Abstract:
An air sampling system for a low-temperature space is disclosed. The air sampling system includes an air sampling pipe for passing sampling air to an air sampling device, and a sampling conduit extending from the low-temperature space to outside the low-temperature space. The sampling conduit is connected to the sampling pipe. The sampling conduit is selectively accessible from outside the low-temperature space for removal of ice build-up within the sampling conduit. Also disclosed is a kit for an air sampling system. Also disclosed is a method, computing system, air-sampling device and air monitoring system that evaluates an air sampling network.

Description:
RELATED APPLICATION 
       [0001]    This application claims the benefit of Australian provisional patent application 2013900547, filed 19 Feb. 2013, which is incorporated herein by reference for all purposes. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to an air monitoring and/or sampling for a low-temperature space. In a preferred form, although not exclusively, the invention relates to an aspirating smoke detection system for a refrigerated storage facility. However, it will be understood that the invention may have application to other types of air monitoring systems e.g. gas detection systems, aerosol detection of biological material or other types of smoke detection systems that may be used in low temperature spaces. The invention also relates to a kit for an air sampling system for a low-temperature space. 
         [0004]    2. Discussion of the Related Art 
         [0005]    Cold environments, and in particular refrigerated storage facilities, are unique and challenging environments for any smoke detection system. They are characterised by varying low temperatures and frequent traffic flow from workers transporting machinery in and out of the rooms. While most have some form of fast acting automatic doors or plastic barrier curtains to limit warm air ingress, it is inevitable that warm air will enter the room. This constant traffic flow with regular warm air ingress often creates condensation within the rooms and, in situations where the surrounding temperature is below 0 degrees Celsius icing occurs. Icing tends to form on any and all ceiling mounted equipment and structures, generally within close proximity to the entry points. 
         [0006]    Smoke detection systems in refrigerated storage facilities are known. Aspirating smoke detection systems generally have a sampling pipe network with a number of sampling points to draw sampling air for testing. These sampling points are generally positioned on the ceiling or walls of the refrigerated space. However, over time, with warm air ingress, the sampling points and associated pipes can become blocked with ice. This causes air flow issues and inoperative detection of smoke. 
         [0007]    The maintenance required to rectify this problem (i.e. unblocking of holes or pipes) can be very costly. In some instances, the simplest known solution is to remove the section of pipe closest to the sampling point and fit a new pipe section. In addition, access to equipment within the refrigerated storage facility may become inconvenient during repairs. 
         [0008]    Similar problems exist for air sampling systems for other low-temperature environments, such as cold outdoor environments. Some of the condensation related problems begin to arise at temperatures about 4 degrees Celsius (or possibly higher if certain conditions exist), and typically get worse as the temperature drops down to, or below the freezing point of water, 0 degrees Celsius. It is therefore an object of the present invention to provide an air sampling system and a kit for an air sampling system which overcomes or at least ameliorates one of the abovementioned problems associated with low-temperature environments, especially refrigerated environments. 
         [0009]    Reference to any prior art in the specification is not, and should not be taken as, an acknowledgment or any form of suggestion that this prior art forms part of the common general knowledge in Australia or any other jurisdiction or that this prior art could reasonably be expected to be ascertained, understood and regarded as relevant by a person skilled in the art. 
       SUMMARY OF THE INVENTION 
       [0010]    In accordance with a first aspect of the present invention there is provided, an air sampling system for a low-temperature space, the air sampling system including: an air sampling pipe for passing sampling air to an air sampling device; a sampling conduit extending from an entry port from the low-temperature space to outside the low-temperature space; the sampling conduit being connected to the sampling pipe, wherein the sampling conduit is selectively accessible from outside the low-temperature space for removal of ice build up within the sampling conduit. 
         [0011]    The sampling conduit is preferably a straight length of conduit of sufficient length to extend through a partition, wall or ceiling defining a boundary of the low-temperature space, as the case may be. Thus, the conduit has an entry port within the low-temperature space and an exit port external to the low-temperature space. The entry port may be “within” the low-temperature space by being at the boundary of the low-temperature space, for example by being a hole in the partition that faces the low-temperature space. 
