Patent Publication Number: US-2023149578-A1

Title: Inactivation device and inactivation method

Description:
TECHNICAL FIELD 
     The present invention relates to an inactivation device and an inactivation method of inactivating harmful microorganisms and viruses. 
     BACKGROUND ART 
     Facilities where people frequently gather, such as medical facilities, schools, and government offices, are places where harmful microorganisms (bacteria, molds, etc.) and viruses can easily proliferate. These harmful microorganisms and viruses are especially prone to proliferate in confined spaces (enclosed spaces such as hospital rooms, restrooms, and elevators) in the above-mentioned facilities. 
     The above-mentioned harmful microorganisms proliferate on the floors, walls, and other surfaces in the above-mentioned confined spaces, or inside humans (or animals in some cases) entering or leaving the above-mentioned confined spaces, or the harmful microorganisms float in the above-mentioned confined spaces. This tendency is particularly pronounced in medical facilities. Specifically, infectious microorganisms derived from patients spread in confined spaces such as hospital rooms, restrooms in hospital rooms, and restrooms near outpatient reception areas. The spread infectious microorganisms adhere to the surfaces (floors, walls, etc.) constituting the confined spaces, or float in the spaces. As a result, the next person (such as another patient or visitor) entering the spaces (such as a restroom) can be infected, and in some cases, the infectious disease may spread in the medical facility. 
     In order to improve the situation described above, facilities where humans (and animals in some cases) gather (especially medical facilities) are required to take measures to decontaminate (sterilize) the above-mentioned harmful microorganisms (e.g., infectious microorganisms). 
     Patent Document 1 discloses a decontamination device that irradiates a space targeted for decontamination with ultraviolet light (UVC light) and decontaminates the space. This decontamination device radiates ultraviolet light into the space targeted for decontamination when it detects the absence of a person in the space targeted for decontamination. 
     Patent Document 2 discloses a system in which a motion sensor and a door sensor are mounted in an elevator, and the system radiates ultraviolet light for sterilization to the interior of the elevator when the above-mentioned sensors detect that no human is present in the elevator and the door is closed. Here, the radiated ultraviolet light has a wavelength of between approximately 240 nm and 280 nm. 
     Citation List 
     Patent Documents 
     
         
         Patent Document 1: JP-A-2017-528258 
         Patent Document 2: US 2010/0032859A 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     The proliferation or floating of harmful microorganisms in the confined spaces of the facilities is often caused by humans (patients) or animals with harmful microorganisms entering or leaving the above-mentioned spaces. Thus, for the efficient decontamination of such facilities, it is essential to decontaminate not only the surfaces and spaces inside the facilities, but also the surfaces of humans (patients) and animals present in the areas. 
      However, ultraviolet light having a wavelength suitable for decontamination has an adverse effect on humans or animals when radiated thereto. Hence, Patent Document 1 and Patent Document 2 disclose decontamination systems using the irradiation with ultraviolet light, in which emission of ultraviolet light stops during the presence of humans in the irradiation area to ensure the safety of humans or animals. 
     Thus, the above-mentioned conventional decontamination systems cannot decontaminate the facilities efficiently. Also, the conventional decontamination systems cannot decontaminate the surfaces of humans (patients) and animals, thereby the area to be decontaminated needs to be broadened in consideration of the activity range of humans (patients) and animals. 
     It is an object of the present invention to provide an inactivation device and an inactivation method that can efficiently inactivate harmful microorganisms and/or viruses. 
     Solution to Problem 
     To solve the above-described problems, an inactivation device according to one aspect of the present invention of inactivating microorganisms and/or viruses that are harmful to a human body includes: an ultraviolet light irradiation unit that irradiates an enclosed space where a human can enter and leave with light containing ultraviolet light having a wavelength of inactivating the microorganisms and/or viruses that are harmful to the human body; a sensor that detects presence of the human in the enclosed space; and a control unit that controls irradiation and non-irradiation with the light from the ultraviolet light irradiation unit based on a detection signal from the sensor. The control unit controls the ultraviolet light irradiation unit to irradiate a space including the human with the light for a predetermined time in accordance with the wavelength of the ultraviolet light contained in the light radiated from the ultraviolet light irradiation unit, during a period in which the human is determined to be present in the enclosed space based on the detection signal from the sensor. 
     In this way, intentionally irradiating a human with light containing ultraviolet light is capable of inactivating at least one harmful microorganism and/or virus present on a surface of the human body (skin or surface of clothes). Hence, the irradiation prevents the harmful microorganisms or viruses attached to humans from spreading into an enclosed space. In addition, the irradiation prevents a human leaving the enclosed space from spreading the harmful microorganisms or viruses outside the enclosed space. Therefore, the irradiation avoids the expansion of the area to be decontaminated in the facility, resulting in efficient decontamination of the facility. 
     It is noted that the time of irradiating a human with ultraviolet light is determined in accordance with the wavelength of the ultraviolet light. The extent to which ultraviolet irradiation adversely affects to a human body depends on the wavelength of the ultraviolet light. Therefore, irradiating the human with ultraviolet light for the predetermined time in accordance with the wavelength of the ultraviolet light enables the efficient decontamination without adversely affecting to the human body. 
     In the above-described inactivation device, if it is determined that no human is present in the enclosed space based on the detection signal from the sensor, the control unit may control the ultraviolet light irradiation unit to irradiate the enclosed space where no human is present with the light. In this way, emission of light containing ultraviolet light to the enclosed space where no human is present is capable of efficiently inactivating at least part of the harmful microorganisms or viruses already present in the enclosed space, the harmful microorganisms or viruses spreading inside the enclosed space upon entering of the human into the enclosed space, the harmful microorganisms or viruses attached to a surface of the enclosed space upon contacting of the human with a part of the surface inside the enclosed space, or the harmful microorganisms or viruses floating in the flow of air inside the enclosed space upon entering of the human into the enclosed space. 
     In the above-described inactivation device, the control unit may control the ultraviolet light irradiation unit to irradiate the enclosed space where no human is present with the light for a predetermined time, and to stop radiation of the light after the predetermined time. 
     This control enables a light source mounted in the ultraviolet light irradiation unit to have a pause time, extending a service life of the light source. 
     In the above-described inactivation device, the sensor may include a first sensor that detects the human entering or leaving the enclosed space, and the control unit may control the ultraviolet light irradiation unit to irradiate the space including the human with the light for the predetermined time after the first sensor detects that the human has entered the enclosed space. 
     This control enables the human to be irradiated with light containing ultraviolet light immediately after the human enters the enclosed space, thereby efficiently suppressing the spread of harmful microorganisms or viruses from the human to the enclosed space. 
     In the above-described inactivation device, the first sensor may be at least one of a motion sensor that detects the presence or absence of the human in the enclosed space and a door sensor that detects the opening or closing of a door of the enclosed space. 
     This configuration enables easy and appropriate detection of the entering and exiting of a human into and out of the enclosed space. 
     In the above-described inactivation device, the sensor may include a second sensor that detects the presence of the human at a predetermined position in the enclosed space, and the control unit may control the ultraviolet light irradiation unit to irradiate the space including the human with the light for the predetermined time after the second sensor detects the presence of the human at the predetermined position in the enclosed space. 
     Thus, irradiating the human present in the predetermined position with light containing ultraviolet light enables ultraviolet light to be effectively radiated to the intended location on the surface of the human body. 
     In the above-described inactivation device, the sensor may include a first sensor that detects the human entering or leaving the enclosed space and a second sensor that detects the presence of the human present at a predetermined position in the enclosed space. The control unit may control the ultraviolet light irradiation unit to stop radiation of the light when the first sensor detects that the human has entered the enclosed space and start radiating the light to the space including the human for the predetermined time after the second sensor detects the presence of the human at the predetermined position in the enclosed space. 
     If the light containing the ultraviolet light is radiated to the enclosed space before a human enters, the control unit may control the ultraviolet light irradiation unit to temporarily stop irradiation with the ultraviolet light when a human enters the enclosed space. Once the human is in the predetermined position, the control unit may start irradiating the human with the light containing ultraviolet light for a predetermined time. 
     In the above-described inactivation device, the first sensor may be a door sensor that detects the opening or closing of a door of the enclosed space. If the second sensor does not detect the presence of the human at the predetermined position in the enclosed space, the control unit may control the ultraviolet light irradiation unit to radiate the light to the enclosed space where no human is present after a predetermined time has elapsed after the first sensor detects the opening or closing of the door. 
     This control enables an appropriate judgement that no human is present in the enclosed space, using both of the detection signal from the first sensor and the detection signal from the second sensor. For example, in case that the door unintentionally opens or closes due to forgotten locking or door defect, this configuration can prevent the inactivation device from mistakenly recognizing that the human has left the enclosed space and starting the irradiation with the ultraviolet light. Moreover, keeping ultraviolet irradiation from starting for a predetermined time after the opening or closing of the door can prevent the inactivation device from starting the irradiation with the ultraviolet light in the case that the human, after entering the enclosed space, is present at a position other than a predetermined position. 
     In the above-described inactivation device, the enclosed space may be a restroom stall and the second sensor may be a pressure sensor provided in a toilet seat. 
     In this case, the state that a person sits on the toilet seat of a toilet bowl in a restroom stall can be detected as a state that a person is present in a predetermined position. Since a movement of the human sitting on a toilet seat is relatively small, it is possible to effectively inactivate harmful microorganisms and viruses on the surface of the human body (skin and clothing). 
     In the above-described inactivation device, the ultraviolet light irradiation unit may be mounted at a position such that the light is radiated to the human present at the predetermined position from a back of a head of the human. 
     This configuration prevents human’s eyes from directly being exposed to the light containing ultraviolet light radiated from the ultraviolet light irradiation unit, thereby suppressing the occurrence of eye damage including eye pain, hyperemia, and corneal inflammation. 
     In the above-described inactivation device, the ultraviolet light irradiation unit may be mounted at a position at which the light is radiated downward from an upper area of the enclosed space. 
     This configuration enables the irradiation with the light containing ultraviolet light over the entire enclosed space. Hence, it is possible to effectively inactivate harmful microorganisms and viruses attached to the walls or floors of the enclosed space. 
     In the above-described inactivation device, the predetermined time T1 (seconds) may be set to satisfy a formula as follows: 
     
