Abstract:
An arranging facility, a parking facility, a handling facility, and a ventilation device. A vehicle maintenance facility as the arranging facility comprises a vehicle maintenance booth as an arranging space and a forcible air supply/discharge mechanism. The vehicle maintenance booth is surrounded by side walls and a ceiling wall as partition walls on its periphery. A maintenance vehicle on which a fuel battery as an energy converter is mounted is temporarily disposed in the vehicle maintenance booth. Also, the air supply/discharge mechanism comprises an air intake device feeding air to the vehicle maintenance booth and an air discharge device discharging the air from the vehicle maintenance booth to dilute hydrogen gas leaking from a vehicle under maintenance.

Description:
[0001]    This is a 371 national phase application of PCT/JP2006/308253 filed 13 Apr. 2006, claiming priority to Japanese Patent Application No. 2005-116458 filed 14 Apr. 2005, the contents of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a facility for temporarily arranging a fuel-cell electric vehicle that uses an inflammable gas and on which a fuel cell is mounted, and for performing handling work of such a device. 
       BACKGROUND OF THE INVENTION 
       [0003]    Devices utilizing a fuel cell including fuel-cell electric vehicles have been vigorously developed. Since a strongly inflammable gas such as hydrogen is generally used in the fuel cell as a fuel gas, due attention should be paid to leakage of gas out of the device when performing an experiment, production, maintenance, or inspection of a device using the fuel cell. 
         [0004]    Japanese Patent Application Laid-Open No. 10-310033 discloses a technology for an inspecting facility for carrying out an inspection in an inspection room in which a general vehicle is enclosed by walls. However, the document discloses no technology regarding measures to prevent gas leakage. 
         [0005]    Japanese Patent Application Laid-Open No. 5-180478 discloses a technology to enhance collection efficiency of exhaust gas by providing air intake ports on the ceiling and air discharge ports on the floor surface of a closed terminal for vehicles (such as a bus terminal or a truck terminal) or a closed parking garage (such as an underground parking garage). Also, Japanese Patent Application Laid-Open No. 2005-98616 discloses a configuration in which two cross flow fans are arranged vertically side by side and mutual air blowing directions are set so that air currents merge together in order to efficiently provide ventilation in an indoor parking garage. However, technologies of these documents are intended only for exhaust gases and do not assume gas leakage from fuel-cell electric vehicles. 
         [0006]    Japanese Patent Application Laid-Open No. 2005-353346 discloses a technology for providing ventilation by determining a hydrogen concentration in a closed facility such as an underground parking garage where fuel-cell electric vehicles are parked or stopped, from the hydrogen concentration or an amount of decrease in hydrogen of vehicles and the volume and ventilation capabilities of the facility. However, this document describes as a ventilator only a configuration for simply providing a fan on the ceiling. 
         [0007]    For example, a fuel-cell electric vehicle comprises many components, including, for example, a pipe for fuel gas, and has a complicated structure. Since it is difficult, in particular, to prevent gas leakage from a joint between components in the course of inspection/maintenance work, operators perform inspection/maintenance work with the greatest care. 
         [0008]    However, when fuel-cell electric vehicles come into widespread use in the near future, it is anticipated that vehicle maintenance work thereof will be done in the same manner as for current gasoline-engine vehicles. Thus, it is desirable to prepare an inspection/maintenance facility for which measures for preventing gas leakage that could ensure safety sufficiently are taken even when an operator performs ordinary maintenance work. There is a great necessity for introducing a technology for preventing gas leakage, particularly when a gas is colorless and odorless such as hydrogen gas and an operator himself (herself) cannot detect gas leakage. Moreover, in view of introduction costs, it is desirable to be able to realize such an inspection/maintenance facility by developmentally expanding a conventional inspection/maintenance facility. 
         [0009]    It is also effective to establish the technology for preventing gas leakage to be introduced to an inspection/maintenance facility in a closed-space facility in which fuel-cell electric vehicles are parked or stored such as a residential garage, an underground parking garage, or a multistory parking garage. This is because simple maintenance work is performed also in such a facility and gas leakage could occur there. 
