Abstract:
A system for sealing a building air duct in response to a chemical or biological attack to prevent the building HVAC system from delivering the chemical or biological agent throughout the building. The system can include an inflatable bladder for disposition within an air duct, a source of gas for expanding the bladder, an initiator for initiating the gas expansion, and a detector for detecting the agent. One bladder is formed of a resilient material suitable for extending into duct corners. Another bladder is larger than the duct to be sealed and is formed of a non-resilient material capable of inflating and bunching into duct corners. One source of gas is a gas canister while another source of gas is a chemical composition capable of reacting and forming the gas. One bladder includes a foaming agent which can expand and solidify within the bladder. One initiator utilizes an electronic signal to initiate the gas expansion. Another initiator includes use of an RF signal to initiate the gas expansion. One agent detector samples duct air while another detector includes a horizon detector for detecting agents in the air outside the building.

Description:
FIELD OF THE INVENTION 
     The present invention is generally related to building heating, ventilating, and air conditioning. Specifically, the present invention is related to inflatable bladders for tightly sealing ducts in response to chemical or biological attack. In particular, the present invention includes portable, rapidly expandable bags suitable for quick placement in large air ducts of public buildings. 
     BACKGROUND OF THE INVENTION 
     The recent demise of the cold war and decline in super-power tensions has been accompanied by an increase in concern over the viability of weapons of mass destruction such as chemical and biological (CB) weapons. CB weapons include chemical agents such as phosgene, nerve agents such as Sarin, and biological agents such as anthrax or small pox. CB weapons may be delivered to occupants within a building by releasing the agents external to the building but close to an air intake of the building. The air intake may be located near the ground or near the roof or somewhere in between, depending on the building architecture. Agents may also be released within a public area of a building, and be dispersed to other, private areas of the same building. Agents released in one area of a building may be further dispersed by the heating, ventilating, and air conditioning (HVAC) system of the building. It is possible that building air may be removed from the room of release and dispersed by the HVAC system itself through the building. If building air is recycled by mixing return air with intake air, as is sometimes the case, either intentionally or inadvertently, then the HVAC system may effectively deliver an agent from one room to the entire building. 
     Agents may be delivered in vehicles giving some warnings as to the delivery, such as missiles. Agents may be delivered in vehicles giving no warning, such as a pedestrian held putative asthma inhaler activated near an air intake. 
     Certain buildings, such as key military sites, can be equipped or designed well in advance to deal with the use of CB weapons. Other buildings, however, such as hotels that are hosting dignitaries or a head of state may be more susceptible to a CB weapons attack. What would be desirable therefore, is a system for sealing air ducts of a building that can be placed and activated on short notice. 
     SUMMARY OF THE INVENTION 
     The present invention includes a system for sealing an air duct of a building including an inflatable bladder coupled to means for initiating inflation. A harmful agent detector such as a chemical or biological detector (CBD) can be used in a manual mode to activate an alarm and rely on a human to initiate duct sealing or can be used in conjunction with a controller system in an automatic mode to automatically initiate duct sealing. In one embodiment, the bladder includes a rapidly reacting chemical composition that rapidly creates a volume of gas sufficient to inflate the gas bag. 
     One class of expandable bladders includes envelopes formed of non-resilient material that does not stretch an appreciable amount under pressure. The non-resilient bags are preferably oversized relative to the duct in which they are to be placed. The oversized bladders have sufficient surface area to extend into the duct corners and seal the ducts. Another class of expandable bladders includes envelopes formed of resilient material, which stretches under pressure. The resilient or elastic envelopes can stretch into the corners of, for example, rectangular air ducts to seal the corners. 
     Some expandable bladders are positioned along one internal wall of a duct. Other expandable bladders are pre-positioned between two corners of a rectangular duct and can be paired with another bladder or bladder portion disposed between two different corners of an opposing internal wall. Pre-positioned bladders can be held in place using mechanical, magnetic, or any other means. Pre-positioning bladders in duct internal corners can provide corner and wall sealing at the outset, leaving the duct interior to seal upon inflation. 
     It is contemplated that the duct may be reinforced when an expanding gas filled envelope might compromise duct integrity. Ducts may be reinforced internally with internal sleeves or externally with frame members disposed around the duct exterior. Ducts may also be reinforced by using external frame members held in place by internally disposed cross-members extending through the duct interior. 