       
         
           
             T1 
             ≤ 
             
               D 
               
                 max 
               
             
             / 
             
               
                 W 
                 × 
                 N 
               
             
           
         
       
     
      where D max  (mJ/cm 2 ) is an amount of maximum allowable ultraviolet light exposure to the human body per day, which is determined in accordance with the wavelength of the ultraviolet light to be radiated, W (mW/cm 2 ) is the irradiance of the ultraviolet light radiated on a surface of the human body, and N is the number of times the same person enters the enclosed space per day. 
     Satisfying this formula enables the ultraviolet light having a wavelength suitable for inactivation of harmful microorganisms or viruses to be radiated to the human within the range of the amount of light that does not adversely affect a human body. 
     In the above-described inactivation device, an ultraviolet light irradiation operation of the ultraviolet light irradiation unit may include repetition of the ultraviolet light emission and subsequent pause. A total time of the ultraviolet light emission in the repeated ultraviolet light emission operations of twice or more may be set to be the time T1. In this case, time of the ultraviolet light emission may be between 10 milliseconds (msec) and 1000 milliseconds, and time of the pause may be between 10 milliseconds and 10 seconds (sec). 
     The time of the pause allows the longer ultraviolet light irradiation period until the ultraviolet light irradiation time reaches the predetermined time T1, thereby increasing the chance of radiating ultraviolet light when, for example, bacteria or viruses spread and fly at the time of splash and/or defecation. 
     The ultraviolet light irradiation unit may include a light-emitting diode (LED) that radiates the ultraviolet light or a laser diode (LD) that radiates the ultraviolet light. These devices can repeat the ultraviolet light emission and the pause with high speed by means of power control. 
     In the above-described inactivation device, the ultraviolet light irradiation unit may include a KrCl excimer lamp that radiates the ultraviolet light having a center wavelength of 222 nm. This configuration suppresses an adversely effect on the human body due to the ultraviolet light irradiation. 
     In the above-described inactivation device, the ultraviolet light contained in the light radiated from the ultraviolet light irradiation unit may only have a wavelength band ranging from 190 nm to 235 nm. This configuration appropriately suppress an adverse effect on the human body due to ultraviolet light irradiation. 
     A method according to another aspect of the present invention is directed to an inactivation method of inactivating microorganisms and/or viruses harmful to a human body. The method includes: detecting presence of a human in an enclosed space that the human can enter and leave, with a sensor; and controlling an ultraviolet light irradiation unit that irradiates an enclosed space with light containing ultraviolet light having a wavelength of inactivating microorganisms and/or viruses harmful to the human body to perform irradiation and non-irradiation with the light, and irradiating a space including the human with the light for a predetermined time in accordance with the wavelength of the ultraviolet light contained in the light during a period in which the human is determined to be present in the enclosed space. 
     Hence, intentionally irradiating a human with light containing ultraviolet light for the predetermined time is capable of inactivating at least one harmful microorganism and/or virus present on the surface of human body (surface of skin or clothes). Thus, it is possible to prevent the harmful microorganisms or viruses from spreading into the enclosed space from the human. In addition, it is possible to prevent a human leaving the enclosed space from spreading the harmful microorganisms or viruses outside the enclosed space. Therefore, the irradiation can avoid or reduce the expansion of areas to be decontaminated in a facility, i.e., it is possible to efficiently decontaminate the facility. 
     The time of irradiating human with ultraviolet light is determined in accordance with the wavelength of the ultraviolet light. The extent to which ultraviolet irradiation adversely affects to the human body depends on the wavelength of the ultraviolet light. Therefore, irradiating the human with ultraviolet light for a predetermined time in accordance with the wavelength of the ultraviolet light is capable of performing the efficient decontamination without adversely affecting to human body. 
     Advantageous Effects of Invention 
     The present invention is capable of efficiently inactivating harmful microorganisms or viruses by intentionally irradiating a human with light containing ultraviolet light for a predetermined time. 
     These and other objects, aspects and advantageous effects of the present invention can be understood by those skilled in the art from the following mode of carrying out the invention (detailed description of the invention) by referring to the accompanying drawings and the claims. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a view schematically showing an exemplary configuration of an inactivation system according to an embodiment of the present invention. 
         FIG.  2    is a flowchart describing an operation of a first embodiment. 
         FIG.  3    is a timing chart describing an operation of the first embodiment. 
         FIG.  4    is a flowchart describing an operation of a modification to the first embodiment. 
         FIG.  5    is a timing chart describing an operation of the modification to the first embodiment. 
         FIG.  6    is a flowchart describing an operation of a second embodiment. 
         FIG.  7    is a timing chart describing an operation of the second embodiment. 
         FIG.  8    is a flowchart describing an operation of a modification to the second embodiment. 
         FIG.  9    is a timing chart describing an operation of the modification to the second embodiment. 
         FIG.  10    is a timing chart describing an operation of the modification to the second embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments of the present invention will be described with reference to the drawings. 
     First Embodiment 
     In the present embodiment, an inactivation system will be described that inactivates harmful microorganisms and viruses by irradiating the harmful microorganism and viruses with ultraviolet light, in particular, in confined spaces of facilities where people frequently gather (enclosed spaces such as hospital rooms, restrooms, and elevators). The inactivation system of the present embodiment inactivates harmful microorganisms and viruses by intentionally irradiating living organisms, such as humans (patients) and animals, with ultraviolet light for a predetermined time, which has been conventionally avoided for safety reason. 
       FIG.  1    is a drawing schematically describing an example of a configuration of an inactivation system of the present embodiment. In the present embodiment, an example of an inactivation system that inactivates harmful microorganisms and viruses present in a restroom stall will be described. The inactivation system includes an inactivation device  100 . The inactivation device  100  includes at least one of ultraviolet light irradiation units (UV irradiation units)  10 A  and  10 B that radiate ultraviolet light to an enclosed space (a restroom stall)  200 . It is noted that the wavelength band of the ultraviolet light radiated from each of the UV irradiation units  10 A,  10 B is, for example, 200 nm to 320 nm. 
     The UV irradiation unit  10 A is provided on a ceiling  201  in the restroom stall  200 . It is noted that the UV irradiation unit  10 A may be provided on the upper part in the restroom stall  200 , for example, on the upper area of the wall  202  in the restroom stall  200 . 
     The UV irradiation unit  10 A radiates ultraviolet light in a downward direction and the ultraviolet light is radiated to a space in the restroom stall  200 , the wall  202 , a floor and so on. The ultraviolet light radiated from the UV irradiation unit  10 A hits a human (for example, patient)  300  from above the human  300  when the human  300  enters the restroom stall  200 . 
