Nuclear power plant radiation control area boundary fireproof door

Abstract

The utility model relates to a nuclear power plant radiation control area boundary fireproof door which is provided with a transfer mechanism, so that materials can be transferred without frequently opening a door body. Therefore, the possibility that an external fire source is introduced due to opening of the door body is reduced, and the risk of fire disasters is effectively reduced. And secondly, the transfer box allows necessary operation under the condition that the door body is not opened, so that a constant pressure state in an area can be kept, and potential safety hazards caused by pressure change are prevented. Besides, due to the design of the door body and the fireproof box cover, good sealing performance can be maintained even when the transfer function is used, diffusion of flames, smoke and harmful gas is prevented, and the safety performance of the whole system is improved.

Description

Technical Field

[0001] This utility model relates to the field of nuclear power, and in particular to fireproof doors at the boundaries of radiation control zones in nuclear power plants. Background Technology

[0002] In the safety management of nuclear power plants, boundary doors in radiation control areas play a crucial role. They not only restrict the entry and exit of personnel and goods but also serve as important fire barriers. To ensure safety, these boundary doors are typically constructed of gates, and their management requirement is to keep them closed to prevent the spread of fire. However, in practice, boundary doors, which serve as the main access routes for goods in and out of the control area, need to be opened frequently, which conflicts with the gate management requirements.

[0003] Specifically, fully opening a door during the transfer of items not only increases the risk of fire but may also disrupt the pressure balance within the controlled area. Utility Model Content

[0004] This invention provides a fireproof door for the boundary of the radiation control zone of a nuclear power plant, which can solve the problems of increased fire risk and imbalance of regional pressure caused by the frequent opening of the door.

[0005] This utility model provides a fireproof door for the boundary of a radiation control zone in a nuclear power plant, comprising:

[0006] Door frame;

[0007] The door body is rotatably mounted on the door frame; and

[0008] A transfer mechanism includes a transfer box, a fireproof box cover, and a fireproof movable door. The transfer box is disposed on the door body. The transfer box has a first opening and a second opening that are interconnected. The fireproof box cover is rotatably connected to the door body or the transfer box. The fireproof movable door is rotatably connected to the door body or the transfer box.

[0009] The fireproof movable door is configured to open or cover the second opening when rotating, and the fireproof box cover is configured to open or cover the first opening when rotating, so that opposite sides of the door can communicate with the second opening through the first opening.

[0010] Preferably, the fireproof door at the boundary of the nuclear power plant radiation control zone further includes a rotating hinge, and the door body is rotatably connected to the door frame via the rotating hinge.

[0011] Preferably, the transfer mechanism further includes a plurality of spring hinges, some of which are disposed on the fireproof box cover and the rest of which are disposed on the fireproof movable door, so that the fireproof box cover is driven by the spring hinges to cover the first opening and the fireproof movable door is driven by the spring hinges to cover the second opening.

[0012] Preferably, the transfer box includes a bottom plate, peripheral side plates, and a top plate, wherein the peripheral side plates are disposed on the bottom plate, and the top plate is connected to the peripheral side plates;

[0013] The first opening is located on the top plate, and the second opening is located on the peripheral side plate.

[0014] Preferably, a clearance hole is provided at the bottom of the door body, and the second opening communicates with the clearance hole.

[0015] Preferably, the transfer box passes through the door body, and the first opening and the second opening are respectively located on opposite sides of the transfer box, with the first opening and the second opening respectively exposed on opposite sides of the door body.

[0016] Preferably, the door body is filled with a fireproof layer.

[0017] Preferably, a closing sensing mechanism is provided inside the door frame. The closing sensing mechanism includes a first closing sensor, a second closing sensor, and two closing indicator components. The first closing sensor is disposed in the first opening, and the second closing sensor is disposed in the second opening. Each closing indicator component includes a first closing indicator light and a second closing indicator light.

[0018] The two closing indicator components are respectively disposed on opposite sides of the door body. The first closing sensor is electrically connected to the two first closing indicator lights, and the second closing sensor is electrically connected to the two second closing indicator lights.

