NL2026061B1 - Closing member, air duct system, ventilation system, vessel and method of enabling inspection and/or cleaning of an interior of an air duct - Google Patents

Abstract

Closing member for reversibly closing off an inspection opening in a wall section of an air duct, the closing member comprising: a cover plate configured to cover the inspection opening; a fire resistant gasket configured to provide an air-tight seal between the cover plate and the wall section; and fastening means for reversibly fastening the closing member to the wall section and for thereby forming the seal. Air duct system comprising: an air duct with a wall section which comprises an inspection opening; and the closing member for reversibly closing off the inspection opening. Method of enabling inspection of an interior of an air duct, comprising: providing an inspection opening in a wall section of the air duct; providing the closing member; positioning the cover plate of the closing member over the inspection opening; and reversibly fastening the closing member to the wall section.

Description

P127796NL00 Title: Closing member, air duct system, ventilation system, vessel and method of enabling inspection and/or cleaning of an interior of an air duct The invention concerns a closing member, an air duct system, a ventilation system, a vessel and a method of enabling inspection of an air duct. Air ducts such as those in ventilation systems in ships generally require regular inspection and/or cleaning of their interior, for example in view of fire safety regulations. As requirements for such inspection and/or cleaning procedures can change over time, e.g. due to changing regulations, it can be necessary to modify an already installed ventilation system to ensure compliance to the new requirements. Such modifications, e.g.

installing an additional inspection hatch, can enable inspection and/or cleaning of air ducts at new positions along the air duct. Meanwhile such modifications should themselves also comply to applicable standards, e.g. related to fire safety, energy efficiency, environmental regulations, ete. It is desired that such modifications are also relatively easy and efficient to perform on board a ship, e.g. as part of a regular maintenance cycle.

Known solutions for the above described problems have one or more disadvantages, such as being difficult to install and/or providing insufficient fire safety performance. For example US2002/0184827A1 discloses a method for installing in the field an access panel for providing access to a duct, wherein clip fasteners are attached to the duct around a perimeter of an opening therein and wherein a cover plate is bent and/or cut to fit the air duct, thus a relatively complex method.

Hence there is a need for an improved solution for enabling inspection of an interior of an air duct, in particular in ships. An object of the present invention is to provide such an improved solution, wherein particular easier installation in ships and/or improved fire safety is provided. An object is to at least partly solve at least one of the above described problems or an associated problem.

To that end an aspect of the present invention provides a closing member according to claim 1 for reversibly closing off an inspection opening in a wall section of an air duct. The closing member comprises: a cover plate configured to cover the inspection opening; a fire resistant gasket configured to provide an air tight seal between the cover plate and the wall section; and fastening means for reversibly fastening the closing member to the wall section and for thereby forming the seal.

Such a closing member enables to easily and safely close off such an inspection opening, wherein in particular the fire resistant gasket promotes fire safety at the position of the inspection opening when the closing member is fastened to the wall section. Preferably the cover plate and/or the fastening means are also substantially fire resistant, for example non-combustible, for example being made from metal.

Optionally, the gasket is made from a non-combustible fiber material, for example FireMaster® Paper.

Such a gasket can provide good sealing properties as well as good fire resistance properties.

Optionally, the gasket is dimensioned to substantially cover an inner surface of the cover plate.

As the gasket is fire resistant, such a configuration promotes fire resistivity of other parts of the closing member such as the cover plate. Moreover such a configuration enables particularly easy and versatile installation of the closing member with respect to different sizes, shapes and/or positions of the inspection opening and/or the wall section.

Optionally, the closing member comprises a fire resistant insulation plug configured to extend in the inspection opening, at least when the cover plate covers the inspection opening, to provide thermal insulation of the air duct at the inspection opening.

When the wall section is a thermally insulated wall section, such an insulation plug can at least partly restore the thermal insulation properties of the wall section after first being affected by forming the inspection opening through the wall section.

Optionally, the insultation plug is made from a non-combustible fiber material, for example FireMaster® Board.

Such an insulation plug combines good insulating properties with good fire resistance properties.

Optionally, the insulation plug is configured to substantially conform to the inspection opening, at least when inserted in the inspection opening.

Insulation of the wall section is thereby further promoted and possible thermal bridges between air flowing through the air duct and the outside environment do effectively not occur. Particularly if cool air is flown through the air duct this minimizes or fully prevents condense forming on an outside of the closing member, particularly the metal cover plate. Additionally, enhanced fire resistivity is thereby provided.