     The UV irradiation unit  10 B is provided on the wall  202  in the restroom stall  200 . The UV irradiation unit  10 B mainly radiates ultraviolet light in a downward direction from its mounting position. This UV irradiation unit  10 B is mounted at a position such that its ultraviolet light is emitted to the human  300  who takes a predetermined posture at a predetermined position in the restroom stall  200 . 
     Specifically, the UV irradiation unit  10 B is mounted on the wall  202  of the restroom stall  200  on the assumption that the ultraviolet light from the UV irradiation unit  10 B is radiated to the human  300  when the human takes a posture of sitting on a toilet bowl  211 . More specifically, the UV irradiation unit  10 B is mounted on the wall  202  facing the back of the head of the human  300  when the human sits on the toilet bowl  211 . 
     Hence, mounting the UV irradiation unit  10 B in the above-described manner allows the ultraviolet light radiated from the UV irradiation unit  10 B to be emitted toward the human  200  from a position upward of the back of the head of the human  300  sitting on the toilet bowl  211 , thereby preventing the ultraviolet light from being directly emitted to the eyes of the human  300 . 
     The inactivation device  100  may include at least one of the sensors such as a motion sensor  11 , a pressure sensor  12 , and a door sensor  13  to detect the presence of the human  300  in the restroom stall  200 . 
     The motion sensor  11  and the door sensor  13  are sensors that detect the entry and exit of a person to and from the restroom stall  200 . 
     The pressure sensor  12  is a sensor that detects the presence of a human at a predetermined position in the restroom stall  200 . 
     The motion sensor  11  is mounted on the ceiling  201 , for example, as shown in  FIG.  1   , and detects the presence or absence of the human  300  in the space of the restroom stall  200 . The pressure sensor  12  is mounted in a toilet seat  212 , for example, as shown in  FIG.  1   , and detects whether or not the human  300  sits on the toilet seat  212  provided on the toilet bowl  211 . 
     The door sensor  13  is mounted on the door  203 , for example, as shown in  FIG.  1   , and detects the opening and closing of the door  203  of the restroom stall  200 . 
     Furthermore, the inactivation device  100  includes a control unit  20 . The control unit  20  receives detection signals from each of the sensors  11  to  13  and controls the irradiation and non-irradiation with the ultraviolet light from the UV irradiation units  10 A and  10 B based on the detection signals. 
     Specifically, the control unit  20  controls at least one of the UV irradiation units  10 A and  10 B to irradiate the interior of the restroom stall  200  including the human  300  with the ultraviolet light for a predetermined time in accordance with the wavelength of the ultraviolet light while the human  300  is determined to be present in the restroom stall  200  based on at least one of the detection signals from the sensors  11  to  13 . 
     In the present embodiment, is described the case that the control unit  20  controls the irradiation with ultraviolet light radiated from the UV irradiation unit  10 A based on the detection signal from the motion sensor  11 . Furthermore, in the present embodiment, if the human  300  is absent in the restroom stall  200 , ultraviolet light principally continues to be emitted in the restroom stall  200  from the UV irradiation unit  10 A. 
     Hereinafter the operation of the inactivation device  100  according to the present embodiment will be described. 
       FIG.  2    is a flowchart describing an operation of the inactivation device  100  according to the present embodiment. 
     In Step S 1 , the control unit  20  determines whether or not the presence of the human  300  is detected in the restroom stall  200  based on the detection signal from the motion sensor  11 . If the control unit  20  determines that presence of the human  300  is not detected, the control unit  20  waits until the presence of the human  300  is detected. Upon detecting the presence of the human  300 , the operation proceeds to Step S 2 . 
     In Step S 2 , the control unit  20  causes a timer 1 to start counting as a counter. 
     Next in Step S 3 , the control unit  20  determines whether or not a predetermined time T1 has elapsed since the timer 1 start the counting based on the counter value of the timer 1, i.e., the control unit  20  determines whether or not the predetermined time T1 has elapsed since the detection of the presence of the human  300  in the restroom stall  200 . If the predetermined time T1 has not yet elapsed, the control  20  waits for the predetermined time T1 to elapse. The control unit  20  proceeds to Step S 4  when it determines that the predetermined time T1 has elapsed. 
     It is noted that the predetermined time T1 is determined in accordance with the wavelength of the ultraviolet light radiated from the UV irradiation unit  10 A, and should be set not more than a maximum time that is permitted to be emitted to a living body under safety standards. Details of the predetermined time T1 will be explained later. 
     In Step S 4 , the control unit  20  causes the timer 1 to stop counting and resets the counting value of the timer 1. 
     In Step S 5 , the control unit  20  causes the UV irradiation unit  10 A to stop emitting the ultraviolet light. 
     In Step S 6 , the control unit  20  determines whether or not the human  300  has exited from the restroom stall  200  based on the detection signal from the motion sensor  11 . The control unit  20  waits until it determines the exiting of the human  300 . The control unit  20  proceeds to Step S 7  when it determines that the human  300  has exited. 
     In Step S 7 , the control unit  20  causes the UV irradiation unit  10 A to start emitting ultraviolet light and returns to Step S 1 . 
       FIG.  3    is a timing chart describing an operation of the inactivation device  100  of the present embodiment. 
     Ultraviolet light from the UV irradiation unit  10 A continues to be emitted in the restroom stall  200  before the human  300  enters the restroom stall  200 , i.e., during the absence of the human  300  in the restroom stall  200 . 
     As the human  300  enters the restroom stall  200  at the time A, the motion sensor  11  detects the presence of the human  300 , and the timer 1 starts counting. After the predetermined time T1 has elapsed from the time A, the emission of ultraviolet light in the restroom stall  200  and to the human  300  is stopped. 
     Accordingly, even after the human  300  enters the restroom stall  200 , ultraviolet light from UV irradiation unit  10 A continues to be emitted in the restroom stall  200 , and to the human  300  inside the restroom stall  200  until the predetermined time T1 has elapsed. 
     When the human  300  exits the restroom stall  200  at the time B, the motion sensor  11  detects the exiting of the human  300 , and the emission of the ultraviolet light (irradiation with the ultraviolet light) is resumed in the restroom stall  200 . 
     The irradiation time (predetermined time T1) for irradiating the human  300  with the ultraviolet light will now be explained. 
     Ultraviolet light having a wavelength band of 200 nm to 320 nm radiated from each of the UV irradiation units  10 A and  10 B contains ultraviolet light that adversely affects human bodies. For example, ultraviolet irradiation in the above-mentioned wavelength band can induce erythema and cancer due to DNA damage in the skin, and cause eye damage (eye pain, redness, inflammation of the cornea, etc.). 
     It should be noted, however, that ultraviolet irradiation in the above-mentioned wavelength band does not adversely affect organisms unless integral light intensity (dose amount) to a living body as a subject to be irradiated exceeds a predetermined quantity. The present inventers focus on this point and set irradiation time (predetermined time T1) to intentionally irradiate humans with ultraviolet light. 
      An amount of ultraviolet light exposure to a human using an enclosed space per day (restroom stall) is denoted as D (mJ/cm 2 ) . The amount of ultraviolet exposure per day “D” is expressed by the following equation. 
     
