Abstract:
The system and method provide for the monitoring and trending the rate at which fire detection devices get dirty. This information is used to determine which devices are clogged or getting clogged and to establish that the chambers are open to air flow because they are accumulating dirt over time. Air flow through the detection chamber is proven using this analysis. Further self-testing is also employed for the fire detection devices by including modules that simulate the smoke interference with the light. This can be accomplished in two ways. In one example, light from the chamber light source can be reflected toward the scattered light photodetector to simulate alarm conditions. In another example, an additional chamber light source can be added to the detection chamber that can generate light to simulate alarm conditions.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    Fire detection systems are often installed within commercial, residential, educational, or governmental buildings, to list a few examples. These fire detection systems typically include control panels and fire detection devices, which monitor the buildings for indicators of fire. In one example, the fire detection devices are individually addressable smoke detectors that are part of a network. Other examples include networks of stand-alone detectors with no control panel. 
         [0002]    One common type of fire detection devices are photoelectric (or optical) smoke detectors. The optical smoke detectors often include a baffle system, which defines a detection chamber, to block ambient light while also allowing air to flow into the detection chamber. The optical smoke detectors further include a smoke detection system within the detection chamber for detecting the presence of smoke. The smoke detection system typically comprises a chamber light source and a scattered light photodetector. When smoke fills the detection chamber it causes the light from the chamber light source to be scattered within the chamber and detected by the scattered light photodetector. When no smoke or other scatter medium is present, the photodetector only receives a small background signal from the light source. 
         [0003]    In many systems, the fire detection devices send event data, characterizing the level of detected scatter light for example, to the control panel. There the event data is analyzed. The panel will cause an alarm if the smoke exceeds a threshold, for example. In other examples, this analysis is performed on the detector itself, or a hybrid of on-detector and on-panel analysis. 
         [0004]    As air flows through the detection chamber over time, dirt and dust can accumulate inside and around the detection chamber. This is especially true for fire detection devices installed in harsh environments such as kitchens or rooms with cigarette smoke. Additionally, it is not uncommon for insects or spiders to build nests or webs in or on the detectors. Even in devices installed in environments that are not considered harsh (such as offices), dirt and dust gradually accumulate inside the detection chamber. Typically, as dirt or dust accumulates inside the detection chamber, the background signal level increases. 
         [0005]    Currently, building codes require that the fire detection systems be tested annually. This annual testing is performed because these fire detection devices have a number of different failure modes. For example, the electronics or optics of the device can fail. Likewise, the devices can become so dirty that the baffle systems become clogged. Additionally, it is not uncommon for the fire detection devices to get painted over. 
         [0006]    The annual testing of the fire detection devices is commonly performed by a technician performing a walkthrough test. The technician walks through the building and manually tests each of the fire detection devices of the fire detection system. In the case of smoke detectors, the technician often uses a special testing device including an artificial smoke generating apparatus housed within a hood at the end of a pole. The technician places the hood over the fire detection device and the artificial smoke generating device releases artificial smoke near the detector. If the smoke detector is functioning properly, it will trigger in response to the smoke. The technician repeats this process for every smoke detector of the fire alarm system. 
         [0007]    On the other hand, self-testing fire detection devices have been proposed. In one specific example, a self-test circuit for a smoke detector periodically tests whether the sensitivity of a scattered light photodetector is within a predetermined range of acceptable sensitivities. If the sensitivity of the scattered light photodetector is out of the predetermined range of acceptable sensitivities, then a fault indication is produced. 
       SUMMARY OF THE INVENTION 
       [0008]    One type of fire detection device, conventional optical smoke detectors, works on the principle of smoke interfering with a light source in a dark chamber. A prerequisite to the device operating is for air to flow freely through the chamber. This creates a challenge, however, as on the one hand the design needs to be closed to restrict light from entering the chamber, yet on the other hand, it needs to be open enough for air to flow freely through it. 
         [0009]    The designs currently in use have resolved this challenge of keeping light out while allowing air in, with an intricate framework of filters, channels and mazes. These structures, however, raise the risk that dirt may ultimately clog the channels and reduce or restrict the air flow through the detection chamber of the fire detection device, eventually making it inoperable. The resulting test standards therefore require devices to be tested every year, for example, by external injection of smoke or smoke like material to prove that air still flows through the system. 
