider in both first and second widths while upper and lower stair sets 335 and 345 only get wider only in the second width progressively from upper to lower sections the number of steps and hence the length in upper and lower stair sets 335 and 345 remains constant from floor to floor as long as the height of each floor is the same the values for all widths u201c w 1 u201d through u201c w 6 u201d u201c a 1 u201d through u201c a 9 u201d u201c b 1 u201d through u201c b 6 u201d u201c c 1 u201d through u201c c 7 u201d and u201c d 1 u201d through u201c d 2 u201d and all delta 39 s u03b4 u03b4 u2032 and u03b4 u2033 are primarily functions of the number of occupants of each floor and the number of floors in the building the description of the embodiments of the present invention is given above for the understanding of the present invention it will be understood that the invention is not limited to the particular embodiments described herein but is capable of various modifications rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention for example more than one emergency stairwell according to the present invention may be present within the same building further a single emergency stairwell of the present invention need not run through all floors of the building but only through a contiguous subset of the floors still.