Patent Publication Number: US-2022235473-A1

Title: Hydrogen production apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2021-009862 filed on Jan. 25, 2021, the contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a hydrogen production apparatus including a water electrolysis unit for generating hydrogen gas. 
     Description of the Related Art 
     Conventionally, a hydrogen production apparatus including a water electrolysis device has been known. The hydrogen production apparatus generates hydrogen gas by electrolyzing water. For example, when the generated hydrogen gas leaks inside the hydrogen production apparatus, the hydrogen gas may catch fire due to some cause such as an electrical component or static electricity. At this time, there is a risk that an explosion occurs inside the hydrogen production apparatus and constituent members of the hydrogen production apparatus are scattered to the surroundings. 
     In order to reduce damage caused by explosion inside the hydrogen production apparatus, an explosion release port is provided in a housing. The explosion release port can quickly discharge excessive pressure due to explosion, to the outside. 
     For example, a gas chromatograph oven disclosed in JP 2018-194300 A includes an oven chamber main body and a door. The oven chamber main body has a substantially rectangular parallelepiped shape, and the entire front surface thereof is open. The door opens and closes a front opening of the oven chamber main body. The oven chamber main body is formed by putting together a plurality of metal plate members through fitting or by using screws. The front opening of the oven chamber main body is opened and closed by the door. In the front opening, a substantially frame-shaped front frame metal plate member is attached to an outer metal plate member. 
     An explosion occurs when hydrogen gas or the like is accumulated inside the oven chamber main body and catches fire, in the gas chromatograph oven. Along with this explosion, the gas pressure in the internal space of the oven chamber main body rises rapidly. The strength of the left and right upper corners of the oven chamber main body or the attachment portions of the front frame metal plate member and the outer metal plate member is relatively low. Therefore, when an explosion occurs, the attachment portions of the oven chamber main body is damaged or broken and deformed. Thus, an opening is formed in the oven chamber main body. As a result, hydrogen gas or the like in the internal space flows out to the outside of the oven chamber main body through the opening of the oven chamber main body. Therefore, breakage or the like of the gas chromatograph oven is reduced. 
     SUMMARY OF THE INVENTION 
     For example, it is assumed that an opening/closing operation of the door is locked by a locking mechanism in a state where the front opening of the oven chamber main body is closed by the door. In this case, it is conceivable that the locking mechanism is engaged with a ceiling portion or the corner of the oven chamber main body. However, it is difficult to set the strength of the corner or the like of the oven chamber main body to be lower than the strength of other portions. Therefore, when an explosion occurs inside the oven chamber main body, it is difficult to open the oven chamber main body by the pressure of the explosion and release the pressure to the outside. 
     An object of the present invention is to solve the above-described problems. 
     A hydrogen production apparatus including: a water electrolysis unit that electrolyzes water to generate hydrogen gas; a storage unit that stores the hydrogen gas generated in the water electrolysis unit; a supply unit that supplies the hydrogen gas stored in the storage unit, to outside; an electrical unit that controls operation of at least the water electrolysis unit; and a housing that houses the water electrolysis unit, the storage unit, the supply unit, and the electrical unit, wherein the housing is made up of at least an upper frame disposed on an upper side of the housing in a height direction thereof and a lower frame disposed on a lower side thereof in the height direction, and includes an opening end opened in a lateral direction orthogonal to the height direction, and the housing further includes: an opening/closing door configured to be rotatably supported on the housing and configured to open and close the opening end; and a locking mechanism disposed on the opening/closing door and configured to restrict an opening operation of the opening/closing door with the opening end being closed; and wherein the locking mechanism includes first and second rods configured to move along a height direction of the opening/closing door orthogonal to an opening direction of the opening end; and in an opening operation restricted state in which the opening end is closed by the opening/closing door and the opening operation of the opening/closing door is restricted by the locking mechanism, an upper end of the first rod is disposed on an opposite side of the upper frame from the opening/closing door, and a lower end of the second rod is disposed on an opposite side of the lower frame from the opening/closing door; in the opening operation restricted state, a first enlarged diameter portion formed in the vicinity of the upper end of the first rod and enlarged in diameter radially outwardly is in a state of being inserted into a first guide portion disposed on the opening/closing door and extending in a direction opposite to the opening direction of the opening end, and a second enlarged diameter portion formed in the vicinity of the lower end of the second rod and enlarged in diameter radially outwardly is in a state of being inserted into a second guide portion disposed on the opening/closing door and extending in the direction opposite to the opening direction of the opening end; and an axial distance between an upper end of the second enlarged diameter portion and the second guide portion is larger than an axial distance between a lower end of the first enlarged diameter portion and the first guide portion. 
     According to the present invention, in the hydrogen production apparatus, when the opening end of the housing is closed by the opening/closing door and hydrogen gas produced thereinside leaks and ignites to thereby cause an explosion, there are cases in which the opening/closing door may be pressed outward due to a rapidly increased pressure. In this case, the first enlarged diameter portion disposed in the vicinity of the upper end of the first rod in the locking mechanism is separated from the first guide portion and deformed before the second enlarged diameter portion disposed in the vicinity of the lower end of the second rod is separated. As a result, the first rod is disengaged from the upper frame. With the release of the engagement, the opening operation restricted state of the upper part of the opening and closing door by the first rod can be released. 
     As a result, even when an excessive pressure occurs in the housing, only the upper part of the opening/closing door is opened to thereby open the opening end of the housing, in first. As a result, the pressure can be reliably released from the open portion at and near the upper part to the outside of the housing. It is possible to prevent the lower part and its nearby portion of the opening/closing door from being opened or disengaged. Therefore, for example, when there is a person around the opening/closing door, it is possible to reliably avoid contact between the opening/closing door and the person. 
     The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings, in which a preferred embodiment of the present invention is shown by way of illustrative example. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an external perspective view of a hydrogen production apparatus according to an embodiment of the present invention; 
         FIG. 2  is an overall front view of the hydrogen production apparatus shown in  FIG. 1 ; 
         FIG. 3  is an overall front view showing a state in which an opening/closing door of the hydrogen production apparatus of  FIG. 2  is opened; 
         FIG. 4  is a partially omitted cross-sectional view taken along line IV-IV of  FIG. 2 ; 
         FIG. 5  is a cross-sectional view taken along line V-V of  FIG. 1 ; 
         FIG. 6A  is an enlarged front view of the opening/closing door constituting the hydrogen production apparatus of  FIG. 2  as viewed from the inside of a housing, and  FIG. 6B  is a partially omitted enlarged configuration diagram of an opening/closing switching mechanism in  FIG. 6A ; 
         FIG. 7A  is an enlarged cross-sectional view showing an upper rod and its vicinity of the opening/closing switching mechanism in  FIG. 4 , and  FIG. 7B  is an enlarged cross-sectional view showing a lower rod and its vicinity of the opening/closing switching mechanism in  FIG. 4 ; 
         FIG. 8A  is an enlarged front view of the opening/closing door being released from a locked state by the opening/closing switching mechanism as viewed from the inside of the housing, and  FIG. 8B  is a partially omitted enlarged configuration diagram of the opening/closing switching mechanism in  FIG. 8A ; 
         FIG. 9A  is an enlarged cross-sectional view showing an upper rod and its vicinity of the opening/closing switching mechanism in  FIG. 8A , and  FIG. 9B  is an enlarged cross-sectional view showing a lower rod and its vicinity of the opening/closing switching mechanism in  FIG. 8A ; 
         FIG. 10  is an overall cross-sectional view showing a case where an excessive pressure occurs inside the hydrogen production apparatus of  FIG. 4  and part of the opening/closing door is opened; 
         FIG. 11A  is an enlarged cross-sectional view showing an upper rod and its vicinity of the opening/closing switching mechanism in  FIG. 10 , and  FIG. 11B  is an enlarged cross-sectional view showing a lower rod and its vicinity of the opening/closing switching mechanism in  FIG. 10 ; 
         FIG. 12A  is an enlarged cross-sectional view of an upper rod and its vicinity in an opening/closing switching mechanism according to a modification, and  FIG. 12B  is an enlarged cross-sectional view of a lower rod and its vicinity in the opening/closing switching mechanism; and 
         FIG. 13A  is an enlarged cross-sectional view showing the upper rod and its vicinity when an excessive pressure occurs inside the hydrogen production apparatus having the opening/closing switching mechanism of  FIG. 12A , and  FIG. 13B  is an enlarged cross-sectional view showing the lower rod and its vicinity when an excessive pressure occurs inside the hydrogen production apparatus. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     As shown in  FIGS. 1 to 4 , a hydrogen production apparatus  10  is, for example, a so-called hydrogen gas station that supplies hydrogen as a fuel gas to a fuel cell vehicle (object) (not shown). The hydrogen production apparatus  10  includes a housing  12  and a water electrolysis system  14 . The water electrolysis system  14  is housed inside the housing  12 . 