Optionally, the insulation plug is fixed, at least fixable, to the cover plate, for example by a threaded connection, wherein preferably the fastening means are arranged at a distance from the insulation plug.

Installation of the closing member is thereby made easier. Moreover such a configuration promotes good thermal insulation by reducing transmission of heat through the insulation plug e.g. via fastening screws which connect to the cover plate and/or an outer face of the wall section. To that end the threaded connection preferably extends into but not through the insulation plug, the plug for example being provided with a nut or a bolt which extends inside the plug and optionally extends outside the plug on a side of the plug which during use faces away from an interior of the air duct, e.g. faces the cover plate.

Optionally, the insulation plug is provided with a nut that fastens to a central fastening body that extends from the cover plate. The central fastening body, e.g. a screw or bolt, optionally has a closed head, i.e. a head without socket or head fitting, and/or a rounded head, which prevents erroneous screwing of the central fastening body when in use the closing member is being removed from the air duct for inspection or cleaning thereof.

Optionally the central fastening body comprises a shank part with a rectangular or square cross section and/or the cover plate comprises a preformed rectangular of square shaped central opening. Such formed shank or opening assists in convenient assembly of the cover plate, gasket and insulation plug by attachment of the central fastening body to the nut.

Optionally, the fastening means comprises a plurality of screw holes distributed along a circumference of the cover plate, the screw holes being configured to receive and cooperate with fastening screws.

Such fastening means provide particularly easy installation, e.g. by self-drilling screws which are screwed into the wall section while being held in the screw holes.

Optionally, the cover plate is deformable and configured to deform by fastening, in use, the closing member to the wall section of the air duct, e.g. using fastening screws which cooperate with the fastening means.

In this way fastening the closing member can promote that the cover plate thereby automatically conforms more to the wall section, which in turn can provide improved sealing while being easy to install.

Optionally, the cover plate, when deformed by the fastening, has a resilience configured to secure the fastening for resisting vibratory loosening of the fastening, e.g. loosening of fastening screws which cooperate with the fastening means.

Such deformation can in particular cause a spring loading of the cover plate which spring loading secures the fastening by fastening screws or the-like, thereby resisting loosening e.g. due to vibrations in the ship. The cover plate can in this respect for example act as a leaf spring element. A direction of the spring loading of the screws is preferably directed outward from an outer face of the wall section, preferably substantially opposite to a 5 screwing direction for fastening the closing member to the wall section, thus providing resilient clamping of the screws.

Optionally, the cover plate comprises two or more plate sections, preferably at least substantially flat plate sections, which extend at an angle to each other.

Such a configuration can promote the above described deformability to resist vibratory loosening. Moreover such angled plate sections can promote that the cover plate conforms more to a curved wall section, e.g. being substantially conformable to a range of wall section curvatures. The closing member is as such particularly suited for use with tubular air ducts, or pipes, with a cross sectional diameter of between 80- 500mm.

Optionally, the two or more plate sections define a central section and two lateral sections extending on opposite sides from the central section at an angle with respect to the central section, wherein preferably the angle of each of the lateral sections with respect to the central section is the same.

Such a configuration is particularly suitable for a tubular wall section, wherein for example the plate sections each extend substantially tangential to an arcuate cross sectional circumference of the wall section. Folding lines can be formed between the sections, wherein the folding lines preferably extend substantially parallel to a main axis of the air duct.

Optionally, the fastening means are arranged at the central section, the fastening means in particular comprising screw holes in the central section which screw holes are configured to receive and cooperate with fastening screws.

Resilience of the cover plate as described above as well as good sealing performance are thereby promoted. Moreover such a configuration promotes ease of installation, for example requiring only two self-drilling screws to be fastened after placing the closing member.

A further aspect provides an air duct system, in particular for use in an air ventilation system, comprising: an air duct with a wall section which comprises an inspection opening; and a closing member as described herein for reversibly closing off the inspection opening.

Such an air duct system provides above-described advantages.

Optionally, the inspection opening is substantially circular, preferably having a diameter in the range of 10 to 100 mm, more preferably in the range of 20 to 80 mm, more preferably in the range of 30 to 60 mm, for example about 40 mm. Such an inspection opening can be created relatively easily on board a ship, for example by drilling, while a suitably sized inspection opening is thereby provided.