         [0010]    These points are challenges faced not only by fuel-cell electric vehicles, but also by the fuel cell itself and by other devices on which the fuel cell is mounted. Similar measures are also demanded for devices that contain a power mechanism using an inflammable gas (for example, hydrogen, propane gas, or natural gas) such as a vehicle having an internal combustion engine using an inflammable gas. 
       SUMMARY OF THE INVENTION 
       [0011]    An object of the present invention is to introduce a technology for preventing gas leakage to a facility in which fuel-cell electric vehicle on which a fuel cell is mounted is temporarily arranged and which is subjected to handling work. 
         [0012]    Another object of the present invention is to introduce a technology regarding a function for preventing gas leakage to a facility in which a fuel-cell electric vehicle on which a fuel cell is mounted is temporarily arranged and which is subjected to at least one of experiment, production, inspection, and maintenance. 
         [0013]    Still another object of the present invention is to establish a simple mode in which an inspection/maintenance facility for conventional gasoline-engined vehicles is modified to one for vehicles using an inflammable gas. 
         [0014]    A reference arranging facility in the present invention includes an arranging space whose periphery is surrounded by partition walls and in which an energy converter using an inflammable gas as a fuel or a device on which the energy converter is mounted is temporarily and arrangeably disposed, and a forcible gas supply/discharge mechanism that dilutes the inflammable gas leaking out of the energy converter into the arranging space by supplying a diluent gas to the arranging space and discharging the inflammable gas from the arranging space. 
         [0015]    The inflammable gas is a gas that exists as a gas at room temperature and atmospheric pressure and is easily inflammable by combining with oxygen and more specifically refers to hydrogen, methane, propane, natural gas, and the like. The energy converter includes a fuel cell (including reformers for providing an inflammable gas to the fuel cell and fuel cell unit/assembled stacks) that extracts electric energy by allowing chemical reaction of such an inflammable gas, or an internal combustion engine that extracts kinetic energy by causing an inflammable gas to be subjected to combustion, such as a hydrogen fueled engine or a compressed natural gas (CNG) engine, as well as pipes, valve mechanisms, and the like of fuel gases used for such a fuel cell or internal combustion engine. It is assumed that devices on which an energy converter is mounted include, in addition to floor-type devices, mobile devices such as vehicles, ships, aircraft, mobile robots, and mobile electronic devices. 
         [0016]    Temporarily arranging signifies that, instead of arranging permanently, for example, arranging for a limited period such as an hour, a day, a week, or a month. However, the closing period need not be defined. In an arranging facility, a process in which an energy converter or a mounting device thereof is arranged in an arranging space and then removed from the arranging space will be performed repeatedly. 
         [0017]    A reference parking facility in the present invention is a space converted from the arranging space in the arranging facility so that fuel-cell electric vehicles in which a fuel cell serving as an energy converter is mounted are temporarily stored or parked. Examples of the parking facility include a residential garage in which one or two to three fuel-cell electric vehicles can be parked, and an underground parking garage or multistory parking garage which can accommodate many fuel-cell electric vehicles (for example, 10 or more vehicles, or 100 or more vehicles for a large-scale parking garage). 
         [0018]    A handling facility in the present invention is a work booth converted from the arranging space in the arranging facility to enable handling work of a fuel-cell electric vehicle, which is a device on which a fuel cell is mounted as an energy converter. Incidentally, components and modification modes will be described below with the handling facility in mind, but such descriptions can be applied to the arranging facility and the parking facility in substantially the same manner. 
         [0019]    Handling work of a device refers to work such as performing an experiment involving the device, or manufacturing, inspecting, or maintaining the device. The booth is used as a term referring to a space separated from surroundings by partition walls. Therefore, the work booth refers to a work space separated from an external space by partition walls to perform handling work; in other words, a work room for handling work. Partition walls constitute boundaries for separating the work space inside the work booth from the external space. Partition walls also include vertically or obliquely arranged sides and obliquely or horizontally arranged ceiling surfaces and floor surfaces. Partition walls need not necessarily seal a work space hermetically and may have an opening such as a port for inserting and taking out an energy converter, or a ventilation opening for realizing natural ventilation. 