       
         
           
             D 
             
               
                 mJ 
                 / 
                 
                   
                     cm 
                   
                   2 
                 
               
             
             = 
             W 
             
               
                 mW 
                 / 
                 
                   
                     cm 
                   
                   2 
                 
               
             
             × 
             N 
             × 
             T1 
             
               
                 sec 
               
             
           
         
       
     
     where W (mW/cm 2 ) is the irradiance of the ultraviolet light emitted on the surface of the human body, N is the number of times the human enters the enclosed space (restroom stall) per day, and T1 is the ultraviolet light irradiation time during a single stay in the restroom stall. 
     When D max  (mJ/cm 2 ) denotes the maximum amount of allowable ultraviolet light exposure to the human body using the enclosed space (restroom stall) per day, D max  ≥ D is sufficient to prevent adverse effect on humans caused by ultraviolet light irradiation. 
     Namely, the ultraviolet light irradiation time per stay in the restroom stall T1 is expressed by the following formula. 
     
       
         
           
             T1 
             ≦ 
             
               D 
               
                 max 
               
             
             / 
             
               
                 W 
                 × 
                 N 
               
             
           
         
       
     
     As an example, a low-pressure mercury lamp that emits ultraviolet light having a wavelength of 253.7 nm is used for the ultraviolet light source. The maximum amount of allowable exposure of the ultraviolet light having a wavelength of 253.7 nm is expressed as D max  = 6(mJ/cm 2 ) due to the safety standard. This value is determined by the ACGIH (American Conference of Governmental Industrial Hygienists). 
     The ultraviolet light irradiation time during a single stay in the restroom stall T1 is calculated to be 30 seconds or less by using the equation (2), where the irradiance of the ultraviolet light radiated onto the surface of the human body is 0.022 (mW/cm 2 ) and the number of times N the human uses the restroom stall provided in a hospital room (number of times the human enters the restroom stall) per day is 10. 
     In other words, in the case in which the ultraviolet light source provided in the UV irradiation unit  10 A is a low-pressure mercury lamp that radiates ultraviolet light having a wavelength of 253.7 nm, ultraviolet light irradiation does not adversely affect the human  300  as long as the predetermined time T1 set in  FIG.  2    and  FIG.  3    is 30 seconds or less. Hence, in this case, the predetermined time T1 is set to be, for example, 30 seconds, which is a maximum time. 
     It is noted that the irradiance of the ultraviolet light emitted onto the surface of the human body is determined using the following considerations: the head (top) of the human  300  standing in the enclosed space (restroom stall)  200  is considered to be the surface to which the ultraviolet light is emitted, and the distance from the ceiling  201  of the enclosed space (restroom stall)  200  to the head of the human  300   standing on the floor is considered to be the ultraviolet light travelling distance. 
     The number of times N a human enters the enclosed space (restroom stall) refers to the number of times a human uses the restroom stall provided in a hospital room, thus N = 10. In the case of the restroom stall that is provided in a reception area or a waiting room for outpatients, however, the number of times N′ that each of a plurality of humans waiting in a waiting room uses the restroom stall per day is considered to be smaller than the number of times N a person uses a restroom stall provided in a hospital room. Hence, N′ = 2 or 3 may be used to set the ultraviolet light irradiation time T1. 
     It is preferable that the number of times human enters the enclosed space per day N be set to a larger number for a safety side. 
     In addition, low-pressure mercury lamps do not immediately light up when power is supplied; it takes certain amount of time to light up. Hence, a low-pressure mercury lamp used as an ultraviolet light source cannot repeatedly perform irradiation and non-irradiation with the ultraviolet light at relatively short intervals using the power control. In this case, shutters for light shielding may be provided and controlled to open and close while keeping a low-pressure mercury lamp in a lit state such that emission and non-emission of ultraviolet light is controlled. 
     The example of the ultraviolet light source is a KrCl excimer lamp that radiates ultraviolet light having a center wavelength of 222 nm. 
     Excimer lamps light up immediately after its power is supplied. Unlike low-pressure mercury lamps used for the light source, no shutter for shielding the light needs to be provided. Hence, controlling the power to the excimer lamps enables the repeated irradiation and non-irradiation with ultraviolet light at relatively short intervals. 
     The ultraviolet light having a center wavelength of 222 nm sterilizes germs including bacteria; however, it has less adverse effects on human cells. 
     UV radiation ray having shorter wavelengths penetrates less. For example, UV radiation ray having short wavelengths such as approximately 200 nm is transmitted through water very efficiently; however, it is highly absorbed by the outer portion of human cells (cytoplasm) and may not have enough energy to reach cell nucleus, which contains radiation-sensitive DNA. Hence, the above-mentioned UV radiation ray having the short wavelengths has less adverse effects to human cells, namely, to humans. 
     In contrast, bacteria is typically much smaller in physical size than human cells. Specifically, typical bacteria cell has a diameter of below 1 micrometer, whereas the human cells typically have a diameter of approximately 10 to 30 micrometers depending upon the kind and location of the human cell. 
     Hence, UV radiation having short wavelength can readily penetrate bacteria and sterilize them. 
     The current safety standard permits that the daily maximum amount of allowable exposure of ultraviolet light having a wavelength of 222 nm is D max  = 21 (mJ/cm 2 ) . This value is larger than that of ultraviolet light having a wavelength of 253.7 nm. In other words, from the standpoint of the safety standard, the ultraviolet light having a wavelength of 222 nm has less adverse effects on humans than the ultraviolet light having a wavelength of 253.7 nm. 
     In the case of adopting KrCl excimer lamps that emit ultraviolet light having a center wavelength of 222 nm, the ultraviolet light irradiation time per stay in the restroom stall T1 is calculated to be 95 seconds or less using the equation (2), where the irradiance of the ultraviolet light emitted onto the surface of the human body is 0.022 (mW/cm 2 ) and the number of times N the human uses the restroom stall provided in a hospital room (number of times entering the restroom stall) per day is 10, which is similar to the case of adopting low-pressure mercury lamps that radiate ultraviolet light having a wavelength of 253.7 nm. 
     Thus, in the case that the ultraviolet light source provided in the UV irradiation unit  10 A is KrCl excimer lamps that radiate ultraviolet light having a center wavelength of 222 nm, the predetermined time T1 set in  FIG.  2    and  FIG.  3    is determined to be, for example, a maximum time of 95 seconds. 
     KrCl excimer lamps radiate ultraviolet light having a center wavelength of 222 nm; however, they also slightly radiate light having the other wavelength ranges. Thus, for practical use of KrCl excimer lamps, it is preferable to use a wavelength selection filter that transmits only light having a wavelength band ranging from 190 nm to 235 nm, which has less adverse effect on humans, and blocks light having the other wavelength bands. 
     The wavelength selection filter can be, for example, an optical filter having a dielectric multilayer with HfO 2  and SiO 2  layers. Specifically, the optical filter may have a structure in which a dielectric multilayer film consisting of alternating layers of HfO 2  and SiO 2  is formed on one surface of a substrate made of synthetic quartz (silica) glass, and an AR coating consisting of HfO 2  and SiO 2  layers is applied on the other surface of the substrate. The dielectric multilayer has, for example, HfO 2  layers having a thickness of approximately 240 nm and SiO 2  layers having a thickness of approximately 1460 nm, and consists of 33 layers (sum of the HfO 2  layers and the SiO 2  layers) in total. 
     The wavelength selection filter can also be, for example, an optical filter having a dielectric multilayer with SiO 2  and Al 2 O 3  layers. 
     However, when the optical filter with a dielectric multilayer made of HfO 2  and SiO 2  layers is used as a wavelength selection filter, the total number of layers is reduced as compared to the case where an optical filter with dielectric multilayer made of SiO 2  and Al 2 O 3  layers is used. Therefore, the transmittance of ultraviolet light at an incident angle of 0° increases, ensuring the light intensity of ultraviolet light in the desired wavelength band of 190 nm to 235 nm. In addition, reducing the total number of layers decreases the cost for fabrication correspondingly. 
