JP7177789B2 - NBC filter unit with ventilation bypass - Google Patents

Description

The present invention relates to nuclear biochemistry (NBC) filter units for NBC filtering systems in residential safety rooms, and in particular to NBC filter units with integrated ventilation bypass.

National civilian defense authorities, such as the U.S. Department of Homeland Security (DHS) and Israel's Home Front Command (HFC), require civilians to enter sealed shelters in the event of a nuclear, biological, or chemical attack. instructing. In Israel, all dwellings include sealed explosion-proof safe rooms constructed according to Israeli government standards. Israeli regulations mandate the installation of NBC filtering and ventilation systems in explosion-proof safe rooms in all new individual dwellings. The term NBC, which stands for "nuclear biochemistry", is used throughout this patent application in a broad sense and means at least one of nuclear, biological, and chemical. Thus, an NBC does not imply that all functions are required for this application, e.g., it provides protection against biological and chemical attack, but no protection against nuclear attack, or A filter that provides only partial coverage is also considered an NBC filter unit for the purposes of this application.

Israel Patent No. 124273 (U.S. Pat. No. 6,328,775) to this application describes a compact, portable system for protection against ingress of contaminated air into a protected space. . When the described unit is installed in a blast-protected safety room, the system has an air intake mounted through the exterior wall of the building carrying a backwind valve on the outside of the wall and a quick-connect flange on the inside of the wall. contains. The exhaust unit is mounted through a preferably opposite inner wall of the safety chamber with an overpressure relief valve. The system further includes a portable NBC filter unit attachable to the air inlet by a quick connect flange and a portable electric blower unit powered by mains power and optionally backed up by an internal battery. This blower unit can be attached directly to the outlet of the filter unit or with a flexible extension duct. A manual air pump is also included to provide protection in the event of mains power failure. Under normal conditions, filters and blowers are kept within easy reach and the safety chamber is available for daily use. When an NBC emergency is declared, a portable NBC filter is connected to the air inlet and a portable electric blower is attached to the outlet of the filter.

Prolonged stay in an airtight safety room, even during a mere conventional hazard, requires active ventilation from the inlet. In the above system, an electric blower or manual air pump can be attached directly to the quick connect flange of the air intake, thus ventilating the safe room without NBC filtering. The NBC filter unit remains sealed until an NBC hazard is declared and an NBC filter is installed between the inlet quick connect flange and the electric blower or manual pump.

However, new regulations require NBC filtering systems to be installed fixed in place and ready for immediate use with minimal setup.

Until recently, even newer fixation systems removed the hermetic seals fitted to the inlet and outlet of the NBC filter unit upon declaration of an NBC hazard, allowing the NBC filter unit to be flexed to the inlet and to the electric blower. It was necessary to assemble between the sex duct. According to the Applicant's Israeli Patent Application No. 214,577, the need to assemble the NBC filter unit is eliminated and switching from ventilation mode to NBC filtering mode is accomplished simply by switching a manual state selector handle mounted above the two-way switching valve. A two-way switching valve in an NBC air filtering system is described that allows switching.

The switching valve has a primary inlet with the air flow coupled to the air intake, a primary outlet with the air flow coupled to an electric blower or hand pump, and a secondary inlet with the air flow coupled to the NBC filter unit outlet. and a secondary outlet coupled to the NBC filter unit inlet for air flow. The placement of a swivel flap or plate drag mechanism within the switching valve directs air from the primary inlet to the primary outlet either directly (ventilation mode) or via the NBC filter unit (NBC filtering mode). When the NBC filtering system is set to ventilation mode, flaps or drag plates seal the inlet and outlet of the NBC filter unit to prevent moisture and other contaminants from entering the NBC filter unit. .

A typical NBC filter unit includes a particulate filter and a gas adsorption filter. The gas adsorption filter consists of a packed bed of activated carbon particulates. Compression of the carbon layer is maintained by a spring-loaded perforated plate mounted on top of the carbon layer to maintain the integrity and tightness of the carbon fill.

Applicant's Israeli Patent Application No. 226357 describes a filter unit assembly with a casing consisting of two drawn sheet metal segments permanently joined together by a rim crimp process. The casing holds a particulate filter mounted in the air inlet casing segment and an adsorbent particulate filter packed in the air outlet casing segment. A perforated plate and spring are mounted above the adsorbent particulate filter during assembly. The springs are adapted to apply pressure to the perforated plate when the casing segments are seamed together, thus reducing assembly parts and cost.

