Abstract:
An apparatus for detecting and containing chemical or biological contaminants. The invention includes one or more optical contaminant detectors, capable of detecting chemical and biological agents. A containment assembly is installed in the duct work of a building, just downstream from the main intake. Air flows linearly through the containment assembly. The air first flows through a first damper, then through the contamination sensor or sensors, and then through a second damper. If a sensor senses a contaminant, a controller shuts off the HVAC system, while simultaneously closing the first and second dampers. The containment assembly is thereby hermetically sealed—trapping any contaminants inside. The sensors and second damper are spaced sufficiently far apart so that no contaminant will flow through the second damper before its closure. The controller can also be configured to alert authorized personnel as to the potential contamination.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     Not Applicable 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable 
     MICROFICHE APPENDIX 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to the prevention of chemical or biological attacks on building air circulation systems. More specifically, the invention comprises a detection system which isolates contaminants to prevent their circulation within a building. 
     2. Description of the Related Art 
     It is well known that particulate contamination of a gas will cause the attenuation of a light beam traveling through the gas. As one example, U.S. Pat. No. 5,766,956 to Groger, et al. (1998) discloses the use of a diode laser emitter to detect the presence of chemical or biological agents. The attenuation resulting from the presence of a particular contaminant also varies with the wavelength of the light used. FIGS. 5 through 7 in the &#39;956 disclosure illustrate this phenomenon. It is thus known that certain wavelengths of lights are particularly useful for detecting certain classes of substances. 
     Optical detection systems have become increasingly sophisticated, with an emphasis on eliminating false alarms caused by ambient lighting and contaminant accumulation on the optical surfaces of the device. One example of such a sophisticated detection system is found in U.S. Pat. No. 5,946,092 to DeFreez, et al. (1999). It is also known to combine different types of sensors to eliminate false alarms. This is particularly true in the field of fire detection. U.S. Pat. No. 5,945,924 to Marman, et al. (1999) teaches the combination of a particle sensor with a carbon dioxide sensor to eliminate false alarms. 
     Practically all optical sensors suffer degraded performance over time. This results from the fact that the optical surfaces become dusty with use. If a fixed level of attenuation is used to trigger the detector, this level may be reached by the accumulation of dust. Frequent cleaning is one remedy for this problem. However, techniques have evolved to permit the adjustment of the trigger threshold over time. One such approach is disclosed in U.S. Pat. No. 6,107,925 to Wong (2000). The Wong device adjusts its trigger threshold to account for dust contamination over time. 
     The events of 2001 have raised concerns regarding biological and chemical attacks on commercial buildings. Most such buildings have external intakes for their HVAC systems. Many of these intakes are in exposed positions—in parking garages or along the streets. If a chemical or biological agent is introduced into the HVAC system, the system will quickly circulate the contaminant throughout the building. 
     U.S. Pat. No. 6,217,441 to Pearman, et al. (2001) discloses a gas-activated seal which can restrict the flow of air through a duct. Many other prior-art devices are available to shut off flow through a duct. However, the prior art devices have not combined a contaminant sensor with a control to isolate the spread of the contaminant. 
     The known devices are therefore limited in that although they are capable of detecting contaminants, they do not contain and isolate the contaminant. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention comprises an apparatus for detecting and containing chemical or biological contaminants. The invention includes one or more optical contaminant detectors, capable of detecting chemical and biological agents. A containment assembly is installed in the duct work of a building, just downstream from the main intake. Air flows linearly through the containment assembly. The air first flows through a first damper, then through the contamination sensor or sensors, and then through a second damper. 
     If a sensor senses a contaminant, a controller shuts off the HVAC system, while simultaneously closing the first and second dampers. The containment assembly is thereby hermetically sealed—trapping any contaminants inside. The sensors and second damper are spaced sufficiently far apart so that no contaminant will flow through the second damper before its closure. The controller can also be configured to alert authorized personnel as to the potential contamination. 
     Accordingly, several objects and advantages of the present invention are: 
     1. To detect chemical or biological contaminants in an air duct; 
     2. To shut off the building HVAC system in response to an attack; 
     3. To alert the appropriate persons regarding the existence of an attack; and 
     4. To contain any contaminants already in the air duct in such a fashion that they cannot escape. 
    
    
     These objects and advantages will be fully explained in the details hereafter described, explained, and claimed, with reference being made to the accompanying drawings. 
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     FIG. 1 is an isometric view, showing the proposed invention. 
     FIG. 2 is an elevation view, showing the operation of one optical sensor. 
    