     As described above, the inactivation device  100  of the present embodiment includes the ultraviolet light irradiation unit (UV irradiation unit)  10 A that radiates light containing ultraviolet light having a wavelength of inactivating harmful microorganisms and/or viruses to a human body to the enclosed space (the restroom stall  200 ) where a human can enter and leave. The inactivation device  100  also includes the motion sensor  11  that detects the presence and absence of the human in the restroom stall  200  as a sensor to detect the presence of the human in the restroom stall  200 . The control unit  20  controls the UV irradiation unit  10 A to irradiate the restroom stall  200  including the human with the ultraviolet light for a predetermined time (T1) in accordance with the wavelength of the ultraviolet light radiated from the UV irradiation unit  10 A while the human is determined to be present in the restroom stall  200  based on the detection signal from the motion sensor  11 . 
     In this way, intentionally irradiating a human with light containing ultraviolet light for the predetermined time T1 is capable of inactivating at least one harmful microorganisms and/or viruses present on the surface of human body (skin or surface of clothes). Hence, this irradiation prevents the harmful microorganisms and/or viruses attached to humans from spreading into an enclosed space (the restroom stall  200 ) or reduces the spreading of the harmful microorganisms and/or viruses from humans in the enclosed space. 
     In addition, the human leaves the enclosed space (the restroom stall  200 ) after being irradiated with ultraviolet light. Thus, the harmful microorganisms and/or viruses attached to skin or the surface of clothes has been decreased or eliminated. This prevents the human leaving the enclosed space (the restroom stall  200 ) from spreading the harmful microorganisms and/or viruses outside the enclosed space or reduces the spreading of harmful microorganisms and/or viruses from the human outside the enclosed space. Therefore, it is possible to prevent or reduce expansion of the area to be decontaminated in the facility, and achieve efficient decontamination of the facility. 
     Moreover, the predetermined time T1 of irradiating a human with ultraviolet light is determined in accordance with the wavelength of the ultraviolet light. Because the extent to which ultraviolet irradiation adversely affects to a human body depends on the wavelength of the ultraviolet light, setting the predetermined time T1 in accordance with the wavelength of the ultraviolet light allows ultraviolet light having a wavelength suitable for the decontamination to be emitted to the human within a range of amount of light that does not adversely affect to the human body. 
     Specifically, the predetermined time T1 is determined to satisfy the equation (2). Thus, the ultraviolet light irradiation time is determined in accordance with the wavelength of the emitted ultraviolet light based on the safety standard, and it is, therefore, possible to appropriately suppress the adverse effect of the ultraviolet light on the human body. 
     The control unit  20  may acquire the information on the wavelength of ultraviolet light emitted from the UV irradiation unit  10 A, set the predetermined time T1 based on the acquired information together with the safety standard, and control the light emission and no light emission (irradiation and non-irradiation) of the UV irradiation unit  10 A. In other words, the inactivation device may be configured such that the predetermined time T1 is variable and set in accordance with the light source used. 
     In addition, in the present embodiment, the UV irradiation unit  10 A can be controlled to irradiate the space including a human with ultraviolet light for the predetermined time T1 after the motion sensor  11  detects the human entering the restroom stall  200 . In this way, it is possible to emit the ultraviolet light to the human immediately after the human enters the restroom stall  200 . Therefore, it is possible to suppress the human from spreading harmful microorganisms and/or viruses into the restroom stall  200  in a more efficient manner. 
      Moreover, in the present embodiment, the UV irradiation unit  10 A can be controlled to radiate ultraviolet light in the restroom stall  200  where no human is present at the time when the motion sensor  11  determines that no human is present in the restroom stall  200  (a human has left the restroom stall  200 ) . 
     In this way, irradiation with ultraviolet light in the restroom stall  200  where no human is present is capable of inactivating at least part of harmful microorganisms and viruses already present inside the restroom stall  200 , the harmful microorganisms and viruses spreading inside the restroom stall  200  as a human enters the restroom stall, and the harmful microorganisms and viruses floating in the air introduced into the restroom stall  200  as the human enters the restroom stall. Moreover, ultraviolet light is emitted continuously in the restroom stall  200  when no human is present in the restroom stall  200 , enhancing the above-described inactivation. 
     The UV irradiation unit  10 A may be mounted at a position that allows light to proceed downward from the upper part of the restroom stall  200 . Specifically, the UV irradiation unit  10 A may be mounted on the ceiling  201  in the restroom stall  200 . Thus, the UV irradiation unit  10 A is able to emit light containing ultraviolet light to the entire interior of the restroom stall  200 . Therefore, this configuration appropriately inactivates harmful microorganisms and viruses attached to, for example, the wall  202 , the door  203 , and the floor of the restroom stall  200 . 
     In the present embodiment, the motion sensor  11  for detecting the presence or absence of human in the restroom stall  200  is described as a sensor for detecting the human entering or exiting the restroom stall  200 ; however, any sensor that detects the human entering the restroom stall  200  and the human leaving the restroom stall  200  can be used. 
     Modification to the First Embodiment 
     The first embodiment has described the case in which the UV irradiation unit  10 A continuously radiates ultraviolet light in the restroom stall  200  when no human  300  is present in the restroom stall  200 . However, ultraviolet light may be emitted during a predetermined time T2 in the restroom stall  200  when no human is present in the restroom stall  200 . 
       FIG.  4    is a flowchart describing an operation of the inactivation device  100  according to the present modification. In  FIG.  4   , the processes that are common to those in  FIG.  2    are denoted with the identical step numbers; hereinafter, the processes different from those of  FIG.  2    will be mainly described. 
     When the control unit  20  detects the presence of the human  300  in the restroom stall  200  at Step S 1 , it proceeds to Step S 11  to start ultraviolet light emission from the UV irradiation unit  10 A, and then proceeds to the step S 2 . 
     In Step S 7 , the control unit  20  causes the UV irradiation unit  10 A to start ultraviolet light emission. Subsequently, the control unit  20  proceeds to Step S 12  and causes a timer 2, which is a counter, to start counting. 
     Next, in Step S 13 , the control unit  20  determines whether or not the predetermined time T2 has elapsed since the start of the counting of the timer 2 based on the count value of the timer 2, i.e., whether or not the predetermined time T2 has elapsed since the human  300  exits the restroom stall  200 . In the case that the predetermined time T2 has not yet elapsed, the control unit  20  waits until the predetermined time T2 has elapsed, and proceeds to Step S 14  when the predetermined time T2 is determined to have elapsed. 
     It is noted that the predetermined time T2 is set to a time sufficient to inactivate at least part of harmful microorganisms and viruses present in the restroom stall  200  where the human  300  has exited. 
     In Step S 14 , the control unit  20  stops ultraviolet light emission from the UV irradiation unit  10 A and returns to Step S 1 . 
       FIG.  5    is a timing chart describing an operation of the inactivation device  100  according to the modification. 
     In this modification, it is assumed that the radiation of ultraviolet light from the UV irradiation unit  10 A to the restroom stall  200  has been stopped before the human  300  enters the restroom stall  200 . 
     When the human  300  enters the restroom stall  200  at the time A, the motion sensor  11  detects the presence of the human  300 , the timer 1 starts counting and ultraviolet light is emitted in the restroom stall  200  and to the human  300 . The radiation of ultraviolet light in the restroom stall  200  and to the human  300  is stopped after the predetermined time T1 has elapsed since the time A. 
     In this way, even in the case in which the UV irradiation unit  10 A stops emitting ultraviolet light before the human  300  enters the restroom stall  200 , the UV irradiation unit  10 A starts emitting ultraviolet light once the human  300  enters the restroom stall  200 . The UV irradiation unit  10 A keeps irradiating the human  300  in the restroom stall  200  with ultraviolet light during a period from the time of starting the ultraviolet light emission until the predetermined time T1 has elapsed. 
     After that, when the human  300  exits the restroom stall  200  at the time B, the motion sensor  11  detects the exiting of the human  300 , the timer 2 starts counting and the emission of ultraviolet light to the interior of the restroom stall  200  is restarted. 