However, as described in IL214577, in order to use a standard NBC filter unit as described herein with a diverter valve, the air entering from the air intake must be directed to the primary inlet of the diverter valve. a first duct or additional cover, a second duct or cover communicating between the secondary outlet of the switching valve and the inlet of the NBC filter unit, between the secondary inlet of the switching valve and the outlet of the NBC filter unit A communicating third duct or cover must be provided, a fourth duct or cover directing air from the primary outlet of the switching valve to the electric blower or manual air pump.

Those skilled in the art will appreciate that such ducts or covers are complex in shape and expensive to manufacture. Hermetic sealing of ducts or covers during assembly is difficult and can result in dangerous cross leaks. As a result, there is a need to simplify construction, improve quality and safety, reduce the quantity of parts, and reduce manufacturing and assembly costs.

Israel Patent No. 124273 U.S. Pat. No. 6,328,775 Israel Patent Application No. 214577 Israel Patent Application No. 226357

SUMMARY OF THE INVENTION Accordingly, it is a primary object of the present invention to overcome the drawbacks and limitations of prior art systems and to provide a filter unit for a residential safety room NBC filtering system with an integral ventilation bypass.

According to the invention there is provided an NBC filter unit comprising a casing, at least one inlet and at least one outlet. A casing encloses a particulate filter and a gas adsorption filter. The NBC filter unit further comprises at least one through the integrated ventilation bypass and the integrated ventilation bypass configuring the ventilation mode, or via the particulate filter and the gas adsorption filter configuring the NBC filtering mode. and air flow directing means selectively operable to direct air flow therein from one inlet port to at least one outlet port.

The casing volume further comprises four volume compartments: a primary inlet compartment adjacent to at least one inlet; a primary outlet compartment adjacent to at least one outlet; a secondary inlet compartment upstream of the particulate filter; and a downstream secondary exit section.

The primary inlet section and the primary outlet section are in air flow communication via an integral ventilation bypass when the flow directing means is set to ventilation mode. At the same time, the secondary inlet and secondary outlet compartments are hermetically sealed from the surroundings by the flow directing means.

When the flow directing means is set to the NBC filtering mode, the primary inlet section and the secondary inlet section are in air flow communication and the primary outlet section and the secondary outlet section are in air flow communication. At the same time, the primary inlet section and the primary outlet section are blocked from air flow.

Upon reaching the end of its useful life, or in the event of NBC contamination, the NBC filter unit, including the integrated ventilation bypass and air flow directing means, is replaced as a single disposable unit.

Optionally, the NBC filter unit further comprises an inner shell enclosing a particulate filter, a gas adsorption filter, a secondary inlet section upstream of the particulate filter and a secondary outlet section downstream of the gas adsorption filter. is doing.

The invention and the manner in which it can be practiced will be understood, by way of non-limiting example only, with reference to the following illustrative figures, in which like reference numerals identify like elements: .

1 is a perspective view of an NBC filter unit manufactured according to one embodiment of the present invention; FIG. Vertical perspective view of the NBC filter unit of FIG. FIG. 2 is an elevated cross-sectional view of the NBC filter unit of FIG. 1 with air flow directing means selected to operate in ventilation mode; FIG. 2 is an elevation cross-sectional view of the NBC filter unit of FIG. 1 with air flow directing means selected to operate in the NBC filtering mode; FIG. 4 is a cross-sectional elevational view of a second embodiment of the present invention demonstrating an NBC filter unit with air flow directing means selected to operate in ventilation mode; FIG. 6 is an elevational cross-sectional view similar to FIG. 5 with the airflow directing means selected to operate in the NBC filtering mode; FIG. 4 is an elevated cross-sectional view of a third embodiment of the present invention demonstrating an NBC filter unit with air flow directing means selected to operate in ventilation mode; FIG. 8 is an elevated cross-sectional view similar to FIG. 7 with the airflow directing means selected to operate in the NBC filtering mode;

Referring to the drawings in which like reference numbers identify like elements even through different embodiments of the present invention, FIG. 1 illustrates an NBC filter unit, generally designated 10, manufactured in accordance with one embodiment of the present invention. is shown. The term NBC, which stands for "nuclear biochemistry", is used throughout this patent application in a broad sense and means at least one of nuclear, biological, and chemical. Thus, an NBC does not imply that all functions are required for this application, e.g., it provides protection against biological and chemical attack, but no protection against nuclear attack, or A filter that provides only partial coverage is also considered an NBC filter unit for the purposes of this application. The external appearance of the filter unit 10 can be recognized as a rectangular parallelepiped shape (FIGS. 1-4) or a cylindrical shape (FIGS. 5-8), although any embodiment can be recognized as any type of volumetric shape. . The filter unit 10 comprises a casing 12 which preferably consists of two casing segments 60, 62 permanently joined together.