         [0010]    While this process of injecting smoke or smoke like material into the fire detection device does in fact prove that air flows through it, it does not give an indication of the airflow rate, as the injected smoke is not metered. A technician could simply expose the device to any amount of smoke until it goes into alarm. A potentially bigger issue is that the material typically used to simulate smoke is an oily aerosol that adheres to the external and internal surfaces of the fire detection device, making surfaces more likely to attract and hold dirt. 
         [0011]    The current method for manually testing fire detection devices of a fire detection system is also labor intensive. The technician must walk through the building and manually test each fire detection device of the fire alarm system. This time consuming method is often disruptive to occupants or employees of the building. 
         [0012]    On the other hand, a problem with current self-testing devices is that the devices do not fully validate their operation. That is, the devices only test whether individual components of the devices are working or are within an acceptable range of acceptable sensitivities. It is possible to have a scenario in which a fire detection device “passes” a self-test, but has clogged pathways through the baffle system. In this scenario, the fire detection devices would appear to be fully operational, but in reality, the fire detection device is not able to detect smoke, for example. 
         [0013]    It has been observed that monitoring and trending the baseline background signal levels of the scattered light photodetector r of a fire detection device over extended timeframes makes it possible to observe and predict the rate at which dirt accumulates. While dirt accumulation is proportional to the sensor application (e.g. devices in operating rooms get dirty slower than detectors in boiler rooms), the rate over time is influenced by the airflow in the room and ultimately through the detection chamber. Clogged fire detection devices will not let air flow through them and therefore their baseline light detection levels will remain constant. Additionally, changes in the rate of change in the background signal over two weeks, or two months, or over a year for example, indicate that air flow through the detection chamber has changed and that the chamber may now be partially of fully blocked. By monitoring and trending the rate at which a device gets dirty, it is also possible to determine which devices are clogged or getting clogged. Conversely, it is also possible to establish that the chambers are open to air flow when they are accumulating dirt over time. 
         [0014]    Once air flow through the detection chamber is proven using this analysis, the process of self-testing a fire detection device becomes an exercise in simulating the smoke interference with the light. This can be accomplished in two ways. In one example, light from the chamber light source can be reflected toward the scattered light photodetector to simulate alarm conditions. In another example, an additional chamber light source can be added to the detection chamber that can generate light to simulate alarm conditions. 
         [0015]    In general, according to one aspect, the invention features a fire detection system. This system includes fire detection devices comprising detection chambers and an analytics system for analyzing performance of the detection chambers of the fire detection devices and determining whether the detection chambers are open to the flow of air from the ambient environment. 
         [0016]    In embodiments, the analytics system tracks the performance of the detection chambers over time and determines whether the detection chambers are potentially blocked (for example, based on a static baseline signal or a negative change in the rate of change in the baseline al). Additionally, the fire detection devices are photoelectric smoke sensors that include a self-testing subsystem. 
         [0017]    In one example, the self-testing subsystems of the fire detection devices includes a module for changing the light received by the photodetector in a manner consistent with the presence of smoke. In embodiments, the module can be an additional light source or a movable reflective surface. Additionally, the module can be manually triggered by a tool or magnet, or remotely triggered from a control panel. 
         [0018]    In general, according to another aspect, the invention features a method for testing a fire detection system. The method includes analyzing the performance of the detection chambers of the fire sensors over time, determining whether the detection chambers are open to the flow of air from the ambient environment, initiating a self-test of a photoelectric detection circuit, and using the results to pass or fail the fire sensors. 