     The emission of ultraviolet light to the interior of the restroom stall  200  is stopped at the time C when the predetermined time T2 has elapsed since the time B, i.e., since the human  300  left the restroom stall  200 . 
     In this way, in the case in which the motion sensor  11  determines that no human is present in the restroom stall  200 , ultraviolet light may be emitted from the UV irradiation unit  10 A to the restroom stall  200  where no human is present for a certain period (predetermined time T2), and then the emission of ultraviolet light from the UV irradiation unit  10 A may be stopped. By emitting ultraviolet light to the interior of the restroom stall  200  where no human is present for a certain period, it is possible to set a pause time of the ultraviolet light source provided in the UV irradiation unit  10 A, thereby extending a service life of the ultraviolet light source. 
     Second Embodiment 
     Hereinafter, the second embodiment of the present invention will be described. 
     In the first embodiment described above, described is the case in which the motion sensor  11  detects the human  300  entering the enclosed space (the restroom stall  200 ) and the irradiation with ultraviolet light from the UV irradiation unit  10 A is controlled based on the detection signal of the motion sensor  11 . In the second embodiment, described is the case in which a pressure sensor  12  detects the state that the human  300  sits on the toilet seat  212  in the restroom stall  200  and the irradiation with ultraviolet is controlled based on the detection signal of the pressure sensor  12 . 
     In the present embodiment, ultraviolet light emission generally continues in the restroom stall  200  when no human  300  is present in the restroom stall  200 . 
     The ultraviolet light emission is to be carried out using the UV irradiation unit  10 B. 
       FIG.  6    is a flowchart describing an operation of the inactivation device  100  according to the present embodiment. 
     In Step S 21 , the control unit  20  determines whether or not the presence of the human  300  is detected in the restroom stall  200  based on the detection signal of the motion sensor  11 . In the case of determining that the presence of human  300  is not detected, the control unit  20  waits until the presence of the human  300  is detected. The control unit  20  proceeds to Step S 22  when the presence of the human  300  is detected. 
     In Step S 22 , the control unit  20  stops ultraviolet light emission from the UV irradiation unit  10 B and proceeds to Step S 23 . 
     In Step S 23 , the control unit  20  determines whether or not the human  300  sits on the toilet seat  212  based on the detection signal of the pressure sensor  12 . In the case of determining that no human  300  sitting on the seat is detected, the control unit  20  waits until the human  300  sitting on the seat is detected. The control unit  20  proceeds to Step S 24  when the human  300  sitting on the seat is detected. 
     In Step S 24 , the control unit  20  starts ultraviolet light emission from the UV irradiation unit  10 B and proceeds to Step S 25 . 
     In Step S 25 , the control unit  20  starts the counting of the timer 1, which is a counter. 
     Next, in Step S 26 , the control unit  20  determines whether or not the predetermined time T1 has elapsed since the start of the counting of the timer 1 based on the counter value of the timer 1, i.e., whether or not the predetermined time T1 has elapsed since the detection of the human  300  sitting on the toilet seat  212 . In the case that the predetermined time T1 has not yet elapsed, the control unit  20  waits for the predetermined time T1 to elapse, and then proceeds to Step S 27  upon the determination that the predetermined time T1 has elapsed. 
     It is noted that the predetermined time T1 is determined according to the wavelength of the ultraviolet light radiated from the UV irradiation unit  10 B, and is set to be not more than a maximum allowable time for which a living body is irradiated under the safety standards. The predetermined time T1 may be, for example, a value similar to that of the first embodiment. 
     The UV irradiation unit  10 B is mounted on the wall  202  of the restroom stall  200  on the assumption that its ultraviolet light is emitted from above the back of the head of the human  300  when the human is in a posture of sitting on the toilet bowl  211 . Thus, the irradiance on the surface (head) of the human  300  in this case has a value similar to the irradiance on the surface of the standing human  300  using the UV irradiation unit  10 A in the first embodiment. In other words, the irradiance of the ultraviolet light emitted on the surface of the human body can be 0.092 (mW/cm 2 ). 
     In Step S 27 , the control unit  20  terminates the counting of the timer 1 and resets the count value of the timer 1. 
     In Step S 28 , the control unit  20  stops ultraviolet light emission from the UV irradiation unit  10 B. 
     In Step S 29 , the control unit  20  determines whether or not the human  300  exits the restroom stall  200  based on the detection signal of the motion sensor  11 . In the case of determining that the human  300  does not exit, the control unit  20  waits. The control unit  20  proceeds to Step S 30  upon the determination that the human  300  has exited. 
     In Step S 30 , the control unit  20  causes the UV irradiation unit  10 B to start emitting ultraviolet light and returns to Step S 21 . 
       FIG.  7    is a timing chart describing an operation of the inactivation device  100  of the present embodiment. Ultraviolet light emission from the UV irradiation unit  10 B continues in the restroom stall  200  before the human  300  enters the restroom stall  200 , i.e., during the absence of the human  300  in the restroom stall  200 . 
     When the human  300  enters the restroom stall  200  in this state at the time P, the motion sensor  11  detects the presence of the human  300 , and the irradiation with ultraviolet light in the restroom stall  200  is stopped. 
     After that, when the human  300  sits on the toilet seat  212  in the restroom stall  200  at the time Q, the pressure sensor  12  detects the human  300  sitting on the seat, the timer 1 starts counting and the irradiation with ultraviolet light is started in the restroom stall  200 . The emission of ultraviolet light in the restroom stall  200  and to the human  300  is stopped after the predetermined time T1 has elapsed since the time Q. 
     In this way, when the human  300  enters the restroom stall  200 , the irradiation with ultraviolet light from the UV irradiation unit  10 B is temporarily stopped; when the human  300  sits on the toilet seat  212 , the UV irradiation unit  10 B radiates ultraviolet light in the restroom stall  200  such that the human  300  is irradiated with ultraviolet light for the predetermined time T1. 
     After that, when the human  300  exits the restroom stall  200  at the time R, the motion sensor  11  detects the exiting of the human  300 , and the irradiation with ultraviolet light is restarted in the restroom stall  200 . 
     As described above, in the present embodiment, the control unit  20  causes the UV irradiation unit  10 B to irradiate the space including the human with ultraviolet light for the predetermined time (T1) upon detecting the human siting on the toilet seat  212  based on the detection signal of the pressure sensor  12  during the period in which the human is determined to be present in the restroom stall  200  based on the detection signal of the motion sensor  11 . 
     Hence, by irradiating the human present in the predetermined position in the enclosed space with light containing ultraviolet light, this makes it possible to radiate ultraviolet light effectively to the intended location on the surface of a human body. Incidentally, movements of the human sitting on the toilet seat  212  are relatively small in the restroom stall  200 . Thus, irradiating the human sitting on the toilet seat  212  with ultraviolet light is capable of effectively inactivating harmful microorganisms and viruses on the surface of the human body (skin and clothing). 
     Moreover, the control unit  20  causes the UV irradiation unit  10 B to stop emitting ultraviolet light when the motion sensor  11  detects the human entering the restroom stall  200 , and causes the UV irradiation unit  10 B to start irradiating the space including the human with ultraviolet light for the predetermined time (T1) after the pressure sensor  12  detects the human sitting on the toilet seat  212 . 
     Hence, in the case in which ultraviolet light is emitted in the restroom stall  200  before the human enters there, the emission of ultraviolet light can temporarily be stopped when the human enters the restroom stall  200 , and the emission of ultraviolet light can be started when the human sits on the toilet seat  212  and continue for the predetermined time (T1). Therefore, this operation suitably enables the emission of ultraviolet light in the restroom stall  200  during absence of the human and the emission of ultraviolet light to the human entering the restroom stall  200 . 
     Moreover, since the UV irradiation unit  10 B is mounted on the wall  202  in the restroom stall  200  on the assumption that its ultraviolet light is radiated to the human  300  when the human  300  is in a posture of sitting on the toilet bowl  211 , the emission of ultraviolet light using the UV irradiation unit  10 B increases the dose amount on the floor compared with that using the UV irradiation unit  10 A. Therefore, the UV irradiation unit  10 B effectively inactivates harmful microorganisms and viruses attached to the floor. 