Optionally, the wall section is substantially curved, for example corresponding to a tubular shape of the air duct, wherein the closing member, in particular the cover plate, is configured to substantially conform to a curvature of the wall section, in particular upon fastening applied to the fastening means, e.g. using fastening screws which cooperate with the fastening means.

Optionally, the air duct system further comprises fastening screws, in particular self-drilling screws, for fastening the closing member to the wall section using the fastening means.

Optionally, the air duct is provided with a fire damper, wherein the inspection opening is arranged near the fire damper.

Such a system provides a particularly good way of complying to relevant fire safety regulations for ships.

Optionally, the system comprises a plurality of wall sections with respective inspection openings and respective closing members, wherein the inspection openings are spaced apart from each other along the air duct.

Air duct inspection can thus advantageously be performed from various positions along the air duct.

Optionally, the wall section is provided with a thermal insulation layer for thermal insulation of the air duct, wherein the closing member comprises a fire resistant insulation plug for thermal insulation of the air duct at the inspection opening.

A further aspect provides a ventilation system comprising an air duct system as described herein.

Such a ventilation system provides above-described advantages.

A further aspect provides a vessel, in particular a water vessel, more in particular a ship or a boat, provided with a ventilation system as described herein, wherein the ventilation system is configured to provide ventilation of at least one inner space of the vessel.

Such a vessel provides above-described advantages.

A further aspect provides a method of enabling inspection of an interior of an air duct. The method comprises: providing, e.g. by drilling, an inspection opening in a wall section of the air duct; providing a closing member as described herein; positioning the cover plate of the closing member over the inspection opening; and reversibly fastening, e.g. by screwing, the closing member to the wall section, thereby covering the inspection opening with the cover plate and forming a seal between the cover plate and the wall section.

Such a method provides above-described advantages.

Optionally, the method further comprises reversing the fastening and subsequently removing the closing member from the inspection opening for inspection of an interior of the air duct.

In this way an interior of the air duct can easily be inspected through the inspection opening.

The inspection opening can subsequently be easily and safely closed off again.

Optionally, the fastening comprises deforming the cover plate, thereby tightening the fastening to resist vibratory loosening.

Optionally, the method comprises inserting an insulation plug of the closing member in the inspection opening.

In the following the invention will be explained further using exemplary embodiments and drawings.

The drawings are schematic and merely show examples.

In the drawings, similar or corresponding elements have been provided with similar or corresponding reference signs.

In the drawings: Fig. 1A shows an isometric view of a closing member according to a first embodiment; Fig. 1B shows an exploded isometric view of the closing member of Fig. 1A; Fig. 2A shows an isometric view of a closing member according to a second embodiment; Fig. 2B shows an exploded isometric view of the closing member of Fig. 2A; Fig. 3A shows an isometric view of a closing member according to a third embodiment; Fig. 3B shows an exploded isometric view of the closing member of Fig. 3A; Fig. 3C shows a side view of a cover plate of the closing member of Figs. 3A-B; Fig. 4A shows an isometric view of a closing member according to a fourth embodiment; Fig. 4B shows an exploded isometric view of the closing member of Fig. 4A;

Fig. 5A shows a cross sectional view of a wall section of an air duct of an air duct system according to an embodiment, wherein a step of forming an inspection opening in the wall section is shown; Fig. 5B shows a cross sectional view of the air duct system of Fig.

5A, wherein a step of positioning a cover plate of a closing member over the inspection opening is shown; Fig. 5C shows a cross sectional view of the air duct system of Figs. 5A-B, wherein a step of reversibly fastening the closing member to the wall section 1s shown; Fig. 5D shows a top view of the air duct system of Figs. 5A-C, wherein the closing member is fastened to the wall section; and Fig. 6 shows a side view of a vessel according to an embodiment comprising an air duct system according to an embodiment as part of a ventilation system according to an embodiment.

The drawings show examples of a closing member 101, 201, 301, 401 for reversibly closing off an inspection opening 50 in a wall section 51 of an air duct 55. The closing member 101, 201, 301, 401 comprises: a cover plate 102, 202, 302, 402 configured to cover the inspection opening 50; a fire resistant gasket 103, 203, 303, 403 configured to provide an air tight seal between the cover plate 102, 202, 302, 402 and the wall section 51; and fastening means 104, 204, 304, 404 for reversibly fastening the closing member 101, 201, 301, 401 to the wall section 51 and for thereby forming the seal.