[0019] Preferably, the fire door at the boundary of the nuclear power plant radiation control zone further includes a door handle, which is rotatably mounted on the door body; and / or

[0020] The fireproof box lid is equipped with a lid handle, and the fireproof sliding door is equipped with a sliding door handle.

[0021] Preferably, the side wall of the first opening is provided with a first limiting step, and when the fireproof box cover abuts against the first limiting step, the fireproof box cover covers the first opening;

[0022] The second opening has a second limiting step on its side wall. When the fireproof movable door is held against the second limiting step, the fireproof movable door covers the second opening.

[0023] The following are the beneficial effects of implementing this utility model:

[0024] This utility model relates to a fireproof door at the boundary of a radiation control zone in a nuclear power plant. By incorporating a transfer mechanism, it enables the transfer of materials without frequent door opening. This reduces the possibility of external fire sources being introduced due to door opening, thereby effectively lowering the risk of fire.

[0025] Secondly, the transfer box in this invention allows necessary operations to be performed without opening the door, which helps maintain a constant pressure state within the area and prevents safety hazards caused by pressure changes.

[0026] In addition, the design of the door and fireproof box cover ensures good sealing even when using the transfer function, preventing the spread of flames, smoke and harmful gases, and improving the safety performance of the entire system. Attached Figure Description

[0027] The above and other objects, features and advantages of the present invention will become more apparent from the accompanying drawings, in which like reference numerals generally denote like parts.

[0028] Figure 1 This is a schematic diagram of the structure of the fireproof door at the boundary of the radiation control zone of a nuclear power plant in some embodiments of this utility model;

[0029] Figure 2 This is an exploded view of the fireproof door at the boundary of the radiation control zone of a nuclear power plant in some embodiments of this utility model;

[0030] Figure 3 This is another structural schematic diagram of the fireproof door at the boundary of the radiation control zone of a nuclear power plant, as shown in some embodiments of this utility model.

[0031] Figure 4 From another perspective Figure 3 The diagram shows the structure of the fireproof door at the boundary of the radiation control zone of the nuclear power plant.

[0032] Figure 5 From another perspective Figure 1 The diagram shows the structure of the fireproof door at the boundary of the radiation control zone of a nuclear power plant. Detailed Implementation

[0033] Embodiments of the present invention will now be described in more detail with reference to the accompanying drawings. While embodiments of the present invention are shown in the drawings, it should be understood that the present invention may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the present invention will be more thorough and complete, and will fully convey the scope of the present invention to those skilled in the art.

[0034] It should be understood that although the terms "first," "second," "third," etc., may be used in this invention to describe various information, this information should not be limited to these terms. These terms are only used to distinguish information of the same type from one another. For example, without departing from the scope of this invention, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Thus, features defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0035] In the description of this utility model, it should be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this utility model.

[0036] Unless otherwise explicitly specified and limited, the terms "installation," "connection," "joining," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model according to the specific circumstances.

[0037] Figure 1 and Figure 2 The illustration shows a nuclear power plant radiation control zone boundary fire door 10 in some embodiments of the present invention, which is used to install at the edge of the radiation control zone in the nuclear power plant building, and allows access to and from the radiation control zone through the nuclear power plant radiation control zone boundary fire door 10.

[0038] It should be noted that a radiation control area is a specific area within a nuclear power plant designated for managing and limiting the spread of radioactive materials and protecting workers and the public from unnecessary radiation exposure. Strict radiation protection measures and management systems are implemented within this area, including but not limited to personnel access control, personal dose monitoring, surface contamination detection, and work permit systems.

[0039] In this invention, the radiation control zone specifically refers to a portion of the space inside a nuclear power plant building separated by a boundary fire door. It possesses the aforementioned features and is designed to ensure that even in the event of an accident such as a fire or leak, the risk can be effectively limited to a controllable range, thereby ensuring the safe operation of the nuclear facility and that the surrounding environment remains unaffected.