As is known in the NBC guarded safety room art, the air inlet pipe is embedded in the concrete casting of the safety room exterior wall during building construction. The inlet pipe typically carries a standard or quick connect fixed flange inside the outer wall and may be provided with a blower valve.

The NBC filter unit 10 may be air-flow connected to the air intake by ducting or by an optional standard or quick connect mating flange 13 on a fixed flange of the safety chamber air intake pipe (not shown). may be installed directly on the Casing segment 62 facing the safety chamber inlet pipe is shown in FIG. 1 with flange 13 surrounding at least one inlet port 14 . Casing segment 60 facing the safety chamber space includes at least one exit port 16 (FIG. 2).

Common aspects of different embodiments of the invention are described with reference to FIGS.

Casing 12 has a particulate filter 18 of the radial type as shown, or optionally of the axial type as known in the art, and a gas adsorption filter 20 directly or further inside. Enclosed. The NBC filter unit 10 may also have an integrated ventilation bypass 22 and an integrated ventilation bypass 22 configuring a ventilation mode or through a particulate filter 18 and a gas adsorption filter 20 configuring an NBC filtering mode. and air flow directing means, generally designated 24, selectively operable, for example, by handle 70 (FIG. 1), to direct air flow therethrough.

The internal volume of the casing 12 is four volume compartments, a primary inlet compartment 30 adjacent to the inlet 14, a primary outlet compartment 32 adjacent to at least one outlet 16, and a secondary inlet compartment 34 upstream of the particulate filter 18. and a secondary outlet section 36 downstream of the gas adsorption filter 20 . A minimum space is preferably maintained between the particulate filter 18 and the gas adsorption filter 20 to provide free air flow between the particulate filter 18 and the gas adsorption filter 20 .

Primary inlet section 30 and primary outlet section 32 are in air flow communication via integral ventilation bypass 22 when flow directing means 24 is set to ventilation mode as shown in FIG. 3 and will be described below. 5 and 7 are also applicable. In order to normally keep moisture and contaminant gases away from the gas adsorption filter, the flow directing means 24 allow the secondary inlet section 34 and the secondary outlet section 36 to be separated from the ambient by the flow directing means 24 when the flow directing means 24 is set in the ventilation mode. is hermetically sealed from

When the airflow directing means 24 is set to the NBC filtering mode as shown in FIG. 4 and is also applicable to FIGS. Primary inlet section 30 and primary outlet section 32 are in air flow communication, while primary outlet section 32 and secondary outlet section 36 are in air flow communication, while secondary inlet section 34 is in air flow communication.

As is known in the NBC filter art, there is a certain useful life after which a filter unit must be replaced even if it has not been used. Upon reaching the end of its useful life, or in the event of NBC contamination, the NBC filter unit 10, including the integrated ventilation bypass 22 and air flow directing means 24, is replaced as a single disposable unit. Replacing the entire unit contributes to operator safety by not exposing it to contaminants that may be trapped in the airflow directing means.

2-6, according to an optional embodiment of the present invention, the NBC filter unit further comprises an inner shell 38, which includes the particulate filter 18, the gas adsorption filter 20, the particulate filter It encloses a secondary inlet section 34 upstream of 18 and a secondary outlet section 36 downstream of gas adsorption filter 20 .

According to one embodiment of the invention shown in FIGS. 1-4, the NBC filter unit 10 comprises an inner shell 38 that is preferably not centered in the casing 12 to allow for more free space on one side. An inner shell 38 encloses the particulate and gas adsorption filters described above, a secondary inlet section 34 located upstream of the particulate filter 18, and a secondary outlet section 36 located downstream of the gas adsorption filter 20. ing.

