Abstract:
A fire door designed to slow the progress of a fire in a dwelling or commercial building. More particularly, a fire door having one or more vertical stiles that include a layer of intumescent material.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application claims priority under 35 U.S.C. §119 and applicable foreign and international law and incorporates in their entirety the following U.S. Provisional Patent Application Ser. No. 60/653,389 filed Feb. 15, 2005. 

   FIELD OF THE INVENTION 
   The present disclosure relates generally to fire doors designed to slow the progress of a fire in a dwelling or commercial building. More particularly, the disclosure relates to a fire door having one or more vertical stiles that include a layer of intumescent material. 
   BACKGROUND 
   The principal means of passive fire protection in structures is by completely enclosing areas with fire barriers. Fire barriers may include fire doors, walls, ceilings, and floors. Fire barriers play an integral role in managing a fire by interrupting the spread of smoke, other toxic gases, and the fire itself from one fire zone into another. Often, the potentially weakest points in a fire barrier are the doors to an area, both because the doors may not be as fire retardant as the walls and ceilings of an enclosure, and also because there generally are cracks under and around the doors through which smoke and toxic gases may pass during a fire. 
   Fire doors generally are specifically constructed to retard the progress of fires in at least two ways. First, the doors are constructed of fire resistant materials such as steel, fiberglass, certain types of particle board, or diatomaceous earth, among others. Second, fire doors may include one or more regions of intumescent material that expands when heated, minimizing or eliminating cracks in and around the door. 
   A number of standard tests of fire door effectiveness have been developed for use in the building industry. These are published, for example, in the Uniform Building Code (UBC), the International Building Code (IBC), and by the National Fire Protection Association (NFPA), Underwriter&#39;s Laboratories (UL), and the American Society for Testing and Materials (ASTM), among others. Various agencies test fire doors using these standard tests, and assign ratings to fire doors that indicate their effectiveness at slowing the progress of a fire. Door testing agencies include Intertek Testing Services (USA), Underwriter&#39;s Laboratories (USA), Omega Point Laboratories (USA), Chiltern International Fire, Ltd. (UK), and Warrington Fire Research (UK), among others. Ratings of fire doors are generally provided in minutes, and typically vary from 45 minutes to 120 minutes. 
   Disclosures of fire doors are found in U.S. Pat. Nos. 6,115,976 and 6.643,991. The disclosures of each of these documents are incorporated herein by reference. The advantages of the fire door and fire door components provided in this disclosure will be understood more readily after considering the drawings and the detailed description of the preferred examples. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a fire door shown mounted in a doorway and with sections of an outer surface cut away to show the internal structure of the door, according to aspects of this disclosure. 
       FIG. 2  is a partial sectional view of the lower right corner of the door of  FIG. 1 , showing details of the construction of the door. 
   

   DETAILED DESCRIPTION 
   Referring to  FIG. 1 , a fire door is generally indicated at  10 . Door  10  may include core  12 , top and bottom rails  14   a  and  14   b , and a pair of stiles  16   a  and  16   b . The overall dimensions of door  10 , including its width (the transverse dimension in  FIG. 1 ), height from top to bottom, and thickness, may be chosen as desired to fit any particular doorway and to achieve a desired fire rating. 
   Core  12  is generally substantially rectangular, although other core shapes are within the scope of this disclosure, such as oval, circular, or semicircular cores. As shown in  FIGS. 1 and 2 , core  12  has front and back planar faces generally parallel to the surrounding wall structure. The core has a known and predetermined density, and a thickness selected, in consideration of the overall weight of the door, to retard the progress of a fire for a desired amount of time corresponding to a particular fire rating. For example, a core with a 60 minute rating may have a density of approximately 18 pounds per cubic foot (pcf), and may have a thickness of approximately 1.675 inches. In general, the core may be formed from any suitable mineral or mineral composite material, with density at least approximately 15 pcf. An example of a suitable core for a door with a 60 minute rating is a Thermal Lite core manufactured by Warm Springs Composite Products of Warm Springs, Oreg. 
   Rails  14   a  and  14   b  may be constructed from any suitable fire resistant material, for example a mineral or mineral-based material or composite material. The material forming the rails may be chosen to have density and thickness sufficient to achieve any desired fire rating. For example, the rails may have density in the range from 61-72 pcf and thickness of approximately 2.125 inches for a door with a 60 minute rating. Similarly, the rails may be constructed with any desired height to achieve a particular rating. For example, the rails may be at least approximately 2 inches in height for a 60 minute door. The rails may be formed of a proprietary material such as Tectonite, produced by Warm Springs Composite Products of Warm Springs, Oreg., and in general may have thicknesses in the range of 0.5-2.125 inches. The thickness of the rails may be chosen to approximately match the thickness of core  12  and/or other components of the fire door. 
