JP5372904B2 - Explosion-proof gas detector - Google Patents

Description

  The present invention relates to an explosion-proof gas detector, and more specifically, for example, oxygen concentration monitoring in civil engineering works such as caves and underground, oxygen concentration monitoring in a closed place, oxygen leakage monitoring in an oxygen consumption facility, chemical factory The present invention relates to an explosion-proof gas detector used to prevent the occurrence of an oxygen deficiency accident such as oxygen concentration monitoring.

  Gas detectors used in an environment where ignition or explosion may occur due to the presence of an explosive atmosphere containing flammable gas or steam must have an explosion-proof structure with the prescribed explosion-proof performance. For example, a structure in which an explosion-proof structure is formed by using a gas-permeable metal sintered body as a flame escape prevention member has been proposed (see, for example, Patent Document 1). In the gas detector having an explosion-proof structure using such a metal sintered body, for example, the inspection gas sucked by the gas suction means is supplied to the gas sensor through the metal sintered body by the gas introduction nozzle.

  However, such a gas detector has a problem that the response time (response speed) tends to be slow due to the ventilation resistance of the sintered metal.

In response to such a problem, it is expected that good gas detection responsiveness can be obtained if the gas outlet of the gas introduction nozzle is in close contact with the surface of the sintered metal body. However, in reality, the error of the dimensional accuracy with respect to the thickness of the metal sintered body is large, and the error of the dimensional accuracy of each component is accumulated. As a result, an excessive pressure is applied to the metal sintered body by the gas introduction nozzle. It is extremely difficult to obtain a state of being in close contact with the sintered metal without acting.
If the gas injection port of the gas introduction nozzle is not in close contact with the surface of the sintered metal body, the gas to be inspected ejected from the gas injection port of the gas introduction nozzle diffuses, and the required flow rate of the gas injection nozzle is diffused. Since it takes time to supply the inspection gas to the gas sensor through the flame arrestor, the gas detection responsiveness is lowered. On the other hand, in order to obtain a close contact state between the gas introduction nozzle and the metal sintered body, when the excessive pressure is applied to the metal sintered body by the gas introduction nozzle, the metal sintered body is deformed. Or, due to breakage, the desired explosion-proof performance cannot be obtained.

JP-A-7-260686

The present invention has been made based on the circumstances as described above, and its purpose is that the gas introduction nozzle is in close contact with the flame escape prevention member without applying excessive pressure to the flame escape prevention member. It is an object of the present invention to provide a pressure-resistant explosion-proof gas detector capable of easily and reliably obtaining high gas detection responsiveness.
Another object of the present invention is to provide a pressure / explosion-proof gas detector capable of reducing the load on the gas suction means and obtaining a highly reliable output.

The explosion-proof gas detector of the present invention has a flame escape prevention member made of a metal sinter having gas permeability, and is provided so as to surround the gas sensor, and a gas is provided between the gas sensor and the flame escape prevention member. A frame arrester that partitions the introduction space, a guard member that surrounds the frame arrester, a cover member that covers the guard member, and airtightly penetrates the cover member and is screwed into the guard member And a sleeve-like gas introduction nozzle for supplying the inspection gas introduced by the gas suction means to the gas introduction space via the flame escape prevention member,
The gas introduction nozzle is provided in close contact with a tip portion of the gas introduction nozzle being elastically displaced in the axial direction of the gas introduction nozzle and a tip surface of the gas jet opening being pressed against the surface of the flame escape prevention member. It is characterized by being.

  In the explosion-proof gas detector of the present invention, an excessive pressure releasing concave portion extending radially outward from the gas outlet is formed on a tip surface of the gas introduction nozzle, and the excess pressure releasing concave portion is formed. It is preferable that the tip end surface region other than the region where the concave portion is formed is configured to be in contact with the surface of the flame escape prevention member.

  In the explosion-proof gas detector of the present invention, the gas introduction nozzle is slid in the axial direction of the nozzle body at the tip of the nozzle body, which is screwed onto the guard member. A tip cylindrical member provided in a possible manner, and an extension spring that is inserted between the tip cylindrical member and the nozzle body and elastically deforms in the axial direction in accordance with the displacement of the tip cylindrical member. Or a nozzle body that is screwed onto the guard member and a bellows that is provided at the tip of the nozzle body and can be elastically reduced in the axial direction. Can be used.

