Patent Publication Number: US-2021183232-A1

Title: Self-testing fire sensing device

Description:
PRIORITY INFORMATION 
     This application is a Continuation of U.S. application Ser. No. 16/552,301, filed Aug. 27, 2019, the contents of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates generally to devices, methods, and systems for a self-testing fire sensing device. 
     BACKGROUND 
     Large facilities (e.g., buildings), such as commercial facilities, office buildings, hospitals, and the like, may have a fire alarm system that can be triggered during an emergency situation (e.g., a fire) to warn occupants to evacuate. For example, a fire alarm system may include a fire control panel and a plurality of fire sensing devices (e.g., smoke detectors), located throughout the facility (e.g., on different floors and/or in different rooms of the facility) that can sense a fire occurring in the facility and provide a notification of the fire to the occupants of the facility via alarms. 
     Maintaining the fire alarm system can include regular testing of fire sensing devices mandated by codes of practice in an attempt to ensure that the fire sensing devices are functioning properly. However, since tests may only be completed periodically, there is a risk that faulty fire sensing devices may not be discovered quickly or that tests will not be carried out on all the fire sensing devices in a fire alarm system. 
     A typical test includes a maintenance engineer using pressurized aerosol to force synthetic smoke into a chamber of a fire sensing device, which can saturate the chamber. In some examples, the maintenance engineer can also use a heat gun to raise the temperature of a heat sensor in a fire sensing device and/or a gas generator to expel carbon monoxide (CO) gas into a fire sensing device. These tests may not accurately mimic the characteristics of a fire and as such, the tests may not accurately determine the ability of a fire sensing device to detect an actual fire. 
     Also, this process of manually testing each fire sensing device can be time consuming, expensive, and disruptive to a business. For example, a maintenance engineer is often required to access fire sensing devices which are situated in areas occupied by building users or parts of buildings that are often difficult to access (e.g., elevator shafts, high ceilings, ceiling voids, etc.). As such, the maintenance engineer may take several days and several visits to complete testing of the fires sensing devices, particularly at a large site. Additionally, it is often the case that many fire sensing devices never get tested because of access issues. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an example of a self-testing fire sensing device in accordance with an embodiment of the present disclosure. 
         FIG. 2  illustrates a block diagram of a smoke self-test function of a fire sensing device in accordance with an embodiment of the present disclosure. 
         FIG. 3  illustrates a block diagram of a heat self-test function of a fire sensing device in accordance with an embodiment of the present disclosure. 
         FIG. 4  illustrates a block diagram of a gas self-test function of a fire sensing device in accordance with an embodiment of the present disclosure. 
         FIG. 5  illustrates a plot of example optical scatter chamber outputs used to determine whether a fire sensing device is functioning properly in accordance with an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Devices, methods, and systems for a self-testing fire sensing device are described herein. One device includes an adjustable particle generator and a variable airflow generator configured to generate an aerosol density level sufficient to trigger a fire response without saturating an optical scatter chamber and the optical scatter chamber configured to measure a rate at which the aerosol density level decreases after the aerosol density level has been generated, determine an airflow rate from an external environment through the optical scatter chamber based on the measured rate at which the aerosol density level decreases, and determine whether the self-testing fire sensing device is functioning properly based on the fire response and the determined airflow rate. 
     In contrast to previous fire sensing devices in which a maintenance engineer would have to manually test each fire sensing device in a facility (e.g., using pressurized aerosol, a heat gun, a gas generator, or any combination thereof), fire sensing devices in accordance with the present disclosure are self-testing and can more accurately imitate characteristics of a fire. Accordingly, fire sensing devices in accordance with the present disclosure may take significantly less time to test, can be tested continuously and/or on demand, and can more accurately determine the ability of a fire sensing device to detect an actual fire. 
     In the following detailed description, reference is made to the accompanying drawings that form a part hereof. The drawings show by way of illustration how one or more embodiments of the disclosure may be practiced. 