Preferably the cover plate 102, 202, 302, 402 and the fastening means 104, 204, 304, 404 and any auxiliary materials such as fastening screws 60 are also substantially fire resistant, for example non-combustible, for example being made from a metal or metal alloy, optionally provided with a coating.

The gasket 103, 203, 303, 403 is preferably made from a non- combustible fiber material, for example FireMaster® Paper (marketed by Morgan Advanced Materials plc).

In the shown examples, the gasket 103, 203, 303, 403 1s dimensioned to substantially cover an inner surface of the cover plate 102, 202, 302, 402.

In the examples of Figs. 2A-B, 4A-B, and 5A-D, the closing member 201, 401 comprises a fire resistant insulation plug 206, 406 configured to extend in the inspection opening 50, at least when the cover plate 202, 402 covers the inspection opening 50, to provide thermal insulation of the air duct 55 at the inspection opening 50.

Figs. 5A-D show that when the wall section 51 is a thermally insulated wall section 51 (having a thermal insulation layer 54), such an insulation plug 406 can at least partly restore the thermal insulation properties of the wall section 51 after first being affected (see Fig. 5A) by forming the inspection opening 50 through the wall section 51.

The insultation plug 206, 406 is preferably made from a non- combustible fiber material, for example FireMaster® Board (marketed by Morgan Advanced Materials plc). Here the gasket 203, 403 and insulation plug 206, 406 are made from different (though related) non-combustible fiber materials. Alternatively or additionally these elements can be made from a same material, e.g. a same non-combustible fiber material.

As shown, the insulation plug 406 is configured to substantially conform to the inspection opening 50, at least when inserted in the inspection opening 50 (see Fig. 5B). To that end a diameter of a substantially cylindrical insulation plug 406 can for example be chosen to correspond with a diameter of the inspection opening 50. Alternatively or additionally the insulation plug can for example be substantially deformable, e.g. compressible, being oversized compared to the inspection opening 50 before insertion in the inspection opening 50.

As shown, see in particular Figs. 2B and 4B, the insulation plug 206, 406 is fixed, at least fixable, to the cover plate 202, 402, here by a threaded connection 205a, 205b; 405a, 405b, wherein the fastening means 204, 404 for fastening the cover plate 202, 402 to the wall section 51 are arranged at a distance from the insulation plug 206, 406.

The threaded connection 205a, 205b; 405a, 405b here extends into but not through the insulation plug 206, 406. The plug 206, 406 here 1s provided with a nut 205b, 405b which extends inside the plug 206, 406 and is accessible from a side of the plug 206, 406 which side during use faces away from an interior of the air duct 55, i.e. faces the cover plate 202, 402. The threaded connection 205a, 205b; 405a, 405b 1s thus thermally insulated from an interior of the air duct 55 by the insulation plug 206, 406.

Here the nut 205b, 405b is fixed in the insulation plug 206, 406 by an external thread on the nut 205b, 405b. Here a bolt 205a, 405a 1s provided to form the threaded connection with the nut 205b, 405b, the bolt extending through respective central holes in the cover plate 202, 402 and gasket 203,

403.

As can be seen in the drawings, the threaded connection 205a, 205b; 405a, 405b here additionally fixes the gasket 203, 403 to the cover plate 202, 402.

In the examples of Figs. 1A-B and 3A-C, the cover plate 102, 302 and the gasket 103, 303 are fixed to each other by a central riveting connection 105a, 105b; 305a, 305b.

Such fixing of the cover plate 102, 202, 302, 402 and the gasket 103, 203, 303, 403 with respect to each other prior to installation eases installation efforts and ensured good alignment of the cover plate 102, 202, 302, 402 and the gasket 103, 203, 303, 403 with respect to each other.

In the shown examples, the fastening means 104, 204, 304, 404 comprises a plurality of screw holes 104, 204, 304, 404 distributed along a circumference of the cover plate 102, 202, 302, 402, the screw holes 104, 204,

304, 404 being configured to receive and cooperate with fastening screws 60 (see Fig. 5C), e.g. self-drilling fastening screws 60.

Optionally (not shown), the gasket can be provided with respective screw holes in line with the screw holes 104, 204, 304, 404 of the cover plate 102, 202, 302, 402. Alternatively, for example, self-drilling fastening screws 60 can easily be screwed directly through the gasket 103, 203, 303, 403, i.e.

such screw holes are automatically formed in the gasket upon screwing.