  According to the explosion-proof gas detector of the present invention, when the gas introduction nozzle passes through the guard member in an airtight manner and is screwed onto the cover member, the tip surface of the gas introduction nozzle is the surface of the flame escape prevention member. When the tip of the gas introduction nozzle is elastically displaced in the axial direction when further displaced in the direction of pressing the flame escape member by screwing in the state of being in contact with The error of dimensional accuracy of the flame escape prevention member and other components is compensated and the pressing force acting on the flame escape prevention member is alleviated, so the tip surface of the gas introduction nozzle is appropriate for the surface of the flame escape prevention member It is possible to reliably and easily obtain a close contact state with a large pressing force. Accordingly, since the gas to be inspected is promptly supplied to the gas introduction space via the flame escape prevention member, high gas detection responsiveness can be obtained.

  Further, a surplus pressure release concave portion extending radially outward from the gas outlet is formed on the tip surface of the gas introduction nozzle, and the tip surface region other than the surplus pressure release concave portion is formed of the flame escape prevention member. By being configured to be in contact with the surface, surplus pressure related to gas supply due to the ventilation resistance of the flame escape prevention member when the gas to be inspected is ejected from the gas ejection port via the concave portion for surplus pressure release Since it is opened, it is possible to reduce the air-permeable load caused by the flame escape prevention member, thereby reducing the load on the gas suction means and suppressing the change in internal pressure in the gas introduction space to a small extent. And reliable gas detection can be performed.

It is a front view which shows the outline of a structure in an example of the pressure | voltage resistant explosion-proof type gas detector of this invention. It is the sectional view on the AA line in FIG. It is sectional drawing along the axial direction which shows one structural example of a flame arrester. It is sectional drawing along the axial direction which shows the example of 1 structure of a gas introduction nozzle. 5A is an enlarged cross-sectional view of a portion X in FIG. 4, and FIG. It is a piping diagram showing the outline of the composition in an example of the gas sampling system provided with the explosion-proof type gas detector of the present invention. It is a fragmentary sectional view along the axial direction which shows the other structural example of a gas introduction nozzle. It is a piping diagram which shows the outline of a structure of the gas sampling system for the test constructed | assembled in the experiment example.

Hereinafter, embodiments of the present invention will be described in detail.
FIG. 1 is a front view showing an outline of the configuration of an example of a pressure / explosion-proof gas detector according to the present invention, and FIG. 2 is a cross-sectional view taken along line AA in FIG. In the following, for the sake of convenience, the left side in FIG. 2 is referred to as “front”, and the right side is referred to as “rear”. However, it does not limit the use form of the explosion-proof gas detector.
The explosion-proof gas detector (hereinafter simply referred to as “gas detector”) 10 includes a housing 11 that is mounted by screwing the guard member 12 to the base member 20 at the mounting portion 12A. In addition, a bottomed cylindrical cover member 38 that partitions a sealed space is airtightly provided via a ring-shaped packing P so as to cover the guard member 12. The cover member 38 is provided with a nozzle mounting through hole 39 at the center position on the front wall and a gas discharge nipple 58 on the outer peripheral surface. 1 and 2, reference numeral 18 denotes a cable gland.

  The guard member 12 is of a cylindrical birdcage type as a whole, and each of the guard members 12 is curved in such a manner as to radially extend radially outward from the center position of the front end and to extend rearwardly at the other end portion. For example, there are six columnar beams 13, and a nozzle mounting portion 15 is formed at the center position of the front wall portion 14 formed by concentrating one end side portion of each beam 13. The nozzle mounting portion 15 is configured by forming a thread groove on an inner peripheral surface of a through hole formed in the front wall portion 14. The rear end surface of each beam 13 is integrally connected to the front opening end surface of the cylindrical portion 16, and the rear end side portion of the cylindrical portion is inserted into the front opening of the base member 20.

  Inside the housing 11, for example, a columnar gas sensor 25 is disposed, and a frame arrester 30 is provided so as to surround the gas sensor 25.

  Although it does not specifically limit as the gas sensor 25, For example, when the said explosion-proof gas detector 10 is used for the oxygen concentration monitoring in the air of the environmental atmosphere of a detection object space, a galvanic cell type oxygen sensor Can be used.

  As shown in FIG. 3, the frame arrester 30 includes a substantially cylindrical holder member 31 and a disk-shaped flame escape prevention member 35 held and fixed by the holder member 31. The holder member 31 has a small-diameter cylindrical portion 31A and a large-diameter cylindrical portion 31B continuous to the rear end of the small-diameter cylindrical portion 31A, and the inner peripheral surface of the front-side opening edge portion of the small-diameter cylindrical portion 31A. A projecting edge 32 projecting radially inward is formed over the entire circumference of the inner circumferential surface. A flame escape prevention member 35 is accommodated in a recess defined by the peripheral wall of the small diameter cylindrical portion 31 </ b> A and the protruding edge portion 32, and is held and fixed to the holder member 31 so as to close the front opening of the holder member 31.