     The cross-sectional shape of the housing  12  is, for example, a substantially rectangular shape elongated in a width direction (arrow A1 and A2 directions) as viewed from above. The housing  12  includes a frame  16 , a pair of side panels  18   a  and  18   b , a rear panel  20 , a bottom panel  22 , and a ceiling panel (ceiling plate)  24 . The pair of side panels  18   a  and  18   b  are disposed on respective both sides in the width direction of the housing  12 . The rear panel  20  is disposed at rear ends of the side panels  18   a  and  18   b . The bottom panel  22  is disposed at lower ends of the side panels  18   a  and  18   b  and the rear panel  20 . The ceiling panel (ceiling plate)  24  is disposed on upper ends of the side panels  18   a  and  18   b  and the rear panel  20 . The side panels  18   a ,  18   b , the rear panel  20 , the bottom panel  22 , and the ceiling panel  24  are each mounted to a frame  16 . 
     The frame  16  includes an upper frame portion  26 , a lower frame portion  28 , and a connection frame portion  30 . The upper frame portion  26  constitutes an upper end of the housing  12 . The lower frame portion  28  constitutes a lower end of the housing  12 . The connection frame portion  30  extends in an up-down direction (vertical direction) (directions of arrows B1 and B2). The connection frame portion  30  connects the upper frame portion  26  and the lower frame portion  28 . 
     The upper frame portion  26  includes first front-to-rear frame pieces  32   a  and  32   b , a first rear frame piece  34 , and a first front frame piece (upper frame)  36 . Each of the first front-to-rear frame pieces  32   a  and  32   b  extends horizontally along the front-rear direction (arrow C1 and C2 directions) at both ends of the upper frame portion  26  in the width direction. The first rear frame piece  34  extends along the width direction of the upper frame portion  26  (the direction of arrows A1 and A2). The first rear frame piece  34  connects rear ends of the first front-to-rear frame pieces  32   a  and  32   b  to each other. The first front frame piece  36  extends along the width direction (arrow A1, A2 direction) of the upper frame portion  26 . The first front frame piece  36  connects front ends of the first front-to-rear frame pieces  32   a  and  32   b . Thus, the first front-to-rear frame pieces  32   a  and  32   b  are arranged substantially parallel to each other. The first rear frame piece  34  and the first front frame piece  36  are disposed substantially parallel to each other. 
     The cross-sectional shape of the first front frame piece  36  is substantially rectangular when viewed from the extending direction thereof. A rear end (an end portion in the arrow C2 direction) of the first front frame piece  36  includes a first wall portion  38 . The first wall portion  38  extends in the up-down direction (the direction of arrows B1 and B2). The first wall portion  38  is flat along the up-down direction. The first wall portion  38  extends with the same cross-sectional shape along the width direction (the direction of arrows A1 and A2). The first wall portion  38  extends from one first front-to-rear frame pieces  32   a  to the other first front-to-rear frame piece  32   b.    
     The lower frame portion  28  includes second front-to-rear frame pieces  40   a  and  40   b , a second rear frame piece  42 , and a second front frame piece (lower frame)  44 . The second front-to-rear frame pieces  40   a ,  40   b  extend horizontally along the front-rear direction (arrow C1, C2 direction) at respective both ends of the lower frame portion  28  in the width direction. The second rear frame piece  42  extends along the width direction of the lower frame portion  28  (the direction of arrows A1 and A2). The second rear frame piece  42  connects rear ends of the second front-to-rear frame pieces  40   a  and  40   b  to each other. The second front frame piece  44  extends along the width direction of the lower frame portion  28 . The second front frame piece  44  connects front ends of the first front-to-rear frame pieces  32   a  and  32   b.    
     The cross-sectional shape of the second front frame piece  44  is substantially rectangular when viewed from the extending direction thereof. A rear end (an end portion in the arrow C2 direction) of the second front frame piece  44  includes a second wall portion  46 . The second wall portion  46  extends in the up-down direction (the direction of arrows B1 and B2). The second wall portion  46  is flat along the up-down direction. The second wall portion  46  extends with the same cross-sectional shape along the width direction (arrow A1, A2 direction). The second wall portion  46  extends from one second front-to-rear frame piece  40   a  to the other second front-to-rear frame piece  40   b . The first wall portion  38  of the upper frame portion  26  and the second wall portion  46  of the lower frame portion  28  are located at the same position in the front-rear direction (the direction of arrows C1 and C2) (see  FIG. 4 ). 
     The second front-to-rear frame pieces  40   a  and  40   b  are disposed substantially parallel to each other. The second rear frame piece  42  and the second front frame piece  44  are disposed substantially parallel to each other. 
     The second front-to-rear frame pieces  40   a  and  40   b  are disposed substantially parallel to the first front-to-rear frame pieces  32   a  and  32   b , respectively. The second front frame piece  44  is disposed substantially parallel to the first front frame piece  36 . The second rear frame piece  42  is disposed substantially parallel to the first rear frame piece  34 . 
     The connection frame portion  30  includes a pair of rear end frame pieces  48   a  and  48   b  and a pair of front end frame pieces  50   a  and  50   b . The rear end frame piece  48   a  connects the rear end of the first front-to-rear frame piece  32   a  and the rear end of the second front-to-rear frame piece  40   a . The rear end frame piece  48   a  connects one end of the first rear frame piece  34  and one end of the second rear frame piece  42 . The rear end frame piece  48   b  connects the rear end of the first front-to-rear frame piece  32   b  and the rear end of the second front-to-rear frame piece  40   b . The rear end frame piece  48   b  connects the other end of the first rear frame piece  34  and the other end of the second rear frame piece  42 . The front end frame piece  50   a  connects the front end of the first front-to-rear frame piece  32   a  and the front end of the second front-to-rear frame piece  40   a . The front end frame piece  50   a  connects one end of the first front frame piece  36  and one end of the second front frame piece  44 . The front end frame piece  50   b  connects the front end of the first front-to-rear frame piece  32   b  and the front end of the second front-to-rear frame piece  40   b . The front end frame piece  50   b  connects the other end of the first front frame piece  36  and the other end of the second front frame piece  44 . Thus, the rear end frame pieces  48   a  and  48   b  and the front end frame pieces  50   a  and  50   b  are arranged substantially parallel to each other. The rear end frame pieces  48   a ,  48   b  and the front end frame pieces  50   a ,  50   b  are substantially orthogonal to the first front-to-rear frame pieces  32   a ,  32   b , the second front-to-rear frame pieces  40   a ,  40   b , the first and second front frame pieces  36 ,  44 , and the first and second rear frame pieces  34 ,  42 . 
