a preferred embodiment which has been selected to illustrate the invention comprises a plurality of prefabricated modules or units which are preferably formed of fire resistant , light weight reinforced concrete . the units are joined together by combining steel members which are inserted and anchored into adjoining areas of the units when the units are formed . the units comprise two separate types , upper and lower , which are referred to for convenience as type a and type b . each floor of the building has two complemental , confronting identical upper a units stacked on top of two lower oppositely facing identical lower b units the four units constituting a set . it is also feasible for the total set to comprise one , two , three or more than four units per floor height . at the connection joints the configuration of units a and b is identical and they are therefore interchangeable with each other . each upper type a unit , which is shown in fig2 of the drawings , has adjacent one corner thereof the lower half 10 of an opening which is provided in one side wall 11 thereof for an exit door plus frame ( not shown ). adjacent thereto is a level horizontal entrance platform 12 , the inner end of which leads to an entrance 13 . extending horizontally across the vertical portion of the entrance 13 is a handle or grab bar 14 which requires a user to assume a seated position before entering the adjacent acceleration ramp 15 which adjoins the platform 12 at the entrance 13 . the acceleration ramp 15 slopes sharply downwardly at a steeper angle than the helical upper ramp portion or slope 16 to which it is connected at its opposite end . the purpose of this is to provide an &# 34 ; on &# 34 ; ramp which accelerates the speed of persons entering to approximately equal that of those already on the helical slopes . the helical slope 16 is tapered and cantilevered inwardly from the adjacent vertical shaft walls 17 of the unit . a closed triangular smokestack 18 is provided in the corner of the unit a to act as a combined smokestack and shoe drop . in the interior wall of the triangular smokestack 18 is an opening 19 ( fig4 and 5 ) to receive an exhaust fan to remove smoke that penetrates into the structure . in case the structure is pressurized the opening can be used for a blower and stack 18 becomes the supply air duct . each lower unit type b , which is shown in fig3 of the drawings , has adjacent one corner thereof the upper half 20 of an opening for the upper part of the frame of an exit door ( not shown ) which is provided in one side wall 21 thereof . the unit b has in one corner thereof a triangular smokestack 22 . in case the structure is pressurized the opening can be used for a blower and stack 22 becomes a supply air duct . each unit b has a semicircular lower ramp portion of a helical slope 24 which is tapered and cantilevered inwardly from the shaft wall 25 . the portion of the wall 25 disposed beneath its helical slope 24 is cut away at 26 to provide head room 26 ( fig5 ) above the other entrance 13 to the helical slope to another unit a therebeneath . the inner edges of the helical slopes 16 and 24 of units a and b are semi - circular when viewed from above , defining a hollow core adapted to mount boundary means in the form of a central circular smokestack 30 , which may be formed of a plurality of vertically extending sections attached together at their ends as shown in fig5 of the drawings . the smokestack 30 is provided with one or more openings 31 on each floor adjacent to which is a suction cap 31a to enhance the exhaustion of smoke upon upward movement of forced air through the smokestack 30 and away from the helical slides formed by the joined helical slopes 16 and 24 . all of the helical slopes are preferably treated with enamel paint to provide a smooth surface . the adjacent vertical shaft walls and the exterior of the smokestack 30 are preferably painted in the same manner . the suction caps 31a may be omitted , if desired , but whether or not caps 31a are used , there are fans disposed inside the smokestack 30 at spaced intervals along the total height to force the air flow . the smokestack 30 would then function as an air supply duct to pressurize the total escape structure , to prevent the penetration of smoke into the escape structure . one lower corner of each unit a is provided with a downwardly directed projection 35 which supports the helical slope above it and which is adapted to fit within a downwardly directed recess 36 formed in one upper corner of the unit b therebeneath . each unit b also has downwardly directed projection 37 which is adapted to fit within a recess 38 formed in an upper corner of the unit a therebeneath . the upper and lower units a and b are thereby interengaged with each other when arranged vertically . both of the units a and b are provided at their adjoining vertical edges with continuous structural angle irons 40 and tees 41 which are anchored with studs 42 in the concrete . angle iron 40b ( fig3 and 10 ) is a continuous structural angle in the upper perimeter of unit b . all the angle irons 40 and 40a and 40b and tees 41 of the respective units are anchored in the concrete and are welded to each other as shown in fig1 and 11 . they are also welded to u - shaped horizontal frame members 43 and to h - shaped vertical supporting frame members 44 as shown in fig1 , 5 , and 9 . as shown in detail fig9 the combined or superposed sets of units are located in a vertically oriented shaft generally defined by the channels 43 and the h - frames 44 to which the channels 44 are welded . the frames 44 comprise supporting columns in general , or columns of the building if the structure is incorporated in the building at the time it is originally built . instead of being welded the members may be bolted , riveted or otherwise suitably connected . as shown in fig1 of the drawings , the concrete joints where the slopes of the units abut are preferably filled with suitable sealant 47 . as shown in fig4 the central smokestack 30 is provided with a water supply line 48 which is connected to an adjacent sprinkler head 49 and through a plurality of pipes 50 to additional sprinkler heads 49 at various levels adjacent both helical slopes . the sprinklers supply water to both slides . control circuits may be provided for automatic operation of the sprinkler system on all floors upon opening of any fire exit door . each of the helical slopes 16 and 24 is provided with a pair of vertically directed welding plates 51 which are anchored in the concrete and which are fastened to the adjacent portions of the central circular smokestack 30 to support it . the triangular smokestack formed by the sections 22 of units b are provided with a shoe drop opening 23 on each floor . the opening is preferably covered with a hinged flap door and enclosed with a smash glass protector on its exterior surface . the shoes drop into a space at the ground floor level where they may be retrieved through a suitable opening 70 , which may comprise a manhole with a metal closure plate , after the emergency period . with reference to fig1 , in the event that the foregoing escape structure is to be pressurized , as previously mentioned in connection with the description of the triangular smokestacks , the central circular smokestack 30 and its associate openings 31 would be designed for use as an air duct to effect such pressurization . in addition , the triangular smokestacks 18 and 22 in the two corners of the unit would be fitted with access elevators to enable firemen and necessary equipment to be transported to any floor and to permit occupants on any floor to escape . auxiliary doors 18b would be provided on all floor levels to afford firemen access to all floor levels from the elevator side of the doors 18b . fig6 and 8 show modified untis which are used at ground level . they are essentially similar to the units b which are used on the floors above ground level . each of the helical slides terminates in a transition slope 60 followed by a terminal section 61 which is straight and slopes slightly upwardly at the end to slow the descent to a halt prior to leaving the slope . the ground unit is provided with a concrete plate 62 and support angle 63 for supporting the central smokestack 30 . an opening 64 in the plate 62 may be provided at the bottom of the smokestack 30 for air intake and an exhaust blower . a metal closure plate 71 is disposed between a wall 72 and the smokestack 30 . the bottom unit 66 and the modified unit b ( 65 ) directly above are provided with a recess 67 to fit a frame for the ground floor exit door . this door opens also automatically by opening exit door on any floor ( this simultaneous with activating the sprinkler system ). each entrance to the slope 13 may be controlled by an electric eye 68 and a buzzer signal system to signal the user the proper time for entering the helical slides . it would be possible to make sectional precast escape units of the type shown and described without exterior walls , if desired . various modifications and changes may be made with regard to the foregoing detailed description without departing from the spirit of the invention .
a double helical earthquake and fire escape structure for multiple story buildings formed mainly of a plurality of prefabricated section of precast concrete . two identically formed upper sectional units and two identically formed lower units are arranged in facing relationship to each other for each floor of the building . complementary portions of the assembled units combine to form a pair of oppositely disposed entrances on each floor leading to two separate helical slides arranged about a separately formed central circular smokestack . the units are provided with steel members adjacent their edges which are connected together and secured to a surrounding supporting steel framework . two additional smokestacks formed within the corners of the assembled units may also be used as shoe drops .