         [0012]    The access to the sampling conduit is preferably in line with the longitudinal axis of the sampling conduit to enable line-of-sight visual inspection and also to enable the insertion of a rod or similar instrument to remove ice build up, which typically occurs at the entry port of the sampling conduit inside the low-temperature space, i.e. at the sampling point. For this reason, the entry port of the sampling conduit is preferably at least the same dimension (in terms of cross-section) as the access opening. Typically, for ease of construction and cleaning-access, the sampling conduit will have a continuous cross-section. Another feature is a bell or dome shaped nozzle at the entry port of the sampling conduit. Typically the sampling conduit is formed of cylindrical pipe, preferably plastic and typically of about 25 mm in diameter. The entry port may be coated with silicone to prevent ice build up. Insulation of the sampling conduit is also possible. The sampling conduit may be a one-piece construction but this need not be the case. 
         [0013]    Preferably, the air sampling system includes a restrictor, such as a small entry port or restriction fitting, which is outside the low-temperature space. Most preferably the restrictor is positioned proximate an end of the sampling conduit, or downstream thereof. In some cases the restrictor may be located in or near the sampling pipe. 
         [0014]    The sampling conduit may be selectively accessible from outside the low-temperature space through the use of an access opening. This may be in the form of an access hatch such as a sliding or hinged closure. Preferably any such access hatch has a self-closing feature. 
         [0015]    In one form of the invention, the sampling conduit is connected to the sampling pipe with an access opening formed therein. In a preferred form of the invention, the sampling pipe connects to an exit port on the outside of the sampling conduit by means of a connection assembly on the downstream end of the sampling conduit such that the connection assembly which is selectively removable from the exit port of the sampling conduit. In this embodiment, it will be understood that the sampling pipe may have a number of connection assemblies and sampling conduits arranged at spaced intervals along the sampling pipe to draw air from the low-temperature space at a number of respective spaced sampling points. The invention may include more than one sampling pipe. For example, there may be a sampling pipe network arranged in spaced rows, establishing a grid pattern of sampling points within the low-temperature space. 
         [0016]    The selectively removable connection assembly may be or include a flexible connector pipe. The connection assembly preferably either additionally or alternatively includes a fitting, such as an adaptor, union or T-piece, that fits to the sampling pipe and also joins directly or indirectly to the sampling conduit. The connection assembly has a restriction fitting at a mating portion or end which is connectable with the exit port of the sampling conduit and selectively removable therefrom. The restriction fitting may be defined by a separate or separable end piece of the connection assembly or may be integrally formed with the connection assembly. 
         [0017]    The restriction fitting of the connection assembly includes a restrictor, for example in the form of a small entry port, for sampling air and defining the flow rate from the low-temperature space, through the sampling conduit, to the sampling pipe. The restrictor may be located at an end of the restriction fitting which mates with the sampling conduit. For example, the restrictor may be comprised of a hole or holes forming a small entry port at the end of the restriction fitting, whereby the end is closed but for the hole(s). Alternatively, the restrictor may be downstream from the end of the connection assembly that mates with the sampling conduit. In either case, it will be understood that the restrictor is selectively removable with the connection assembly from the sampling conduit, enabling access to the full cross-section of the sampling conduit to allow for cleaning of the conduit by pushing debris and/or ice through the upstream end of the sampling conduit, i.e. the end that faces the low-temperature space. 
         [0018]    The sampling conduit is preferably shaped so that the cross section of the sampling conduit&#39;s duct remains substantially constant (or increases rather than decreases) from its downstream end to its upstream end, so that the ice or debris does not clog at its upstream end when pushed through the sampling conduit during cleaning. 
         [0019]    It is appreciated that since the restrictor forms part of the connection assembly, the restrictor may be easily inspected and, if necessary, cleaned or replaced. This is in contrast with arrangements in which the restrictor is integral to the sampling conduit or only is accessible only from within the low-temperature space (e.g. by forming at least part of the sampling hole in the low-temperature space). 
         [0020]    It is also appreciated that the restrictor may be a collection of apertures, rather than a single aperture, forming the small entry port. The restrictor may cause restriction, at least in part, by increasing turbulent flow in comparison with flow either side of the restrictor. 