     These embodiments are described in sufficient detail to enable those of ordinary skill in the art to practice one or more embodiments of this disclosure. It is to be understood that other embodiments may be utilized and that mechanical, electrical, and/or process changes may be made without departing from the scope of the present disclosure. 
     As will be appreciated, elements shown in the various embodiments herein can be added, exchanged, combined, and/or eliminated so as to provide a number of additional embodiments of the present disclosure. The proportion and the relative scale of the elements provided in the figures are intended to illustrate the embodiments of the present disclosure and should not be taken in a limiting sense. 
     The figures herein follow a numbering convention in which the first digit or digits correspond to the drawing figure number and the remaining digits identify an element or component in the drawing. Similar elements or components between different figures may be identified by the use of similar digits. For example,  104  may reference element “ 04 ” in  FIG. 1 , and a similar element may be referenced as  204  in  FIG. 2 . 
     As used herein, “a”, “an”, or “a number of” something can refer to one or more such things, while “a plurality of” something can refer to more than one such things. For example, “a number of components” can refer to one or more components, while “a plurality of components” can refer to more than one component. 
       FIG. 1  illustrates an example of a self-testing fire sensing device  100  in accordance with an embodiment of the present disclosure. The self-testing fire sensing device  100  can be, but is not limited to, a fire and/or smoke detector of a fire control system. 
     A fire sensing device  100  (e.g., smoke detector) can sense a fire occurring in a facility and trigger a fire response to provide a notification of the fire to occupants of the facility. A fire response can include visual and/or audio alarms, for example. A fire response can also notify emergency services (e.g., fire departments, police departments, etc.) In some examples, a plurality of fire sensing devices can be located throughout a facility (e.g., on different floors and/or in different rooms of the facility). 
     A self-testing fire sensing device  100  can automatically or upon command conduct one or more tests contained within the fire sensing device  100 . The one or more tests can determine whether the self-testing fire sensing device  100  is functioning properly. 
     As shown in  FIG. 1 , fire sensing device  100  can include an adjustable particle generator  102 , an optical scatter chamber  104  including a transmitter light-emitting diode (LED)  105  and a receiver photodiode  106 , a heat source  108 , a heat sensor  110 , a gas source  112 , a gas sensor  114 , a variable airflow generator  116 , a proximity sensor  118 , and an additional heat source  119 . In some examples, a fire sensing device  100  can also include a microcontroller including memory and/or a processor, as will be further described in connection with  FIGS. 2-4 . 
     The adjustable particle generator  102  of the fire sensing device  100  can generate particles which can be mixed into a controlled aerosol density level by the variable airflow generator  116 . The aerosol density level can be a particular level that can be detected by an optical scatter chamber  104 . In some examples, a fire response can be triggered in response to the optical scatter chamber  104  detecting the aerosol density level. Once the aerosol density level has reached the particular level, the adjustable particle generator  116  can be turned off and the variable airflow generator  116  can increase the rate of airflow through the optical scatter chamber  104 . The variable airflow generator  116  can increase the rate of airflow through the optical scatter chamber  104  to reduce the aerosol density level back to an initial level of the optical scatter chamber  104  prior to the adjustable particle generator  116  generating particles. For example, the variable airflow generator  116  can remove the aerosol from the optical scatter chamber  104  after it is determined whether the fire sensing device  100  is functioning properly. If the fire sensing device  100  is not blocked or covered, then airflow from the external environment through the optical scatter chamber  104  will cause the aerosol density level to decrease. The rate at which the aerosol density level decreases after the aerosol density level has been generated is proportional to airflow from the external environment through the optical scatter chamber  104 , so the optical scatter chamber  104  can measure the airflow to determine whether the sensing device  100  is impeded and whether the sensing device  100  is functioning properly. 