     The side panel  18   a  is fitted into a rectangular frame formed by the first front-to-rear frame piece  32   a  of the upper frame portion  26 , the second front-to-rear frame piece  40   a  of the lower frame portion  28 , the rear end frame piece  48   a , and the front end frame piece  50   a . The side panel  18   b  is fitted into a rectangular frame formed by the first front-to-rear frame piece  32   b  of the upper frame portion  26 , the second front-to-rear frame piece  40   b  of the lower frame portion  28 , the rear end frame piece  48   b , and the front end frame piece  50   b . Each of the side panels  18   a  and  18   b  is fixed to the frame  16  by fastening screws (not shown). Thus, the pair of side panels  18   a  and  18   b  constitute side walls on both sides of the housing  12  in the width direction. 
     The rear panel  20  is fitted into a rectangular frame formed by the first rear frame piece  34  of the upper frame portion  26 , the second rear frame piece  42  of the lower frame portion  28 , and the pair of rear end frame pieces  48   a  and  48   b . The rear panel  20  is fixed to the frame  16  by a plurality of fastening screws (not shown). 
     The bottom panel  22  is fitted into a rectangular frame formed by the second front-to-rear frame pieces  40   a  and  40   b , the second rear frame piece  42 , and the second front frame piece  44  in the lower frame portion  28 . The bottom panel  22  is fixed to the frame  16  by a plurality of fastening screws (not shown). Thus, the bottom panel  22  constitutes a bottom wall of the housing  12 . 
     The ceiling panel  24  is fitted into a rectangular frame formed by the first front-to-rear frame pieces  32   a  and  32   b , the first rear frame piece  34 , and the first front frame piece  36  in the upper frame portion  26 . The ceiling panel  24  includes a first panel body (divided piece)  52  and a second panel body (divided piece)  54 . The first panel body (divided piece)  52  is disposed on one side in the width direction (arrow A1 direction) of the frame  16 . The second panel body (divided piece)  54  is disposed adjacent to the first panel body  52  on the other side in the width direction (direction of arrow A2) of the frame  16 . That is, the ceiling panel  24  is divided into two parts (two pieces) in the width direction of the housing  12  (the direction of arrows A1 and A2). 
     The second panel body  54  is disposed above a water electrolysis unit  122  in the water electrolysis system  14  described later. The second panel body  54  includes a ventilation opening (opening)  56 . The ventilation opening  56  penetrates through the second panel body  54  and opens in a substantially rectangular shape. Thus, the inside and the outside of the housing  12  communicate with each other through the ventilation opening  56  penetrating the ceiling panel  24 . 
     The first panel body  52  is firmly fixed to the first front-to-rear frame piece  32   a , the first rear frame piece  34 , and the first front frame piece  36  by a plurality of (for example, four) fastening screws  55 . 
     One end of the second panel body  54  in the width direction is disposed adjacent to the first panel body  52  (in the arrow A1 direction). One end of the second panel body  54  in the width direction (end portion in the arrow A1 direction) is placed on the first rear frame piece  34  and the first front frame piece  36 . The other end of the second panel body  54  in the width direction (end portion in the arrow A2 direction) is placed on the first front-to-rear frame piece  32   b . An outer edge of the second panel body  54  is placed on the first rear frame piece  34 , the first front frame piece  36 , and the first front-to-rear frame piece  32   b . The second panel body  54  includes three panel holes  58  provided in the vicinity of the outer edge thereof. Each of the panel holes  58  penetrates the second panel body  54  in the up-down direction (the direction of the arrows B1 and B2). Each of the panel holes  58  is spaced apart from the other panel holes  58  along the outer edge of the second panel body  54 . 
     Each of the first rear frame piece  34 , the first front frame piece  36 , and the first front-to-rear frame piece  32   b  has a frame hole  60  (see  FIG. 5 ) that opens toward the corresponding panel hole  58 . The outer edge of the second panel body  54  is placed on the first rear frame piece  34 , the first front frame piece  36 , and the first front-to-rear frame piece  32   b . Thereafter, three rivets  62  are engaged with the panel holes  58  and the frame holes  60  of the frame pieces  34 ,  36 , and  32   b , respectively. Thus, the outer edge of the second panel body  54  is fixed to the frame  16 . 
     As shown in  FIG. 5 , the rivet  62  is formed of, for example, a plastically deformable metal material. The rivet  62  includes a main body portion  64 , a flange portion  66 , and a crimped portion  68 . The cross-sectional shape of the main body portion  64  is circular. The main body portion  64  has a shaft shape. The main body portion  64  is inserted through each of the panel holes  58  of the ceiling panel  24  and each of the frame holes  60  of the frame pieces  32   b ,  34 , and  36 . The flange portion  66  is disposed at one end (upper end) of the main body portion  64 . The flange portion  66  has a circular disk shape radially outwardly extending from the main body portion  64 . The crimped portion  68  is disposed at the other end (lower end) of the main body portion  64 . 
     When the outer edge of the second panel body  54  is placed on the first rear frame piece  34 , the first front frame piece  36 , and the first front-to-rear frame piece  32   b , the frame holes  60  of the frame pieces  32   b ,  34 , and  36  are aligned with the respective panel holes  58  in a straight line in the up-down direction (the direction of the arrows B1 and B2). The main body portion  64  of the rivet  62  is inserted into the panel hole  58  from the upper surface of the second panel body  54 , and the flange portion  66  is brought into contact with the upper surface of the second panel body  54 . As a result, the main body portions  64  of the three rivets  62  protrude from the lower surfaces of the first rear frame piece  34 , the first front frame piece  36 , and the first front-to-rear frame piece  32   b . The lower end of each main body portion  64  is pressed and deformed in the axial direction (upward, arrow B1 direction). As a result, the lower end of each main body portion  64  enlarges in diameter radially outward and becomes the crimped portion  68 . 
     The crimped portion  68  regulates attachment and detachment of the second panel body  54  to and from the frame  16  in the up-down direction (directions of arrows B1 and B2). The rivet  62  including the crimped portion  68  fixes the second panel body  54  and the frame  16  to each other. The ceiling panel  24  including the first and second panel bodies  52  and  54  constitutes an upper wall of the housing  12 . The first panel body  52  is fixed to the frame  16  by four fastening screws  55 . The second panel body  54  is fixed to the frame  16  by the three rivets  62 . Thus, the fixing strength of the second panel body  54  to the frame  16  is lower than the fixing strength of the first panel body  52  to the frame  16 . In other words, the second panel body  54  is fixed to the housing  12  with a lower fixing strength than the first panel body  52  so as to be easily detached from the housing  12 . 
     One end of the second panel body  54  in the width direction (end portion in the arrow A1 direction) is fixed by two of the rivets  62 . The other end of the second panel body  54  in the width direction (end portion in the arrow A2 direction) is fixed by one of the rivets  62 . Therefore, the fixing strength of the second panel body  54  to the frame  16  at the other end in the width direction is lower than the fixing strength of the second panel body  54  to the frame  16  at the one end in the width direction. 
     The side panels  18   a  and  18   b  of the housing  12  are arranged upright in the up-down direction (directions of arrows B1 and B2). One side panel  18   a  and the other side panel  18   b  are arranged substantially parallel to each other. Each of the bottom panel  22  and the ceiling panel  24  is arranged substantially horizontally. The bottom panel  22  and the ceiling panel  24  are arranged substantially orthogonal to the side panels  18   a ,  18   b . That is, the housing  12  has a box shape recessed rearward (in the direction of the arrow C2) from the front end (opening end)  70 . The front end  70  of the housing  12  has a substantially rectangular shape which is long in the width direction. The housing  12  is open toward the front side (the arrow C1 direction, opening direction). 
     An opening/closing door  72  is disposed at the front end  70  of the housing  12 . The opening/closing door  72  is divided at the center of the front end  70  in the width direction. The opening/closing door  72  can open and close the front end  70 . The opening/closing door  72  includes a pair of door bodies  74   a  and  74   b , for example, formed by dividing a plate into two in the width direction (the direction of arrows A1 and A2) of the housing  12 . 