         [0020]    The gas supply/discharge mechanism is a mechanism for forcibly providing ventilation inside the work booth by using mechanical power, such as by means of a fan or by means of releasing a compressed gas stored in a gas cylinder. A process forcibly performed may be only supply, only discharge, or both the supply and discharge. As the diluent gas there may be used, for example, a non-inflammable gas/inert gas such as nitrogen and helium, or air. 
         [0021]    According to the configuration, there can be realized a handling facility (such as an inspection/maintenance facility, a manufacturing facility, or a laboratory facility) that quickly dilutes an inflammable gas leaked from an energy converter into a work booth and discharges gas from the work booth. Therefore, safety can be sufficiently ensured in the work booth even when a gas leak occurs. In addition, this technology can also be implemented in a facility shown in the above Patent Document 1 by introducing a gas supply/discharge mechanism, providing an advantage of simple introduction at low cost. 
         [0022]    In an aspect of the handling facility of the present invention, the inflammable gas is a gas lighter than the diluent gas, and the gas supply/discharge mechanism supplies the diluent gas from below a work booth (for example, below the arranging position of an energy converter) and the gas is discharged from above the work booth. In this case, the inflammable gas in the diluent gas rises due to convection caused by a density difference. Therefore, in consideration that it is desirable not to reverse the flow of this natural convection, the flow of diluent gas is set from below upward. A discharge from above the work booth typically refers to a discharge from the ceiling surface of partition walls. Supplying from below the arranging position of an energy converter is implemented, for example, by supplying from the floor surface. If, in this configuration, the diluent gas is different from a gas filling the work booth during the course of normal work (normally air), it is particularly desirable that the inflammable gas is lighter than the gas filling the work booth, in order to quickly discharge the inflammable gas. If the diluent gas (and the gas filling the work booth during normal work) are lighter than the inflammable gas, the gas supply/discharge mechanism may be set to supply the diluent gas from above the arranging position of an energy converter and the gas is discharged from below the work booth (such as from the floor surface). 
         [0023]    In another aspect of the handling facility of the present invention, there are provided an inflammable gas sensor for detecting an inflammable gas having leaked into the work booth, and a control device for controlling supply or discharge of the gas supply/discharge mechanism in accordance with a detection result of the inflammable gas sensor. The inflammable gas sensor is a sensor for detecting whether any inflammable gas is present, as well as a concentration thereof. The inflammable gas sensor is desirably set up on a side to which the inflammable gas is likely to flow and also near a region where a gas is likely to be condensed (accumulated). If, for example, the inflammable gas is lighter than a surrounding gas and the diluent gas supplied by the gas supply/discharge mechanism does not flow or flows slowly, the inflammable gas sensor may be provided in an upper part of the work booth (may be within the work booth or within an air discharge duct or the like led from the work booth). It is also effective, if necessary, to devise a method of preventing a detection error by making the gas passage thinner or stirring the gas by a fan or the like in the vicinity of the inflammable gas sensor. From the viewpoint of enhancing detectability, it is also effective to provide a plurality of inflammable gas sensors. 
         [0024]    In another aspect of the handling facility of the present invention, if an inflammable gas satisfying a predetermined condition is detected, the control device activates the gas supply/discharge mechanism. That is, the supply/discharge mechanism is set so that the gas supply/discharge mechanism is not normally activated, but if an inflammable gas is detected (at a level equal to or greater than a set value), the gas supply/discharge mechanism is activated to quickly discharge the gas. This configuration is effective in realizing energy conservation and a silent environment. Also, when handling work of a device using no inflammable gas and that of a device using an inflammable gas are performed in combination, the present configuration in which the gas supply/discharge mechanism is activated only when necessary functions effectively. 
         [0025]    In another aspect of the handling facility of the present invention, an inclined-face structure accumulating an inflammable gas that rises or falls due to a density difference from the gas filling the work booth during the course of normal work is provided in an upper part or lower part of the work booth and the inflammable gas sensor detects the accumulated inflammable gas. The inclined-face structure refers to a structure having an inclined face for guiding and accumulating a convecting inflammable gas. The inclined-face structure may be formed using partition walls or a floor surface or separately from them. Although no particular limitation is imposed on the shape of the inclined face, if the inclined face has a two-dimensional curve like that of a funnel, horizontal motion can be controlled toward one point, increasing the degree of condensation of the inflammable gas. The inflammable gas concentrated in this way may be discharged by means of the gas supply/discharge mechanism, but also may be discharged using natural convection (for example, by simply providing a discharge port in an upper part or a lower part) without using the gas supply/discharge mechanism. 