The frame arrester 30 is a large-diameter cylindrical portion of the holder member 31 in a state where the step portion 31C of the holder member 31 is locked to the frame arrester holding portion formed on the inner peripheral surface of the cylindrical portion 16 of the guard member 12. The outer peripheral surface of 31B is fitted to the inner peripheral surface of the cylindrical portion 16 of the guard member 12 and is airtightly attached.
In addition, inside the holder member 31, a bottomed cylindrical sensor holder 26 that holds the gas sensor 25 in a state where the front end side portion is accommodated is mounted, and an opening formed in the front wall of the sensor holder 26. A gas introduction space S formed by an opening formed by the protruding edge 32 in the holder member 31 of the frame arrester 30 is formed between the gas sensor 25 and the flame escape prevention member 35.

The flame escape prevention member 35 is made of, for example, a sintered metal body such as a sintered body of stainless steel powder or a sintered body of copper alloy powder, so that sufficient gas permeability is obtained and flame escape is reliably prevented. Therefore, it is preferable to use one having a pore size of 40 to 100 μm, a density of 4.0 to 7.0 g / cm ³ , and a thickness of 3 to 5 mm.

The gas detector 10 includes a gas introduction nozzle 40 having a substantially sleeve-like shape as a whole for supplying a gas to be inspected introduced by an appropriate gas suction means to the gas introduction space S through the flame escape prevention member 35.
As shown in FIGS. 4 and 5, the gas introduction nozzle 40 used in the gas detector 10 according to this embodiment includes a sleeve-like nozzle body 41 and a base end portion (gas introduction side front end portion) of the nozzle body 41. A cylindrical head 43 having a larger outer diameter than the nozzle body 41, which is continuous with the nozzle body 41, and a bottomed cylindrical tip provided in a state where the tip of the nozzle body 41 (the gas ejection side rear end) is accommodated. Between the cylindrical member 45 and the inner surface of the end wall of the front end cylindrical member 45 and the front end surface of the nozzle body 41, the coil shaft is elastically inserted in the axial direction in a state of extending in the axial direction of the nozzle body 41. The extension spring 51 is deformed.
A sleeve member 50 is provided on the inner peripheral surface of the opening of the distal end tubular member 45, and the rear end of the flange-shaped locking portion 44 formed at the distal end of the nozzle body 41 on the distal end surface of the sleeve member 50. The end surface is locked, and thereby the distal end tubular member 45 is provided so as to be slidable in the axial direction of the nozzle body 41 (left and right direction in FIG. 5A).

  The gas introduction nozzle 40 is formed on the outer peripheral surface of the nozzle body 41 with the head 43 in contact with the front surface of the front wall of the cover member 38 and the nozzle body 41 penetrating the front wall of the cover member 38 in an airtight manner. The screw portion 42 is attached by being screwed to the nozzle attachment portion 15 of the guard member 12, and the tip end surface of the tip cylindrical member 45 is in close contact with the surface of the flame escape prevention member 35. Is provided.

  A gas outlet 46 is formed at the central position on the end wall of the distal end tubular member 45, and a concave part for releasing excessive pressure is formed on the front end surface of the slit 48 extending radially outward from the gas outlet 46. Thus, the tip end surface region other than the excessive pressure release concave portion is brought into contact with the surface of the flame escape prevention member 35. In this example, the slits 48 are formed so as to open at circumferential positions (two locations) facing each other on the outer peripheral surface of the distal end tubular member 45.

The opening area of the slit 48 on the outer peripheral surface of the distal end tubular member 45 is preferably, for example, 0.50 to 2.0 mm ² in total, and thereby the metal sintered body constituting the flame escape prevention member 35 is formed. An increase in pressure at the gas outlet 46 due to ventilation resistance can be suppressed, the load on the gas suction means can be reduced, and a highly reliable detection output can be obtained.

  Further, the movable distance in the axial direction of the distal end tubular member 45 is preferably, for example, 0.5 to 2.0 mm, and thus, for example, the entire gas detector 10 including an error in the thickness dimension of the flame escape prevention member 35. The dimensional error of the gas introduction nozzle 40 can be reliably compensated, and the pressing force of the gas introduction nozzle 40 against the flame escape prevention member 35 can be adjusted to an appropriate magnitude, so that the gas introduction nozzle 40 and the flame escape prevention member 35 are appropriate. Can be reliably obtained.