In the examples of Figs. 3A-C, 4A-B and 5A-D, the cover plate 302, 402 is deformable and configured to deform by fastening, in use, the closing member 301, 401 to the wall section 51 of the air duct 55, e.g. using fastening screws 60 which cooperate with the fastening means 304, 404.

Here the cover plate 302, 402, when deformed by the fastening, has a resilience configured to secure the fastening for resisting vibratory loosening of the fastening, e.g. loosening of fastening screws 60 which cooperate with the fastening means 304, 404.

With reference to Fig. 5C, this deformation here causes a spring loading of the cover plate 302, 402 which spring loading secures the fastening by fastening screws 60, thereby resisting loosening e.g. due to vibrations in the ship 80. The cover plate 302, 402 in this respect acts as a leaf spring element. The spring loading of the screws 60 is directed outward from an outer face of the wall section 51, thus substantially opposite to a screwing direction for fastening the closing member 301, 401 to the wall section 51, thus providing resilient clamping of the screws 60.

With continued reference to the examples of Figs. 3A-C, 4A-B and 5A-D, the cover plate here comprises two or more plate sections 302a, 302b, 302c; 402a, 402b, 402c, here substantially flat plate sections, which extend at an angle a (see Fig. 3C) to each other.

Here the two or more plate sections 302a, 302b, 302c; 402a, 402b, 402c define a central section 302a, 402a and two lateral sections 302b, 302c; 402b, 402c extending on opposite sides from the central section 302a, 402a at an angle a with respect to the central section 302a, 402a, wherein the angle a of each of the lateral sections 302b, 302c; 402b, 402c with respect to the central section 302a, 4024, is the same, see Fig. 3C.

Here the angle a is about 22.5°. Alternatively a different angle can be used, in particular in the range of 5° to 45°, more in particular in the range of 10° to 35°, more in particular in the range of 15° to 30°, more in particular in the range of 20° to 25°.

Here a thickness d (see Fig. 3C) of the cover plate 302 is about 0.6 mm and the thickness d is substantially uniform throughout the cover plate

302. Alternatively or additionally the cover plate can have a different thickness and/or a non-uniform thickness.

While Fig. 3C shows a side view of the cover plate 302 of the closing member 301 of Figs. 3A-B, it will be appreciated that the cover plate 402 of Fig. 4A-B is configured correspondingly.

As shown in Figs. 5B-C, such a configuration with a central section 3024, 402a and two lateral sections 302b, 302c; 402b, 402c is particularly suitable for a tubular wall section 51. Here the plate sections 402a, 402b, 402c each extend substantially tangential to an arcuate cross sectional circumference of the wall section 51.

Folding lines 307, 407 can be formed between the sections, wherein the folding lines 407 here extend substantially parallel to a main axis C (see Figs. 5A-D) of the air duct 55.

Here the fastening means 304, 404 are arranged at the central section 302a, 402a, the fastening means 304, 404 here comprising screw holes 304, 404 in the central section 302a, 402a which screw holes 304, 404 are configured to receive and cooperate with fastening screws 60.

In the shown examples the fastening means 104, 204, 304, 404 comprises only two screw holes, enabling particularly easy and fast installation. It will be appreciated that alternatively the fastening means can comprise a different number of screw holes or no screw holes.

Alternatively or additionally the fastening means can for example comprise clamping means for clamping the closing member to the wall section of the air duct. Further alternative or additional fastening means are possible, as will be appreciated by the skilled person.

Figs. 5A-D and 6 show examples of an air duct system 70, in particular for use in an air ventilation system 73, comprising: an air duct 55 with a wall section 51 which comprises an inspection opening 50; and a closing member 101, 201, 301, 401 as described herein for reversibly closing off the inspection opening 50.

Here the inspection opening 50 is substantially circular, preferably having a diameter in the range of 10 to 100 mm, more preferably in the range of 20 to 80 mm, more preferably in the range of 30 to 60 mm, for example about 40 mm.

Fig. 5A shows that such an inspection opening 50 can be created relatively easily on board a ship 80, for example by drilling using a suitable drill D. As shown, a suitably sized inspection opening 50 is thereby efficiently provided.