   Referring now to  FIG. 2 , stile  16   a  may include two layers  18 ,  22  of fire resistant particle board, and a layer of intumescent material  20  sandwiched between the two particle board layers. For some applications, it may be possible to achieve desired fire ratings with conventional fiber board such as MDF (medium density fiberboard) in place or instead of fire resistant layers  18  and  22 . Stile  16   b  (not shown in  FIG. 2 ) may be similarly constructed. The fire resistant particle board may be constructed from any fire resistant material, such as monoammonium phosphate or monopotassium phosphate, among others. In some embodiments, the particle board layers each may be approximately 10-12 millimeters wide and may have thickness chosen to approximately match the thickness of the core and/or rails of the fire door. An example of suitable particle boards for a door with a 60 minute fire rating are 11 mm wide particle boards manufactured by the Spano Corporation of Oostrozebeke, Belgium. Alternatively, acceptable performance for some applications may be achieved using medium density fiberboard. 
   As shown in  FIG. 2 , axis A extends through core  12 , perpendicular to edge  26  of door  10 , and parallel to rail  14   b  of door  10 . Cross-section of stile  16   a  includes a series of layers stacked in the direction of axis A going from core  12  toward edge  26  including (a) fire-resistant particle board  18 , (b) intumescent layer  20 , (c) fire-resistant particle board  22 , and (d) wood layer  24 . Wood layer  24  should be selected to have a density and thickness sufficient to achieve a desired fire rating from 45 minutes to 120 minutes. 
   Intumescent layer  20  is formed of a material such as sodium silicate that expands upon reaching a certain temperature. This causes the fire door to expand and thereby reduces the size of cracks and other gaps around the door through which heat, smoke, and toxic gases may pass during a fire. An example of a suitable intumescent material is Palusol 100, manufactured by the BASF AG Corporation of Ludwigshafen, Germany. Layer  20  may have any suitable width, and in particular it may have width in the range of 1.7-1.9 millimeters, or approximately 0.07 inches, in some embodiments. Layer  20  also may have any suitable thickness, and in particular may have a thickness chosen to approximately match the thickness of surrounding particle board layers  18  and  22 . In some embodiments, layer  20  may have a thickness substantially less than the thickness of the surrounding particle board layers, if the thickness of layer  20  is sufficient to cause the desired expansion of the fire door when the door is heated. 
   One or both of stiles  16   a  and  16   b  further may include a wood layer adjacent to one of the layers of fire resistant particle board. For example,  FIG. 2  shows wood layer  24  adjacent to particle board layer  22  of stile  16   a , such that wood layer  24  forms an external edge  26  of the fire door. Similarly, a wood layer (not shown) may be included in stile  16   b  such that it forms an external edge of the door opposite to edge  26 . The wood layers may be formed of any suitable wood, selected to have density and thickness to maintain a certain desired fire rating of door  10 . For example, layer  24  may be constructed substantially of hemlock, fir, maple, oak, or a combination of those materials, and may be approximately ½ inch wide. The thickness of the wood layers such as layer  24  may be chosen to approximately match the thickness of the core and/or other portions of the fire door, such as particle board layers  18  and  22  of the stile. 
   Door  10  may be finished with an outer layer  28  of wood and/or other suitable materials as desired, for decorative purposes or to increase the fire retarding or other properties of the door. For example, wood paneling may be used as an outer layer if the fire door is intended for indoor use in an office setting or in a dwelling, and metal sheeting may be used as an outer layer if the door is intended for outdoor or industrial use. 
   While the present description has been provided with reference to the foregoing embodiments, those skilled in the art will understand that many variations may be made therein without departing from the spirit and scope defined in the following claims. The description should be understood to include all novel and non-obvious combinations of elements described herein, and claims may be presented in this or a later application to any novel and non-obvious combination of these elements. The foregoing embodiments are illustrative, and no single feature or element is essential to all possible combinations that may be claimed in this or a later application. Where the claims recite “a” or “a first” element or the equivalent thereof, such claims should be understood to include incorporation of one or more such elements, neither requiring, nor excluding, two or more such elements.