[0040] like Figures 1 to 5 As shown, the fireproof door 10 at the boundary of the radiation control zone of a nuclear power plant includes a door frame 1, a door body 2, and a transfer mechanism 3. The door frame 1 is located on the boundary of the radiation control zone, the door body 2 is rotatably mounted on the door frame 1, and the transfer mechanism 3 is mounted on the door body 2.

[0041] The transfer mechanism 3 includes a transfer box 31, a fireproof box cover 32, and a fireproof movable door 33. The transfer box 31 is mounted on the door body 2 and has a first opening 3131 and a second opening 3121 that are interconnected. The fireproof box cover 32 is rotatably connected to the door body 2 or the transfer box 31, and the fireproof movable door 33 is rotatably connected to the door body 2 or the transfer box 31. The fireproof movable door 33 is configured to open or cover the second opening 3121 when rotating, and the fireproof box cover 32 is configured to open or cover the first opening 3131 when rotating, so that opposite sides of the door body 2 can communicate with the second opening 3121 through the first opening 3131.

[0042] Understandably, the transfer box 31 serves as a closed transition space. The transfer box 31 has two interconnected openings: a first opening 3131 and a second opening 3121. The first opening 3131 and the second opening 3121 face different areas on either side of the door 2, allowing items to be transferred through the transfer box 31 without fully opening the main fire door.

[0043] The function of the fireproof box cover 32 is to maintain the airtightness of the transfer box 31 when it is not in use, to prevent radiation leakage and fire spread, and to open the internal space of the transfer box 31 when necessary.

[0044] Fireproof sliding door 33 is used to open or cover a second opening 3121 when needed. It works in conjunction with fireproof cover 32 to ensure that at least one opening is closed at all times to maintain the safety barrier.

[0045] like Figures 1 to 5As shown, in some embodiments of the fire door 10 at the boundary of the radiation control zone of a nuclear power plant, the fire door 10 further includes a rotating hinge 4, through which the door body 2 is rotatably connected to the door frame 1. Understandably, the rotating hinge is used to achieve a stable and reliable connection between the door body 2 and the door frame 1, and to support the smooth rotational movement of the door body 2.

[0046] like Figures 1 to 5 As shown, in some embodiments of the fireproof door 10 at the boundary of the radiation control area of ​​a nuclear power plant, the transfer mechanism 3 also includes several spring hinges 434. Some of the spring hinges 434 are disposed on the fireproof box cover 32, and the remaining spring hinges 434 are disposed on the fireproof movable door 33. Thus, the fireproof box cover 32 is driven by the spring hinges 434 to cover the first opening 3131, and the fireproof movable door 33 is driven by the spring hinges 434 to cover the second opening 3121.

[0047] Understandably, the spring hinge 434 provides additional closing force when closed, ensuring that the fireproof box cover 32 and the fireproof sliding door 33 can automatically and tightly cover their respective first opening 3131 and second opening 3121. This not only simplifies the operation process but also enhances the sealing effect.

[0048] Some of the spring hinges 434 are installed on the fireproof box cover 32. When the fireproof box cover 32 is rotated to the closed position, the pressure applied by the spring hinges 434 makes it firmly fit against the first opening 3131. The remaining spring hinges 434 are installed on the fireproof sliding door 33. Similarly, when the fireproof sliding door 33 is rotated to the closed position, the spring hinges 434 ensure that it tightly covers the second opening 3121.

[0049] like Figures 1 to 5 As shown, in some embodiments of the fire door 10 at the boundary of the radiation control area of ​​a nuclear power plant, the transfer box 31 includes a bottom plate 311, a peripheral side plate 312 and a top plate 313. The peripheral side plate 312 is disposed on the bottom plate 311 and the top plate 313 is connected to the peripheral side plate 312. The first opening 3131 is located on the top plate 313 and the second opening 3121 is located on the peripheral side plate 312.

[0050] Understandably, the base plate 311 provides a stable bottom support surface, ensuring that items placed within it will not slide or shift. Peripheral side plates 312 form side walls around the entire perimeter of the transfer box 31. The peripheral side plates 312 not only provide the necessary structural strength for the transfer box 31 but also define the boundaries of the internal space. Specifically, a second opening 3121 is located on the peripheral side plates 312, allowing items to enter and exit the transfer box 31 from the side. A first opening 3131 on the top plate 313 allows items to enter or leave the transfer box 31 from above, cooperating with the second opening 3121 to achieve the safe transfer of items.

