Patent Publication Number: US-2021178197-A1

Title: Nbc filtration system with air exchange backup unit

Description:
FIELD OF THE INVENTION 
     The present invention relates to an NBC filtration system of collective protection shelters. More particularly to an NBC filtration system provided with an air exchange backup unit. 
     BACKGROUND OF THE INVENTION 
     In Israel, public constructions such as office buildings, shopping malls, industrial facilities, entertainment centers and the like, must preserve an NBC protected space for use at emergency. The protected space should include an NBC filtration system. The preserved space may be used for other periodical purposes at normal times. Commonly the space is used as meeting or waiting rooms that do not require heavy furniture and can be rapidly cleared during an emergency event. Due to the high cost per square meter of floor-space in such buildings, it is desired that the NBC filtration system would take up minimal space. 
     The regulations indicate that such public NBC filtration system should include a filter unit composed of a particulate filter and a gas adsorption filter, and an electric blower appropriate for certain rate of air exchange. Furthermore, the NBC filtration system should have an air exchange backup unit energized by human power, including a human power interface such as a hand crank for manual operation in an event of power failure. The air exchange backup unit introduces fresh air into the protection shelter using human power instead of electric power if such is not available. Typically, the air exchange backup unit includes a speed increasing gear having an input shaft manually rotated by the hand crank and an output shaft engaged to rotate the electric blower. The hand crank may be detachable in order to free space during normal times. 
     The term NBC, standing for “Nuclear Biological Chemical”, is used here at the broad interpretation, meaning one or more of: Nuclear, Biological, Radiological and Chemical. Accordingly not all of the capabilities are necessarily implemented in a filtration system. For example a filtration system providing Biological and Chemical attack protection, but none or only partial Nuclear attack protection, is yet considered an NBC filtration system. 
     Israeli patent application 244631 suggests a ventilation and filtration system for a security room, including: a blower to blow air to ventilate the security room; an air filter that is connectable to the blower to filter the air; a housing within which the air filter and the blower are enclosable; and a mechanism for raising the housing to a storage position at the ceiling of the security room so as to enable utilization of a space beneath the housing, and for lowering the housing to an operating position at the floor of the security room. 
     The suggested solution however is cumbersome and requires lowering of the entire filtration system in an event of emergency. The entire system weight may reach 100 kg, and the lifting and lowering mechanism which must enable easy operation for an average person becomes complicated by itself. 
     Israeli patent application 246827 to the present applicant, also published as PCT/IL2017/050747 describes a floor-space saving and general space saving, simple to operate NBC filtration system for collective protection shelters. According to application 246827, the NBC filtration system is contained in a space located out of a comfortable reach of the shelter occupants thus saving usable floor-space, while the means for activation, manual operation and for changing the NBC filtration system state are operated from a location within the comfortable reach of the shelter occupants. The above application also suggests basic constructional options for implementation of the invention. 
     Specifically, there is suggested an option to operate the NBC filtration system, where the NBC filtration system and the air exchange backup unit is located higher than an average person height. The option suggests that the human power interface such as hand crank or foot pedals is remotely mechanically or electrically linked to the unreachable NBC filtration system. 
     The suggested air exchange backup unit is remotely powered by a hand crank located as a separate unit at the proper height for use by an average person. The hand crank is supported to the wall at one side and optionally supported with a detachable floor stand at the other side to firmly hold the hand crank during usage. Optionally, the hand crank could be fitted to the wall only using appropriate carrying capacity bearings such that floor stand is not needed. The power is transmitted through a mechanical power transmission means such as drive-belt or chain with pulleys or sprockets fitted on the hand crank and on the electric blower shaft. 
     However, in real installations it appears that the NBC filtration system is fitted at different locations and different heights. The different locations are enforced by variations in position of the intake pipe between building constructions. Such varying locations makes it difficult to use a single drive solution for different installations. 
     Additionally, the suggested chain or belt drive lowers the efficiency of the air blow system, being external and additional to the speed increasing gear. Furthermore, the solutions provided in application 246827 are principal while more specific constructional implementations are required. 
     Accordingly there is a need to further optimize the above prior art systems in order to enable efficient power saving operation, ease of installation in different construction sites and reduced maintenance costs. 
     SUMMARY OF THE INVENTION 
     Consequently, it is a principal object of the present invention to overcome the disadvantages and limitations of prior art systems and provide an NBC filtration system of collective protection shelters having an optimized structure of an air exchange backup unit. The proposed optimized structure provides efficient operation and integration of the various elements of the air exchange backup unit, while preserving flexibility of installation. As a result filtration systems can be easily installed at different positions and orientations using a single type of air exchange backup unit. 
     According to an embodiment of the invention, there is provided an NBC filtration system mounted at a near ceiling position, comprising: a filter unit, a blower airflow coupled to the filter unit, and an air exchange backup unit mechanically coupled to the blower. The air exchange backup unit comprising a plurality of hinged segments serially linked to each other to form a foldable arm. The hinged segments are configured for transmission of rotational motion between each other. A first end of the air exchange backup unit drives the blower and a second end of the air exchange backup unit carries a detachable hand crank. Manual rotation of the hand crank rotates an impeller of the blower. The air exchange backup unit is selectively folded up at normal times. 
     According to an aspect of the embodiment each of the hinged segments is provided with a mechanical drive transmitting rotational motion from one end of the segment to the other end. 
     According to another aspect of the embodiment each link pairing the hinged segment is provided with a rotatable shaft sharing the same axis as the hinge axis. 
     According to an aspect of the embodiment, at least one of the hinged segments further comprises at least one stage of a first speed increasing transmission. 
     According to another aspect, the first end of the air exchange backup unit is swiveably attached to an electric motor driving the blower. Manual rotation of the hand crank rotates a shaft of the electric motor at substantially a rated speed of the electric motor. 
     According to yet another aspect, the second end of the air exchange backup unit is firmly attachable to a wall of the protection shelter at a convenient position for manual cranking of the hand crank. 
     According to another aspect of the invention, a method of introducing fresh air into a protection shelter during an event of a power failure is provided. The method comprising one or more of the steps: 
     a. Providing a near ceiling mounted NBC filtration system comprising: a filter unit; a blower driven by an electric motor; an air exchange backup unit having a first end swiveably attached to said electric motor; and a detachable hand crank selectively fitted to a second end of said air exchange backup unit; said air exchange backup unit comprising a plurality of hinged segments serially linked to each other to form a foldable arm, the hinged segments are configured for transmission of rotational motion between each other.
 