     Each of the door bodies  74   a  and  74   b  is, for example, a flat panel having substantially the same height as the side panels  18   a  and  18   b . One end portion of each of the door bodies  74   a  and  74   b  in the width direction is rotatably supported by the front end  70  of the corresponding one of the side panels  18   a  and  18   b . The one end portion of each of the door bodies  74   a  and  74   b  in the width direction is supported by a support shaft  76  extending in the up-down direction (the direction of arrows B1 and B2). That is, the pair of door bodies  74   a  and  74   b  are double doors that laterally open in the left-right direction (directions of arrows A1 and A2) from the center of the housing  12  in the width direction with the end portions of the housing  12  in the width direction as pivot points. 
     As shown in  FIGS. 1, 2, and 4 , for example, the opening/closing door  72  is substantially parallel to the rear panel  20  when the front end  70  of the housing  12  is closed. When the opening/closing door  72  is opened from the front end  70 , as shown in  FIG. 3 , for example, the door bodies  74   a  and  74   b  rotate, and the door bodies  74   a  and  74   b  are separated from each other at the center of the opening/closing door  72  in the width direction. As a result, the door body  74   a  is placed in substantially parallel to the side panel  18   a , and the door body  74   b  is placed in substantially parallel to the side panel  18   b . (See a two-dot chain line in  FIG. 1 ). 
     As shown in  FIGS. 2 to 4 and 6A to 9B , each of the end portions of the door bodies  74   a  and  74   b  located at the center of the opening/closing door  72  in the width direction includes an opening/closing switching mechanism (locking mechanism)  78  and a support mechanism  80 . The opening/closing switching mechanism  78  switches the opening/closing door  72  at the front end  70  of the housing  12  between an open state and a closed state. The support mechanism  80  supports an upper rod (first rod)  86  and a lower rod (second rod)  88  of the opening/closing switching mechanism  78 . 
     The opening/closing switching mechanism  78  extends in the up-down direction (the direction of arrows B1 and B2) along the width-direction end portions of the door bodies  74   a  and  74   b.    
     The opening/closing switching mechanism  78  includes opening/closing levers (operating members)  82 , cam plates (connecting bodies)  84 , the upper rods  86 , and the lower rods  88 . The opening/closing lever  82  is disposed outside the opening/closing door  72 . The cam plate  84  is disposed inside the opening/closing door  72  and connected to the opening/closing lever  82 . The upper rod  86  is disposed inside the opening/closing door  72  and extends upward (in the direction of the arrow B1) from the center in the height direction. The upper rod  86  is connected to the cam plate  84 . The lower rod  88  is disposed inside the opening/closing door  72  and extends downward (in the direction of the arrow B2) from the center in the height direction. Each of the lower rods  88  is connected to the cam plate  84 . 
     The opening/closing lever  82  is, for example, substantially L-shaped. Each of the opening/closing levers  82  is disposed near the center of the door bodies  74   a  and  74   b  in the height direction. The opening/closing lever  82  includes a shaft portion  90  and a grip portion  92 . The shaft portion  90  linearly extends toward the opening/closing door  72  and penetrates the opening/closing door  72 . The grip portion  92  is disposed apart from the door bodies  74   a  and  74   b  by a predetermined distance. The grip portion  92  extends substantially orthogonal to an end portion of the shaft portion  90 . 
     One end portion of the shaft portion  90  of the opening/closing lever  82  is inserted into a hole (not shown) opened in the opening/closing door  72 . Thus, the opening/closing lever  82  is rotatably supported by the opening/closing door  72 . When the opening/closing door  72  is opened and closed, an operator (not shown) grips and rotates the grip portion  92  of the opening/closing lever  82 . 
     In a locked state in which an opening operation of the opening/closing door  72  is restricted by the opening/closing switching mechanism  78 , the grip portion  92  of the opening/closing lever  82  is aligned with the up-down direction (the direction of the arrows B1 and B2). In an unlocked state in which the opening operation of the opening/closing door  72  is allowed, the grip portion  92  of the opening/closing lever  82  is disposed at an inclined position at which the grip portion is rotated by a predetermined angle from the up-down direction (the directions of the arrows B1 and B2). 
     As shown in  FIGS. 4, 6A, 6B, 8A and 8B , the cam plate  84  is substantially T-shaped. The shaft portion  90  of the opening/closing lever  82  is connected to a central portion of the cam plate  84 . The cam plate  84  includes a first connecting portion (first end portion)  94  and a second connecting portion (second end portion)  96 . The first connecting portion  94  extends from the center of the cam plate  84  toward one side. The second connecting portion  96  extends from the center of the cam plate  84  toward the other side, i.e., in a direction opposite to the direction in which the first connecting portion  94  extends from the center portion of the cam plate  84 . 
     The first connecting portion  94  is disposed substantially so as to extend upward, in the opening/closing door  72 . The first connecting portion  94  protrudes from the center of the cam plate  84  by a predetermined length. The distal end of the first connecting portion  94  includes a support hole  98 . The support hole  98  penetrates through the first connecting portion  94 . A lower end of the upper rod  86  to be described later is rotatably inserted into the support hole  98 . 
     The second connecting portion  96  is disposed so as to extend substantially downward, in the opening/closing door  72 . The second connecting portion  96  protrudes from the center of the cam plate  84  by a predetermined length. The second connecting portion  96  is arranged in alignment with the first connecting portion  94 . The distal end of the second connecting portion  96  includes a support hole  100 . The support hole  100  penetrates through the second connecting portion  96 . An upper end of the lower rod  88 , which will be described later, is rotatably inserted into the support hole  100 . 
     The cam plate  84  rotates integrally with the opening/closing lever  82  by rotating the opening/closing lever  82  connected to the shaft portion  90 . As the opening/closing lever  82  rotates, the first and second connecting portions  94  and  96  rotate about the center of the cam plate  84  by a predetermined angle. 
     At the time of locking in which the opening operation of the opening/closing door  72  is restricted, as illustrated in  FIGS. 1, 2, 4, 6A, and 6B , the grip portion  92  of the opening/closing lever  82  is aligned with the up-down direction (the direction of arrows B1 and B2). The first and second connecting portions  94 ,  96  of the cam plate  84  are disposed along the up-down direction. 
     In an unlocked state in which the opening operation of the opening/closing door  72  can be performed, as shown in  FIGS. 8A and 8B , the first and second connecting portions  94  and  96  of the cam plate  84  are inclined at a predetermined angle from the up-down direction. 
     The upper rod  86  is a shaft body having a constant diameter and made of, for example, a metal material. The upper rod  86  is disposed on the upper side of the center of the opening/closing door  72  in the height direction (in the direction of the arrow B1) and extends along the up-down direction. A lower end of the upper rod  86  is bent substantially at a right angle toward a side opposite to the opening/closing door  72 . In other words, the lower end of the upper rod  86  is bent rearward (in the direction of the arrow C2) substantially at a right angle. The lower end of the upper rod  86  is inserted into the support hole  98  of the first connecting portion  94  of the cam plate  84  (see  FIG. 4 ). 
     As illustrated in  FIGS. 4, 6A, 6B, 7A, 8A, 8B, and 9A , the upper rod  86  is inserted into a first rod hole  118   a  of a first slider  106 , which will be described later, disposed on an inner surface of the opening/closing door  72 . Accordingly, the upper rod  86  is supported by the opening/closing door  72  so as to be movable in the up-down direction (the direction of the arrows B1 and B2). 
     An upper end (axially upper end)  86   a  of the upper rod  86  is covered with a first cap member  101 . The first cap member  101  has a bottomed tubular shape having a bottom portion on an upper side (in a direction of an arrow B1). The first cap member  101  is formed of an elastic material such as rubber or resin, for example. An upper collar member (first enlarged diameter portion)  102  is mounted near the upper end  86   a  of the upper rod  86 . The upper collar member  102  covers the outer peripheral surface of the upper end  86   a.    