Here the wall section 51 1s substantially curved, corresponding to a tubular shape of the air duct 55, wherein the closing member 301, 401, in particular the cover plate 302, 402, is configured to substantially conform to a curvature of the wall section 51, in particular upon fastening applied to the fastening means 304, 404, e.g. using fastening screws 60 which cooperate with the fastening means 304, 404.

It will be appreciated that here “substantially conform to a curvature of the wall section” particularly refers to the air-tight seal being formed by the gasket 303, 403 between the cover plate 302, 402 and the wall section 51. Thus, depending on a thickness and compressibility of the gasket, 303, 403, the conforming can be more or less precise. Herein the fastening can cause the cover plate 302, 402 to conform more to the wall section 51 compared to an unfastened state of the cover plate 302, 402.

Here the air duct system 70 further comprises fastening screws 60, in particular self-drilling screws 60, for fastening the closing member 101, 201, 301, 401 to the wall section 51 using the fastening means 104, 204, 304,

404.

As shown in Fig. 6, the air duct 55 can be provided with a fire damper 71, wherein the inspection opening 50, at least one inspection opening 50, is arranged near the fire damper 71. It will be appreciated that an inspection opening 50 can alternatively or additionally be arranged elsewhere. It will be appreciated that a plurality of fire dampers, e.g. each with one or more respective inspection openings, can be provided.

Also shown in Fig. 6, the air duct system 70 can comprise a plurality of wall sections 51 with respective inspection openings 50 and respective closing members 401 wherein the inspection openings 50 are spaced apart from each other along the air duct 55.

As shown in Figs. 5A-C, the wall section 51 here is provided with a thermal insulation layer 54 for thermal insulation of the air duct 55, wherein the closing member 401 comprises a fire resistant insulation plug 406 for thermal insulation of the air duct 55 at the inspection opening 50. Here the thermal insulation layer 54 is arranged between an outer layer 52 and an inner layer 53 of the wall section 51 which outer and inner layer 52, 53 are e.g. each made from metal.

Fig. 6 also shows an exemplary ventilation system 73 comprising an air duct system 70 as described herein. Here the ventilation system 73 is configured to provide ventilation of, e.g. feed air to and/or extract air from, an inner space 81.

Fig. 6 also shows an example of a vessel 80, in particular a water vessel 80, more in particular a ship or a boat, provided with the ventilation system 73, wherein the ventilation system 73 is configured to provide ventilation of at least one inner space 81 of the vessel 80.

With reference to the drawings, in particular Figs. 5A-D, an exemplary method of enabling inspection of an interior of an air duct 55 comprises: providing, e.g. by drilling (see Fig. 5A), an inspection opening 50 in a wall section 51 of the air duct 55; providing a closing member 101, 201, 301, 401 as described herein; positioning the cover plate 102, 202, 302, 402 of the closing member 101, 201, 301, 401 over the inspection opening 50 (see Fig. 5B); and reversibly fastening, e.g. by screwing, the closing member 101, 201, 301, 401 to the wall section 51, thereby covering the inspection opening 50 with the cover plate 102, 202, 302, 402 and forming a seal between the cover plate 102, 202, 302, 402 and the wall section 51 (see Fig. 5C).

The exemplary method further comprises reversing the fastening and subsequently removing the closing member 101, 201, 301, 401 from the inspection opening 50 for inspection of an interior of the air duct 55.

In the examples of Figs. 3A-C, 4A-B, 5A-D, the fastening comprises deforming the cover plate 302, 402, thereby tightening the fastening to resist vibratory loosening of fastening screws 60 which cooperate with the fastening means 304, 404.

In examples the method comprises inserting an insulation plug 206, 406 of the closing member 201, 401 in the inspection opening 50.

While the invention has been explained further using exemplary embodiments and drawings, these do not limit the scope of the invention as defined by the claims. Many variations, combinations and extensions are possible, as will be appreciated by the skilled person. Examples thereof have been provided throughout the description.