     A preferred source of expansion gas includes chemical compositions that generate large amounts of gas when a reaction is initiated, often by an electrical spark or rapidly heated wire. Gas may be supplemented or even supplanted by use of an expanding foaming agent. The foaming agent can be used in part to force an envelope into duct corners to insure corner sealing. The foaming agent can be used to make the envelope&#39;s expansion permanent, insuring that the duct will remain sealed even if the gas leaks from the envelope. The foam is preferably rapidly expanding and hardening, and can be similar to foams used for in-place foam packing applications and home and building insulation applications. 
     In use, a building can be protected by selecting proper ducts and disposing expandable gas bladders within the ducts. Wiring can be extended to the outside of the duct, and may terminate locally through wires to a receiver which can be connected to an antenna. Chemical or biological detectors can be installed in select locations, including locations within ducts and within public areas of the building, and also can be located external to the building. Horizon detectors can be installed external to the building. The detectors can be either hardwired or linked with RF signals to a controller. The controller can either be run in manual mode, requiring a human to initiate envelope inflation, or can be run in automatic mode, using the controller to initiate envelope inflation. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a highly diagrammatic, perspective, cutaway view of a conventional building HVAC system shown delivering a harmful agent from a public area return air duct to private areas in the building interior; 
     FIG. 2 is a highly diagrammatic, perspective, cutaway view of the building HVAC system of FIG. 1 having local harmful agent detectors, a horizon detector, and duct isolation devices; 
     FIG. 3 is a schematic view of a system for sealing an air duct including a harmful agent detector, a controller, an initiator and an inflatable bladder disposed inside a duct; 
     FIG. 4 is a transverse, cross-sectional view of an uninflated, oversized bladder disposed within an air duct; 
     FIG. 5 is a transverse, cross-sectional view of the bladder of FIG. 4 in an inflated state; 
     FIG. 6 is a transverse, cross-sectional view of an un-inflated bladder having a first portion and a second portion, secured to the duct internal walls; 
     FIG. 7 is a transverse, cross-sectional view of the bladder of FIG. 6 in an inflated state; 
     FIG. 8 is a transverse, cross-sectional view of a bladder device installed around all duct inner walls; 
     FIG. 9 is a transverse, cross-sectional view of the bladder device of FIG. 8 in an inflated state; 
     FIG. 10 is a transverse, cross-sectional view of a bladder device having a first portion installed around all duct inner walls and a second portion disposed along one duct inner wall; 
     FIG. 11 is a transverse, cross-sectional view of the bladder device of FIG. 10 showing both bladder portions in an inflated state; 
     FIG. 12 is a transverse, cross-sectional view of a bladder device installed in a circular air duct; 
     FIG. 13 is a highly diagrammatic, transverse cross-sectional view of a foaming device installed external to an air duct; 
     FIG. 14 is a transverse, cross-sectional view of an internal duct-reinforcing device; 
     FIG. 15 is a transverse, cross-sectional view of an external duct-reinforcing device; and 
     FIG. 16 is a transverse, cross-sectional view of an external duct-reinforcing device using internally disposed cross members. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 illustrates a building  20  including a public atrium area  23  and having a conventional building heating, ventilating, and air conditioning (HVAC) system  22  not having any duct isolation equipment in place. HVAC system  22  includes an outside air intake  24  and an outside air exhaust  26 . Air intake  24  and exhaust  26  are connected to a series of ducts including large, usually rectangular chambers or ducts such as chamber  28 , and intermediate sized, usually rectangular, ducts  30 . Intermediate ducts  30  split off into a series of smaller, often circular, ducts  32 , which feed a series of room diffusers  38 . Return air vents  36  and return air ducts  34  return air either to be expelled outside the building or be mixed with fresh air intake. Heating, cooling, humidification, and dehumidification functions are often performed in large chambers such as chamber  28 , and in more local intermediate sized chambers  42 . Mixing and/or recirculation can be performed by a return air duct  48 . 