     The upper collar member  102  has a predetermined length along the axial direction of the upper rod  86  (the directions of the arrows B1 and B2). The upper collar member  102  is fixed, for example, to a position spaced downward from the upper end  86   a  (in the direction of the arrow B2) by a predetermined distance. The upper collar member  102  is fixed to the upper end  86   a  of the upper rod  86  by welding or the like, for example. That is, in the vicinity of the upper end  86   a  of the upper rod  86 , the shaft diameter of the upper rod  86  is increased by mounting the upper collar member  102 . Therefore, the mounting portion of the upper collar member  102  functions as an enlarged diameter portion having an increased strength in the upper rod  86 . 
     A portion (first enlarged diameter portion) of the upper rod  86  to which the upper collar member  102  is attached is inserted into a second rod hole  120   a  of a first stopper (first guide portion)  110  described later. 
     When the cam plate  84  rotates together with the opening/closing lever  82 , the upper rod  86  moves along the up-down direction (the directions of the arrows B1 and B2). In the locked state in which the opening operation of the opening/closing door  72  illustrated in  FIGS. 6A to 7A  is restricted, the first connecting portion  94  and the upper rod  86  are disposed substantially in a straight line. The upper end  86   a  of the upper rod  86  is located rearward (in the direction of the arrow C2) of the first wall portion  38  of the first front frame piece  36 . The upper end  86   a  of the upper rod  86  is disposed upward (in the direction of arrow B1) of the lower end of the first wall portion  38 . 
     In the unlocked state in which the restriction on the opening operation of the opening/closing door  72  shown in  FIGS. 8A to 9A  is released, the first connecting portion  94  is inclined at a predetermined angle from the up-down direction. As the first connecting portion  94  is displaced, the upper rod  86  is pulled downward (in the direction of the arrow B2) and lowered. The upper end  86   a  of the upper rod  86  is positioned on the lower side (in the direction of arrow B2) of the lower end of the first wall portion  38 . 
     Similarly to the upper rod  86 , the lower rod  88  is a shaft body having a constant diameter and made of a metal material. The lower rod  88  is disposed below the center of the opening/closing door  72  in the height direction (in the direction of the arrow B2) and extends along the up-down direction. The lower rod  88  is arranged coaxially with the upper rod  86 . An upper end of the lower rod  88  is bent substantially at a right angle toward a side opposite to the opening/closing door  72 . In other words, the upper end of the lower rod  88  is bent rearward (in the direction of the arrow C2) substantially at a right angle. The upper end of the lower rod  88  is inserted into the support hole  100  of the second connecting portion  96  of the cam plate  84  (see  FIG. 4 ). 
     As illustrated in  FIGS. 4, 6A, 6B, 7B, 8A, 8B, 9A, and 9B , the lower rod  88  is inserted into a first rod hole  118   b  of a second slider  108 , which will be described later, disposed on an inner surface of the opening/closing door  72 . Accordingly, the lower rod  88  is supported by the opening/closing door  72  so as to be movable in the up-down direction (the direction of the arrows B1 and B2). 
     A lower end (axially lower end)  88   a  of the lower rod  88  is covered with a second cap member  103 . The second cap member  103  has a bottomed tubular shape having a bottom portion on the lower side (in the arrow B2 direction). The second cap member  103  is formed of an elastic material such as rubber or resin. A lower collar member (second enlarged diameter portion)  104  is mounted in the vicinity of the lower end  88   a  of the lower rod  88 . The lower collar member  104  covers the outer peripheral surface of the lower end  88   a.    
     The lower collar member  104  has a predetermined length along the axial direction of the lower rod  88  (the directions of the arrows B1 and B2). The lower collar member  104  is fixed at a position spaced upward from the lower end  88   a  (in the direction of the arrow B1) by a predetermined distance. The lower collar member  104  is fixed to the lower end  88   a  of the lower rod  88  by welding or the like, for example. 
     The axial distance between the lower end of the lower collar member  104  and the lower end  88   a  of the lower rod  88  is the same as the axial distance from the upper end  86   a  of the upper rod  86  to the upper end of the upper collar member  102 . That is, in the vicinity of the lower end  88   a  of the lower rod  88 , the shaft diameter of the lower rod  88  is increased by mounting the lower collar member  104 . Therefore, the mounting portion of the lower collar member  104  functions as an enlarged diameter portion having an increased strength in the lower rod  88 . 
     The lower rod  88  has a mounting portion to which the lower collar member  104  is mounted. This mounting portion is inserted into a second rod hole  120   b  of a second stopper (second guide portion)  112  described later. In the locked state in which the opening/closing door  72  is closed as shown in  FIG. 4  and  FIGS. 6A to 7B , the axial distance L2 from the second stopper  112  to the upper end of the lower collar member  104  is set larger than the axial distance L1 from the first stopper  110  to the lower end of the upper collar member  102  (L2&gt;L1). 
     Accordingly, when the cam plate  84  rotates together with the opening/closing lever  82 , the lower rod  88  moves along the up-down direction (the direction of the arrows B1 and B2). In the locked state in which the opening operation of the opening/closing door  72  illustrated in  FIGS. 6A to 7B  is restricted, the second connecting portion  96  and the lower rod  88  are disposed substantially in a straight line. The lower end  88   a  of the lower rod  88  is disposed rearward (in the arrow C2 direction) of the second wall portion  46  of the second front frame piece  44 . The lower end  88   a  of the lower rod  88  is positioned below (in the direction of arrow B2) the upper end of the second wall portion  46 . 
     As shown in  FIGS. 8A to 9B , in the unlocked state in which the restriction on the opening operation of the opening/closing door  72  is released, the second connecting portion  96  is inclined at a predetermined angle from the up-down direction. As the second connecting portion  96  is displaced, the lower rod  88  is pulled upward (in the direction of the arrow B1) and rises. The lower end  88   a  of the lower rod  88  is positioned above (in the arrow B1 direction) the upper end of the second wall portion  46 . 
     The support mechanism  80  includes the first slider  106 , the second slider  108 , the first stopper  110 , and the second stopper  112 , as shown in  FIGS. 4, and 6A to 9B . The support mechanism  80  is disposed on an inner surface of the opening/closing door  72  in the vicinity of the center in the width direction. The first slider  106  supports the upper rod  86  so as to be movable in the up-down direction (the direction of arrows B1 and B2). The second slider  108  supports the lower rod  88  so as to be movable in the up-down direction. The first stopper  110  is disposed above the first slider  106 . The upper rod  86  is inserted through the first stopper  110 . The second stopper  112  is disposed below the second slider  108 . The lower rod  88  is inserted through the second stopper  112 . 
     The first slider  106  and the second slider  108  have substantially the same shape. The first slider  106  and the second slider  108  protrude rearward (in the direction of the arrow C2) from the inner surface of the opening/closing door  72 . The first slider  106  and the second slider  108  protrude from the inner surface of the opening/closing door  72  in a direction orthogonal to the inner surface. The first slider  106  is disposed near the upper end of the opening/closing door  72 . The second slider  108  is disposed near the lower end of the opening/closing door  72 . Specifically, the first slider  106  and the second slider  108  are disposed symmetrically with respect to the height-direction center of the opening/closing door  72 . The first rod hole  118   a  is provided in the vicinity of the rear end of the first slider  106 . The upper rod  86  is inserted through the first rod hole  118   a . The upper rod  86  is guided by the first rod hole  118   a  of the first slider  106  so as to be movable in the up-down direction (the direction of arrows B1 and B2). 
     The first rod hole  118   b  is provided in the vicinity of the rear end of the second slider  108 . The lower rod  88  is inserted through the first rod hole  118   b . The lower rod  88  is guided by the first rod hole  118   b  of the second slider  108  so as to be movable in the up-down direction (the direction of the arrows B1 and B2). 