According to the above embodiment, the air flow directing means, indicated generally at 24, comprises a pair of swivel flaps 26. As shown in FIG. Selection of the ventilation mode or the NBC filtering mode is accomplished using a handle 70 and a pair of mating gears 72 (FIG. 1) to rotate the flaps 26 one clockwise and the other counterclockwise a quarter turn simultaneously. performed by rotating. As shown in FIGS. 3 and 4, a spring (not shown) is provided to force the flap into one of two stable states. Ventilation bypass 22 is configured as a lateral channel 73 (FIG. 3) located at one end of the NBC filter unit in the space between inner shell 38 and casing 12 .

In normal times and even in conventional hazards, the initial position of the swivel flaps 26 is the ventilation mode (FIG. 3), where the elastomeric or elastomer-covered flaps are spring loaded. , against an opening located in the wall of the inner shell 38 , thereby blocking passage into the secondary inlet section 34 and out of the secondary outlet section 36 . Flap 26 has suitable sealing properties to protect gas adsorption filter 20 from ingress of moisture, gases, and foreign matter. During an NBC hazard, the flap 26 is rotated and pushed by the spring load on the separator fins 85 which are part of the shell 38, thereby changing the mode of operation, thus closing the path of the bypass 22 and allowing the air to pass through the NBC. Flow is forced through the particulate filter 18 and the gas adsorption filter 20 (FIG. 4) by the motorized blower (not shown) of the filtering system.

In the NBC filtering mode, the two flaps 26 are closed together, but the ventilation slots 68 formed between the two mating shell 38 halves extend through the casing 12 and into the safety chamber space. , providing double security in case the flap leaks. Vent slots 68 equalize the pressure in the portion of bypass 22 located between flaps 26 to the pressure in the safety chamber, resulting in an upstream flap facing primary inlet section 30 and a downstream flap facing primary outlet section 32. should both leak, clean air is drawn back from the safe room space through the ventilation slots 68 without endangering the safe room occupants.

One or more outlet ports 16 are provided with resilient one-way valves 77 to prevent backflow as required for proper operation of additional components (not shown) of the NBC filtering system. can be provided.

As shown in FIGS. 5 and 6, according to a second embodiment of the present invention, the NBC filter unit 10 preferably comprises a centrally located and axially movable inner shell within a casing 12. 38. The inner shell encloses a secondary inlet section 34 located upstream of the particulate filter 18 and a secondary outlet section 36 located downstream of the gas adsorption filter 20 . According to this embodiment, the air flow directing means, generally indicated at 24 , comprise a peripheral gasket 40 and radial holes 44 arranged around the primary inlet section 30 and casing segments at the secondary outlet section 36 . and a seat 42 with an associated radial hole 45 mounted approximately centrally inside 60 . Ventilation bypass 22 ( FIG. 5 ) is configured as a peripheral gap located between inner shell 38 and casing 12 .

Selection of the ventilation mode or the NBC filtering mode is performed by axially sliding the inner shell 38 fully forward (FIG. 5) or fully rearward (FIG. 6) within the casing 12 respectively. Sliding the inner shell 38 back and forth is accomplished by axially pushing or pulling at least one handle 54 projecting through a slot 56 formed in the wall of the casing segment 62 . It is understood that other mechanisms, such as push handles with spring return, eccentric transverse shafts, bolt and nut arrangements, or any other mechanism, can provide the same motion and are within the scope of the present invention. Yo. A spring or other mechanical means is provided to force the inner shell 38 into one of two stable modes of operation, thereby avoiding undesirable intermediate positions.

During operation in ventilation mode (FIG. 5), air enters primary inlet section 30, passes through holes 44 into ventilation bypass 22, and directly through primary outlet section 32 to optional one-way valve 77. into exit port 16 with .

In the NBC filtering mode (FIG. 6), ventilation bypass 22 is blocked by gasket 40 in contact with seat 42 . Air enters the primary inlet section 30, passes through the holes 44, the secondary inlet section 34, the particulate filter 18, then the gas adsorption filter 20, the secondary outlet section 36, and then through the open holes. 45 into primary exit section 32 and then to exit port 16 with optional one-way valve 77 .

A peripheral seal 81 mounted on the casing segment 62 around the hole 44 seals between the downstream primary inlet compartments 30 towards the ventilation bypass 22 and provides double security in the event that the gasket 40 leaks. do. The vent slot 68 equalizes the pressure in the bypass 22 space between the seal 81 and the gasket 40 to the pressure in the safety chamber, so that even if both the gasket 40 and the double safety seal 81 leak, Clean air is drawn back from the safe room space through the ventilation slots 68 without endangering the safe room occupants.