         [0019]    The above and other features of the invention including various novel details of construction and combinations of parts, and other advantages, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular method and device embodying the invention are shown by way of illustration and not as a limitation of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    In the accompanying drawings, reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale; emphasis has instead been placed upon illustrating the principles of the invention. Of the drawings: 
           [0021]      FIG. 1  is a block diagram of a fire detection system; 
           [0022]      FIG. 2A  is a plan view of a detection chamber in a fire detection device, illustrating an example of a self-testing system including a reflective surface, in which the device is in an operating state; 
           [0023]      FIG. 2B  is a plan view of a detection chamber in a fire detection device, illustrating an example of a self-testing system including a reflective surface, in which the device is in a testing state; 
           [0024]      FIG. 3A  is a plan view of a detection chamber in a fire detection device, illustrating an example of a self-testing system including a testing light source, in which the device is in an operating state; 
           [0025]      FIG. 3B  is a plan view of a detection chamber in a fire detection device, illustrating an example of a self-testing system including the testing light source, in which the device is in a testing state; 
           [0026]      FIG. 4  is a block diagram of the analytics system, which can be part of the fire detection device, incorporated into a control panel, or implemented at a remote cloud system, which controls the control panel; 
           [0027]      FIG. 5A  is a graph illustrating a typical example of measured background signal levels over time characteristic of a chamber that is open to air flow; 
           [0028]      FIG. 5B  is a graph illustrating an example of measured background signal levels over time, in which the light detected increases more rapidly characteristic of a chamber that is open to air flow in a dirty environment; 
           [0029]      FIG. 5C  is a graph illustrating an example of measured background signal levels over time, in which the light detected stops increasing (i.e. there is a change in the rate of change), characteristic of a chamber that became blocked to air flow; 
           [0030]      FIG. 6  is a flow diagram illustrating the automated process by which fire detection devices of a fire detection system are tested; 
           [0031]      FIG. 7  is a flow diagram illustrating the process for populating a queue of testable fire detection devices and selecting the next device in the queue; 
           [0032]      FIG. 8  is a flow diagram illustrating the process for testing fire detection devices using simulated pre-alarm and alarm conditions; and 
           [0033]      FIG. 9  is a flow diagram illustrating the process for determining the pre-alarm and alarm test values. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0034]    The invention now will be described more fully hereinafter with reference to the accompanying drawings, in which illustrative embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. 
         [0035]    As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. Further, the singular forms and the articles “a”, “an” and “the” are intended to include the plural forms as well, unless expressly stated otherwise. It will he further understood that the terms: includes, comprises, including and/or comprising, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. Further, it will be understood that when an element, including component or subsystem, is referred to and/or shown as being connected or coupled to another element, it can be directly connected or coupled to the other element or intervening elements may be present. 
         [0036]      FIG. 1  is a block diagram of a fire detection system  100  that includes a control panel  102  and fire detection devices  108 - 1  to  108 - n . The fire detection system  100  would typically be installed within a building, which could be residential, commercial, educational or governmental. Some examples of buildings include hospitals, warehouses, retail establishments, malls, schools, or casinos, to list a few examples. While not shown in the illustrated example, fire alarm systems typically include other fire detection or annunciation/notification devices such as carbon monoxide or carbon dioxide detectors, temperature sensors, pull stations, speakers/horns, and strobes, to list a few examples. 
         [0037]    Each fire detection device  108  includes a base unit  110  and a head unit  112 . A device network interface  402  is housed within the base unit  110 , typically. The device network interface  402  enables the fire detection device  108  to communicate with the control panel  102  via a safety and security interconnect  116 , such as addressable loop or a SLC (signal line circuit), to list a few examples. The safety and security interconnect  116  supports data and/or analog communication between the devices  108  and the control panel  102 . 
         [0038]    In other examples, the fire detection devices are more stand-alone devices, with no control panel. 
         [0039]    A device controller  404  is housed in the head unit  112  of the fire detection device  108 . The device controller  404  drives a smoke detection system  406  and a self-testing system  408 , both of which are located within a detection chamber  205 . 
         [0040]    The control panel  102  includes a panel network interface  412  which enables the control panel  102  to communicate with the fire detection devices  108  via the safety and security data interconnect  116 . The control panel  102  receives event data from the fire detection devices  108 . Typically, the event data include a physical address of the activated device, a date and time of the activation, and at least one analog value directed to smoke levels or background light levels, and possibly ambient temperature detected by the fire detection device. Light levels detected by the scattered light photodetector  220  of each fire detection device  108  is also communicated to the control panel  102 . The data received by the control panel  102  is saved in memory and communicated to an analytics system  410 . 