     The first stopper  110  and the second stopper  112  have substantially the same shape. Similarly to the first slider  106 , the first stopper  110  protrudes rearward (in the direction of the arrow C2) from the inner surface of the opening/closing door  72 . The first stopper  110  is separated from the first slider  106  by a predetermined distance upward (in the direction of the arrow B1). The first stopper  110  is substantially parallel to the first slider  106 . Similarly to the second slider  108 , the second stopper  112  protrudes rearward (in the direction of the arrow C2) from the inner surface of the opening/closing door  72 . The second stopper  112  is spaced apart from the second slider  108  by a predetermined distance downward (in the direction of the arrow B2). The second stopper  112  is substantially parallel to the second slider  108 . 
     The second rod hole  120   a  is provided in the vicinity of the rear end of the first stopper  110 . The second rod hole  120   a  is coaxial with the first rod hole  118   a  of the first slider  106 . The second rod hole  120   b  is provided near the rear end of the second stopper  112 . The second rod hole  120   b  is arranged coaxially with the first rod hole  118   b  of the second slider  108 . The second rod holes  120   a ,  120   b  are larger in diameter than the first rod holes  118   a ,  118   b , respectively. Accordingly, the upper collar member  102  and the lower collar member  104  can be inserted into the second rod holes  120   a  and  120   b , respectively. When the opening/closing door  72  is opened, the upper rod  86  passed through the second rod hole  120   a  can tilt, and the lower rod  88  passed through the second rod hole  120   b  can tilt. 
     In a locked state in which the opening operation of the opening/closing door  72  is locked by the opening/closing switching mechanism  78 , the upper end  86   a  of the upper rod  86  is disposed behind the first front frame piece  36 . In the locked state, the first cap member  101  is in sliding contact with the first wall portion  38 . In the locked state, the lower end  88   a  of the lower rod  88  is disposed behind the second front frame piece  44 . In the locked state, the second cap member  103  is in sliding contact with the second wall portion  46 . Note that the first cap member  101  protrudes slightly downward (in the direction of the arrow B2) from the lower end of the first wall portion  38 . The second cap member  103  protrudes slightly upward (in the direction of arrow B1) from the upper end of the second wall portion  46 . 
     As shown in  FIG. 3 , the water electrolysis system  14  includes a water electrolysis unit  122 , a storage unit  124 , a supply unit  126 , and an electrical unit  128 . 
     The water electrolysis unit  122  and the electrical unit  128  are disposed forward (in the direction of the arrow C1) inside the housing  12 . The supply unit  126  and the storage unit  124  are accommodated rearward (in the direction of the arrow C2) inside the housing  12 . The electrical unit  128  is disposed at an upper portion of the housing  12  on one side in the width direction (arrow A1 direction). The water electrolysis unit  122  is disposed on the other side in the width direction of the housing  12  (the direction of the arrow A2). The electrical unit  128  controls operation of the supply unit  126  and the water electrolysis unit  122 . 
     Next, the operation and effects of the hydrogen production apparatus  10  will be described. 
     First, a circulation pump (not shown) constituting the water electrolysis unit  122  is driven. When the circulation pump is driven, water (pure water) is supplied to a water electrolysis stack (not shown). Water is electrolyzed in the water electrolysis stack to which a voltage is applied. Thus, hydrogen gas is obtained in the water electrolysis stack. After moisture (water) is removed, the hydrogen gas is sent to the storage unit  124  and stored therein. The hydrogen gas is supplied from the storage unit  124  to an external device (for example, a fuel cell electric vehicle) (not shown) through the supply unit  126  as necessary. 
     Next, a case where the opening/closing door  72  of the above-described hydrogen production apparatus  10  is opened and closed will be described. 
     First, in the hydrogen production apparatus  10 , the grip portion  92  of the opening/closing lever  82  illustrated in  FIGS. 2, 4, and 6A to 7B  extends in the up-down direction (the direction of the arrows B1 and B2), so that the opening/closing door  72  is in a locked state. In the locked state of the opening/closing door  72 , the opening/closing switching mechanism  78  and the support mechanism  80  are in the following states. The first and second connecting portions  94 ,  96  of the cam plate  84  are arranged in a straight line along the up-down direction. The upper end  86   a  of the upper rod  86  is disposed behind (in the direction of the arrow C2) the first wall portion  38  of the first front frame piece  36 . The lower end  88   a  of the lower rod  88  is disposed behind (in the direction of the arrow C2) the second wall portion  46  of the second front frame piece  44 . The upper collar member  102  is inserted into the second rod hole  120   a  of the first stopper  110 . The lower collar member  104  is inserted into the second rod hole  120   b  of the second stopper  112 . 
     In this way, the upper end  86   a  of the upper rod  86  is disposed on the rear side (the arrow C2 direction) of the first front frame piece  36 , and the first cap member  101  is in sliding contact with the first wall portion  38 . The lower end  88   a  of the lower rod  88  is disposed rearward (in the direction of the arrow C2) of the second front frame piece  44 , and the second cap member  103  is in sliding contact with the second wall portion  46 . As a result, movement of the opening/closing door  72  toward the front (in the direction of the arrow C1) is restricted, and the opening/closing door  72  is placed in a locked state (opening operation restricted state). The opening operation of the opening/closing door  72  is restricted with the opening/closing door  72  closing the front end  70  of the housing  12 , and the opening/closing door  72  does not open. 
     In a state where the opening/closing door  72  is closed and locked, airtightness inside of the housing  12  is ensured. 
     Next, when the opening/closing door  72  is opened from the housing  12 , an operator (not shown) grips the grip portions  92  of the pair of opening/closing levers  82 . For example, the opening/closing levers  82  rotate the lower ends of the grip portions  92  in directions away from each other, that is, toward the outer sides in the width direction with the shaft portions  90  as fulcrums. 
     As a result, as shown in  FIGS. 8A and 8B , each of the cam plates  84  rotates by a predetermined angle together with the shaft portion  90  inside the opening/closing door  72 . As the cam plate  84  rotates, the first and second connecting portions  94 ,  96  of the cam plate  84  are inclined by a predetermined angle from the up-down direction. As the cam plate  84  rotates, the lower end of the upper rod  86  inserted into the support hole  98  is pulled downward (in the direction of the arrow B2). As the cam plate  84  rotates, the lower end  88   a  of the lower rod  88  inserted into the support hole  100  is pulled upward (in the direction of the arrow B1). Specifically, the second connecting portions  96  of the pair of cam plates  84  approach each other. The pair of first connecting portions  94  are disposed to be separated away from each other. Thus, the upper rod  86  and the lower rod  88  move in directions to approach each other due to the rotation of the cam plate  84 . Each of the upper rod  86  and the lower rod  88  is inclined by a predetermined angle with respect to the up-down direction (directions of arrows B1 and B2). 
     As a result, the upper rod  86  is inclined with respect to the up-down direction, and thus moves downward along the first rod hole  118   a  of the first slider  106 . The upper collar member  102  tilts in the width direction in the second rod hole  120   a  of the first stopper  110 . The upper end  86   a  of the upper rod  86  is disposed below (in the direction of arrow B2) the lower end of the first front frame piece  36  together with the first cap member  101  (see  FIG. 8B ). 
     The lower rod  88  is inclined with respect to the up-down direction, and then moves upward along the first rod hole  118   b  of the second slider  108 . The lower collar member  104  tilts in the width direction in the second rod hole  120   b  of the second stopper  112 . The lower end  88   a  of the lower rod  88  is disposed above (in the direction of the arrow B1) the upper end of the second front frame piece  44  together with the second cap member  103  (see  FIG. 8B ). 
     As a result, the engagement between the upper rod  86  and the first front frame piece  36  is released. The engagement between the lower rod  88  and the second front frame piece  44  is released. The opening/closing door  72  having the opening/closing switching mechanism  78  can be opened forward (in the direction of the arrow C1). An operator (not shown) pulls the opening/closing levers  82  forward (in the direction of the arrow C1) while holding the opening/closing levers  82 . As a result, the pair of door bodies  74   a  and  74   b  laterally open in the left-right direction (directions of arrows A1 and A2) with the left and right support shafts  76  serving as fulcrums (see a two-dot dashed line shape in  FIG. 1 ). 