Claims (26)

Conclusions Closing element for reversibly closing an inspection opening in a wall section of an air duct, the closing element comprising: - a cover plate adapted to cover the inspection opening; - a fire-resistant gasket arranged to provide an airtight seal between the cover plate and the wall section; and - fastening means for reversibly fastening the closure element to the wall section and thereby forming the seal. Closing element according to claim 1, wherein the gasket is made of a non-combustible fiber material, for instance FireMaster® Paper. A closure element according to claim 1 or 2, wherein the gasket is sized to substantially cover an inner surface of the cover plate. 4. Closure element as claimed in any of the foregoing claims, comprising a fire-resistant insulating plug adapted to extend into the inspection opening, at least when the cover plate covers the inspection opening, to provide thermal insulation of the air duct at the inspection opening. 5. Closing element according to claim 4, wherein the insulating plug is made of a non-combustible fiber material, for instance FireMaster® Board. 6. Closing element according to claim 4 or 5, wherein the insulating plug is adapted to substantially conform to the inspection opening, at least when inserted into the inspection opening. Closing element as claimed in any of the claims 4-6, wherein the insulating plug is fixed, or at least fixable, to the cover plate, for instance by means of a screw thread connection, wherein the fastening means are preferably arranged at a distance from the insulating plug. A closure element according to any one of the preceding claims, wherein the fastening means comprise a plurality of screw holes distributed along a periphery of the cover plate, the screw holes being adapted to receive and cooperate with fastening screws. A closing element according to any one of the preceding claims, wherein the cover plate is deformable and adapted to be deformed by fixing the closing element to the wall section of the air duct during use, e.g. using fixing screws which cooperate with the fixing means. A closure element according to claim 9, wherein the cover plate, when deformed by fastening, has a spring force adapted to lock the fastening to resist vibrational loosening of the fastening, e.g. loosening of fastening screws cooperating with the fastening means. 11. Closing element according to claim 9 or 10, wherein the cover plate comprises two or more plate sections, preferably at least substantially flat plate sections, which extend at an angle relative to each other. The closure element of claim 11, wherein the two or more plate sections define a central section and two lateral sections, the lateral sections extending on opposite sides of the central section at an angle to the central section, preferably the angle of each of the lateral sections relative to the central section is the same. A closure element according to claim 12, wherein the fastening means are arranged at the central section, the fastening means in particular comprising screw holes in the central section which screw holes are adapted to receive and cooperate with fastening screws. An air duct system, in particular for use in an air ventilation system, comprising: - an air duct with a wall section comprising an inspection opening; - a closing element according to any one of the preceding claims for reversibly closing the inspection opening. An air duct system according to claim 14, wherein the inspection opening is substantially circular, preferably with a diameter in the range of 10 to 100 mm, more preferably in the range of 20 to 80 mm, more preferably in the range range from 30 to 60 mm, e.g. about 40 mm. An air duct system according to claim 14 or 15, wherein the wall section is substantially curved, for instance according to a tubular shape of the air duct, wherein the closing element, in particular the cover plate, is designed to substantially conform to a curvature of the wall section. , especially once attachment is applied to the fasteners. An air duct system according to any one of claims 14 - 16, further comprising fastening screws, in particular self-drilling screws, for fastening the closing element to the wall section using the fastening means. An air duct system according to any one of claims 14 - 17, wherein the air duct is provided with a fire damper, wherein the inspection opening is arranged near the fire damper. 19. Air duct system according to any one of claims 14 - 18, comprising a plurality of wall sections with respective inspection openings and respective closing elements, wherein the inspection openings are spaced apart along the air duct. An air duct system according to any one of claims 14 to 19, wherein the wall section is provided with a thermal insulation layer for thermal insulation of the air duct, the closing element comprising a fire-resistant insulating plug for thermal insulation of the air duct at the inspection opening. 21. Ventilation system comprising an air duct system as claimed in any of the claims 14 - 20. A vessel, in particular a watercraft, more in particular a ship or a boat, provided with a ventilation system according to claim 21, wherein the ventilation system is adapted to provide ventilation of at least one interior space of the vessel. A method for enabling inspection of an interior of an air duct, comprising: - providing, e.g. by drilling, an inspection opening in a wall section of the air duct; - providing a sealing element according to any one of claims 1 to 13; - positioning the cover plate of the closing element over the inspection opening; and - reversibly fastening, e.g. by screwing, the closing element to the wall section, wherein the inspection opening is covered with the cover plate and a seal is formed between the cover plate and the wall section. The method of claim 23, further comprising reversing the attachment and then removing the closure element from the inspection opening for inspection of an interior of the air duct. A method according to claim 23 or 24, wherein the fastening comprises deforming the cover plate, whereby the fastening is tensioned to resist vibrational loosening. A method according to any one of claims 23 - 25, comprising inserting an insulating plug of the closing element into the inspection opening.