         [0026]    In another aspect of the handling facility of the present invention, if an inflammable gas satisfying the predetermined condition is detected, the control device increases supply and discharge amounts by the gas supply/discharge mechanism. That is, if an inflammable gas is detected (at a level equal to or greater than a set value), the amount of ventilation is increased. Switching to an increase may be one-step, or multi-step or infinite-step in accordance with the amount of gas. 
         [0027]    In another aspect of the handling facility of the present invention, the gas supply/discharge mechanism has a plurality of supply ports provided at mutually different positions or a plurality of exhaust ports provided at mutually different positions and, if an inflammable gas satisfying the predetermined condition is detected, among the plurality of supply ports or exhaust ports, the control device changes a combination of supply ports or exhaust ports to be activated. Typically, if an inflammable gas is detected (at a level equal to or greater than a set value), the number of supply ports or exhaust ports is increased. As a result of this, it becomes possible to increase the flow rate of gas and to change the flow direction of gas, thereby promoting ventilation. An example of changing the direction includes a mode in which the flow set in the vertical direction normally by supplying and discharging through the floor surface and ceiling surface of the work booth is changed to the horizontal direction by supplying and discharging through opposite sides of the work booth. Another example is a mode example in which, if the handling work facility is huge, a pattern of supply ports or exhaust ports to be activated is changed to enhance ventilation efficiency in a detection target range of sensors satisfying the predetermined condition among a plurality of disposed sensors. 
         [0028]    In another aspect of the handling facility of the present invention, the gas supply/discharge mechanism includes a circuit for resupplying at least a portion of the gas discharged from the work booth to the work booth and, if an inflammable gas satisfying the predetermined condition is detected, the control device suppresses or stops a gas circulation. That is, if no inflammable gas is detected (at a level equal to or greater than a set value), at least a portion of the gas is circulated (after providing any necessary treatment to remove any inflammable gas). However, when an inflammable gas is detected (at a level equal to or greater than a set value), a dilution effect shall be enhanced by reducing the amount of circulation or setting the amount of circulation to 0 to thereby allow a new diluent gas to flow in. 
         [0029]    In another aspect of the handling facility of the present invention, a vehicle on which an energy converter is mounted is inspected and maintained in the work booth. 
         [0030]    A ventilation device in the present invention is a device that includes the gas supply/discharge mechanism provided in the handling facility. The ventilation device may also be formed as a device by separately mounting a plurality of components in any of these facilities. When the gas supply/discharge mechanism is controlled by the control device, the ventilation device includes its control device. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0031]      FIG. 1  is a schematic view showing a configuration outline of a vehicle maintenance facility according to an embodiment of the present invention; 
           [0032]      FIG. 2  is a diagram showing an example control mode of the vehicle maintenance facility of  FIG. 1 ; 
           [0033]      FIG. 3A  is a diagram showing a ventilation mode of the vehicle maintenance facility according to a modification; 
           [0034]      FIG. 3B  is a diagram showing the ventilation mode of the vehicle maintenance facility according to the modification; and 
           [0035]      FIG. 4  is a schematic view showing the configuration outline of the vehicle maintenance facility according to another modification. 
       
    
    
     DETAILED DESCRIPTION  
       [0036]    A typical embodiment of the present invention will be described below. In the descriptions that follow, a facility for maintaining vehicles on which a fuel cell using hydrogen (and oxygen in the air) as a fuel is mounted is taken as an example. Here, hydrogen is an inflammable gas and the fuel cell is an energy converter that extracts electric energy through chemical reaction of hydrogen. However, needless to say, the present invention can also be applied in the same manner to other inflammable gases and energy converters such as internal combustion engines. It is also evident that the present invention can be applied not only to inspection/maintenance facilities (equipment), but also to laboratory facilities (equipment) and manufacturing facilities (equipment). 