     The adjustable particle generator  102  can include a reservoir to contain a liquid and/or wax used to create particles. The adjustable particle generator  102  can also include a heat source, which can be heat source  108  or a different heat source. The heat source  108  can be a coil of resistance wire. A current flowing through the wire can be used to control the temperature of the heat source  108  and further control the number of particles produced by the adjustable particle generator  102 . The heat source  108  can heat the liquid and/or wax to create airborne particles to simulate smoke from a fire. The particles can measure approximately 1 micrometer in diameter and/or the particles can be within the sensitivity range of the optical scatter chamber  104 . The heat source  108  can heat the liquid and/or wax to a particular temperature and/or heat the liquid and/or wax for a particular period of time to generate an aerosol density level sufficient to trigger a fire response from a properly functioning fire sensing device without saturating the optical scatter chamber  104  and/or generate an aerosol density level sufficient to test a fault condition without triggering a fire response or saturating the optical scatter chamber  104 . The ability to control the aerosol density level can allow a smoke test to more accurately mimic the characteristics of a fire and prevent the optical scatter chamber  104  from becoming saturated. 
     The optical scatter chamber  104  can sense the external environment due to a baffle opening in the fire sensing device  100  that allows air and/or smoke from a fire to flow through the fire sensing device  100 . The optical scatter chamber  104  can be an example of an airflow monitoring device. In some examples a different airflow monitoring device can be used to measure the airflow through the fire sensing device  100 . 
     As previously discussed, the rate of reduction in aerosol density level can be used to determine an airflow rate from the external environment through the optical scatter chamber  104 , and a determination of whether fire sensing device  100  is functioning properly can be made based on the determined air flow rate and/or the fire response. For example, the fire sensing device  100  can be determined to be functioning properly responsive to the airflow rate exceeding a threshold airflow rate and/or a fire response being triggered. In some examples, the fire sensing device  100  can trigger a fault if the airflow rate fails to exceed a threshold airflow rate. For example, the fire sensing device  100  can send a notification of the fault to a monitoring device when an impeded airflow is detected. In some examples, the impeded airflow can be caused by a person deliberately attempting to mask (e.g., cover) the fire sensing device  100 . 
     The fire sensing device  100  can include an additional heat source  119 , but may not require an additional heat source  119  if the heat sensor  110  is self-heated. In some examples, heat source  119  can generate heat at a temperature sufficient to trigger a fire response from a properly functioning heat sensor  110 . The heat source  119  can be turned on to generate heat during a heat self-test. Once the heat self-test is complete, the heat source  119  can be turned off to stop generating heat. 
     The heat sensor  110  can normally be used to detect a rise in temperature caused by a fire. Once the heat source  119  is turned off, the heat sensor  110  can measure a rate of reduction in temperature. The rate of reduction in temperature can be proportional to the airflow from the external environment through the fire sensing device  100  and as such the rate of reduction in temperature can be used to determine the airflow rate. The airflow rate can be used to determine whether air is able to enter the fire sensing device  100  and reach the heat sensor  110 . The airflow rate can also be measured and used to compensate the generation of an aerosol used to self-test the fire sensing device  100 . 
     A fire response can be triggered responsive to the heat sensor  110  detecting a temperature exceeding a threshold temperature. The fire sensing device  100  can be determined to be functioning properly responsive to the triggering of the fire response and the determined airflow rate. 
     A fault can be triggered by the fire sensing device  100  responsive to a determined change in temperature over time failing to exceed a threshold temperature change over time. In some examples, the fault can be sent to a monitoring device. The determined change in temperature over time can determine whether the fire sensing device  100  is functioning properly. In some examples, the fire sensing device  100  can be determined to be functioning properly responsive to an airflow rate derived from the determined change in temperature over time exceeding a threshold airflow rate. 
     A gas source  112  can be separate and/or included in the adjustable particle generator  102 , as shown in  FIG. 1 . The gas source  112  can be configured to release one or more gases. The one or more gases can be produced by combustion. In some examples, the one or more gases can be carbon monoxide (CO) and/or a cross-sensitive gas. The gas source  112  can generate gas at a gas level sufficient to trigger a fire response from a properly functioning fire sensing device and/or trigger a fault in a properly functioning gas sensor  114 . 