[0051] like Figures 1 to 5 As shown, in some embodiments of the fire door 10 at the boundary of the radiation control zone of a nuclear power plant, a clearance hole 21 is provided at the bottom of the door body 2, and a second opening 3121 connects to the clearance hole 21.

[0052] Understandably, the clearance hole 21 allows the second opening 3121 to directly connect to the outside of the door 2, thereby simplifying the transfer path of items from one side to the other and improving operational efficiency.

[0053] like Figures 1 to 5 As shown, in some embodiments of the fire door 10 at the boundary of the radiation control area of ​​a nuclear power plant, a transfer box 31 is installed through the door body 2, and the first opening 3131 and the second opening 3121 are respectively located on opposite sides of the transfer box 31, with the first opening 3131 and the second opening 3121 exposed on opposite sides of the door body 2.

[0054] Understandably, the transfer box 31 is installed through the door 2 to avoid the transfer box 31 occupying too much space on one side of the door 2, thereby preventing the transfer box 31 from interfering with the position of other structures, and thus ensuring that the door 2 can move smoothly to complete the opening and closing.

[0055] like Figures 1 to 5 As shown, in some embodiments of the fire door 10 at the boundary of the radiation control zone of a nuclear power plant, the door body 2 is filled with a fireproof layer.

[0056] Understandably, the fire-resistant layer can effectively slow down the speed at which flames penetrate door 2, buying more time for evacuation and firefighting, and improving overall safety. The fire-resistant layer also typically has good thermal insulation properties, reducing heat transfer to the other side of door 2 during a fire, protecting unaffected areas from high temperatures.

[0057] like Figures 1 to 5 As shown, in some embodiments of the fire door 10 at the boundary of the radiation control area of ​​a nuclear power plant, a closing sensing mechanism 5 is provided inside the door frame 1. The closing sensing mechanism 5 includes a first closing sensor 51, a second closing sensor 52 and two closing indicator components 53. The first closing sensor 51 is located at the first opening 3131, and the second closing sensor 52 is located at the second opening 3121. Each closing indicator component 53 includes a first closing indicator light 531 and a second closing indicator light 532.

[0058] Two closure indicator components 53 are respectively disposed on opposite sides of the door body 2. The first closure sensor 51 is electrically connected to two first closure indicator lights 531, and the second closure sensor 52 is electrically connected to two second closure indicator lights 532.

[0059] Understandably, the first closure sensor 51 is used to detect whether the fireproof box cover 32 completely covers and closes the first opening 3131. The second closure sensor 52 is used to detect whether the fireproof sliding door 33 completely covers and closes the second opening 3121. Each closure indicator component 53 includes a first closure indicator light 531 and a second closure indicator light 532, which are used to display the closure status of the first opening 3131 and the second opening 3121, respectively.

[0060] Two closure indicator components 53 are respectively disposed on opposite sides of the door body 2. The first closure indicator light 531 in each closure indicator component 53 is electrically connected to the first closure sensor 51. When the first opening 3131 is fully closed, the corresponding first closure indicator light 531 illuminates, indicating that the first opening 3131 has been safely closed. Similarly, the second closure indicator light 532 in each closure indicator component 53 is electrically connected to the second closure sensor 52. When the second opening 3121 is fully closed, the corresponding second closure indicator light 532 illuminates, indicating that the second opening 3121 has been safely closed.

[0061] It should be noted that the first closure sensor 51 and the second closure sensor 52 can monitor the closure status of the fireproof box cover 32 and the fireproof movable door 33 in real time, and feed the information back to the closure indicator component 53. This instant feedback mechanism ensures that operators can quickly understand the closure status of each opening, improving the safety and reliability of the operation. Since the closure indicator components 53 are respectively set on both sides of the door 2, whether inside or outside the radiation control area, staff can confirm whether the opening has been correctly closed by observing the corresponding indicator lights. This provides double confirmation for the item transfer process and reduces the risk of misoperation.