     In addition, the UV irradiation unit  10 B is mounted at a position where ultraviolet light is emitted to the back of the head of the human  300  when the human  300  is in a posture of sitting on the toilet bowl  211 . Hence, this configuration prevents the human’s eyes from directly being exposed to ultraviolet light radiated from the UV irradiation unit  10 B. Thus, it is possible to suppress the occurrence of eye damages (e.g., eye pain, hyperemia, and corneal inflammation). 
     Although the present embodiment has described the case in which the irradiation with ultraviolet light is carried out using the UV irradiation unit  10 B, the UV irradiation unit  10 A mounted on the ceiling  201  in the restroom stall  200  can be used in the present embodiment. 
     In the case of using the UV irradiation unit  10 A, the irradiance of the ultraviolet light on the surface of the human  300  sitting on the toilet seat  212  is small compared with that on the surface of the human  300  standing on the floor, and is, for example, 0.010 (mW/cm 2 ). 
     Hence, in the case in which a light source provided in the UV irradiation unit  10 A is a low-pressure mercury lamp, the ultraviolet light irradiation time during a single stay in the restroom stall (the predetermined time T1) is calculated to be 60 seconds by using the equation (2), where the number of times N using the restroom stall provided in a hospital (number of times entering the restroom stall) per day is  10 . 
     In the case in which a light source provided in the UV irradiation unit  10 A is a KrCl excimer lamp, the ultraviolet light irradiation time during a single stay in the restroom stall (the predetermined time T1) is calculated to be 210 seconds by using the equation (2), where the number of times N using the restroom stall provided in a hospital (number of times entering the restroom stall) per day is 10. 
     Hence, the UV irradiation unit  10 A has a longer ultraviolet light irradiation time (the predetermined time T1) than the UV irradiation unit  10 B. 
     Although the present embodiment has described the case in which a pressure sensor  12  provided in the toilet seat  212  is used as a sensor to detect a state that the human sits on the toilet seat  212  in the restroom stall  200 , any sensor that detects the state that the human sits on the toilet seat  212  can be used. 
     Modification 1 to the Second Embodiment 
     The above-described second embodiment has dealt with the case in which the UV irradiation unit  10 A continuously radiates ultraviolet light in the restroom stall  200  when no human  300  is present in the restroom stall  200 . However, ultraviolet light may be emitted for only a predetermined time T2 in the restroom stall  200  when no human is present in the restroom stall  200 . 
       FIG.  8    is a flowchart describing an operation of the inactivation device  100  according to the present modification. In  FIG.  8   , the processes that are common to those in  FIG.  6    are denoted with the identical step numbers; hereinafter, the processes different from those of  FIG.  6    will be mainly described. 
     When the control unit  20  detects the presence of the human  300  in the restroom stall  200  in Step S 21 , then it proceeds to Step S 23 . 
     In addition, the control unit  20  causes the UV irradiation unit  10 B to start radiating ultraviolet light in Step S 30 , and then it proceeds to Step S 31  to cause the timer 2, which is a counter, to start counting. 
     Next, in Step S 32 , the control unit  20  determines whether or not the predetermined time T2 has elapsed since the start of counting the timer 2 based on the count value of the timer 2, i.e., whether or not the predetermined time T2 has elapsed since the human  300  exits the restroom stall  200 . Then, in the case that the predetermined time T2 has not yet elapsed, the control unit  20  waits until the determined time T2 has elapsed. The control unit  20  proceeds to Step S 33  when the predetermined time T2 is determined to have elapsed. 
     It is noted that the predetermined time T2 is set to a time sufficient to inactivate at least part of harmful microorganisms and viruses present in the restroom stall  200  where the human has exited. In Step S 33 , the control unit  20  controls the UV irradiation unit  10 B to stop emitting ultraviolet light and returns to Step S 21 . 
       FIG.  9    is a timing chart describing an operation of the inactivation device  100  according to the present modification. 
     It is assumed here that the irradiation with ultraviolet light from the UV irradiation unit  10 B in the restroom stall  200  has been stopped before the human enters the restroom stall  200 . 
     When the human  300  enters the restroom stall  200 , the motion sensor  11  detects the presence of the human  300  at the time P. After that, when the human  300  sits on the toilet seat  212  at the time Q, the pressure sensor  12  detects the human  300  sitting on the seat. Then, the timer 1 starts counting and ultraviolet light is emitted in the restroom stall  200  and to the human  300 . The emission of ultraviolet light in the restroom stall  200  and to the human  300  is stopped after the predetermined time T1 has elapsed since the time Q. 
     In this way, even in the case in which the UV irradiation unit  10 A has stopped the irradiation with ultraviolet light before the human  300  enters the restroom stall  200 , the UV irradiation unit  10 B starts emitting ultraviolet light once the human  300  enters the restroom stall  200  and sits on the toilet seat  212 . The UV irradiation unit  10 B emits ultraviolet light to the human  300  in the restroom stall  200  for a period from the time of starting the ultraviolet light emission until the predetermined time T1 has elapsed. 
     As the human  300  exits the restroom stall  200  at the time R, the motion sensor  11  detects the exiting of the human  300 . Then, the timer 2 starts counting and the irradiation with ultraviolet light in the restroom stall  200  is restarted. 
     The irradiation with ultraviolet light is stopped at the time S, i.e., when the predetermined time T2 has elapsed since the time R that indicates the exiting of the human  300  from the restroom stall  200 . 
     Thus, in the case in which the motion sensor  11  determines that no human is present in the restroom stall  200 , ultraviolet light may be emitted from the UV irradiation unit  10 B to the restroom stall  200  where no human is present for a certain period (predetermined time T2). After that, the irradiation with ultraviolet light from the UV irradiation unit  10 B may be stopped. By emitting ultraviolet light in the restroom stall  200  where no human is present for a certain period, it is possible to set a pause time of the ultraviolet light source provided in the UV irradiation unit  10 B, thereby extending a service life of the ultraviolet light source. 
     Modification 2 of the Second Embodiment 
     Although the second embodiment has described the case in which the motion sensor  11  detects the presence of the human  300  in the restroom stall  200 , the door sensor  13  may be used to detect the human  300  entering or leaving the restroom stall  200 . 
       FIG.  10    is a timing chart describing an operation of the inactivation device  100  according to the present modification. The UV irradiation unit  10 B continuously emits ultraviolet light in the restroom stall  200  before the human  300  enters the restroom stall  200 , i.e., during the absence of the human  300  in the restroom stall  200 . 
     In this state, when the human  300  opens the door  203  to enter the restroom stall  200  at the time P1, the door sensor  13  detects the door  203  opening and the irradiation with ultraviolet light in the restroom stall  200  is stopped. After that, when the human  300  enters the restroom stall  200  and closes the door  203  at the time P2, the door sensor  13  detects the door  203  closed. 
     Then, the timer 0 starts counting at the time P2. It is noted that the timer 0 is set to terminate the counting at the time when the predetermined time T0 has elapsed since the start of the counting, and reset the count while sending a counting terminate signal to the control unit  20 . The timer 0 is also set to be reset by the control unit  20  in the case in which the pressure sensor  12  detects the human  300  sitting on the toilet seat  212  even during the middle of its counting. 
     The predetermined time T0 is set to a time sufficiently longer than a time for the human  300  to sit on the toilet seat  212  after entering the restroom stall  200 . 
     After that, when the human  300  sits on the toilet seat  212  in the restroom stall  200  at the time Q, the pressure sensor  12  detects the human  300  sitting on the seat, the timer 1 starts counting and ultraviolet light emission starts in the restroom stall  200 . At this moment, the timer 0 terminates its counting. The emission of ultraviolet light in the restroom stall  200  and to the human  300  is stopped after the predetermined time T1 has elapsed since the time Q. 
     In this way, when the human  300  enters the restroom stall  200 , the irradiation with ultraviolet light from the UV irradiation unit  10 B is temporarily stopped; however, when the human  300  sits on the toilet seat  212 , the UV irradiation unit  10 B radiates ultraviolet light in the restroom stall  200  and ultraviolet light is radiated to the human  300  in the restroom stall  200  during the predetermined time T1. 
     After that, when the human  300  opens the door  203  to exit the restroom stall  200  at the time R1, the door sensor  13  detects the door  203  opening. Then, when the human  300  exits the restroom stall  200  and the door  203  is closed at the time R2, the door sensor  13  detects the door  203  closed. 