[Gas sampling device]
The gas detector 10 is used by constructing a gas sampling system together with gas suction means such as an aspirator or a suction pump and other components.
FIG. 6 is a block diagram showing an outline of a configuration in an example of a gas sampling system provided with the above explosion-proof gas detector. In FIG. 6, 61 is a dustproof filter, 62 is a three-way solenoid valve (gas flow path switching means), 63 is a flow meter with a valve for monitoring the gas flow rate flowing through the entire gas sampling system, 64 is a needle valve, 65 is An aspirator (gas suction means), 66 is a pressure reducing valve, 60A is a gas inlet to be inspected, 60B is a calibration gas inlet, 60C is a gas outlet, and 60D is a compressed air inlet. Here, the aspirator 65 has a performance capable of supplying a certain large flow rate to the gas detector 10 in order to ensure a sufficient gas transport capacity, for example, a performance having a maximum flow rate of about 2.6 liters / min. Is preferably used.

  In this gas sampling system, the operation state of the three-way solenoid valve 62 is controlled, and the main gas introduction where the inspected gas introduction path 70A from the inspected gas inlet 60A to the three-way solenoid valve 62 reaches the pressure-proof explosion-proof gas detector 10 is performed. In a state where the calibration gas introduction path 70B extending from the calibration gas inlet 60B to the three-way solenoid valve 62 is shut off while being connected to the path 71, the compressed air is reduced from the compressed air inlet 60D by an appropriate air supply means (not shown). When the aspirator 65 is operated by being supplied to the aspirator 65 via 66, the air (inspected gas) in the environmental atmosphere in the detection target space is sucked by the aspirator 65 and the gas introduction nozzle 40 of the gas detector 10. The gas to be inspected introduced into the gas injection nozzle 46 from the gas outlet 46 of the gas introduction nozzle 40 is a flame escape prevention member 35. Is supplied to the gas introducing space S is the concentration detection of the detection target gas component due to the gas sensor 25 is performed via.

  On the other hand, when the calibration operation of the gas sensor 25 is performed, the operation state of the three-way solenoid valve 62 is controlled, and the calibration gas introduction path 70B from the calibration gas inlet 60B to the three-way solenoid valve 62 reaches the gas detector 10. In a state where the inspection gas introduction passage 70A connected to the introduction passage 71 and extending from the inspection subject gas inlet 60A to the three-way solenoid valve 62 is shut off, the aspirator 65 is actuated to turn the calibration gas into the gas of the gas detector 10. Calibration gas introduced into the introduction nozzle 40 and ejected from the gas ejection port 46 of the gas introduction nozzle 40 is supplied into the gas introduction space S via the flame escape prevention member 35.

  Thus, according to the gas detector 10 having the above-described configuration, when the gas introduction nozzle 40 is screwed and attached to the nozzle attachment portion 15 of the guard member 12, the tip cylindrical member 45 of the gas introduction nozzle 40 is fitted. When the tip surface is further displaced from the state of contact with the surface of the flame escape prevention member 35 in a direction to press the flame escape prevention member 35 by screwing, the extension provided at the distal end portion of the gas introduction nozzle 40 When the spring 51 is elastically compressed and deformed, the distal end tubular member 45 is slid in the axial direction and the position of the distal end surface of the distal end tubular member 45 is displaced. 35 and other structural members are compensated for errors in dimensional accuracy, and the pressure applied to the flame escape prevention member 35 by the gas introduction nozzle 40 is reduced. It can be the distal end surface of the end tubular member 45, a state in close contact by the pressing force of the proper size to securely and easily to the surface of the flame escape prevention member 35 at 40. Accordingly, since the gas to be inspected is quickly supplied to the gas introduction space S through the flame escape prevention member 35, high gas detection responsiveness can be obtained. Moreover, what has the expected performance can be obtained with high productivity.

  In addition, a slit 48 extending radially outward from the gas outlet 46 is formed on the distal end surface of the distal end tubular member 45 in the gas introduction nozzle 40, and the distal end surface region other than the slit 48 is the flame escape prevention member 35. By being configured to be in contact with the surface, excess pressure related to gas supply due to the ventilation resistance of the flame escape prevention member 35 when the gas to be inspected is ejected from the gas ejection port 46 is released through the slit 48. Therefore, the air permeability load due to the flame escape prevention member 35 can be reduced, thereby reducing the load on the gas suction means and suppressing the change in internal pressure in the gas introduction space S to a small extent. And reliable gas detection can be performed.