         [0041]    The analytics system  410  in some examples is implemented as a process that runs on the panel controller  414 . In other examples, it is a separate system, possibly housed in the control panel  102 . In still other examples, the panel controller  414  forwards device event data over network(s) (possibly including the Internet) to the analytics system that is implemented as a cloud system, for example. Such a cloud analytics system is often maintained by a business entity that is different from the owner of the fire detection system, such that the owner of the fire detection system is a client of the owner of the cloud analytics system. 
         [0042]      FIG. 2A  is a plan view of an example detection chamber  205  in the head unit  112  of the fire detection device  108 . 
         [0043]    The detection chamber  205  is defined by the baffle system  230 , which includes individual baffles  230 - 1  to  230 - n . The arrangement of the baffles  230 - 1  to  230 - n  form channels or pathways  234 - 1  to  234 - n  that allow air, smoke, and also dirt and dust to flow through to the detection chamber  205 . The baffles are also commonly referred to as vanes, walls, or labyrinths, to list a few examples. 
         [0044]    The smoke detection system detects the presence of smoke within the detection chamber  205 . In the illustrated example, the smoke detection system comprises a chamber light source  222  for generating light and a scattered light photodetector  220  for detecting light that has been scattered due to the smoke or other scattering medium collecting within the detection chamber  205 . 
         [0045]    If smoke is present in the detection chamber  205 , the light from the source  222  is reflected and scattered by the smoke and detected by the scattered light photodetector  220 . A blocking baffle  226  is installed within the detection chamber  205  to prevent the light from having a direct path to the scattered light photodetector  220 . 
         [0046]    The self-testing system  408  is used to determine whether the smoke detection system  406  is operating normally. In general, the self-testing system  408  simulates the presence of smoke by generating or directing light into the visible path of the photodetector  220  to simulate the conditions of light being scattered by smoke and detected by the light photodetector  220 . In this way the operation and sensitivity of the photodetector  220  can be tested. 
         [0047]    In one embodiment of the self-testing system  408 , a reflective surface  228 , which is a small, slightly opaque plastic or glass film, is interjected into the light path  236  generated by the light source  222  such that the scattered light photodetector  220  detects a step change in light consistent with a smoke event. In the illustrated example, the reflective surface  228  is rotated around a pivot  232 . In one embodiment, the reflective surface  228  can be interjected into the light path  236  with an Allen key or similar tool inserted into the base of the detector. In another embodiment, a magnet can be used to move the reflective surface  228 . In yet another embodiment, the control panel  102  can remotely trigger a relay or stepper motor which in turn moves the reflective surface  228 . In a further aspect, the command to trigger the self-test can be initiated by a cloud system and sent to the control panel. 
         [0048]    In the illustrated example, the smoke detection system  406  is in an operating state. Therefore, the reflective surface  228  of the self-testing system  408  is reflecting the light  236  away from the light photodetector  220 . 
         [0049]      FIG. 2B  illustrates an example of the smoke detection system  406  when it is in a testing state. The reflective surface  228  of the self-testing system  408  has been rotated around the pivot  232  such that the light  236  is directed toward the light photodetector  220 , which would cause the fire detection device  108  to signal to the control panel  102  that the presence of smoke was detected. A combination of the surface finish, opacity and angle of the reflective surface  228  will permit for varying degrees of light to he received by the photodetector  220 . In one example, the angle at which the reflective surface is set is dictated by a command from the control panel  102 . 
         [0050]    An alternative embodiment of the self-testing system  408 , a second light source is placed in the detection chamber  205  such that the light is injected into the entrance aperture of the light photodetector  220 . The second light source can then be covered with a diffuser (so as to remove any point source effect and soften the light). Since only a small percentage of the original light source is required, this second light is much smaller and lower in intensity. During normal operation, the second light is off completely. During testing, the second light can be stepped through various light intensities, proportional to predefined smoke obscuration levels. 