     When the opening/closing door  72  is closed again, an operator (not shown) grips the opening/closing levers  82  and rotates the pair of door bodies  74   a  and  74   b . After the front end  70  of the housing  12  is closed by the opening/closing door  72 , the opening/closing levers  82  are rotated in directions in which the lower ends of the opening/closing levers  82  approach each other. The cam plates  84  rotate with the rotation of the opening/closing levers  82 . Since each opening/closing lever  82  is disposed along the up-down direction, the first and second connecting portions  94 ,  96  of the cam plate  84  are aligned in a straight line in the up-down direction. As the first connecting portion  94  is displaced, the upper end  86   a  of the upper rod  86  moves upward, and the upper end  86   a  moves to the rear of the first wall portion  38  of the first front frame piece  36 . Along with the displacement of the second connecting portion  96 , the lower end  88   a  of the lower rod  88  moves downward, and the lower end  88   a  moves to the rear of the second wall portion  46  of the second front frame piece  44 . 
     As a result, the upper end  86   a  of the upper rod  86  is engaged with the first front frame piece  36 , and movement of the upper rod  86  toward the front (the direction of the arrow C1) is restricted. The lower end  88   a  of the lower rod  88  is engaged with the second front frame piece  44 , and movement of the lower rod  88  toward the front (the direction of the arrow C1) is restricted. As a result, movement of the opening/closing door  72  from the front end  70  toward the front (in the direction of the arrow C1) is restricted by the opening/closing switching mechanism  78 . That is, a locked state in which opening and closing of the opening/closing door  72  is restricted is brought about. 
     In the hydrogen production apparatus  10  shown in  FIG. 1 , when the front end  70  of the housing  12  is closed by the opening/closing door  72 , hydrogen gas produced in the water electrolysis unit  122  may leak into the housing  12  and accumulate therein for some reason, for example. Next, a case where hydrogen gas is ignited by sparks, static electricity, or the like generated in the electrical unit  128  and an explosion occurs will be described with reference to  FIGS. 9A to 11B . 
     First, when the hydrogen gas accumulated in the housing  12  explodes, the internal pressure of the housing  12  rapidly increases due to the explosion. An excessive pressure is applied to the side panels  18   a  and  18   b , the rear panel  20 , the ceiling panel  24 , and the opening/closing door  72  constituting the housing  12  so as to press them from the inside toward the outside. At this time, part of the pressure is released to the outside through the ventilation opening  56  opened in the ceiling panel  24 . The ceiling panel  24  is pressed upward by the pressure (in the direction of the arrow B1). 
     As shown in  FIG. 3 , the fixing strength of the second panel body  54  of the ceiling panel  24  is lower than the fixing strength of the first panel body  52 . Therefore, the fixed state of the second panel body  54  to the frame  16  by the three rivets  62  is released by the application of pressure. The second panel body  54  is pushed upward and detached from the housing  12  (see a two-dot chain line shape in  FIG. 3 ). Thus, the upper portion of the housing  12  opens. 
     Specifically, as shown in  FIG. 3 , the other end of the second panel body  54  in the width direction fixed by one rivet  62  comes off the frame  16  before the one end of the second panel body  54  in the width direction fixed by two rivets  62  comes off. At this time, one end of the second panel body  54  in the width direction remains fixed to the frame  16 . As a result, part of the pressure inside the housing  12  is released to the outside from the upper portion of the housing  12  through the ventilation opening  56 , and is also released to the outside from the upper portion of the housing  12  that is opened by part of the second panel body  54  being detached. 
     The center and its vicinity of the opening/closing door  72  in the height direction are pressed outward (forward) by the pressure remaining in the housing  12 . The cam plate  84  of the opening/closing switching mechanism  78 , the lower end of the upper rod  86  supported by the cam plate  84 , and the upper end of the lower rod  88  supported by the cam plate move forward (in the direction of the arrow C1) together with the opening/closing door  72 . Along with the forward movement of the opening/closing door  72 , the first and second sliders  106 ,  108  and the first and second stoppers  110 ,  112  also move integrally forward (in the direction of the arrow C1). 
     As a result, as shown in  FIG. 11A , the upper end  86   a  of the upper rod  86  is engaged with the first front frame piece  36 . The upper rod  86  moves forward while being inserted into the first rod hole  118   a  of the first slider  106 . As a result, the upper rod  86  is deformed and inclined at a predetermined angle. The upper collar member  102  is pulled out upward (in the direction of arrow B1) from the second rod hole  120   a  of the first stopper  110 . The upper end  86   a  of the upper rod  86  is further bent rearward (in the direction of the arrow C2) from the lower end of the upper collar member  102 . As a result, along with the deformation of the upper rod  86 , the upper end  86   a  of the upper rod  86  bends backward and moves under the lower end of the first wall portion  38  of the first front frame piece  36 . The upper end  86   a  moves toward the front of the housing  12  (in the direction of the arrow C1). 
     As shown in  FIG. 11B , the lower end  88   a  of the lower rod  88  is engaged with the second front frame piece  44 . The lower rod  88  moves forward while being inserted into the first rod hole  118   b  of the second slider  108 . As a result, the lower rod  88  is deformed and inclined at a predetermined angle. When the upper rod  86  and the lower rod  88  are not deformed, the axial distance L2 from the second stopper  112  to the upper end of the lower collar member  104  is greater than the axial distance L1 from the first stopper  110  to the lower end of the upper collar member  102  (see  FIG. 7A  and  FIG. 7B ). Therefore, when the lower rod  88  is deformed as illustrated in  FIG. 11B , the lower collar member  104  does not come off the second rod hole  120   b  of the second stopper  112 . The lower collar member  104  remains inserted into the second rod hole  120   b.    
     Therefore, a portion of the lower rod  88  (second enlarged diameter portion) to which the lower collar member  104  is attached and having high strength is suitably held by the second stopper  112  (second rod hole  120   b ). Therefore, the lower rod  88  is not largely bent unlike the upper rod  86 . The lower end  88   a  of the lower rod  88  does not climb over the second wall portion  46  of the second front frame piece  44 . Therefore, the lower end  88   a  of the lower rod  88  is maintained in a state of being engaged with the rear side (the arrow C2 direction) of the second front frame piece  44 . The lower end  88   a  of the lower rod  88  remains restricted from moving toward the front of the housing  12  (in the direction of the arrow C1). 
     As a result, the engagement of the upper rod  86  with the first front frame piece  36  (the first wall portion  38 ) is released at the upper portion of the housing  12  (in the direction of the arrow B1) when the housing is pressed from the inside to the outside with an excessive pressure accompanying an explosion occurring inside the housing  12 . On the other hand, the engagement of the lower rod  88  with the second front frame piece  44  (the second wall portion  46 ) is not released at the lower portion of the housing  12  (in the arrow B2 direction). That is, the engagement between the second front frame piece  44  and the lower rod  88  is maintained. Therefore, as shown in  FIG. 10 , the upper part of the opening/closing door  72  is slightly opened by moving outward (forward) from the front end  70  of the housing  12  and thereby opening. In the lower part of the opening/closing door  72 , the front end  70  of the housing  12  is kept closed. In other words, when viewed from the width direction of the hydrogen production apparatus  10  shown in  FIG. 10 , a portion of the opening/closing door  72  that lies above the center in the height direction (in the direction of the arrow B1) is deformed so as to be inclined forward. As a result, a gap (opening) is formed between the opening/closing door  72  and the housing  12 . 
     As a result, the pressure remaining inside the housing  12  is released to the outside through the opening portion opened between the upper part of the opening/closing door  72  and the housing  12 . As a result, the pressure in the housing  12  decreases. 