     At the time R2, the timer 0 starts counting. Since the human  300  has exited the restroom stall  200 , the pressure sensor  12  does not detect the human sitting on the toilet seat  212  even when the predetermined time T0 elapses from the time R2. Hence, the irradiation with ultraviolet light in the restroom stall  200  is restarted at the time R3, i.e., when the predetermined time T0 elapses from the time R2. 
     In this way, even in the case in which the door sensor  13  is used instead of the motion sensor  11 , the effect similar to that of the second embodiment described above is achieved if the count of the timer 0 is used. Since the door sensor  13  detects the opening and closing of the door  203 , ultraviolet light can be radiated in the enclosed space (the restroom stall  200 ) with the door  203  closed. This configuration prevents ultraviolet light from being accidentally emitted to objects outside the enclosed space. 
     Here, described is the case in which the control unit  20  controls the timer 0 to start counting when the door sensor  13  detects the door  203  closed; however, the control unit  20  may control the timer 0 to start counting when the door sensor  13  detects the door  203  closed and, at the same time, the pressure sensor  12  does not detect the human  300  sitting on the seat. 
     This case makes it possible to have the timer 0 not to start counting in the case in which the door  203  undesirably opens or closes due to reasons including forgotten locking of the door  203  or the defect of the door  203  while the human  300  is sitting on the toilet seat  212 . 
     In other words, in the case in which the control unit  20  receives the detection signal from the pressure sensor  12  indicating the human  300  sitting on the seat, even when the control unit  20  receives the detection signal from the door sensor  13  indicating the door  203  closed, the control unit  20  does not cause the timer 0 to start counting, unless the control unit  20  receives the detection signal from the pressure sensor  12  indicating the exiting of the human  300 . 
     Therefore, the absence of the human in the restroom stall  200  is appropriately determined by checking both of the detection signal from the door sensor  13  and the detection signal from the pressure sensor  12 . 
     Similar to the modification 1 to the second embodiment, if no human is present in the restroom stall  200 , ultraviolet light may be radiated only during a predetermined time T2 in the restroom stall  200 , i.e., the irradiation with ultraviolet light in the restroom stall  200  may be stopped when the predetermined time T2 has elapsed since the time R3 in  FIG.   10   . 
     Other Modifications 
     In each of the above-described embodiments, the case in which the inactivation device  100  is disposed in the restroom stall is described; however, the present invention is not limited to the above-described embodiments. The inactivation device  100  can be particularly disposed in confined spaces in facilities where people frequently gather, such as hospital rooms, elevators, and conference rooms. 
     The timing at which the inactivation device  100  irradiates a human with ultraviolet light can be any timing during a period when the human is present in the enclosed space. When a timing at which harmful microorganisms or viruses is likely to spread is detectable during the period when the human is present in the enclosed space, it is preferable that ultraviolet light be radiated at that timing. 
     In each of the above-described embodiments, the case in which the inactivation device  100  is disposed in the enclosed space where a human can enter or leave is described; however, the enclosed space can be a space where an animal other than a human can enter or leave. 
     In each of the above-described embodiments, ultraviolet light is radiated to the human or the space including the human just for the predetermined time T1; however, in the case of a light source repeatedly operating the light emission and the non-light emission, the sum of the light emission operation time may be the predetermined time T1. 
     For example, in the case of controlling the power to the excimer lamp to repeat the light emission operation and the pause, with the light emission operation time of the excimer lamp being between 10 milliseconds and 1000 milliseconds, and the subsequent pause time being between 10 milliseconds and 10 seconds, the predetermined time T1 is a sum of the light emission operation time. 
     Specifically, in the case that the light emission operation time of the KrCl excimer lamp is 100 milliseconds, the pause time is 100 milliseconds and the predetermined time T1 is 30 seconds, for example, the light emission operation count of the KrCl excimer lamp reaches 300 and the operation time of the KrCl excimer lamp including the pause time reaches 60 seconds. 
     In other word, in the case that a light source continuously operates, the irradiation period of ultraviolet light to the human or the space including the human is the predetermined time T1; however, in the case that the light source intermittently operates including a pause time, the irradiation period of ultraviolet light becomes longer than the predetermined time T1. 
     In the case that the space including the human is, for example, a restroom, the light source can be controlled to intermittently operate so that the irradiation period of ultraviolet light is set to be longer, thereby increasing the chance of radiating ultraviolet light when, for example, the dispersion of bacteria and/or viruses takes place upon defecation or splash. 
     In the above-described case in which the light emission operation time is set to between 10 milliseconds and 1000 milliseconds and the pause time is set to between 10 milliseconds and 10 seconds, a shutter for shielding light is controlled to open and close in the case of low-pressure mercury lamp as described above; however, in some cases, the opening and closing of the shutter needs to be carried out with high speed, which is difficult to achieve. 
     Hence, a suitable ultraviolet light source is capable of repeating the ultraviolet light emitting operation and the pause time using the power control. 
     Examples of such light sources are excimer lamps (KrCl excimer lamps) and solid state light sources (light-emitting diodes (LED), laser diodes (LD)) as described above. 
     The inactivation device and inactivation method of the present invention are capable of providing sterilization intrinsic to ultraviolet light and inactivation of viruses while preventing the radiation of ultraviolet light from adversely affecting humans. In particular, unlike the conventional ultraviolet light sources, the inactivation device and inactivation method of the present invention have the feature of being able to be used in manned environments and are capable of utilizing this feature to reduce and sterilize viruses in the air and the surface of components placed in a space when the device is installed in the space such as a facility or a vehicle where people or animal are present and irradiates the entire space with its ultraviolet light. 
     This feature corresponds to the Goal 3 of the United Nations-led Sustainable Development Goals (SDGs) “Ensure healthy lives and promote well-being for all at all ages”, and also significantly contributes to achieving the Target 3.3 “By 2030, end the epidemics of AIDS, tuberculosis, malaria and neglected tropical diseases and combat hepatitis, water-borne diseases and other communicable diseases”. 
      The certain embodiments have been described in the foregoing; however, they are merely illustrative and are not intended to limit the scope of the present invention. The devices and methods described herein may be embodied in forms other than those described above. In addition, omissions, substitutions, and modifications may be made to the above-described embodiments as appropriate without departing from the scope of the present invention. Such omissions, substitutions and modifications are encompassed in the scope of the claims and their equivalents, and belong to the technical scope of the present invention. 
     Reference Signs List 
     
       
         
           
               
               
               
            
               
                   10 A,  10 B 
                 UV irradiation unit 
               
               
                 
                   11 
                 
                 Motion sensor 
               
               
                 
                   12 
                 
                 Pressure sensor 
               
               
                 
                   13 
                 
                 Door sensor 
               
               
                 
                   20 
                 
                 Control unit 
               
               
                 
                   100 
                 
                 Inactivation device 
               
               
                 
                   200 
                 
                 Enclosed space (restroom stall) 
               
               
                 
                   201 
                 
                 Ceiling 
               
               
                 
                   202 
                 
                 Wall 
               
               
                 
                   203 
                 
                 Door 
               
               
                 
                   300 
                 
                 Human