         [0051]    In one implementation, the test sequence is structured to either put the detector into alarm (by reaching an obscuration level above the current alarm level set for the detector) or is done at a level slightly below the alarm level so as to achieve a pre-alarm response. In this way, different intensities of light would correlate directly to smoke obscuration levels and would permit for the creation of a sensitivity benchmark as well as testing pre-alarm levels, which are levels of light below the predetermined threshold at which the presence of smoke is determined. 
         [0052]      FIG. 3A  illustrates the alternative embodiment of the self-testing system  408  in which a second light source  238  is placed in the detection chamber  205 . In this embodiment, the detection chamber  205  includes the testing light source  238 , which is a small dimmable light source in a direct path to the light photodetector  220 . In the illustrated example, the smoke detection system  406  is in an operating state. Therefore, the testing light source  238  is not generating light. 
         [0053]      FIG. 3B  illustrates an example of the smoke detection system  406  with a testing light source when it is in a testing state. The testing light source  238  generates light  236  that is detected by the light photodetector  220 . In one example, the intensity of the light  236  is high enough to cause the fire detection device  108  to enter an alarm state and signal to the control panel  102  that the presence of smoke is detected. In another example, the testing light source  238  generates light  236  below the alarm level of the device, in which case the level of light detected is communicated with the control panel  102  but the device does not enter an alarm state. 
         [0054]      FIG. 4  is a block diagram of the database maintained by the analytics system  410 . Specifically, the analytics system  410  includes an analytics database  418 , which includes historical data  420 . The historical data  420 , in turn, includes measured background signal levels over time  422  for each fire detection device  108  monitored by the control panel  414 . 
         [0055]    The background signal level (also referred to as baseline signal) of a fire detection device  108  is the level of light detected by the light photodetector  220  in its operating state, when there is no smoke scattering the light within the detection chamber  205 , nor any light being intentionally directed toward the light photodetector  220  as in the testing state. For example, the background signal level over the course of a day would be calculated from the lowest level background signal levels detected, excluding any short term (minute long or hour long) temporal spikes in the background signal due to transient effects such as short term presence of low levels of smoke. 
         [0056]    The background signal level of a fire detection device  108  will change over time, such as over a month, a 6-month period, a year or several years. As air flows through the detection chamber  205 , dirt and dust particles accumulate within the chamber, causing the surfaces of the detection chamber to become dirty. The increased dirt and dust scatter the light within the detection chamber  205 , causing small increases in the amount of light detected by the scattered light photodetector  220  from the light source  222 . Because the accumulation of dirt and dust is typically gradual, it is possible to differentiate the increase in the light level due to dirt and dust from that caused by the presence of smoke, which causes a very rapid increase in light levels. Typically, the measured background signal levels over time  422  show a gradual increase. When a gradual increase is observed, it can be inferred that air is properly flowing through the detection chamber  205 , because dirt and dust are accumulating inside. Without the flow of air, dirt and dust will not accumulate on the surfaces and the baseline will remain constant or flat-line. 
         [0057]    Dirt accumulation is proportional to the specific application and condition of the fire detection device  108  for which background signal levels over time  422  are being collected. In one example, a fire detection device  108  installed in an operating room shows an increase in light detected that is slower than that of a device installed in a boiler room. In another example, a fire detection device  108  with a baffle system  230  that is clogged shows a point at which the light detected no longer increases (as dirt and dust are no longer accumulating within the detection chamber  205 ). By monitoring and trending the rate at which a fire detection device gets dirty, it is possible to determine whether it is clogged or getting clogged. 
         [0058]      FIG. 5A  is a graph illustrating a typical example of measured background signal levels over time  422 . These background levels present average signals for an extended time period such as over several hours or over a day. They can also be calculated based on the lowest background signals detected for some time period, such as a day. The y-axis represents the amount of light detected by the light photodetector  220  of a fire detection device  108 . The x-axis represents time elapsed, such as over a month, a 6-month period, a year or several years. 
         [0059]    In the illustrated example, the graph shows a gradual increase of the measured background signal levels over time  422 . The gradual increase in light detected indicates that dirt and dust are accumulating inside the detection chamber  205  of the fire detection device  108 . Therefore, it is determined that air is properly flowing through the detection chamber  205 . 