         [0037]      FIG. 1  is a schematic view showing a configuration outline of a vehicle maintenance facility  10  according to the present embodiment. The vehicle maintenance facility  10  includes, as its main components, a vehicle maintenance booth  20 , an air intake device  30 , an air discharge device  40 , a duct  50 , a hydrogen sensor  80 , and a control device  90 . 
         [0038]    The vehicle maintenance booth  20  is a work booth of a rectangular parallelepiped shape and therein, inspection/maintenance work on a maintenance vehicle  110  set to a work position is performed. The periphery of a work space  22 , which is an inner part of the vehicle maintenance booth  20 , is surrounded by side walls  24  and a ceiling wall  26  serving as partition walls. Many fine vent holes are provided on a floor surface  28 . 
         [0039]    The air intake device  30  is a device provided by the side of the vehicle maintenance booth  20  and supplies air to the vehicle maintenance booth  20  by means of an internal fan  32 . The air discharge device  40  is a device consisting of air discharge sections  42 ,  44 , and  46  mounted on the upper side of the ceiling wall  26  of the vehicle maintenance booth  20 . In each of the air discharge sections  42 ,  44 , and  46 , an air discharge port and a fan are provided to discharge, together with air, hydrogen leaking from the maintenance vehicle  110 . 
         [0040]    The duct  50  constitutes a flow channel of air outside the vehicle maintenance booth  20 . The duct  50  includes an air discharge duct  52 , an exhaust port  54 , a circulating duct  56 , an intake  58 , and a supply duct  60 . One end of the air discharge duct  52  is connected to the air discharge device  40  and the other end is connected to the exhaust port  54  to lead air discharged from the vehicle maintenance booth  20  to the outside. One end of the circulating duct  56  is connected to an intermediate part of the air discharge duct  52  and the other end is connected to the air intake device  30  to form a channel for resupplying discharged air. The intake  58  is provided in an intermediate part of the circulating duct  56 . If air is fed to the air intake device  30  from the intake  58  instead of the air discharge duct  52 , fresh air will be supplied to the vehicle maintenance booth  20 . One end of the supply duct  60  is connected to the air intake device  30  to lead air to below the floor surface  28  of the vehicle maintenance booth  20 . As has been described, many fine vent holes are provided on the floor surface  28  and air is supplied from the supply duct  60  to the vehicle maintenance booth  20  through these vent holes. 
         [0041]    Dampers  70 ,  72 , and  74  are provided in the duct  50  as movable plates for controlling the flow of air. The damper  70  is provided between branching to the circulating duct  56  and the exhaust port  54  in the air discharge duct  52  to adjust the amount of circulation and that of discharge to the outside. The damper  72  is provided between branching from the air discharge duct  52  and the intake  58  in the circulating duct  56  to adjust the amount of circulation. Then, the damper  74  is provided at the intake  58  to adjust the amount of intake of fresh air. These dampers  70 ,  72 , and  74  constitute, together with the air intake device  30 , the air discharge device  40 , and the duct  50 , the gas supply/discharge mechanism to realize ventilation of the vehicle maintenance booth  20 . 
         [0042]    The hydrogen sensor  80  is a gas sensor disposed in the air discharge duct  52  and can detect the amount of hydrogen. 
         [0043]    The control device  90  is a computer device for controlling air conditioning of the vehicle maintenance facility  10 . The device can be formed by specifying operations of hardware such as a personal computer (PC) and microcomputer having operation/storage functions using software (programs). The control device  90  includes an input/output section  92 , a comparison section  94 , and a threshold table  96 . The input/output section  92  acquires output data of the hydrogen sensor  80  before sending the output data to the comparison section  94  and also sends operation instruction signals to the fan  32  of the air intake device  30 , the air discharge device  40 , and the dampers  70 ,  72 , and  74  according to instructions of the comparison section  94 . After acquiring the amount of detected hydrogen from the input/output section  92 , the comparison section  94  determines an optimal control state with reference to the threshold table  96 . Then, the comparison section  94  instructs the input/output section  92  to send a control signal to realize the determined control state. 
