Abstract:
A system for introducing make-up air into a building from above the roof for smoke control includes air shafts extending from the roof into a space in the building below a layer of smoke. The air shafts can be rigid or can be made of a flexible material which folds up when not in use. Air shafts of a flexible material have a contraction at the exit to inflate the shaft, unless the shaft extends to within one diameter from the floor.

Description:
BACKGROUND OF THE INVENTION 
   The state of the art in control of smoke from fire in large-volume spaces is to exhaust smoke at one or several openings in the ceiling and to provide low-velocity air make-up through wall openings near the floor. Under optimum conditions, the smoke accumulates in, and is exhausted from, an upper layer, while a clear layer is maintained above the floor. This facilitates egress of occupants and access to the fire by fire fighters, and limits smoke damage. Often, it is difficult to provide the required wall entry area for make-up air. 
   SUMMARY OF THE INVENTION 
   The present invention allows outside air to enter from openings in the roof without the lower, clear layer being contaminated by smoke entrained from the upper layer. The system of introducing uncontaminated make-up air for smoke control into a building from above the roof uses air shafts from the roof to a level below the smoke interface. The air shafts can be rigid or can be made of a flexible material which folds up when not in use. The operation of a shaft of flexible material is made stable with a slight contraction at the exit of the shaft, which is below the smoke interface and which inflates the shaft in cooperation with incoming air. Alternatively, if the contents of the large-volume space permit the flexible shaft to extend to within one shaft diameter or shaft width from the floor, a ground effect inflates the shaft and allows stable operation. In the latter case, a contraction is not required. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic cross-section of a space employing the system according to the present invention for exhausting smoke from the space; 
       FIG. 2  is a top plan view of the upper boundary of the space of  FIG. 1 ; 
       FIG. 3  is a schematic front elevation of a make-up air shaft according to the present invention in a condition primarily at or near the upper boundary of a space; 
       FIG. 4  is a schematic front elevation of the air shaft of  FIG. 3  in an extended, deployed condition; and 
       FIG. 5  is a schematic front elevation of another embodiment of an air make-up shaft according to the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1 and 2  depict a system according to the present invention for bringing outside air into a smoke-controlled space  12  by using rigid make-up air shafts  14 . As can be seen from  FIG. 2 , ventilators  16 , which can be either powered or buoyancy driven, remove smoke from the space  12  with the help of two of the make-up air shafts  14  that passively admit air from the outside, thereby replacing the flow removed by the ventilators. A fire plume  20  in the space  12  entrains air from the surroundings. Some of the air entrained near the base of the fire is consumed in combustion reactions, while the remainder mixes with combustion products to form smoke, which is deposited in an upper layer  22  by the plume. Air entering through the rigid make-up air shafts  14  is delivered to a lower, clear layer  24  beneath the smoke  22  without entraining any smoke, where the flow first forms a jet entraining clean air, then diffuses throughout the lower, clear layer and is eventually entrained in the fire plume  20 . A stable smoke layer is formed when the air mass removal rate by the ventilators  16  is equal to the air mass entrainment rate by the fire plume  20 . 
   The rigid make-up air shafts  14  extend from an upper boundary  26  of the space  12  to below the design elevation of the smoke interface, which is the boundary between the accumulated upper layer of smoke  22  and the lower, clear layer of air. The design elevation of the smoke interface is determined by factoring the air mass removal rate by the ventilators  16  and the air mass entrainment rate by the fire plume  20 , using known calculations. It is contemplated that the system according to the present invention will often be used in commercial or industrial buildings, e.g., warehouses. In many of these buildings, goods or equipment will take up considerable space, and the lower ends of the make-up air shafts  14  will be above the goods or equipment, for example, at 20 feet above the floor. It is preferable that the lower ends of the make-up air shafts  14  extend well below the layer of smoke. Thus, where the lower ends of the make-up air shafts  14  are 20 feet above the floor, the design elevation of the smoke interface may well be 30 feet above the floor. In most installations, the lower ends of make-up air shafts  14  will be no lower than about 8 to 10 feet above the floor. 
   Although the rigid make-up air shafts  14  allow make-up air to enter the space from the roof rather than through openings in the building walls, they may obstruct normal operations in the building.  FIGS. 3 and 4  depict an alternative make-up air shaft  30 , made of a flexible and fire resistant material, which can be folded until required in a fire, as can be seen in  FIG. 3 . In the folded condition, the shaft  30  can be contained in a ceiling storage compartment (not shown) having, for example, a hinged lid. As an alternative, the shaft  30  can be supported in the folded condition by a movable finger  31 . In either case, on a signal from a fire detector  32 , the folded shaft  30  is released simultaneous with activation of the smoke ventilators  16 . Make-up air unfolds the shaft  30  and inflates it to become an effective conduit of fresh air, as can be appreciated from  FIG. 4 . In order to assure inflation, the outlet of the flexible shaft  30  is provided with a slight contraction, as indicated at  33 . Without the contraction  33 , the pressures within the flexible air conduit would be close to the building pressure. The flexible walls would flap in and out, and stable operation would not be possible. The contraction raises the pressure in the flexible shaft above the building pressure, sufficient to establish a stable inflation of the shaft and a steady delivery of air. 
   The fire detector  32  can be, for example, a smoke detector or a heat detector. In response to the detection of fire, the fire detector  32  can send a signal to the movable finger  31  or other mechanism that normally holds the shaft  33  in its folded condition but in response to the signal releases the shaft for deployment to its extended condition. Although  FIGS. 3 and 4  show the fire detector  32  as being adjacent to the shaft, the fire detector can be located in other positions. 
   The cross section of the shaft  30  must closely match the inlet cross section from the roof, but can be circular, square or rectangular. The roof entry is preferably contoured, e.g., as indicated by dashed curves  34  in  FIG. 4 . Roof openings can be covered with shutter units, opened just prior to activation of the ventilators, and with canopies of low air resistance to protect against weather. 
   A contraction is not required in a flexible shaft if the shaft operates in ground effect, as does the flexible shaft  40  of  FIG. 5 . The ground effect embodiment can be used where the building conditions, e.g., the arrangement or absence of goods and equipment and other factors, are such that the shaft  40  can be allowed to extend to within less than one shaft diameter or shaft width (the smaller dimension of rectangular shaft) of an unobstructed floor  42 . The proximity to the floor  42  raises the pressure within the shaft  40 , and stable inflated operation results. 
   The invention has been described with respect to flow induced by ventilators in ventilation openings in a building to produce an underpressure in the building (relative to the atmospheric pressure). However, as an alternative, the make-up air shafts can be attached to powered roof ventilators blowing air into the building, matching the shaft diameter to the discharge diameter of the ventilator and letting the air exhaust through passive roof vents, which results in a building overpressure. A further alternative is to use power ventilators at both air entry to the shaft and air exhaust through roof vents to manage the building pressure during smoke control. 
   The embodiment illustrated and discussed in this specification is intended only to teach those skilled in the art the best way known to the inventors to make and use the invention. Nothing in this specification should be considered as limiting the scope of the present invention. The above-described embodiments of the invention may be modified or varied, and elements added or omitted, without departing from the invention, as appreciated by those skilled in the art in light of the above teachings. It is therefore to be understood that, within the scope of the claims and their equivalents, the invention may be practiced otherwise than as specifically described.