STATEMENT OF GOVERNMENT INTEREST 
   The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefore. 


   FIELD OF THE INVENTION 
   The present invention relates generally to an apparatus for sealing a doorway, more particularly, the present invention relates to a gasket structure capable of sealing a doorway against the entry of water, smoke, and fire. 
   BACKGROUND OF THE INVENTION 
   U.S. Navy watertight arrangements are utilized in watertight boundaries where personnel egress through bulkheads is needed but watertight integrity must be maintained. The sealing mechanism of standard watertight door arrangements comprise a series of dogs sliding across ramped wedges, which are connected to the door panel. The sliding of the dogs across the wedges pulls the panels into a knife edge associated with the door. Navy protocol requires that the knife edge must compress the gasket to one-eight of an inch in order for the door system to be deemed watertight. 
   Until the 1990s, the Navy used primarily three types of gaskets in watertight arrangements: Military Specification Mil-R-900 (rubber gasket material); Federal Specification ZZ-R-765 (silicone rubber, Class 2b Grade 40); and, Military Specification Mil-G-17927 (gaskets, glass-metallic cover with silicone core). The Military Specification Mil-R-900 gaskets were designed with a generally rectangular cross section in which two edges were chamfered. These gaskets had a high durometer rating, requiring excessive dogging forces needed to correctly seal the door. These high dogging forces resulted in accelerated wear on watertight door components, requiring extensive adjustment and replacement of door components such as wedges and linkage bearings. Additionally, these gaskets were difficult to install and even more difficult to remove. 
   The type ZZ-R-765 gaskets were typically used in watertight doors in missile blast areas. The ZZ-R-765 gaskets were also designed with a generally rectangular cross section in which two edges were chamfered. These gaskets had a generally low durometer rating, and were mid-range with respect to costs. For watertight applications, the ZZ-R-765 gaskets were relatively easy to install and remove. 
   The type Mil-G-17927 gaskets had a silicone core and two additional layers of glass metallic-cloth, topped by a silicone rubber coating. The Mil-G-17927 gaskets had a generally rectangular cross section. These gaskets had a high durometer rating and were extremely expensive to procure. 
   If fire and smoke protection are required in addition to water protection, then the gaskets must be able to withstand temperatures of about 2000 degrees Fahrenheit and maintain their fire, smoke, and water sealing integrity. Of the three gaskets types named above, the ZZ-R-765 Class 2B Grade 40 performed best, however there was still a need for improvement. In light of this need, a new watertight door gasket, outlined in U.S. Pat. No. 5,553,871, was developed using Federal Specification ZZ-R-765 as the material requirement. Eventually, this Federal Specification became obsolete and was replaced by Commercial Item Description A-A-59588. This new gasket had an altered profile with a generally rectangular cross section with chamfered edges, and a semi-circular cut-out portion along a surface. This design allowed for easier dogging of watertight door panels and improved fire and smoke protection. However, this gasket design still failed to properly seal exits when exposed to fires of about 1,500 to 2,000 degrees Fahrenheit for prolonged periods of time. Consequently, there is still a need for a seal with a design that protects against the entry of fire, smoke, and water, especially when exposed to fires of from about 1,500 degrees Fahrenheit to 2,000 degrees Fahrenheit and higher. 
   SUMMARY OF THE INVENTION 
   The present invention addresses aspects of problems outlined above. Preferred embodiments of the present invention provide an apparatus for sealing a doorway against the entry of water, smoke, and fire. 
   In one aspect, the invention is a gasket with an elongated silicone rubber member having a ridged rectangular cross-section for mounting to a gasket retainer and a door frame. The ridged rectangular cross-section has a back side with a first end and a second end and a front side with a first end and a second end. The ridged rectangular cross-section also has a first side extending from the first end of the back side to the first end of the front side and a second side extending from the second end of the back side to the second end of the front end. The ridged rectangular cross section further has a ridged portion protruding from the front side, wherein the back side, the front side, the first side, and the second side are for contacting inner walls of the gasket retainer. The ridged portion is for contacting a knife edge of the door frame. In this aspect, the gasket further includes an elongated crush zone within the elongated silicone rubber member formed substantially adjacent to the ridged portion of the elongated silicone rubber member. 
   In another aspect, the invention is an all-purpose sealing arrangement. The sealing arrangement includes a door frame, a door panel attached to the door frame, and a gasket pressing member. The gasket pressing member has a knife edge, and is attached to the door frame. In this aspect, the invention further includes a gasket retainer attached to the door panel, the gasket retainer having a substantially rectangular channel. A wedge is attached to a back side of the door panel and a dogging structure is attached to the door frame for applying a force on the gasket via the wedge. In accordance with this invention, the gasket comprises an elongated silicone rubber member having a ridged rectangular cross-section for mounting to the gasket channel. The ridged rectangular cross-section of the gasket has a back side with a first end and a second end and a front side with a first end and a second end. The ridged cross-section also has a first side extending from the first end of the back side to the first end of the front side, and a second side extending from the second end of the back side to the second end of the front end. The ridged rectangular cross section further includes a ridged portion protruding from the front side, wherein the back side, the front side, the first side, and the second side contact the gasket channel. The ridged portion contacts the knife edge of the pressing member. In this aspect, the all purpose sealing arrangement includes an elongated crush zone within the elongated silicone rubber member formed substantially adjacent to the ridged portion of the elongated silicone rubber member. The arrangement further includes an elongated intumescent section within the elongated silicone rubber member formed substantially adjacent to the back side of the elongated silicone rubber member. 