     FIG. 1 illustrates an internally released harmful agent cloud  46  dispersed in public atrium  23  near return air vents  36 . HVAC system  22  is illustrated transporting harmful agent  46  through return air ducts  34 , through return air duct  48 , into intake chamber  28 , and dispersing it as externally released cloud  44  and internally released harmful agent cloud  47  through diffusers  38 . As illustrated, the harmful agent is delivered from a public portion of the building to the private areas of the building by the HVAC system and to the exterior near the building as well. 
     Referring now to FIG. 2, building  20  and HVAC system  22  have been outfitted with harmful agent detectors or chemical-biological detectors (CBDs) and a ductwork isolation system. In the example illustrated, a CBD  60  is disposed in large chamber  28 , a CBD  62  is disposed near air exhaust  26 , a CBD  64  is disposed in intermediate chamber  40 , and a room air CBD  66  is disposed in public atrium  23 . A horizon CBD  70  can be disposed external to the building, such as on the roof Horizon CBD  70  can detect more distant harmful agents using spectroscopic techniques including those incorporating LIDAR and laser technologies. Horizon CBDs can be useful for detecting harmful agents released a distance from the building, such as those delivered by missile. In the embodiment illustrated, the CBDs are in communication with an Isolation Control System (ICS)  72 , preferably using wires (omitted to simplify the drawing). 
     Disposed within the ducts are a series of duct isolation devices such as inflatable bladders. A duct isolation device  50  is disposed within large duct  28 , duct isolation devices  52  and  54  are disposed within the intermediate sized ducts, and another duct isolation device  56  is disposed within a small, local circular duct. Another duct isolation device  51  is disposed within return air duct  48 . The duct isolation devices are preferably in communication with central Isolation Control System  72  using hard wiring. In some embodiments, radio frequency links are used to link detectors, controllers, and duct isolation devices. In other embodiments, the detector and controller are disposed in close proximity to the duct isolation device. 
     Referring now to FIG. 3, a control system for duct isolation is further illustrated. A duct  80  is shown having a CBD  82  mounted external to the duct and a probe  83  extending into the duct. CBD  82  is linked to a transmitter  84 , which is in communication with a receiver  86 , which is coupled to the input of a controller  88 . The output of controller  88  is coupled to a transmitter  90  which is in communication with a receiver  92  disposed near a duct isolation device  96 . Duct isolation device  96  includes an inflator  94  coupled to receiver  92 . In use, when CBD  82  detects a harmful agent, the system can be run in automatic mode, using controller  88  to trigger inflator  94  automatically. The system can also be run in manual mode, with controller  88  using an annunciator to signal a human operator who is required to operate controller  88  to signal inflator  94 . 
     Referring now to FIG. 4, a duct  100  having corners  103  is illustrated having an un-inflated duct isolation device  101  including a communication wire  106 , an inflator  104 , and an inflatable bladder  102 . Inflatable bladder  102  is shown disposed on the bottom of duct  100 . In some embodiments, duct isolation device  101  can be totally disposed within an air duct, including the CBD for triggering the device. In other embodiments, only an antenna for receiving RF triggering signals extends external to the commonly metallic duct walls. In still other embodiments, a wire such as wire  106  runs to a receiver or controller external to the duct. 
     Referring now to FIG. 5, duct isolation device  101  is illustrated in an inflated state. Duct isolation device  101  has an envelope  108  pressing against the internal duct wall surfaces. In the embodiment illustrated, envelope  108  is oversized relative to duct  100 . This results in a plurality of small folds of material pressing against the internal duct walls. Taken over a short longitudinal distance, the small folds can allow air passage between the folds. Taken over a moderate or long distance, the folds terminate and other folds begin, at random, thus precluding air passage any appreciable distance. One reason for using over sized inflatable envelopes is to insure that corners  103  are filled with envelope material. In particular, the use of round envelopes may be undersized with respect to the corners. In some embodiments, the envelope includes external ribs at regular intervals, extending about partially or totally around the envelope&#39;s circumference. The ribs can act to interrupt any airflow through the folds, where the folds are pressing against the flat duct sides away from the corners. In some embodiments, resilient envelope material is used to allow the envelope to expand elastically under pressure into corners  103 . In still other embodiments, the envelope surfaces are coated with an extremely sticky material which can secure the envelope outer surface to the duct internal surface immediately after expansion of the envelope against the duct walls. 