         [0060]      FIG. 5B  is a graph illustrating another example of measured background signal levels over time  422 . In the illustrated example, the graph shows a relatively steep increase in light detected. In this example, the steep increase indicates that dirt and dust are accumulating inside the detection chamber  205  more quickly than normal. Nevertheless, at the same time, it is determined that air is properly flowing through the detection chamber  205 , because the light detected is nonetheless increasing. 
         [0061]      FIG. 5C  is a graph illustrating another example of measured background signal levels over time  422 . In the illustrated example, the graph shows a point at which the light detected stops increasing, which indicates that dirt and dust are no longer accumulating inside the detection chamber  205 . That is, there is a change in the rate of change, such that the rate of change decreases. It is thus determined that air is being obstructed from flowing through the detection chamber  205 . 
         [0062]    In general, the fire detection system  100  implements a self-testing capability for fire detection devices  108  by first analyzing the measured background signal levels over time  422  for each device to determine whether air is flowing through the detection chambers  205 , and then by activating the self-testing system  408  of the devices to determine whether the smoke detection system  406  is operational. 
         [0063]    In general, the process can be managed with a simple setting or process flag that determines whether the device should be put into a full alarm state. In cases where a full alarm state is requested, the process would expose the scattered light photodetector to light levels that simulate a smoke obscuration level which exceeds the alarm level for that specific device. If the non-alarm test is chosen, the process exposes the scattered light photodetector to pre-alarm light levels, which simulate smoke obscuration below the alarm level for that specific device. In one example, a fire detection device is put into a pre-alarm state without going into a full alarm state (e.g. if an alarm is triggered at 2.5, and the device is brought to a slightly lower value such as 2.3). In this way, it is possible to test the device remotely and without bypassing any of the horns or strobes, or shutting down any of the detection circuits. In this example, the fire detection system  100  remains fully operational during testing. 
         [0064]      FIG. 6  is a flow diagram illustrating the automated process by which the fire detection devices  108  of a fire detection system  100  are tested by the control panel  102 . 
         [0065]    In step  602 , the control panel  102  is placed in self-test mode, which initiates the self-test process. Step  602  can be initiated at the panel by human interaction, by the use of a system timer (daily, weekly, monthly, quarterly as an example) or remotely using a connected infrastructure similarly used in remote service, machine to machine or Internet of Things applications. 
         [0066]    In step  604 , the panel  102  reacts to the stored setting or input of the user whether to perform a full alarm or not. 
         [0067]    At this point, the testing process executed by the panel  102  requires determining the set of fire detection devices  108  to test as required by steps  606 . Therefore, a list of devices that can be tested is created and managed so that all devices get tested. It is also confirmed that all of the fire detection devices have measured background signal levels over time  422  indicating that air is flowing through the detection chambers  205 . If not, the devices are flagged as “Potentially Blocked” or “New Device Insufficient trend data” depending on the state. 
         [0068]      FIG. 7  is a flow diagram illustrating the process for populating a queue of testable fire detection devices  108  and selecting the next device in the queue by the control panel. 
         [0069]    In step  702 , a set of fire detection devices  108  installed in the fire detection system  100  is generated by the panel  102 . 
         [0070]    In step  704 , a subset of installed fire detection devices  108  that include a self-testing system  408  is then determined by the panel  102 . 
         [0071]    In step  706 , for the next device in the queue, the panel  102  determines whether the measured background signal level over time  422  as maintained by the analytics system  410  gradually increases (and therefore whether air is flowing through the detection chamber  205  of the device). This is performed by the analytics system  410  analyzing the trends in the background light levels detected over weeks, or over months, and/or over years. If an increase or trend is observed that is characteristic of a chamber that is open to airflow, the channel and device ID are sent to the next process step in step  714 . 