    
     REFERENCE NUMERALS IN THE DRAWINGS 
     
       
         
               
               
               
               
             
           
               
                   
               
             
             
               
                 10 
                 containment assembly 
                 12 
                 intake duct 
               
               
                 14 
                 first damper 
                 16 
                 second damper 
               
               
                 18 
                 damper drive 
                 20 
                 controller 
               
               
                 22 
                 HVAC system 
                 24 
                 emitter 
               
               
                 26 
                 detector 
                 28 
                 near IR monitor 
               
               
                 30 
                 far IR monitor 
                 32 
                 primary mirror 
               
               
                 34 
                 secondary mirror 
                 36 
                 frame 
               
               
                 38 
                 beam 
                 40 
                 reflection point 
               
               
                 42 
                 louvers 
               
               
                   
               
             
          
         
       
     
     DETAILED DESCRIPTION OF THE INVENTION 
     Most commercial buildings are equipped with HVAC systems which pull in some ambient air from outside the building and circulate the air within the building—often after heating or cooling it to a desired temperature. The intakes for these systems may be located at street level or within a parking garage and inside the buildings where the air is recirculated. Such intakes are accessible to persons walking up to the building. The present design of such HVAC systems therefore render the buildings vulnerable to chemical or biological attack, in that a terrorist could introduce a chemical or biological agent to the intake. The HVAC system would then circulate the agent throughout the building, potentially exposing thousands of people. The present invention seeks to eliminate this concern. 
     Referring now to FIG. 1, containment system  10  must be installed in close proximity to the building intake. The view incorporates a cutaway to show internal features. The primary structural element is intake duct  12 . Intake duct  12  has a first open end, which is closest to the viewer in FIG.  1 . First damper  14  is attached to this first open end. First damper  14  is equipped with a set of louvers  42 . In the position shown, louvers  42  allow the free passage of air into intake duct  12 . However, damper drive  18  can reorient louvers  42  so as to hermetically seal the first end of intake duct  12 . 
     Second damper  16  is attached to the second end of intake duct  12 . It is identical to first damper  14  —including the ability to hermetically seal the second end of intake duct  12 . In the position shown, air flows freely through second damper  16 , and from then on into the building HVAC system. However, if second damper  16  is closed, then containment assembly  10  is shut off from the building HVAC system. 
     Although intake duct  12  has numerous openings to admit control wires and the like, all these openings are hermetically sealed. Thus, the only way for air to enter or leave intake duct  12  is through first damper  14  or second damper  16 . When the two dampers are closed, intake duct  12  becomes a sealed vessel. 
     In FIG. 1, the air will flow through the device from left to right. Thus, near IR monitor  28  is downstream of first damper  14 . Likewise, far IR monitor  30  is downstream from near IR monitor  28 . Near IR monitor  28  and far IR monitor  30  are configured to detect chemical or biological agents in the airstream. If either monitor detects such an agent, it sends a message to controller  20 . Controller  20  then activates the two damper drives  18  to shut off first damper  14  and second damper  16 . Controller  20  may also be used to shut down the building HVAC  22 . It can also be configured to send an alert signal to authorized persons within the building. 
     When the dampers have been closed, the chemical or biological agents should be sealed within containment system  10 . The reaction time of the components is therefore an important consideration. There must be enough distance between the monitors and second damper  16  to allow second damper  16  to completely close before the agent passes through second damper  16 . This distance will be determined by the speed of the airflow, the speed of the monitors, the speed of controller  20 , and the speed of the dampers in completely shutting off the flow. As a practical matter, containment assembly  10  will typically need to be longer than the version shown in FIG.  1 . 
     The nature of the monitors will now be described in detail. It is well known that electromagnetic energy—particularly visible light and the infrared portion of the spectrum—are attenuated by the presence of solid aerosols, liquid aerosols, or gases. A given aerosol or gas will attenuate different wavelengths of light to different degrees. See for example FIGS. 5 through 7 of U.S. Pat. No. 5,766,956. Thus, it is well known that selected bands of the electromagnetic spectrum are better for detecting certain types of aerosols or gases than others. This fact means that a particular aerosol or gas will have an absorption “signature” which will allow its identification via the technique of shining a beam of light through the air containing the aerosol or gas and measuring the attenuation. 
     Turning now to FIG. 2 of the present invention, the reader will observe that near IR sensor  28  has a square frame  36 , which fits within intake duct  12 . Emitter  24  shines beam  38  across the moving air stream. Beer&#39;s Law describes how a beam of electromagnetic energy is attenuated as it passes through a medium (gas, liquid, or solid). It states that the beam&#39;s energy is exponentially reduced by the concentration of particles in the medium, by the length of travel through the medium, and by the attenuation coefficient of the medium. Attenuation effects are best measured using a substantial length of travel for beam  38 . In order to avoid an unduly large device, it is therefore advantageous to reflect beam  38  back and forth using mirrors. Beam  38  first encounters primary mirror  32 , where it is reflected back toward secondary mirror  34  (directly across from primary mirror  32 ). As shown in the view, beam  34  is reflected back and forth several more times before ultimately falling on detector  26 . 