   
     BRIEF DESCRIPTION OF DRAWINGS 
     A more complete appreciation of the invention and many of its attendant advantages will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing wherein: 
       FIG. 1A  is a sectional view of a gasket in accordance with an embodiment of the present invention; 
       FIG. 1B  is a sectional view of a gasket in accordance with an embodiment of the present invention; 
       FIG. 2A  is a perspective view of a general sealing arrangement in accordance with an embodiment of the present invention; 
       FIG. 2B  is a perspective view of an all purpose sealing arrangement in accordance with an embodiment of the present invention; 
       FIG. 2C  is a perspective enlarged view of the all purpose sealing arrangement illustrated in  FIG. 2B . 
   


   DETAILED DESCRIPTION 
     FIG. 1A  illustrates a sectional view of a gasket  100  in accordance with an embodiment of the present invention. The gasket is used to create an all purpose seal at a doorway that facilitates egress through bulkheads. As shown in  FIG. 1A  the gasket  100  has a ridged rectangular cross section.  FIG. 1A  also shows the gasket  100  having a back side  110  with a first end shown generally at  112  and a second end shown generally at  114 . The ridged rectangular cross section of the gasket  100  further includes a front side  120  having a first end shown generally at  122  and a second end shown generally at  124 . 
   A ridged portion  150  protrudes from the front side  120 , forming a ridge-like protrusion. As shown in  FIG. 1A , the ridged portion  150  protrudes from the front side  120 , protruding at locations corresponding to a first corner portion  156  and at a second corner portion  158 . The protrusion at the first corner portion  156  extends to a first end  152  of the ridged portion  150 . The protrusion at the second corner portion  158  extends to a second end  154  of the ridged portion  150 . 
   The gasket  100  primarily comprises silicone rubber, preferably of a Commercial Item Description A-A-59588 type. The A-A-59588 is preferably class 3B, grade 30, but may also be of other A-A-59588 silicone rubber classes and grades. The gasket  100  also includes a crush zone  160  within the silicone rubber body. The crush zone is the region immediately surrounding an air pocket  165  within the silicone rubber body. The crush zone is located adjacent to a surface  155  of the ridged portion  150 . The air pocket enables the crush zone to collapse inwards in a predetermined manner to form a proper sealing relationship when placed in a gasket channel. Alternatively, the air pocket may be replaced by a material that is significantly less rigid than the surrounding silicone material, creating a crush zone around that material. This softer material would also enable a predetermined inward collapse upon the application of pressure. 
   The gasket  100  also includes an intumescent section  170  adjacent to the back side  110 . The intumescent section  170  comprises intumescent material, which expands upon exposure to escalated temperatures. The intumescent material may comprise any known intumescent chemical, such as intercalated graphite, mica, perlite, vermiculite, hydrated sodium silicate, and phosphorus, or combinations thereof. The intumescent material may be chosen depending on the environmental conditions and the required amount of expansion. If fire-zone sealing is not required, the intumescent section  170  may be omitted. 
     FIG. 1B  illustrates the gasket  100  and possible dimensions for the device. As shown in  FIG. 1B , the back side  110  has a length of a. The first side  130  and the second side  140  each have a length of b. As shown in  FIG. 1B , the ridged portion  150  protrudes from the front side by a distance of c. The distance from the first end  122  of the front side to the first corner portion  156  is d. The distance from the second end  124  of the front side to the second corner portion  158  is e.  FIG. 1B  also illustrates the first and second ends  112 ,  114  of the back side and the second end  124  of the front side having rounded edges, each edge having a radius of curvature of R x . The first end  122  of the front side, the first and second ends  152 ,  154  of the ridged portion, and the first and second corner portions  156 ,  158  of the ridged portion, all have rounded edges with a radius of curvature of R y . 
   Lengths, distances, and radii of curvature a, b, c, d, e, R x  and R y  may vary according to specific applications. According to one embodiment, the length of the back side a may be about 1.25 inches. The length b of the first and second sides  130 ,  140  may each be about 0.50 inches. The amount of protrusion c that the ridged portion  150  protrudes from the front side  122  may be about 0.1875 inches. The distance d from the first end of the front side  122  to the first corner portion  156  may be about 0.25 inches. The distance e from the second end of the front side  124  to the second corner portion  158  may be about 0.375 inches. According to this embodiment, the radius of curvature R x  of the first and second ends may be about 0.125 inches, and the radius of curvature of the remaining rounded edges R y  may be about 0.0625 inches. The dimensional measurements of this embodiment are especially suited for a particular sealing arrangement as illustrated in  FIGS. 2A ,  2 B, and  2 C. 