As mentioned above, although embodiment of this invention was described, this invention is not limited to said embodiment, A various change can be added.
FIG. 7 is a partial cross-sectional view along the axial direction showing another configuration example of the gas introduction nozzle.
4 and 5, the gas introduction nozzle 40A has a bellows 55 that can be elastically reduced in the axial direction at the tip of the nozzle body 41 in place of the tip cylindrical member and the extension spring. Except for the configuration provided, the configuration is the same as the configuration shown in FIGS. 4 and 5.
Examples of the material constituting the bellows 55 include fluorine rubber, EPDM (ethylene propylene diene rubber), urethane rubber, and the like, and a material having gas resistance is preferable.
Also with the gas introduction nozzle 40A having such a configuration, it is possible to obtain the same effect as that of the explosion-proof gas detector according to the above embodiment.

  In the gas introduction nozzle, the shape, the formation position, and other configurations of the excessive pressure release concave portion formed on the front end surface having the gas ejection port are not particularly limited.

  Furthermore, for example, the piping configuration when using the explosion-proof gas detector according to the present invention is not limited to that exemplified above, and the gas suction means is upstream of the explosion-proof gas detector in the gas flow direction. It may be provided at the side position.

Hereinafter, experimental examples performed for confirming the effects of the present invention will be described.
<Experimental example 1>
In accordance with the configuration shown in FIGS. 1 to 5, five explosion-proof gas detectors according to the present invention having the same specifications were produced. The specifications of this flameproof gas detector are as follows. [Specifications of explosion-proof gas detector]
Gas sensor (25): Galvanic cell type oxygen sensor,
Flame escape prevention member (35): Sintered spherical SUS powder having a particle size in the range of 300 to 500 nm, pore size of 77 to 85 μm, density of 6.1 g / cm ³ , thickness of 3 mm, outer Diameter is φ40mm,
Gas introduction space (S): Volume 3600mm ³
Front end cylindrical member (45) of gas introduction nozzle: inner diameter φ4 mm, length 6 mm, opening diameter φ2.6 mm of gas outlet (46), slit (48) width (w) 1.0 mm, slit (48) The depth (h) is 0.5 mm, the opening area is 1.0 (= 0.5 + 0.5) mm ² ,
Extension spring (51): material: SUS, a wire rod having a wire diameter of φ0.26 mm wound with a coil diameter of 3.5 mm, an axial length of 5.5 mm,
Nozzle body (41) of gas introduction nozzle: tip opening diameter φ2.6 mm, full length (including head) 38.8 mm

As shown in FIG. 8, a mass flow flow meter “SEF-21A” (manufactured by ESTEC, flow rate range 5 L / min) 80 and a buffer 81 having a capacity of 1 liter are provided for each of the produced explosion-proof gas detectors. A gas sampling system for testing was constructed by piping a manometer (range 10 kPa) 82 and a pump 83 having a maximum flow rate of 2.6 liters / min. For each explosion-proof gas detector, By using N ₂ gas (purity 99.9%) as a sample gas, the gas flow rate flowing through the gas sampling system is measured by the mass flow flow meter 80 and the gas pressure is measured by the manometer 82. Evaluation of the responsiveness of detection and (b) evaluation of the air permeability load by the flame escape prevention member were performed. The results are shown in Table 1 below. The gas detection responsiveness measures the time (gas response time T90 [s]) from when the sample gas with the specified concentration is introduced into the gas introduction nozzle until it reaches the concentration value of 90% of the specified concentration. Evaluation was performed.

<Experimental example 2>
The explosion-proof gas detector manufactured in Experimental Example 1 has the same specifications as those of the explosion-proof gas detector in Experimental Example 1 except that the gas introduction nozzle having the configuration shown in FIG. 7 is used. A single explosion-proof gas detector was prepared, and (b) evaluation of gas detection response and (b) evaluation of air permeability by a flame escape prevention member were performed in the same manner as in Experimental Example 1 above. It was. The results are shown in Table 1 below.
Bellows (55) in the gas introduction nozzle: material: urethane rubber, hardness (JIS-A) 50 °, maximum outer diameter 4.2 mm, maximum axial reduction amount 2.0 mm, opening diameter of gas outlet φ3.6 mm, The minimum inner diameter φ of the bellows portion is 2.6 mm, the width (w) of the slit (48) is 1 mm, the depth (h) of the slit (48) is 0.5 mm, and the opening area is 1.0 (= 0.5 + 0.5) mm ^2. ,