     The gas sensor  114  can detect one or more gases in the fire sensing device  100 , such as, for example, the one or more gases released by the gas source  112 . For example, the gas sensor  114  can detect CO and/or cross-sensitive gases. In some examples, the gas sensor  114  can be a CO detector. Once the gas source  112  is turned off, the gas sensor  114  can measure the gas level and determine the change in gas level over time to determine the airflow rate. The airflow rate can be used to determine whether air is able to enter the fire sensing device  100  and reach the gas sensor  114 . 
     A fire response of the fire sensing device  100  can be triggered responsive to the gas sensor  114  detecting one or more gases and/or one or more gases exceeding a threshold level. The fire sensing device  100  can be determined to be functioning properly responsive to the fire response, the gas sensor  114  detecting the one or more gases and/or the one or more gases exceeding the threshold level and the fire sensing device  100  properly triggering a fire response. 
     The fire sensing device  100  can be determined to be functioning properly based on the change in the gas level over time. In some examples, the fire sensing device  100  can be determined to be functioning properly responsive to the change in the gas level over time exceeding a threshold gas level change and/or a threshold airflow rate, derived from the determined change in gas level over time, exceeding a threshold airflow rate. The fire sensing device  100  can trigger and/or send a fault responsive to the change in gas level over time failing to exceed the threshold change in gas level and/or the airflow rate failing to exceed the threshold airflow rate. In some examples, the fire sensing device  100  can be determined to be functioning properly responsive to the triggering of a fire response and/or triggering of a fault. 
     The variable airflow generator  116  can control the airflow through the first sensing device  100 , including the optical scatter chamber  104 . For example, the variable airflow generator  116  can move gases and/or aerosol from a first end of the fire sensing device  100  to a second end of the fire sensing device  100 . In some examples, the variable airflow generator  116  can be a fan. The variable airflow generator  116  can start responsive to the adjustable particle generator  102 , the heat source  119 , and/or the gas source  112  starting. The variable airflow generator  116  can stop responsive to the adjustable particle generator  102 , the heat source  119 , and/or the gas source  112  stopping, and/or the variable airflow generator  116  can stop after a particular period of time after the adjustable particle generator  102 , the heat source  119 , and/or the gas source  112  has stopped. 
     The fire sensing device  100  can include one or more proximity sensors  118 . A proximity sensor  118  can detect objects within a particular distance of the fire sensing device  100 , and therefore can be used to detect tampering intended to prevent fire sensing device  100  from functioning properly. For example, the proximity sensor  118  can detect an object (e.g., a hand, a piece of clothing, etc.) placed in front of or on the fire sensing device  100  to impede heat, gas, and/or smoke from entering the optical scatter chamber  104  in an attempt to prevent the triggering of a fire response from the fire sensing device  100 . In some examples, a fire response of the fire sensing device  100  can be triggered responsive to the proximity sensor  118  detecting an object within a particular distance of the fire sensing device  100 . 
       FIG. 2  illustrates a block diagram of a smoke self-test function  220  of a fire sensing device in accordance with an embodiment of the present disclosure. The block diagram of the smoke self-test function  220  includes a fire sensing device  200  and a monitoring device  201 . The fire sensing device  200  includes a microcontroller  222 , an adjustable particle generator  202 , an optical scatter chamber  204 , and a variable airflow generator  216 . 
     The monitoring device  201  can be a control panel, a fire detection control system, and/or a cloud computing device of a fire alarm system. The monitoring device  201  can be configured to send commands to and/or receive test results from a fire sensing device  200  via a wired or wireless network. The network can be a network relationship through which monitoring device  201  can communicate with the fire sensing device  200 . Examples of such a network relationship can include a distributed computing environment (e.g., a cloud computing environment), a wide area network (WAN) such as the Internet, a local area network (LAN), a personal area network (PAN), a campus area network (CAN), or metropolitan area network (MAN), among other types of network relationships. For instance, the network can include a number of servers that receive information from, and transmit information to, monitoring device  201  and the fire sensing device  200  via a wired or wireless network. 