According to a third embodiment of the invention shown in FIGS. 7 and 8, the casing 12 is axially movable with respect to the hollow member 50 and the secondary inlet section 34 located upstream of the particulate filter 18 . and a secondary outlet section 36 located downstream of the gas adsorption filter 20 in a substantially central and sealing manner. Hollow member 50 includes a primary inlet section 30 adjacent inlet port 14 and a primary outlet section 32 adjacent outlet port 16 .

According to this embodiment, the airflow directing means 24 are formed in the radial holes 74 formed in the stationary hollow member 50 around the primary inlet section 30 and in the stationary hollow member 50 around the primary outlet section 32 . , and a radial hole 76 formed in the inner wall of the secondary outlet section 36 in combination with the circular channel 46 surrounding the hollow member 50 . The ventilation bypass 22 is constituted by radial holes 74 , 75 in the walls of the fixed hollow member 50 and a gasket-sealed circumferential channel 46 surrounding the hollow member 50 .

Selection of ventilation mode or NBC filtering mode is performed by axially sliding casing 12 fully rearward (FIG. 7) or fully forward (FIG. 8) respectively around hollow member 50. be done. Likewise, it will be appreciated that casing 12 is fixed in place and hollow member 50 is pushed or pulled against casing 12 . A spring or other mechanical means is provided to force the casing 12 into one of two stable modes of operation, thereby avoiding undesirable intermediate positions.

During operation in the ventilation mode (FIG. 7), air enters the primary inlet section 30, passes through holes 74 into the circumferential channels 46 of the ventilation bypass 22, and then passes through holes 75 directly to the primary. Pass through exit compartment 32 to exit port 16 with optional one-way valve 77 .

In the NBC filtering mode (FIG. 8), ventilation bypass 22 is closed by seal 79 sealing between circumferential channel 46 and hollow member 50 . Air enters primary inlet section 30, passes through holes 74, secondary inlet section 34, particulate filter 18, then gas adsorption filter 20, secondary outlet section 36, and then opens. It passes through hole 76 to primary outlet section 32 and outlet port 16 with optional one-way valve 77 .

A planar plug 82 having a peripheral seal 84 attached to the casing segment 60 by a spacer 86 is provided in the ventilation bypass 22 upstream of the seal 84 to provide double security should the seal 79 leak. Partially sealed. Vent hole 68 equalizes the pressure of ventilation bypass 22 volume located between seal 79 and seal 84 to the pressure of the safety chamber, so that both seal 79 and double safety seal 84 Clean air is drawn back from the safe room space through the ventilation holes 68 without endangering the safe room occupants in the event of a leak.

An option common to all embodiments of the present invention suggests that at least one of the casing 12 and shell 38, where applicable, consist of two segments permanently joined together using a rim crimp process. do.

The gas adsorption filter 20 consists of a packed bed of activated carbon particles clamped by a perforated plate 64 mounted over the layer of carbon particles. A perforated plate 64 mounted over the layer of carbon particulate was mounted thereon (schematically shown) for applying pressure to the perforated plate 64 when the segments of the casing 12 or shell 38 are brought together. loaded) by at least one spring 66 .

For double safety, part of the ventilation bypass 22 in each of the above embodiments is provided with upstream and downstream seals. A pressure equalizing vent 68 is provided between the ventilation bypass 22 and the safety chamber space. Air passage 68 provides another safety feature when the NBC system operates in the NBC filtering mode. 4, or upstream seal 81 in FIG. 6, or upstream seal 79 in FIG. 6, or the downstream seal 84 of FIG. As explained above in connection therewith, it recirculates clean air from the safe room space without drawing contaminated air through the inlet port.

The specific embodiments of the invention described above and shown in the accompanying drawings are presented for purposes of illustration only. Other variations, modifications, and applications of the present invention will readily occur to those skilled in the art. Accordingly, all such modifications are within the scope and spirit of this invention. Accordingly, the protection sought herein is as set forth in the claims below.