         [0044]    Subsequently, operations of the vehicle maintenance facility  10  will be described with reference to  FIG. 1  and  FIG. 2 . Like  FIG. 1 ,  FIG. 2  is a diagram showing the vehicle maintenance facility  10 , and like reference numerals are assigned to like components, and repeated descriptions are omitted. 
         [0045]    As shown in  FIG. 1 , the maintenance vehicle  110  on which a fuel cell is mounted is brought into the work space  22  inside the vehicle maintenance booth  20  before being set to the work position. Using equipment and tools (not shown) provided in the work space  22 , an operator performs various kinds of inspection/maintenance work. 
         [0046]    At least when performing work related to the fuel cell, the operator manipulates the control device  90  to activate an air conditioning system inside the vehicle maintenance booth  20 . That is, the air intake device  30  and the air discharge device  40  are set to ON to allow a small amount of air in the work space  22  to flow from the floor surface  28  toward the ceiling wall  26 . At this point, the damper  70  is set to a slightly open state so that approximately 10% of discharged air is discharged to the outside. The damper  72  is maintained in a completely open state to maintain a smooth flow of circulation. The damper  74  is also set to a slightly open state to take in approximately 10% of air from outside through the intake  58  to compensate for the air discharged by the damper  70 . As a result, approximately 90% of air flowing in the work space  22  is re-ventilated air and approximately 10% is air freshly taken in. 
         [0047]    Hydrogen gas may leak while the operator performs maintenance work on the maintenance vehicle  110 . The leaked hydrogen gas swiftly rises, due to its low density. Although under certain circumstances the hydrogen gas may remain in hollow portions or the like in the vehicle, most of the hydrogen gas is swiftly forced out by the flow of air. Then, after reaching the upper part of the work space  22 , the hydrogen gas enters the air discharge duct  52  from the air discharge device  40  following an overall flow of air. In this way, hydrogen is diluted by natural convection and ventilation in the vehicle maintenance booth  20 . 
         [0048]    Inside the air discharge duct  52 , the hydrogen sensor  80  detects the amount of hydrogen gas at fine sampling intervals (for example, one second). The flow inside the air discharge duct  52  is generally made turbulent under the influence of the fan of the air discharge device  40 , and the hydrogen sensor  80  can equally make any air flowing out of the air discharge sections  42 ,  44 , and  46  a detection target. Then, the hydrogen sensor  80  detects hydrogen mixed therein without omission. 
         [0049]    In the control device  90 , the comparison section  94  compares the amount of hydrogen detected by the hydrogen sensor  80  and the preset threshold table  96  to determine the mode of air conditioning operation to be performed. When, for example, the amount of detected hydrogen is 0 or very small, as described above, an operation in which approximately 90% of air is circulated is performed. Moderately fresh air can thereby be introduced also when the work space  22  is heated or cooled without lowering efficiency thereof. 
         [0050]    Here, assume that a rather larger amount of hydrogen gas has leaked. In this case, the hydrogen sensor  80  detects this relatively large amount of hydrogen and outputs detection information to the control device  90 . Then, the comparison section  94  refers to the threshold table  96  to determine that for the detected amount of hydrogen, the air conditioning operation of the next step must be performed. 
         [0051]      FIG. 2  shows an example of the air conditioning operation in this case. This operation is characterized in that, although the amount of ventilation by the air intake device  30  and the air discharge device  40  is not changed, the circulation of air is stopped. That is, the damper  70  is in a completely open state to smoothly lead air from the air discharge duct  52  to the exhaust port  54 . The damper  72  is in a closed state to inhibit the circulation of air. Then, the damper  74  is in a completely open state so that a sufficient amount of air can be taken in through the intake. 
         [0052]    As a result, leaked hydrogen will be swiftly discharged from the exhaust port  54  to the outside. Therefore, the concentration of hydrogen in the vehicle maintenance booth  20  will be maintained at a sufficiently low level to thereby ensure safety. If a still larger amount of hydrogen is detected, the operation level of the air intake device  30  and the air discharge device  40  can be raised while keeping the dampers  70 ,  72 , and  74  in the states shown in  FIG. 2 . Hydrogen can thereby be swiftly expelled to the outside to be diluted. 