     Referring now to FIG. 6, duct  100  is illustrated having a duct isolation device or bladder including a first part  112  installed along one internal wall of duct  100 . First part  112  is substantially rectangular in the embodiment illustrated, and extends to two corners of the duct. In some embodiments, the un-inflated bladder is secured to the duct interior wall using mechanical fasteners inserted through the duct walls. In other embodiments, the un-inflated bladder is secured using magnetic material, preferably covering a large amount of duct internal surface area. By using a pre-installed inflatable portion extending from one corner to a second corner, two corners can be covered prior to inflation. Upon inflation, the inflatable device can inflate across the rectangular duct and seal the opposite two corners as well, along with blocking the intervening duct interior. In one embodiment, the corner-to-corner inflatable envelope is sized to match the dimension of the duct wall upon which it will be installed. In another embodiment, more suitable for quick installation, the corner-to-corner inflatable envelope is sized larger than the wall upon which it is installed, with the excess material allowed to bulge out either in the middle of the wall, or to wrap around the corners onto the adjacent perpendicular walls. In the embodiment illustrated in FIG. 6, a second inflatable device  114  is secured to the internal duct wall opposite first inflatable device  112 . Device  114  illustrates one device for sealing the other two corners of a rectangular duct. Inflators  104  and wires  106  are illustrated being coupled to devices  112  and  114 . 
     Referring now to FIG. 7, inflatable devices  112  and  114  are illustrated in an inflated state, meeting along a common boundary  116 . FIG. 7 further illustrates a method for sealing the difficult to seal corners using two opposed inflatable devices, which may more easily seal along common boundary  116 . 
     Referring now to FIG. 8, another inflatable device  118  is illustrated, installed so as to cover all interior surfaces of the duct, while presenting only a small profile to obstruct airflow. Inflatable device  118  can be used in one of two ways. Device  118  can be fully inflated to totally occlude duct  100 . Fully inflated device  118  is illustrated in FIG.  9 . The inflatable bladder comes together at the center to totally occlude duct  100 . Device  118  can be used in a second way, illustrated by FIGS. 10 and 11, as a corner sealing aid used in conjunction with second inflatable device  102  illustrated in FIG.  4 . Used in this way, device  118  can be inflated as illustrated in FIG. 11, to present a non-perpendicular corner to be sealed by second device  102 . Used in this way, device  118  need only be partially inflated, as illustrated by FIG.  11 . Device  102  can be inflated in conjunction with device  118  to totally occlude duct  100 . Device  118  can be precisely sized to fit the duct or can be oversized, with ends overlapping within the duct. In some embodiments, device  118  has one edge cut to length and sealed or crimped at the point of installation. 
     Referring now to FIG. 12, a circular duct  120  is illustrated having an expandable device  122  including inflator  104  and wires  106 . FIG. 12 illustrates a device suitable for installation in circular ducts, which present no corner-sealing problem to be dealt with. Device  122  can be used for sealing circular, local ducts feeding a small number of rooms. 
     Referring now to FIG. 13, another device for sealing ducts is illustrated in foaming device  124 , including a foam generator  126  and nipple  128  extending into duct  100 . Foaming device  124  uses a rapidly-expanding and rapidly-hardening foam to seal duct  100 . Rapidly expanding and hardening foams are well known to those skilled in the art. Polyurethane or phenolic foams are believed suitable for the present invention. Foaming device  124  presents another device used to seal duct corners and to seal the center of the duct as well. In a preferred embodiment, air-handling equipment such as fans are turned off prior to triggering foam generator  128 . Foam generators can also be used in conjunction with inflatable envelopes, discussed below. 
     The use of rapidly expandable envelopes, in particular those using variants of automobile air bag technology, may cause some deformation or damage to ducts, especially if not sized properly. To lessen or eliminate this problem, ducts may be reinforced close to where the inflatable devices are deployed. In particular, the duct wall may be reinforced either internally or externally, to maintain the integrity of the duct walls. 
     Referring now to FIG. 14, duct  100  is illustrated having an internal, rectangular duct reinforcement liner  130  installed within duct  100 . Liner  130  is preferably formed of metal such as heavy gauge sheet metal and can be sized to fit a particular duct. Liner  130  is preferably at least as long as the expected length of the inflated envelope, nominally at least two feet long. A liner such as liner  130  may require too much time to install for some applications. 