Claims (18)

An NBC filter unit for use in a safety room NBC filtering system comprising:
said integrated ventilation comprising a casing, at least one inlet, at least one outlet, a particulate filter and a gas adsorption filter, said NBC filter unit further comprising an integrated ventilation bypass and a ventilation mode; directing airflow internally from said at least one inlet port to said at least one outlet port via a bypass or via said particulate filter and said gas adsorption filter configuring an NBC filtering mode; and air flow directing means selectively operable to
Upon reaching the end of its useful life, or in the event of NBC contamination, said NBC filter unit, including said integrated ventilation bypass and said air flow directing means, is replaced as a single disposable unit for operator safety. An NBC filter unit characterized by: a primary inlet section adjacent to said at least one inlet, a primary outlet section adjacent to said at least one outlet, a secondary inlet section upstream of said particulate filter, and a gas adsorption filter comprising four volume sections; 2. The NBC filter unit of claim 1, further comprising a downstream secondary outlet section. 3. The NBC filter of claim 2, wherein said primary inlet section and said primary outlet section are in air flow communication via said integral ventilation bypass when said flow directing means is set in said ventilation mode. unit. 3. The secondary inlet compartment and the secondary outlet compartment of claim 2, wherein the secondary inlet compartment and the secondary outlet compartment are hermetically sealed from the environment by the flow directing means when the flow directing means are set in the ventilation mode. NBC filter unit. When said flow directing means is set to said NBC filtering mode, said primary inlet section and said secondary inlet section are in air flow communication; said primary outlet section and said secondary outlet section are in air flow communication; 3. The NBC filter unit of claim 2, wherein the primary inlet section and said primary outlet section are airflow blocked. An inner shell encloses the particulate filter, the gas adsorption filter, the secondary inlet section upstream of the particulate filter, and the secondary outlet section downstream of the gas adsorption filter. The NBC filter unit according to claim 2. 7. The NBC filter unit of claim 6, wherein said air flow directing means comprises a pair of swivel flaps and selection between said ventilation mode and said NBC filtering mode is effected by rotating said flaps simultaneously. 8. The NBC filter unit of claim 7, wherein said ventilation bypass is configured as a lateral channel located at one end of said filter unit between said inner shell and said casing. The inner shell is axially moveable within the casing, and the air flow directing means comprises a peripheral gasket, radial holes disposed about the primary inlet section, and the secondary outlet section. and a seat interlaced with radial holes generally centrally located in the casing, wherein the selection of said ventilation mode or said NBC filtering mode causes said inner shell to be fully forward or fully rearward respectively within said casing. 7. The NBC filter unit of claim 6, wherein the NBC filter unit is performed by moving axially to . 10. The NBC filter unit of claim 9, wherein said ventilation bypass is configured as a peripheral gap located between said inner shell and said casing. 10. The NBC filter unit of claim 9, wherein moving the inner shell is performed by axially pushing or pulling at least one handle projecting through a slot formed in the wall of the casing. . The casing is axially moveable relative to the hollow member and passes substantially centrally and sealingly through the secondary inlet section, the particulate filter, the gas adsorption filter, and the secondary outlet section. wherein said hollow member comprises said primary inlet section adjacent said inlet port and said primary outlet section adjacent said outlet port, said air flow directing means extending said hollow member around said primary inlet section; a radial hole formed in the hollow member around the primary outlet section; a radial hole formed in an inner wall of the secondary outlet section; 3. The NBC filter unit of claim 2 in combination with a circular channel surrounding the hollow member. 13. Selection of the ventilation mode or the NBC filtering mode is performed by axially sliding the casing fully rearward or fully forward, respectively, relative to the hollow member. NBC filter unit as described. 13. The NBC filter unit of claim 12, wherein said ventilation bypass is configured as said radial hole formed in said fixed hollow member and said circular channel surrounding said hollow member. 7. The NBC filter unit of claim 6, wherein at least one of said casing and said shell consists of two segments permanently joined together using a rim crimp process. 16. The gas adsorption filter of claim 15, wherein the gas adsorption filter comprises a packed bed of activated carbon granules, the layer of carbon granules being clamped by a perforated plate mounted over the layer of carbon granules. NBC filter unit. The perforated plate mounted over the layer of carbon particulate has at least one mounted thereon for applying pressure to the perforated plate when the casing segments or the shell segments are joined. 17. The NBC filter unit of claim 16, which is spring loaded. 2. The NBC filter unit of claim 1, wherein a pressure equalizing vent path is provided between the ventilation bypass and the safety chamber space.

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