b. Expanding the air exchange backup unit in an event of a power failure.
 
c. Attaching the second end of the air exchange backup unit to a wall of a protection shelter at a convenient position for manual cranking of said hand crank.
 
d. Attaching the detachable hand crank to the second end of the air exchange backup unit.
 
e. And cranking the hand crank while the power failure continues.
 
     The method may further comprise one or more of the steps: 
     f. Stopping the cranking operation when electric power is revived.
 
g. Detaching the detachable hand crank from the second end of the air exchange backup unit.
 
h. Detaching the second end of the air exchange backup unit from the wall of the protection shelter.
 
i. And folding up the air exchange backup unit.
 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention and a way it may be carried out in practice, will be understood with reference to the following illustrative figures, by way of non-limiting example only, in which like reference numerals identify like elements, and in which: 
         FIG. 1  is a front view of an NBC filtration system using an air exchange backup unit made according to an embodiment of the invention; 
         FIG. 2  is a perspective view of the NBC filtration system of  FIG. 1 ; 
         FIG. 3  is a perspective view of the NBC filtration system of  FIG. 1 , demonstrating the air exchange backup unit halfway folded; 
         FIG. 4  is a perspective view of the NBC filtration system shown in  FIG. 3  with a mounting bracket and cover of the blower removed; 
         FIG. 5  is a perspective rear view of the air exchange backup unit and blower; 
         FIG. 6  is perspective schematic view of an open frame type air exchange backup unit; 
         FIG. 7  is an exploded perspective view of two of the segments shown in  FIG. 6 ; 
         FIG. 8  is an exploded perspective view of the air exchange backup unit and blower of  FIG. 5 ; 
         FIG. 9  is a perspective skeleton view demonstrating the electrical and manual drive systems of the blower and the air exchange backup unit; 
         FIG. 10  is a perspective view of an air exchange backup unit made according to another embodiment of the invention; 
         FIG. 11  is a perspective view of an air exchange backup unit made according to yet another embodiment of the invention; and 
         FIG. 12  is a flowchart demonstrating a method of operation of the NBC filtration system. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Several terms relating to the present invention will be defined prior to describing the invention in detail. It should be noted that the following definitions are used throughout this application. 
     For the purpose of the present invention, directional terms such as “top”, “bottom”, “below”, “above”, “left”, “right”, “horizontal”, “vertical”, “upper”, “lower”, “up”, “down”, etc. are merely used for convenience in describing the various implementations of the present invention. The assemblies demonstrating the present invention may be oriented in various ways. 
     For the purpose of the present invention, the term “plurality” refers to two or more than two. 
     For the purpose of the present invention, the term “hinged element” refers to an element provided with at least one hinge or having at least one hinge point enabling swivel of the element about the hinge point. 
     For the purpose of the present invention, the term “segment” refers to one of the parts into which an assembly is separates or is divided. 
     For the purpose of the present invention, the term “air exchange backup unit” refers to a device, energized by human power, configured for introducing fresh air into a protection shelter during an event of electric power failure. 
     For the purpose of the present invention, the term “foldable” refers to a structure that can be folded down into a small space when it is not being used. 
     For the purpose of the present invention, the term “inverted tooth chain” or “silent chain” refers to a type of drive chain with teeth formed on its links to engage with standard or modified gear wheels. 
     For the purpose of the present invention, the term “pitch” refers to the distance between successive corresponding physical occurrences, such as rollers in a roller chain. 
     The term “NBC” is used throughout this text as a general abbreviate for all kinds of hazardous agents including any one of Nuclear, Biological, Chemical and Radiological threats or any combination thereof. Such combinations may include for instance: NBC, CBRN, CBR, BC, B and C. 