     Electronic analysis means (typically incorporated in controller  20 ) are employed to compare the electromagnetic energy leaving emitter  24  to the energy received at detector  26 . A set trigger level is established so that if the ratio of these energies falls below the trigger level, a signal will be sent indicating the presence of a chemical or biological agent. 
     Those skilled in the art will know that the mirror employed in the system must have a high reflectivity for the wavelengths of light being emitted by emitter  24 . The embodiment shown in FIG. 2 is a simplified version with relatively few reflections. In practice, it is advantageous to use 20 reflections or more. Every time beam  38  strikes a mirror, it creates a reflection point  40 . The energy of the beam will be attenuated at each reflection point  40  —even in the absence of chemical or biological agents. This inherent attenuation must be accounted for. If, as an example, the beam is reflected twenty times off a mirror having a reflectivity of 95 percent, then approximately 36 percent of the original beam energy would reach detector  26 . At a reflectivity of 85 percent, only 4 percent of the original beam energy would reach detector  26 . It is therefore advantageous to use highly reflective mirrors. Gold-plated mirrors are particularly effective, having a reflectivity of approximately 98 percent. 
     The monitors employed in the device should be tuned to be most effective on likely biological or chemical agents. Solid particles or liquid droplets that can be effectively inhaled and retained through normal human breathing lie within the range of 1 micron to 5 microns in diameter. Electromagnetic energy having a wavelength between 0.8 microns and 1.2 microns is substantially attenuated by particles in this size range. This wavelength range is often referred to as the “near infrared.” Thus, referring to FIG. 1, near IR monitor  28  should ideally be tuned to this near infrared band. It will therefore be primarily responsible for detecting solid particles or liquid droplets in the range of 1 to 5 microns. 
     Far IR monitor  30 , which has the same physical structure as near IR monitor  28 , is tuned to two or more other specific bands. The first of these is in the range of 2.7 microns to 3.7 microns. The second is in the range of 5.4 microns to 10 microns. Virtually all airborne materials, with alkali halides being an exception, will attenuate electromagnetic energy in these bands. The selection of the bands can be accomplished using numerous prior art methods—including tuning the emitters to produce only these bands, or using a broad-spectrum emitter in conjunction with band pass filters on the detectors. 
     Either or both of near IR monitor  28  or far IR monitor  30  could be triggered by the presence of foreign materials within intake duct  12 . As an example—biological agents are often produced in the form of small particles. These particles are difficult to transport through the air. Thus, a terrorist who wanted to spread the particles might use a volatile liquid carrier. The particles and the liquid carrier would be placed in a pressurized container, then vented into a building&#39;s air intake. The solid particles and the liquid carrier droplets would be detected by near IR monitor  28 . If the droplets evaporated, they would be detected by far IR monitor  30 . Likewise, if a finely ground solid is introduced using a pressurized air blast, it would be detected by near IR monitor  28 . 
     Those skilled in the art will know that particle accumulation on the emitters, mirrors, and detectors will over time degrade the performance of the system. If the monitors are not cleaned, then the gradual accumulation of this dust will eventually produce a false alarm. This problem can obviously be cured by routinely cleaning the monitors. However, in order to extend the time between such routing cleanings, another technique is employed: Those skilled in the art will know that energy attenuation resulting from dust buildup will occur gradually. In contrast, energy attenuation resulting from the introduction of foreign chemical or biological agents will be quite sudden. Thus, controller  20  will ideally include logic circuitry—possibly including the use of computer software—which will adjust the triggering ratio for each pair of emitters and detectors over time. The triggering ratio will be adjusted downward to reflect the gradual reduction caused by dust accumulation. A signal will then only be sent if a monitor detects a rapid reduction in the ratio of the detector to the emitter. In this way, false alarms can be greatly reduced. 
     As mentioned previously, the detection of a chemical or biological agent will cause controller  20  to seal containment system  10 . Controller  20  can also send a signal to shut down the building&#39;s HVAC  22 . A specific alarm signal can be sent to authorized personnel within the building, informing them of which monitor was triggered (thereby suggesting what type of agent is present). 
     Accordingly, the reader will appreciate that the proposed invention can detect the presence of chemical or biological agents in the intake of a building HVAC system. The invention has further advantages in that it: 
     1. Prevents the chemical or biological agents from entering the HVAC system and thereby circulating throughout the building; 
     2. Shuts off the circulation of the HVAC system; 
     3. Prevents the agents within the invention from escaping back into the air around the building; and 
     4. Provides an alarm to the appropriate persons. 
     Although the preceding description contains significant detail, it should not be construed as limiting the scope of the invention but rather as providing illustrations of the preferred embodiment of the invention. As an example, a single emitter could be used to emit the necessary bandwidths of light, rather than a group of two or three separate emitters. Likewise, a single detector with the appropriate bandpass filters could be used to detect three separate wavelengths of light, rather than using three separate detectors. Thus, the scope of the invention should be fixed by the following claims, rather than by the examples given, with the understanding that a single device could incorporate several emitters or detectors.