[0062] like Figures 1 to 5 As shown, in some embodiments of the fire door 10 at the boundary of the radiation control zone of a nuclear power plant, the fire door 10 at the boundary of the radiation control zone of a nuclear power plant also includes a door handle 6, which is rotatably mounted on the door body 2.

[0063] Understandably, door handle 6 provides a convenient gripping point, enabling workers to easily open and close the fire door. Door handle 6 is rotatably mounted on the door body 2 via a mechanical connection or bearing structure, ensuring smooth and reliable operation. Door handle 6 is typically located on both sides of the door body 2 so that the fire door can be easily operated from either side. Considering both safety and ease of use, the position and shape of door handle 6 are optimized to accommodate the needs of different operators.

[0064] like Figures 1 to 5 As shown, in some embodiments of the fireproof door 10 at the boundary of the radiation control zone of a nuclear power plant, the fireproof box cover 32 is provided with a box cover handle 321, and the fireproof movable door 33 is provided with a movable door handle 6.

[0065] Understandably, the lid handle 321 is used to conveniently open and close the first opening 3131. The lid handle 321 is designed to provide a comfortable grip for the operator, ensuring that the operator can easily and securely lift or lower the fireproof lid 32. The movable door handle 6 is used to conveniently open and close the second opening 3121, improving operational convenience.

[0066] like Figures 1 to 5 As shown, in some embodiments of the fire door 10 at the boundary of the radiation control zone of a nuclear power plant, a first limiting step 3132 is provided on the side wall of the first opening 3131. When the fireproof box cover 32 abuts against the first limiting step 3132, the fireproof box cover 32 covers the first opening 3131. A second limiting step is provided on the side wall of the second opening 3121. When the fireproof movable door 33 abuts against the second limiting step, the fireproof movable door 33 covers the second opening 3121.

[0067] Understandably, when the fireproof box cover 32 is fully closed and abuts against the first limiting step 3132, the first limiting step 3132 ensures that the fireproof box cover 32 tightly covers the first opening 3131, preventing any substance from leaking from the opening. Similarly, when the fireproof sliding door 33 is fully closed and abuts against the second limiting step, it ensures that the fireproof sliding door 33 tightly covers the second opening 3121, maintaining a sealed state.

[0068] It should be noted that the first limiting step 3132 and the second limiting step provide a clear stop position for the fireproof box cover 32 and the fireproof movable door 33, ensuring that they can accurately cover the corresponding openings each time they close, thus improving the closing accuracy.

[0069] like Figures 1 to 5 As shown, in some embodiments, the fireproof box cover 32 has several viewing windows 322.

[0070] Understandably, the viewing window 322 allows staff to directly observe the inside of the transfer box 31 without opening the fireproof box cover 32, thus improving ease of use.

[0071] Specifically, the viewing window 322 is made of transparent fireproof material to ensure that the fireproof box cover 32 remains sealed and fireproof.

[0072] More specifically, it can be made of borosilicate glass, ceramic glass (microcrystalline glass), polycarbonate sheets, or other materials available in the prior art. Of course, to improve the fire resistance rating, flame retardants can be added during the manufacturing process.

[0073] The following are the beneficial effects of implementing this utility model:

[0074] This utility model relates to a fireproof door at the boundary of a radiation control zone in a nuclear power plant. By incorporating a transfer mechanism, it enables the transfer of materials without frequent door opening. This reduces the possibility of external fire sources being introduced due to door opening, thereby effectively lowering the risk of fire.

[0075] Secondly, the transfer box in this invention allows necessary operations to be performed without opening the door, which helps maintain a constant pressure state within the area and prevents safety hazards caused by pressure changes.

[0076] In addition, the design of the door and fireproof box cover ensures good sealing even when using the transfer function, preventing the spread of flames, smoke and harmful gases, and improving the safety performance of the entire system.