     With reference to the figures, according to one embodiment of the invention, there is shown in  FIG. 1  a front view of an NBC filtration system for collective protection shelters generally referenced  10 .  FIG. 2  depicts a perspective view of a similar NBC filtration system with dashed lines representing nearby internal boundary of the protection shelter. Visible in  FIGS. 1 and 2 , are a prefilter  14 , a filter unit  30  and an air exchange backup unit generally referenced  20 . The prefilter  14 , intended to hold coarse particles, is fitted to an air intake embedded in the concrete wall of the building during construction. The air intake may further include a blast valve as known in the art. The filter unit  30  typically includes a particulate filter and a gas adsorption filter. The filter unit  30  may further include an internal bypass and a change-over valve (not shown) which are out of the scope of the present invention. Further shown in  FIG. 4  is a blower  40  airflow coupled to the filter unit  30 . The blower  40  is typically covered by a cover  32  serving also as a mounting bracket fixing the blower  40  to the wall of the protection shelter. The air exchange backup unit  20  is mechanically coupled to the blower  40  and manually operated in an event of power failure to power the blower  40  by transmission of rotational motion which rotates an impeller  76  ( FIG. 9 ) of the blower  40 . 
     According to an embodiment, the blower  40  is normally driven by an electric motor  42  as long as electric power is available. The air exchange backup unit  20  may be mechanically coupled to the blower  40  directly, or through the electric motor  42  as will be explained herein below. The air exchange backup unit comprises a plurality of hinged segments, here shown by a way of example with three segments  22 ( a, b  and  c ) serially linked to each other. The linked hinged segments forming a foldable arm, shown partially folded in  FIGS. 3 and 4 . 
     With reference to  FIG. 5 , a first end  24  of the air exchange backup unit  20  is swiveably attached to the electric motor  42  driving the blower  40 . During operation of the air exchange backup unit, in an event of power failure, rotational motion is transmitted from the hand crank  28  through the hinged segments  22 ( a, b  and  c ) as will be hereinafter explained, typically through an unidirectional freewheel, to a shaft  44  ( FIG. 8 ) of the electric motor  42 . 
     A second end  26  of the air exchange backup unit  20  carries a detachable hand crank  28 . Rotation of the hand crank  28  at normal manual operation of about 40 rpm, rotates the shaft  44  of the electric motor  42  at substantially a rated speed of the electric motor. The second end  26  of the air exchange backup unit  20  is firmly attachable for instance by a dedicated fixed bracket  60  to a wall of the protection shelter at a convenient position for manual cranking of the hand crank. The air exchange backup unit  20  may selectively be folded up at normal times as shown in  FIGS. 3 and 4 . 
     With reference to  FIGS. 3 and 4 , the air exchange backup unit  20  is shown in a partially folded state, in which the hinged segments  22  are folded about the hinges to form a Z letter shape. It will be understood that the segments may be further folded up to a point where the lower segment  22   a  is in contact with the upper segment  22   c  such that the air exchange backup unit  20  is hidden behind the cover  32  serving also as a mounting bracket of the blower  40 . As a result, the air exchange backup unit  20  practically turns invisible to the occupants of the protection shelter. As shown in  FIG. 2  the NBC filtration system  10  as a whole is fitted to a wall of the protection shelter near the ceiling. Accordingly, during normal times, when the air exchange backup unit  20  is folded up, the NBC filtration system  10  does not interfere with regular activity taking place in the protection shelter. 
     As mentioned in the background, in real installations the NBC filtration system is fitted at different locations and different heights. The different locations are enforced by variations in position of the intake pipe between building constructions. The embodiments of the present invention solves this difficulty by simple adaptation of the air exchange backup unit  20  folding arm construction to any installation position. It should be noted that although shown vertically oriented in  FIGS. 1 and 2 , the air exchange backup unit  20  may compensate for different mounting positions by being partially folded or diagonally fixed to the wall of the protection shelter even during operation at power failure. The above described rotational motion is transmitted from the hand crank  28  through the hinged segments  22 ( a, b  and  c ) with the same efficiency in any angular settlement of the hinged segments. 