         [0072]    If, on the other hand, an increase is not observed, in step  708  it is determined whether the fire detection device  108  has been online for enough time to have a meaningful measured background signal level over time  422 . If not, in step  710 , the fire detection device  108  is flagged as having limited trend data available such as if the fire detection device has only been online for a month or less, or a year or less, in specific examples. In contrast, if the fire detection device  108  is determined to have been online for enough time, in step  712 , the fire detection device is flagged as being potentially blocked (air is not flowing through the detection chamber  205 ). In either case, the device is then returned to the next process step in step  714 . 
         [0073]    Returning to  FIG. 6 , if the test was determined to be a pre-alarm test in step  604 , in step  616 , the self-testing system  408  of the fire detection device  108  is instructed to simulate pre-alarm conditions. If, on the other hand, the test was determined to be an alarm test in step  604 , in step  608 , the self-testing system  408  of the device is instructed to simulate alarm conditions. 
         [0074]    For the alarm test scenario, the current alarm-at value for the fire detection device  108  is determined. The alarm-at value is the threshold at which it is determined that smoke is present and a full alarm state is initiated. The fire detection device  108  is then tested at a test level just below and just above the alarm-at level. This allows for verification of value changes in the observed smoke obscuration level in both the pre-alarm and alarm state. The current methodology using canned smoke is uncontrolled and incapable of repeatedly and predictably performing this pre-alarm and alarm level verification. The small sub processes within this test sequence are used to determine how much simulated smoke to apply based on the current reading. Basically, a device that currently reports it is at 30% of its alarm-at level (due to dirt, dust or moisture in its environment) needs less external stimulus than a detector at 0%. Current reading is different than the background or baseline reading. Background is a long-term average that moves slowly and effectively reports the level of dirt and dust buildup on the chamber  205  and optics  220 ,  222 . Current reading reacts to environmental conditions real-time. A rise in the current reading is in response to a stimulus like dirt, smoke and or in the case of the invention, the simulated smoke resulting from the position of the reflective surface  228  or the active state of the second light source  238 . 
         [0075]      FIG. 8  is a flow diagram illustrating the process for testing fire detection devices  108  using simulated pre-alarm and alarm conditions performed by the control panel  102 . 
         [0076]    In step  802 , the sensitivity, current and alarm-at values for the fire detection device  108  are determined by the control panel  102 . 
         [0077]      FIG. 9  is a flow diagram illustrating the process for determining the pre-alarm and alarm test values performed by the control panel  102 . In step  902 , the available range is calculated as the alarm-at level minus the current or background light level. In step  904 , the default range is determined. The default range is a typical range of a device installed in the same conditions as the fire detection device  108  being tested. In step  906 , a % alarm value is calculated as the available range divided by the default range. In step  908 , it is determined whether the % alarm value is less than 40%. If it is not less than 40%, in step  910  the test is postponed. If the % alarm value is less than 40%, in step  912 , 75%, 85% and 125% of the alarm-at value are calculated. Step  908  is performed to reduce the possibility of a smoke detector being tested while it is being exposed to real smoke. An alternate embodiment of this step would be to look at the slope of the current reading in relationship to the overall background trend. A current reading that is rising significantly faster than the background (order of magnitude or more) would be indicative of a potential fire condition. 
         [0078]    Returning to  FIG. 8 , in step  804 , the fire detection device  108  is tested using a test value just below the alarm-at value. In step  806 , it is determined whether the amount of light detected changed but no alarm was indicated by the fire detection device  108 . If not, the fire detection device fails the test in step  808  and the control panel initiates a warning flag. 
         [0079]    If, on the other hand, the amount of light detected changed in step  804 , and no alarm was indicated, in step  810 , the fire detection device  108  is tested again using a test value just above the alarm-at value. 
         [0080]    In step  812 , if an alarm is indicated by the fire detection device  108 , the device passes in step  814 . On the other hand, if no alarm is indicated, the device fails in step  808 . 
         [0081]    Returning to  FIG. 6 , the results of the test conducted in either step  608  or step  616  are recorded in step  610 . 
         [0082]    In step  612 , it is determined whether there are fire detection devices  108  remaining in the queue of testable devices. If so, the process returns to step  606 , and the test values are determined, and the tests conducted, for the next device. 
         [0083]    When there are no devices remaining in the queue, a report is generated in step  614 . 
         [0084]    While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.