         [0053]    Subsequently, a modification will be described with reference to  FIG. 3A  and  FIG. 3B .  FIG. 3A  and  FIG. 3B  are schematic views showing the vehicle maintenance booth  20  shown in  FIG. 2  from the side of the maintenance vehicle  110 .  FIG. 3A  shows an appearance of air conditioning under normal conditions and  FIG. 3B  shows an appearance of air conditioning when hydrogen exceeding the set condition is detected. 
         [0054]    The ventilation state in  FIG. 3A  is the same as that described in  FIG. 1 . That is, a small amount of hydrogen gas is discharged by allowing air to flow from air intake ports  120 ,  122 , and  124  provided on the floor surface toward air discharge ports  130 ,  132 , and  134  provided on the ceiling wall. 
         [0055]    If a large amount of hydrogen is detected, the hydrogen must be swiftly discharged to the outside. In  FIG. 3B , a large amount of air is blown from the front toward the rear of the vehicle maintenance booth  20  to swiftly perform the discharge. That is, ventilation from below upward under normal conditions is stopped and, instead, air intake ports  140  and  142  provided on the front wall of the vehicle maintenance booth  20  and air discharge ports  150  and  152  provided on the rear wall are opened and air is blown to the outside by a large fan in a surge. The upper side air intake port  140  and air discharge port  150  are provided near the ceiling wall so that, even if hydrogen remains near the ceiling wall due to convection, the hydrogen can be sufficiently expelled. Thus, when a large amount of hydrogen is detected, not only the amount of ventilation, but also the direction of ventilation is changed to realize an efficient discharge, as described above, so that further safety can be ensured. 
         [0056]    If no operator enters the vehicle maintenance booth  20 , it is also effective to blow, instead of air, an inert gas (non-inflammable gas) such as nitrogen or helium. That is, by providing a function to blow an inert gas instead of air as a diluent gas or to mix an inert gas with air and also to change at least the ratio of air to the inert gas to flow as a diluent gas, the ratio of the inert gas in the diluent gas may be increased or the diluent gas may be changed to the inert gas only when an inflammable gas satisfying the set condition is detected. This configuration has a scope for implementation even if the operator enters the vehicle maintenance booth  20 . For example, by pouring a helium gas from a position higher than the operator, it becomes possible to ensure safe respiration of the operator and also to isolate hydrogen, which is the lightest and remains rear the ceiling, from air by wrapping the hydrogen with helium, which is the next lightest gas. 
         [0057]    Lastly, another modification will be described with reference to  FIG. 4 .  FIG. 4  is a diagram almost identical to  FIG. 1  and like reference numerals are assigned to like components, with repeated descriptions omitted. A major difference between  FIG. 4  and  FIG. 1  is that a vehicle maintenance booth  158  whose ceiling wall  160  is formed in a tilted state is introduced. The ceiling wall  160  is set in such a way that the ceiling becomes higher towards a center point. Then, a thin tube  162  is disposed upward from the top position of the ceiling wall  160 . Also, a hydrogen sensor  164  is mounted inside the thin tube  162 . 
         [0058]    An air discharge device  170  is mounted on the inside of the ceiling wall  160 . The air discharge device  170  includes air discharge sections  172 ,  174 ,  176 , and  178 , and each of these air discharge sections has an air discharge port and a fan. 
         [0059]    Subsequently, operations according to the configuration shown in  FIG. 4  will be described. Here, no ventilation is provided when the leakage amount of hydrogen is 0 or very small. However, when hydrogen leakage occurs, the hydrogen rises due to natural convection and can further exit after being led along the slope of the ceiling wall  160  and through the thin tube  162 . Thus, the vehicle maintenance booth  158  can be maintained sufficiently safe without providing ventilation even if a small amount of hydrogen leaks. 
         [0060]    Meanwhile, in the thin tube  162  the hydrogen sensor  164  detects the amount of hydrogen at fine sampling intervals. Then, a detection result is sent to the control device  90  and control based on the threshold table  96  is performed. That is, if the amount of hydrogen exceeding the threshold is detected, the air intake device  30  and the air discharge device  170  are activated and also the dampers  70 ,  72 , and  74  are adjusted to swiftly discharge hydrogen to the outside.