     As mentioned above, during operation of the air exchange backup unit  20 , in an event of power failure, rotational motion is transmitted from the hand crank  28  through the hinged segments  22  to the electric motor  42 . The way of transmittal of the rotational motion will be explained with reference to  FIGS. 6 and 7 . According to an embodiment there are shown in  FIG. 6  three hinged segments  22  linked to each other. The hinged segments use a simple open construction exposing the drive system. Each of the hinged segments  22  is provided with a mechanical drive  52  transmitting rotational motion from one end of the segment to the other end. For example by a pair of sheaves, pulleys or sprockets, each fitted at one end of the segment, rotatively connected by a belt or chain drive. Alternately a pair or plurality of mating gears may be used. Optionally one or all of the mechanical drives  52  may define a transmission ratio or a transmission stage. According to an optional embodiment, at least one of the hinged segments  22  comprises at least one stage of a first speed increasing transmission. Alternately the first speed increasing transmission may be located separately at one end of the air exchange backup unit  20 , as will be hereinafter demonstrated. 
     In addition to the above mechanical drive, transmitting rotational motion from one end of the segment to the other end, the hinged segments  22  are configured for transmission of rotational motion between each other. This is shown with more clarity in  FIG. 6 , where two segments  22  of  FIG. 5  are shown exploded. The structural elements  53  are made as a flat elongated body provided with openings  54  at both ends. An integral shaft bearing  55  (also known as water pump bearing), or a dedicated bearing assembly having a shaft  56  passing through and extending at both sides, is provided to each of the openings  54 . The outer diameter of the bearing  55  or the housing of the bearing  55  serves as a hinge linking the structural elements  53 . The structural elements  53  are swiveable about the bearing  55 , by the bearings  55  having a free fit in the openings  54 . A retaining clip may be further provided to hold the bearing  55  in position. Sprockets  57 ,  58  are fitted to both ends of the shaft  56  of bearing  55 . The sprockets  57 ,  58  may be fixedly fitted to the shaft  56  by a press fit, a key, a flat face, a locking screw or any other locking element that prevents free rotation of the sprockets  57 ,  58  about the shaft  56 . As a result, the shaft  56  is transmitting rotational motion between sprocket  58  fitted to one end of the shaft  56  and sprocket  57  fitted to the other end of the shaft  56 . Sprocket  58  is driven by mechanical drive  52   a  of segment  22   a  as described above. And Sprocket  57  is driving the mechanical drive  52   b  of segment  22   b . It will be noted that the shaft  56  shares the same axis as the hinge between the segments  22   a ,  22   b  defined by bearing  55 . Accordingly, each of the hinges pairing the hinged segments  22 ( a, b  and  c ) ( FIG. 6 ), is provided with a rotatable shaft  56  transmitting rotational motion from one segment to the other and sharing the same axis as the hinge axis. The shaft  56  transmitting rotational motion between the segments  22 ( a, b  and  c ). The ratio between diameter or teeth number of sprockets  57  and  58  indicates the speed increasing amount of each stage or mechanical drive of each segment. 
       FIG. 5 , depicts a perspective rear view of the air exchange backup unit  20  and blower  40  taken out of the NBC filtration system. The air exchange backup unit generally referenced  20  is shown halfway folded. The second end  26  of the air exchange backup unit  20  is provided with a circumferential protrusion  36  and a locking pin  34 . The second end  26  may be firmly attached to the dedicated fixed bracket  60  ( FIG. 4 ), by engagement of the circumferential protrusion  36  into a compatible pocket  62  provided with circumferential recess  64  of the dedicated fixed bracket  60 . The locking pin  34  may be engaged into a locking hole  66  of the bracket  60  to prevent movement of the second end  26  of the air exchange backup unit  20 , during operation of the hand crank  28 . The route of directing the second end  26  of the air exchange backup unit  20  into the fixed bracket  60  is demonstrated by an arrow marked  68  ( FIG. 4 ). It will be understood that other means for firmly attaching the second end  26  of the air exchange backup unit  20  to a wall of the protection shelter may be provided. Such other means may include a mortise and tenon, hand operated fasteners, lever latching fasteners, cone couplers and other known means. 