     As used herein, a “network” can provide a communication system that directly or indirectly links two or more computers and/or peripheral devices and allows a monitoring device to access data and/or resources on a fire sensing device  200  and vice versa. A network can allow users to share resources on their own systems with other network users and to access information on centrally located systems or on systems that are located at remote locations. For example, a network can tie a number of computing devices together to form a distributed control network (e.g., cloud). 
     A network may provide connections to the Internet and/or to the networks of other entities (e.g., organizations, institutions, etc.). Users may interact with network-enabled software applications to make a network request, such as to get data. Applications may also communicate with network management software, which can interact with network hardware to transmit information between devices on the network. 
     The microcontroller  222  can include a memory  224  and a processor  226 . Memory  224  can be any type of storage medium that can be accessed by processor  226  to perform various examples of the present disclosure. For example, memory  224  can be a non-transitory computer readable medium having computer readable instructions (e.g., computer program instructions) stored thereon that are executable by processor  226  to test a fire sensing device  200  in accordance with the present disclosure. For instance, processor  226  can execute the executable instructions stored in memory  224  to generate a particular aerosol density level, measure the generated aerosol density level, determine an airflow rate from an external environment through the optical scatter chamber  204 , and transmit the determined airflow rate. In some examples, memory  224  can store the aerosol density level sufficient to trigger a fire response from a properly firing sensing device, the aerosol density level sufficient to test a fault condition without triggering a fire response, the threshold airflow rate to verify proper airflow through the optical scatter chamber  204 , and/or the particular period of time that has passed since previously conducting a smoke self-test function (e.g., generating a particular aerosol density level and measuring the generated aerosol density level). 
     The microcontroller  222  can execute the smoke self-test function  220  of the fire sensing device  200  responsive to a particular period of time passing since previously conducting a smoke self-test function and/or responsive to receiving a command from the monitoring device  201 . 
     The microcontroller  222  can send a command to the adjustable particle generator  202  to generate particles. The particles can be drawn through the optical scatter chamber  204  via the variable airflow generator  216  creating a controlled aerosol density level. The aerosol density level can be sufficient to trigger a fire response without saturating an optical scatter chamber. The aerosol density level can be measured and the airflow rate can be determined by the optical scatter chamber  204 . As shown in  FIG. 2 , the scatter chamber  204  can include a transmitter light-emitting diode (LED)  205  and a receiver photodiode  206  to measure the aerosol density level. 
     Once the aerosol density level is measured and/or the airflow rate is determined, the fire sensing device  200  can store the test result (e.g., fire response, aerosol density level, rate at which the aerosol density level decreases after the aerosol density level has been generated, and/or airflow rate) in memory  224  and/or send the test result to the monitoring device  201 . In some examples, the fire sensing device  200  can determine whether the fire sensing device  200  is functioning properly based on the test result and/or the monitoring device  201  can determine whether the fire sensing device  200  is functioning properly based on the test result. For example, the monitoring device  201  can determine the fire sensing device  200  is functioning properly responsive to the triggering of a fire response and/or the airflow rate exceeding a threshold airflow rate. 
       FIG. 3  illustrates a block diagram of a heat self-test function  330  of a fire sensing device in accordance with an embodiment of the present disclosure. The block diagram of the heat self-test function  330  includes a fire sensing device  300  and a monitoring device  301 . The fire sensing device  300  includes a microcontroller  322 , a heat source  319 , a heat sensing element  310 , and a variable airflow generator  316 . 