<Comparative Experimental Example 1>
In the explosion-proof gas detector manufactured in Experimental Example 1, except that a gas introduction nozzle having no tip cylindrical member and an extension spring was used, the explosion-proof gas detector in Experimental Example 1 Three comparative explosion-proof gas detectors having the same specifications were produced, and (b) evaluation of gas detection responsiveness and (b) prevention of flame escape by the same method as in Experimental Example 1 above. The air permeability load by the member was evaluated. The results are shown in Table 1 below.

As is clear from the above results, according to the explosion-proof gas detectors of Experimental Example 1 and Experimental Example 2 according to the present invention, high gas detection responsiveness can be obtained and air permeability by the flame escape prevention member can be obtained. It was confirmed that the load can be reduced and the load on the gas suction means can be reduced.
On the other hand, in the explosion-proof explosion-proof gas detector of Comparative Experimental Example 1, it was confirmed that the gas detection responsiveness was low and the air permeability load by the flame escape prevention member was high. The reason for this is that despite the same design conditions, due to individual differences in dimensional accuracy caused by the accumulation of dimensional errors of each component, good contact between the gas inlet nozzle tip surface and the flame escape prevention member surface This is probably because the

DESCRIPTION OF SYMBOLS 10 Explosion-proof gas detector 11 Housing 12 Guard member 12A Mounting part 13 Beam 14 Front wall part 15 Nozzle mounting part 16 Cylindrical part 18 Cable gland 20 Base member 25 Gas sensor 26 Sensor holder 30 Frame arrester 31 Holder member 31A Small diameter cylindrical shape Part 31B Large-diameter cylindrical part 31C Step part 32 Projection edge part 35 Flame escape prevention member S Gas introduction space 38 Cover member 39 Nozzle mounting through hole P Packing 40, 40A Gas introduction nozzle 41 Nozzle body 42 Screw part 43 Head 44 Locking portion 45 End tubular member 46 Gas outlet 48 Slit 50 Sleeve member 51 Extension spring 55 Bellows 58 Gas discharge nipple 60A Inspected gas inlet 60B Calibration gas inlet 60C Gas outlet 60D Compressed air inlet 61 Dustproof Filter 62 Three-way solenoid valve (gas flow path switching means)
63 Flow meter with valve 64 Needle valve 65 Aspirator (gas suction means)
66 Pressure reducing valve 70A Inspected gas introduction path 70B Calibration gas introduction path 71 Main gas introduction path 80 Mass flow flow meter 81 Buffer 82 Manometer 83 Pump

Claims (4)

A flame arrester having a flame escape prevention member made of a metal sinter having gas permeability, surrounding the gas sensor and defining a gas introduction space between the gas sensor and the flame escape prevention member, and the frame A guard member provided to surround the arrester, a cover member provided to cover the guard member, and introduced by a gas suction means that is airtightly penetrated through the cover member and screwed into the guard member. A sleeve-like gas introduction nozzle that supplies the gas to be inspected to the gas introduction space via the flame escape prevention member,
The gas introduction nozzle is provided in close contact with a tip portion of the gas introduction nozzle being elastically displaced in the axial direction of the gas introduction nozzle and a tip surface of the gas jet opening being pressed against the surface of the flame escape prevention member. Explosion-proof gas detector, characterized by   On the tip surface of the gas introduction nozzle, a surplus pressure releasing concave portion extending radially outward from the gas outlet is formed, and a tip surface region other than the region where the surplus pressure releasing concave portion is formed. 2. The explosion-proof gas detector according to claim 1, wherein is in contact with a surface of the flame escape prevention member.   The gas introduction nozzle includes a nozzle body that is screwed onto the guard member, a tip cylindrical member that is provided at the tip of the nozzle body so as to be slidable in the axial direction of the nozzle body, and the tip cylinder 2. An extension spring that is inserted between the cylindrical member and the nozzle main body and elastically deforms in the axial direction in accordance with the displacement of the distal cylindrical member. The explosion-proof gas detector according to claim 2.   The gas introduction nozzle is composed of a nozzle body that is screwed onto the guard member and a bellows that is provided at the tip of the nozzle body and can be elastically reduced in the axial direction. The pressure / explosion-proof gas detector according to claim 1 or 2, characterized in that

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