     With reference to  FIGS. 4 and 5 , a suction port  46  of the blower  40  is airflow coupled to the filter unit  30  through a flexible duct  70 . The blowout port  48  of blower  40 , is open to the space of the protection shelter such that filtered air is spread into the space without restriction. The blower  40  is driven by the electric motor  42  either directly or through a second speed increasing transmission  74  as shown in  FIG. 4 . For economic and long term reliability reasons a standard 4-pole induction motor  42  may be preferable. 
     With reference to  FIG. 8 , the blower  40  and motor  42  are moved from position in relation to the air exchange backup unit  20 . Covers  38   a  and  38   c  of segments  22   a  and  22   c  respectively are also moved from position to expose transmission stages  72   a  and  72   c  of the first speed increasing transmission of air exchange backup unit generally referenced  20 . It will be noted that according to the embodiment the structural elements are made with a cavity  23  and provided with a cover  38  protecting the user from contact with moving drive elements. According to the embodiment, each of the hinged segments  22  is provided with a mechanical drive  72 ( a, b  and  c ) transmitting rotational motion from one end of the segment to the other end. According to the shown embodiment, each of the hinged segments  22 ( a, b  and  c ) includes one stage of the first speed increasing transmission of the air exchange backup unit  20 . 
     With reference to  FIG. 9 , an air exchange backup unit is shown with the structural elements removed, exposing the transmission elements. According to an embodiment, the first speed increasing transmission is configured as a roller chain drive including 3 stages  72 ( a,b  and  c ). Each of the links pairing the hinged segment  22 ( a, b  and  c ) is provided with a rotatable shaft  88 ,  98  sharing the same axis as the hinge axis. Obviously any other number of hinged segments and transmission stages may be used, however for reason of efficiency, the optimal number is the minimum number that delivers the desired speed increasing ratio. The pitch size of the roller chain drive is selected between 6 mm and 10 mm. It will be understood that the different stages of the first speed increasing transmission may accept different pitch size due to the different moment and rotational speed related to each of the stages. 
     In more detail, yet with reference to  FIG. 9 , during manual operation of the hand crank  28  in an event of power failure, a first sprocket  82  is directly rotated by the hand crank  28  through an input shaft  81 . The first sprocket  82  rotates a second sprocket  84  preferably smaller than the first sprocket  82 , via a first drive chain  86 . The first sprocket  82 , first drive chain  86  and second sprocket  84  are forming together the first stage  72   a  of the first speed increasing transmission of air exchange backup unit  20 . As shown in  FIG. 9 , the second sprocket  84  is mounted on one end of a first intermediate shaft  88  defining also a hinge axis between the first segment  22   a  and the second segment  22   b  of the foldable arm constituting the air exchange backup unit  20 . A third sprocket  92  is mounted on the other end of the first intermediate shaft  88 , thus accepting the same rotational speed as the second sprocket  84 . 
     The third sprocket  92  rotates a forth sprocket  94  preferably smaller than the third sprocket  92 , via a second drive chain  96 . The third sprocket  92 , second drive chain  96  and fourth sprocket  94  are forming together the second stage  72   b  of the first speed increasing transmission of air exchange backup unit  20 . The fourth sprocket  94  is mounted on one end of a second intermediate shaft  98  defining also a hinge axis between the second segment  22   b  and the third segment  22   c  of the foldable arm constituting the air exchange backup unit  20 . A fifth sprocket  102  is mounted on the other end of the second intermediate shaft  98 , thus accepting the same rotational speed as the fourth sprocket  94 . 
     The fifth sprocket  102  rotates a last sprocket  104  preferably smaller than the fifth sprocket  102 , via a third drive chain  106 . The fifth sprocket  102 , third drive chain  106  and last sprocket  104  are forming together the third stage  72   c  of the first speed increasing transmission of air exchange backup unit  20 . 