     Referring now to FIG. 15, an external reinforcing frame  132  is illustrated, having frame members  134  joined externally at corners  136 . Reinforcing frame  132  can be rapidly installed. Frame members  134  need not be sized exactly to the size of duct  100 , as they can be oversized, extending past corners  136 . Multiple external frames  132  can be installed over the length of the duct near the location of the duct-sealing device. In some locations however, the duct may not be accessible around all four sides and four corners. 
     Referring now to FIG. 16, an external reinforcing frame  138  is illustrated, having external frame members  140  held to duct  100  by internal cross members  142  extending through duct  100  and held to frame members  140  by nuts  144  threaded onto a threaded portion of cross members  142 . FIG. 14 illustrates two pairs of external frame members, which need not be located exactly opposite each other. External reinforcing frame  138  may be suitable where the entire duct cannot be enclosed, but where opposing duct surfaces can be accessed. Other methods and devices for reinforcing ducts are  1 presented in U.S. Pat. No. 4,315,361 to Brooks, U.S. Pat. No. 4,519,177 to Russell, U.S. Pat. No. 5,253,901 to Hunter, and U.S. Pat. No. 5,660,212 to Elder, hereby incorporated by reference. 
     Various methods for expanding inflatable devices are suitable for use with the present invention. One class of inflators includes compressed gas sources such as air cylinders. The compressed gas sources may be relatively bulky and too slow to respond for some applications. Another class of inflators includes chemical compositions that react to generate gas, such as those used in automobile air bags. Such inflators are rapid, relatively compact, and relatively stable when properly handled. Gas generating compositions and devices are well known to those skilled in the art. See, for example, U.S. Pat. No. 3,715,131 to Hurley et al., U.S. Pat. No. 3,741,585 to Hendrickson et al., U.S. Pat. No. 3,904,221 to Shiki et al, and U.S. Pat. No. 4,005,876 to Jorgensen et al., hereby incorporated by reference. 
     While inflators using gas can be rapidly acting, it may sometimes be desirable to seal an inflatable envelope and duct with something even longer lasting. In such cases, the use of expandable, hardening foam may be desirable, as discussed above. In general, the foam may be less rapidly expanding than an inflator such as those used in automobile air bag technology. If the slower speed is acceptable, then foam, itself, may be used as the expansion media. If the slower speed is not acceptable, then a rapidly expanding gas may be used to expand the envelope against the duct walls, followed by an expanding foam material within the envelope. The rapidly expanding gas filled envelope will occlude the duct and the hardening foam will make the occlusion more permanent. Foamed plastics and foaming or foam blowing agents, well known to those skilled in the polymer art, are often used in foam-in-place packing applications. Polyurethane foams and phenolic foams are believed suitable for duct sealing applications. 
     In use, the duct isolation devices can be installed with varying degrees of speed, coverage, and permanence. Ducts of all sizes can be rapidly protected using the devices previously described. Devices as illustrated in FIG. 4, for example, can be set within a duct and a wire or antenna may be extended inside or outside of the duct. The device can be bolted to existing structure within the duct or bolted to newly formed holes through the duct wall. The wire or antenna can be extended through a newly drilled hole in the duct wall or through existing conduit commonly found in large ducts. A CBD can be installed where desired in the building. An RF triggering device can be installed where desired. For example, if an important meeting is to be held in a public building, an inflatable device can be disposed in a duct with an antenna extending from the duct. An RF triggering device can be manually or automatically tripped when a harmful agent is detected by any means. 
     The various duct isolation devices can likewise be rapidly installed in a variety of duct sizes and shapes. Some duct reinforcing structures, in particular those of FIGS. 15 and 16, can be quickly installed to persevere the integrity of the duct, if the nature of the duct and duct isolation device makes maintaining duct integrity an issue. 
     Numerous advantages of the invention covered by this document have been set forth in the foregoing description. It will be understood, however, that this disclosure is, in many respects, only illustrative. Changes may be made in details, particularly in matters of shape, size, and arrangement of parts without exceeding the scope of the invention. The inventions&#39;s scope is, of course, defined in the language in which the appended claims are expressed.