     FIG. 2A  is a perspective view of an all purpose sealing arrangement  200  in accordance with an embodiment of the present invention. The all purpose sealing arrangement has a door frame  210  and a door  220  attached to the frame  210  via an attaching means  230 . Preferably, the attaching means  230  is a hinge, allowing the door  220  to pivot with respect to the frame  210 . The door  220  may comprise a hollow panel filled with a heat insulating material that reduces heat transfer from one side of the door panel to the other during a fire. A gasket retainer  240  with a channel is attached to the door  210  at a peripheral location around the outer circumference of the door  220 . The gasket  100  is mounted within the inner walls of the gasket channel. Dogging structures  250  are provided on the frame  210  for slidably forcing the gasket  100  into the gasket channel  240 . 
     FIG. 2B  is a more detailed illustration of the all purpose sealing arrangement  200  in accordance with an embodiment of the present invention.  FIG. 2B  shows the door in a closed locked position. The arrangement  200  includes the door panel  222  mounted to the frame  210 . As shown in  FIG. 2B , the arrangement  200  includes bearings  215  for providing movement between elements. A wedge  265  is mounted at the back of the door panel  222 .  FIG. 2B  shows dogs  255  of the dogging structure  250 , pushing down on the wedge  265 . The gasket retainer  240  is mounted to the door panel  222 , with the gasket  100  mounted within the inner walls of the gasket channel of the retainer. A knife edge  275  of a pressing member  270  presses against the gasket  100 . In the all purpose sealing arrangement, the dogging structure  250  and the knife edge  275  apply forces in substantially opposite directions, sandwiching the gasket  100 , the door panel  222 , and the wedge  265 . 
     FIG. 2C  is a perspective enlarged view of the all purpose sealing arrangement illustrated in  FIG. 2B . The enlarged view shows the gasket retainer  240  having a channel, with the gasket  100  mating with the walls of the channel. As shown, the gasket retainer  240  includes a first hook portion  242  and a second hook portion  244  which mates with first and second portions of the front side of the gasket  100 . The first and second hook portions may have length substantially equal to the first and second portions of the front side, respectively. The ridged portion  150  of the gasket protrudes between an opening formed between the first and second hook portions  242  and  244 . In the sealed arrangement, the knife edge  275  of the pressing member  270  presses against the surface  155  of the ridged portion  150 . 
     FIG. 2C  shows water intrusion paths generally at  280  and  282 . In order to provide complete water integrity, both water intrusion paths must be blocked. The water intrusion path  280  may be formed where the knife edge contacts the gasket. The water intrusion path shown generally at  282  may be formed at the points of contact where the gasket contacts the gasket channel. When the knife edge  275  contacts the gasket  100 , a force that is substantially normal to the surface  155  compresses the gasket. The existence of the air pocket  165  and surrounding crush zone  160  allows the gasket to collapse inwards. This creates a strong seal between the knife edge and the gasket blocking the water intrusion path  270 . The internal collapse of the gasket  100  due to the crush zone  165  also pushes the gasket against the inner walls of the channel, creating a proper seal and blocking water intrusion path  282 . If the gasket were not designed to collapse inwards, the force created by the knife edge would pull the corners of the gasket away from the walls of the channel. Therefore, the gasket designed with the ridged rectangular shape and crush zone allows for a watertight seal. 
     FIGS. 1A and 2C  show the intumescent portion  170 . If the gasket  100  is exposed to fire for a prolonged period, silicone rubber may eventually char, exposing the intumescent portion  170  to high temperatures and/or direct fire. The temperatures may be from about 1,500 degrees Fahrenheit to 2,000 degrees Fahrenheit and above. The inherent properties of the intumescent inner core will result in the expansion of about twenty to forty times its original volume. This voluminous expansion of the intumescent portion will fill up any voids left by the deterioration of the silicone rubber, retaining the fire-tight and smoke-tight seal. 
   What has been described and illustrated herein are preferred embodiments of the invention along with some variations. The terms, descriptions and figures used herein are set forth by way of illustration only and are not meant as limitations. Those skilled in the art will recognize that many variations are possible within the spirit and scope of the invention, which is intended to be defined by the following claims and their equivalents, in which all terms are meant in their broadest reasonable sense unless otherwise indicated.
An apparatus for sealing a doorway, more particularly, an all purpose gasket structure capable of sealing a doorway against the entry of water, smoke, and fire. The gasket is primarily an elongated silicone rubber structure having a ridged rectangular cross section for mounting to a gasket retainer. The gasket also includes a crush zone which collapses inwardly when pressure is applied to the gasket surface, resulting in improved sealing and the blockage of water intrusion paths. The gasket may further include an intumescent section within the elongated silicone rubber structure. In the sealing arrangement, the gasket is arranged within a gasket retainer that surrounds the doorway, thereby sealing boundaries between areas of personal egress.