     The last sprocket  104  is fitted to a first end  107  of the motor shaft  44  through an unidirectional freewheel also known as freewheel clutch or freewheel bearing. The unidirectional freewheel permits rotation of the motor shaft  44  by the air exchange backup unit  20 , but prevents rotation of the first speed increasing transmission elements by freewheeling when the motor is electrically energized. It will be understood that different types of unidirectional or clutch mechanisms can be used alternately, for instance a ratchet mechanism or a wound spring mechanism as known in the art. 
     Yet with reference to  FIG. 9 , The second speed increasing transmission  74 , if applicable, comprises a first sprocket  110  fixed to a second end  108  of the motor shaft  44 , a drive chain  112 , and a second sprocket  114 , smaller than the first sprocket  110 . The second sprocket  114  of the second speed increasing transmission  74  is fitted to a first end of a blower shaft  116 . The second end of the blower shaft  116  carries an impeller  76  of the blower  40 . 
     The second speed increasing transmission  74  driving the blower  40  is capable of driving the impeller  76  of the blower at a rotational speed of above 3000 rpm using a motor  42  of the known 4-pole induction type. To minimize transmission losses, the second speed increasing transmission  74  may be a low friction, efficient drive system selected between some options including: a multi-groove V belt drive, toothed belt drive, a roller chain drive or an inverted tooth chain drive also known as silent chain. Due to the high speed and low torque of this second speed increasing transmission, if a roller chain drive or a silent chain drive is utilized, than the pitch size is selected between 3 mm and 6 mm. It will be understood that other transmission types can be used such as direct gear drive, single or multiple V belt drive, flat belt drive and ladder chain drive. 
     With reference to  FIG. 10  there is shown a different embodiment where four segments  22 ( a, b, c  and  d ) are used. Each of the segments is provided with one stage  52 ( a, b, c  and  d ) of the first speed increasing transmission. Due to a possible higher overall transmission ratio than that of the three segment construction, there is no need for a second speed increasing transmission and a motor  42  of rated speed preferably higher than 3000 rpm is directly driving the blower  40 . The air exchange backup unit  20  is driving the other end of the shaft of motor  44 , in an event of power failure and manual operation of the hand crank  28 . 
     With reference to  FIG. 11  there is shown an additional embodiment where only two segments  22   a  and  22   b  are used. As shown in the embodiment of  FIG. 11 , the sprockets  59  at both ends of each segment  22   a  and  22   b  are of the same size. Accordingly there is no speed increasing in the air exchange backup unit  20 . For the speed increasing task there is provided a dedicated speed increasing transmission  39  which is fitted between the air exchange backup unit  20  and the motor  42 . It will be understood however that any combination of speed increasing transmission stages may be used. The air exchange backup unit  20  may be provided with certain first speed increasing ratio while the dedicated speed increasing transmission  39  provides an additional second speed increasing ratio calculated to provide the overall required speed increasing ratio. 
     The present invention seeks protection regarding the device as described above, as well as the method steps taken to accomplish the desired result of introducing fresh air into the protection shelter during an event of a power failure, using a near ceiling mounted NBC filtration system and an air exchange backup unit of a foldable arm structure. 
     Accordingly and with reference to  FIG. 12 , a method is provided comprising one or more of the steps below: 
     a. Providing a near ceiling mounted NBC filtration system comprising: a filter unit; a blower driven by an electric motor; an air exchange backup unit having a first end swiveably attached to the electric motor; and a detachable hand crank selectively fitted to a second end of the air exchange backup unit. The air exchange backup unit comprising a plurality of hinged segments serially linked to each other to form a foldable arm. The hinged segments are configured for transmission of rotational motion between each other.
 