     As described above, even in a case where an explosion occurs due to ignition caused by leakage of hydrogen gas in the housing  12 , an excessive pressure that rapidly rises thereinside can be released to the outside through the ventilation opening  56  opened in the ceiling panel  24 . The application of pressure causes the second panel body  54  of the ceiling panel  24  to separate from the frame  16 . Thus, the upper portion of the housing  12  is opened to thereby release the pressure to the outside. When an excessive pressure is applied to the opening/closing door  72 , the opening operation restricted state of the opening/closing door  72  by the upper rod  86  of the opening/closing switching mechanism  78  is released. Thus, only the upper part of the opening/closing door  72  is opened and the pressure can be released to the outside. 
     As described above, in this embodiment, in the hydrogen production apparatus  10  in which the opening/closing door  72  is closed, even when hydrogen gas explodes in the housing  12 , the upper rod  86  and the lower rod  88  of the opening/closing switching mechanism  78  are pushed outward (forward) together with the opening/closing door  72  and the cam plate  84  due to a rapidly increased pressure. With the movement of the opening/closing switching mechanism  78 , the upper collar member  102  attached to the upper rod  86  is separated from the first stopper  110  and deformed. The lower collar member  104  mounted near the lower end  88   a  of the lower rod  88  remains held by the second stopper  112 . 
     Therefore, in a locked state in which the opening operation of the opening/closing door  72  is restricted by the opening/closing switching mechanism  78 , the upper end  86   a  of the upper rod  86  can bent backward, and move forward under the lower end of the first front frame piece  36 . Accordingly, the upper portion of the opening/closing door  72  can be opened from the housing  12 , and the front end  70  of the housing  12  can be opened. 
     As a result, even when an excessive pressure is generated inside the hydrogen production apparatus  10 , the upper part of the opening/closing door  72  is opened before the lower part of the opening/closing door  72  opens. Thus, the pressure can be released to the outside from the opened portion between the opening/closing door  72  and the housing  12 . Therefore, damage or the like to the water electrolysis system  14  inside the housing  12  due to pressure can be reduced. For example, even if a person is present around the opening/closing door  72  when an explosion occurs, the opening/closing door  72  is not fully opened. The opening/closing door  72  does not come off the frame  16 . Therefore, contact between the opening/closing door  72  and a person can be surely avoided to protect the person. 
     The upper part of the opening/closing door  72  is opened to thereby reduce the pressure in the housing  12 . Thus, it is possible to prevent the side panels  18   a ,  18   b , the rear panel  20 , or the like constituting the housing  12  from coming off and flying off by the pressure. 
     The ceiling panel  24  is made up of the first and second panel bodies  52 ,  54  which can be divided in the width direction (arrow A1, A2 direction). The first panel body  52  is arranged on one side in the width direction (arrow A1 direction) of the ceiling panel  24 . The first panel body  52  is secured to the frame  16  with a plurality of fastening screws  55 . The second panel body  54  is arranged on the other side in the width direction of the ceiling panel  24 . The second panel body  54  is adjacent to the first panel body  52 . The second panel body  54  is fixed to the frame  16  by rivets  62 . Accordingly, the fixing strength of the second panel body  54  to the frame  16  is lower than the fixing strength of the first panel body  52  to the frame  16 . 
     As a result, when the pressure in the housing  12  rapidly increases due to the explosion and the ceiling panel  24  is pushed up to the outside by the pressure, the second panel body  54  having lower fixing strength comes off the frame  16  upward before the first panel body  52  comes off. Therefore, only the second panel body  54  can be detached from the frame  16  without the entire ceiling panel  24  coming off the frame  16 . In other words, since the fixing strength of the first panel body  52  and the fixing strength of the second panel body  54  are different from each other, it is possible to control the opening portion of the ceiling panel  24  at the time of explosion. 
     The ceiling panel  24  includes a ventilation opening  56 . The ventilation opening  56  opens at a position facing the water electrolysis unit  122 . Therefore, even when the hydrogen gas leaked inside the housing  12  is ignited and exploded, the internal pressure that rapidly increases inside the housing  12  can be suitably released to the outside by using the ventilation opening  56 . As a result, the rapid pressure increase in the housing  12  can be suppressed. 
     The fixing strength of the ceiling panel  24  to the housing  12  is lower than the fixing strength of the opening/closing door  72  to the housing  12 . Thus, when the internal pressure of the housing  12  increases due to explosion, the ceiling panel  24  comes off the housing  12  before the opening/closing door  72  comes off the housing  12 . As a result, the internal pressure can be released to the outside from the portion of the housing  12  from which the ceiling panel  24  has been detached. Therefore, when an explosion occurs, deformation of the opening/closing door  72  and flying-off of the opening/closing door  72  can be suppressed. For example, even when a person is present around the opening/closing door  72 , it is possible to preferably avoid contact between the opening/closing door  72  and the person. 
     The upper end  86   a  of the upper rod  86  is covered with the first cap member  101  made of an elastic material. The lower end  88   a  of the lower rod  88  is covered with the second cap member  103  made of an elastic material. Therefore, in the locked state in which the opening operation of the opening/closing door  72  is restricted, contact sound and impact generated when the upper end  86   a  contacts the first front frame piece  36  can be suitably alleviated by the first cap member  101 . Contact sound and impact generated when the lower end  88   a  contacts the second front frame piece  44  can be suitably alleviated by the second cap member  103 . 
     In the opening/closing switching mechanism  78  of the hydrogen production apparatus  10 , in the locked state in which the opening operation of the closed opening/closing door  72  is restricted, the axial distance L2 from the second stopper  112  to the upper end of the lower collar member  104  is larger than the axial distance L1 from the first stopper  110  to the lower end of the upper collar member  102  (L2&gt;L1). However, the present invention is not limited to this configuration. 
     For example, the opening/closing switching mechanism  130  according to a modification shown in  FIGS. 12A to 13B  may be employed. In the opening/closing switching mechanism  130 , an axial distance (axial lap length) L4 from the upper end of the second front frame piece  44  to the lower end  132   a  of the lower rod  132  is larger than an axial distance (axial lap length) L3 from the lower end of the first front frame piece  36  to the upper end  134   a  of the upper rod  134  (L3&lt;L4). 
     In order to realize the above-described configuration, the axial length of the upper rod  134  and the axial length of the lower rod  132  may be different from each other. The relative positional relationship between the upper rod  134  and the lower end position of the first front frame piece  36  and the relative positional relationship between the lower rod  132  and the upper end position of the second front frame piece  44  may be changed. 
     With the above configuration, the upper end  134   a  of the upper rod  134  is lowered (in the direction of the arrow B2) and disengaged from the first front frame piece  36  before the lower rod  132  is disengaged even when an explosion occurs due to ignition of hydrogen gas leaked inside the housing  12  in the hydrogen production apparatus  10  and the opening/closing door  72  is consequently pressed outward due to the rapidly increasing pressure. As a result, the state in which the opening operation of the upper part of the opening/closing door  72  is restricted by the upper rod  134  is released. Restriction of the opening operation of the lower part of the opening/closing door  72  by the lower rod  132  can be maintained. 
     As a result, only the upper part of the opening/closing door  72  can be opened so as to be separated from the front end  70  of the housing  12 . Therefore, the pressure inside the housing  12  can be suitably released to the outside. Even when a person is present around the hydrogen production apparatus  10 , only the upper part of the opening/closing door  72  can be opened. As a result, contact between the opening/closing door  72  that has been pushed outward and deformed and a person can be suitably avoided and the person can be protected. 
     That is, the structure is not particularly limited as long as the structure allows the upper rod  134  to be disengaged from the frame  16  constituting the housing  12  before the lower rod  132  is disengaged, and allows the upper part of the opening/closing door  72  to be opened before the lower part thereof is opened, when an excessive pressure is applied to the opening/closing door  72  from the inside of the housing  12  toward the outside. 
     The present invention is not limited to the above-described embodiment, and various configurations can be adopted therein without departing from the essence and gist of the present invention.