     The microcontroller  322  can include a memory  324  and a processor  326 . Memory  324  can be a non-transitory computer readable medium having computer readable instructions (e.g., computer program instructions) stored thereon that are executable by processor  326  to test a fire sensing device  300  in accordance with the present disclosure. For instance, processor  326  can execute the executable instructions stored in memory  324  to generate heat at a temperature sufficient to trigger a fire response using the heat source  319 , detect a rise in temperature using the heat sensor  310 , turn off the heat source  319 , measure a rate of reduction in temperature, and/or determine an airflow rate based on the rate of reduction in temperature. In some examples, memory  324  can store the threshold temperature sufficient to trigger a fire response from a properly functioning heat sensing element  310  and/or the period of time that has passed since previously conducting a heat self-test function (e.g., generating heat, detecting a rise in temperature, turning off the heat source, measuring a rate of reduction in temperature, determining an airflow rate based on the rate of reduction in temperature, and/or transmitting the temperature reading). 
     The microcontroller  322  can execute the heat self-test function  330  of the fire sensing device  300  responsive to a particular period of time passing since previously conducting a heat self-test function and/or responsive to receiving a command from the monitoring device  301 . 
     The microcontroller  322  can send a command to the heat source  319  to produce heat. The heat can be drawn past the heat sensor  310  via the variable airflow generator  316 , the heat source  319  can be turned off, the variable airflow generator  316  can be turned off, the heat sensor  310  can measure a rate of reduction in temperature, and/or determine an airflow rate based on the rate of reduction in temperature. The fire sensing device  300  can store the measured rate of reduction in temperature and/or the determined airflow rate in memory  324  and/or send the test result (e.g., the measured rate of reduction in temperature and/or the determined airflow rate to the monitoring device  301 . In some examples, the fire sensing device  300  can determine whether the fire sensing device  300  is functioning properly based on the fire response, the measured rate of reduction in temperature and/or the determined airflow rate and/or the monitoring device  301  can determine whether the fire sensing device  300  is functioning properly based on the measured rate of reduction in temperature and/or the determined airflow rate. For example, the monitoring device  301  can determine the fire sensing device  300  is functioning properly responsive to the measured rate of reduction in temperature exceeding a threshold rate of reduction in temperature and/or the determined airflow rate exceeding a threshold airflow rate. 
       FIG. 4  illustrates a block diagram of a gas self-test function  440  of a fire sensing device  400  in accordance with an embodiment of the present disclosure. The block diagram of the gas self-test function  440  includes a fire sensing device  400  and a monitoring device  401 . The fire sensing device  400  includes a microcontroller  422 , a gas source  412 , a gas sensor  414 , and a variable airflow generator  416 . 
     The microcontroller  422  can include a memory  424  and a processor  426 . Memory  424  can be a non-transitory computer readable medium having computer readable instructions (e.g., computer program instructions) stored thereon that are executable by processor  426  to test a fire sensing device  400  in accordance with the present disclosure. For instance, processor  426  can execute the executable instructions stored in memory  424  to release one or more gases using the gas source  412  and detect one or more gases using the gas sensor  414 . In some examples, memory  424  can store the threshold level of gas sufficient to trigger a fire response from a properly functioning gas sensor  414  and/or the period of time that has passed since previously conducting a gas self-test function  440  (e.g., releasing gas, detecting gas, determining a change in gas level over time, transmitting the gas level, and/or transmitting the change in gas level over time). 
     The microcontroller  422  can execute the gas self-test function  440  of the fire sensing device  400  responsive to a particular period of time passing since previously conducting a gas self-test function and/or responsive to receiving a command from the monitoring device  401 . 
     The microcontroller  422  can send a command to the gas source  412  to release gas. The gas can be drawn past the gas sensor  414  via the variable airflow generator  416 , the gas sensor  414  can measure the gas level, and determine the change in gas level over time. Once the gas level is measured, the fire sensing device  400  can store the test result (e.g., gas level and/or change in gas level over time) in memory  424  and/or send the test result to the monitoring device  401 . The fire sensing device  400  and/or the monitoring device  401  can determine an airflow rate based on the change in gas level over time. In some examples, the fire sensing device  400  can determine whether the fire sensing device  400  is functioning properly based on the test result and/or the determined airflow rate and/or the monitoring device  401  can determine whether the fire sensing device  400  is functioning properly based on the test result and/or the determined airflow rate. For example, the monitoring device  401  can determine the fire sensing device  400  is functioning properly responsive to the fire response, detecting one or more gases, detecting one or more gas levels, determining the change in gas level over time exceeds a threshold level and/or determining the determined airflow rate exceeds a threshold airflow rate. 