b. Expanding the air exchange backup unit in an event of a power failure. Indicated as activities  120  and  122  of the flowchart of  FIG. 12 .
 
c. Attaching the second end of the air exchange backup unit to a wall of a protection shelter at a convenient position for manual cranking of the hand crank. Indicated as activity  124  of the flowchart.
 
d. Attaching the detachable hand crank to the second end of the air exchange backup unit. Indicated as activity  126  of the flowchart.
 
e. Cranking the hand crank while said power failure continues. Indicated as activity  128  and decision  130  of the flowchart.
 
The method may further include the steps of:
 
f. Stopping the cranking operation when electric power is revived. Indicated as activity  132  of the flowchart.
 
g. Detaching the detachable hand crank from the second end of the air exchange backup unit. Indicated as activity  134  of the flowchart.
 
h. Detaching the second end of the air exchange backup unit from the wall of the protection shelter. Indicated as activity  136  of the flowchart.
 
i. Folding up the air exchange backup unit. Indicated as activity  138  of the flowchart.
 
     It will be understood that while activities  120  to  128  of the flowchart are required to start manual operation of the air exchange backup unit, the following activities  132  to  138  are optional or may be carried out at a later time or by a dedicated maintenance person that may further check the system before bringing it back to the folded state. 
     It will be appreciated that the specific embodiments of the present invention described above and illustrated in the accompanying drawings are set forth merely for purposes of example. Other variations, modifications, and applications of the present invention will readily occur to those skilled in the art. It is therefore clarified that all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below.