[0077] The present invention has been described in detail above with reference to the accompanying drawings. In the above embodiments, the descriptions of each embodiment have different focuses; for parts not described in detail in a certain embodiment, please refer to the relevant descriptions of other embodiments. Those skilled in the art should also understand that the actions and modules involved in the specification are not necessarily essential to the present invention. Furthermore, it is understood that the steps in the method of the present invention embodiments can be adjusted, combined, and deleted according to actual needs, and the modules in the device of the present invention embodiments can be combined, divided, and deleted according to actual needs.

[0078] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or improvement of the technology in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A fireproof door for the boundary of a radiation control zone in a nuclear power plant, characterized in that, include: Door frame; The door body is rotatably mounted on the door frame; and A transfer mechanism includes a transfer box, a fireproof box cover, and a fireproof movable door. The transfer box is disposed on the door body. The transfer box has a first opening and a second opening that are interconnected. The fireproof box cover is rotatably connected to the door body or the transfer box. The fireproof movable door is rotatably connected to the door body or the transfer box. The fireproof movable door is configured to open or cover the second opening when rotating, and the fireproof box cover is configured to open or cover the first opening when rotating, so that opposite sides of the door can communicate with the second opening through the first opening.

2. The fireproof door at the boundary of the radiation control zone of a nuclear power plant according to claim 1, characterized in that, The fireproof door at the boundary of the radiation control zone of the nuclear power plant also includes a rotating hinge, and the door body is rotatably connected to the door frame via the rotating hinge.

3. The fireproof door at the boundary of the radiation control zone of a nuclear power plant according to claim 1, characterized in that, The transfer mechanism also includes several spring hinges, some of which are disposed on the fireproof box cover and the rest of which are disposed on the fireproof movable door. Thus, the fireproof box cover is driven by the spring hinges to close the first opening, and the fireproof movable door is driven by the spring hinges to close the second opening.

4. The fireproof door at the boundary of the radiation control zone of a nuclear power plant according to claim 1, characterized in that, The transfer box includes a bottom plate, peripheral side plates, and a top plate. The peripheral side plates are disposed on the bottom plate, and the top plate is connected to the peripheral side plates. The first opening is located on the top plate, and the second opening is located on the peripheral side plate.

5. The fireproof door at the boundary of the radiation control zone of a nuclear power plant according to claim 1 or 4, characterized in that, The bottom of the door is provided with a clearance hole, and the second opening is connected to the clearance hole.

6. The fireproof door at the boundary of the radiation control zone of a nuclear power plant according to claim 1 or 4, characterized in that, The transfer box is installed through the door, and the first opening and the second opening are respectively located on opposite sides of the transfer box, with the first opening and the second opening respectively exposed on opposite sides of the door.

7. The fireproof door at the boundary of the radiation control zone of a nuclear power plant according to claim 1, characterized in that, The door is filled with a fireproof layer.

8. The fireproof door at the boundary of the radiation control zone of a nuclear power plant according to claim 1, characterized in that, A closing sensing mechanism is provided inside the door frame. The closing sensing mechanism includes a first closing sensor, a second closing sensor, and two closing indicator components. The first closing sensor is located at the first opening, and the second closing sensor is located at the second opening. Each closing indicator component includes a first closing indicator light and a second closing indicator light. The two closing indicator components are respectively disposed on opposite sides of the door body. The first closing sensor is electrically connected to the two first closing indicator lights, and the second closing sensor is electrically connected to the two second closing indicator lights.

9. The fireproof door at the boundary of the radiation control zone of a nuclear power plant according to claim 1, characterized in that, The fireproof door at the boundary of the nuclear power plant's radiation control zone also includes a door handle, which is rotatably mounted on the door body; and / or The fireproof box lid is equipped with a lid handle, and the fireproof sliding door is equipped with a sliding door handle.

10. The fireproof door at the boundary of the radiation control zone of a nuclear power plant according to claim 1, characterized in that, The side wall of the first opening is provided with a first limiting step. When the fireproof box cover abuts against the first limiting step, the fireproof box cover covers the first opening. The second opening has a second limiting step on its side wall. When the fireproof movable door is held against the second limiting step, the fireproof movable door covers the second opening.

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