       FIG. 5  illustrates a plot (e.g., graph)  550  of example optical scatter chamber (e.g., sensor) outputs  558 - 1  and  558 - 2  used to determine whether a fire sensing device (e.g., fire sensing device  200  in  FIG. 2 ) is functioning properly in accordance with an embodiment of the present disclosure. The optical scatter chamber outputs  558 - 1  and  558 - 2  can be a rate of reduction in aerosol density level. 
     In the example illustrated in  FIG. 5 , a variable airflow generator (e.g., variable airflow generator  216  in  FIG. 2 ) and an adjustable particle generator (e.g., adjustable particle generator  202  in  FIG. 2 ) can be powered off (e.g., turned off) at time  552 - 1 . At time  552 - 2 , the variable airflow generator and the adjustable particle generator can be powered on (e.g., turned on) to start a smoke self-test function, as previously described in connection with  FIG. 2 . When powered on the adjustable particle generator (e.g., fan) can generate particles (e.g., aerosol particles) and the generated particles can be mixed into a controlled aerosol density level by the variable airflow generator. The variable airflow generator can move the generated particles through an optical scatter chamber (e.g., optical scatter chamber  204  in  FIG. 2 ). The optical scatter chamber can determine the airflow rate by measuring the rate at which the aerosol density level decreases after the aerosol density level has been generated. 
     Particles can be generated until a threshold aerosol density level (e.g., set-point)  556  is met. The threshold aerosol density level can be a sufficient aerosol density level to trigger a fire response (e.g., fire threshold)  554  from a properly functioning fire sensing device without saturating an optical scatter chamber, for example. Once the threshold aerosol density level  556  is met, the adjustable particle generator can stop generating particles at time  552 - 3  and the variable airflow generator can continue and/or increase the airflow, moving the generated particles through the optical scatter chamber. 
     The measured aerosol density level after the adjustable particle generator has stopped can reduce over time, as shown by the example optical scatter chamber outputs  558 - 1  and  558 - 2 . In the example optical scatter chamber output  588 - 1 , the aerosol density level remains higher than the example optical scatter chamber output  558 - 2  after the adjustable particle generator stops generating particles. The example optical scatter chamber output  588 - 1  illustrates an impeded airflow through the optical scatter chamber where the optical scatter chamber is masked, and the fire sensing device cannot function properly. 
     In the example optical scatter chamber output  588 - 2 , the aerosol density level reduces more than the example optical scatter chamber output  588 - 1  after the adjustable particle generator stops generating particles. The example optical scatter chamber output  588 - 2  illustrates sufficient airflow through the optical scatter chamber where the optical scatter chamber is not masked, and the fire sensing device can function properly. Once it is determined whether the fire sensing device is functioning properly, at time  552 - 4 , the smoke self-test function can be complete, and the variable airflow generator can be turned off. 
     Although specific embodiments have been illustrated and described herein, those of ordinary skill in the art will appreciate that any arrangement calculated to achieve the same techniques can be substituted for the specific embodiments shown. This disclosure is intended to cover any and all adaptations or variations of various embodiments of the disclosure. 
     It is to be understood that the above description has been made in an illustrative fashion, and not a restrictive one. Combination of the above embodiments, and other embodiments not specifically described herein will be apparent to those of skill in the art upon reviewing the above description. 
     The scope of the various embodiments of the disclosure includes any other applications in which the above structures and methods are used. Therefore, the scope of various embodiments of the disclosure should be determined with reference to the appended claims, along with the full range of equivalents to which such claims are entitled. 
     In the foregoing Detailed Description, various features are grouped together in example embodiments illustrated in the figures for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the embodiments of the disclosure require more features than are expressly recited in each claim. 
     Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed embodiment. Thus, the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separate embodiment.