         [0021]    The restriction fitting may include one or more apertures which are closable when the connection assembly is assembled correctly to the sampling conduit. Preferably these apertures are large in comparison to the small entry port. The relatively large apertures which are closed when the connection assembly and sampling conduit are properly reassembled, enable detection of mis-assembly of the connection assembly with the sampling conduit. If the connection assembly and the sampling conduit are not properly reassembled then the apertures simulate a broken pipe condition which should trigger an urgent flow fault in the air sampling device, e.g. the smoke detector unit. This safeguards against inadvertent removal of the connection assembly from the sampling conduit, improper reassembly or simply the act of forgetting to reassemble the sampling conduit with the connection assembly. 
         [0022]    In a preferred form of the invention, the one or more large apertures are formed in the side wall of the restriction fitting, being closed by contact with the inside of the side wall of the sampling conduit. Preferably, there are two diametrically opposed apertures. The apertures may be round although other shapes are possible. 
         [0023]    In one embodiment, the restriction fitting also includes a flanged end opposite the closed end of the connection assembly. This preferably acts as a stop for insertion of the connection assembly into the sampling conduit, to ensure that the connection assembly and sampling conduit are correctly reassembled. 
         [0024]    In one form of the invention, the restriction fitting includes a fitting portion that is formed by any union or coupling part or assembly for joining one pipe to another. However, preferably, the fitting portion has a first component that seals with the sampling conduit, a second component that seals with either a sampling pipe or a component such as a connector pipe that is in fluid communication with the sampling pipe. The restriction fitting also includes a fastening component that seals together the first and second components. Preferably the fastening is by a threaded connection to one of the first and second components. Preferably the seal between the first and second components is provided by at least one O-ring, gasket etc. that is between the first and second components. 
         [0025]    Preferably, the restrictor is integral to or held by the fitting portion. Preferably, the restrictor acts as to limit flow through the sampling conduit to a pre-determined flow-rate. Preferably the restrictor is held between the first component and the second component when the fitting portion is assembled. In one embodiment the restrictor is a flow-restricting washer or orifice-plate, which preferably has an inner diameter that is less than the inner diameter of the sampling conduit and of the connection assembly downstream and upstream from the restrictor. 
         [0026]    In accordance with a second aspect of the present invention there is provided air sampling system for a low-temperature space, the air sampling system including: an air sampling pipe for passing sampling air to an air sampling device; a sampling conduit extending from the low-temperature space to outside of the low-temperature space, the sampling conduit being connectable to the sampling pipe through a connection assembly which is removably connectable with an exit port of the sampling conduit, outside of the low-temperature space, wherein the removable connection assembly includes: (i) a restrictor for restricting flow of sampling air, the restrictor having a first characteristic flow-impedance, and (ii) a passageway between the restrictor and the sampling pipe, wherein the passageway has a second characteristic flow-impedance that is less than the first characteristic flow impedance. 
         [0027]    Preferably, the location of the restrictor in a removable connection assembly facilitates inspection and any necessary clearing of the small entry port. Any of the other features described above in connection with the first aspect of the invention may also be applied. For example, the removable connection assembly may include one or more relatively larger apertures and/or a flanged end opposite the substantially closed end. The connection assembly may include a connector pipe extending between the air sampling pipe and the sampling conduit. In another embodiment, the connection assembly may directly connect the sampling conduit to the sampling pipe, without including an intermediate connector pipe. 
         [0028]    In a third aspect of the present invention there is provided an air sampling system for a low-temperature space, the air sampling system including: an air sampling pipe for passing sampling air to an air sampling device; a sampling conduit extending from the low-temperature space to outside of the low-temperature space, the sampling conduit being connectable to the sampling pipe through a connection assembly which is removably connectable with an exit port of the sampling conduit, outside of the low-temperature space, wherein the removable connection assembly includes: (i) a restrictor having an opening having a first cross-sectional area for restricting flow of sampling air, and (ii) a passageway between the restrictor and the sampling pipe, wherein the passageway has a minimum cross-sectional area that is greater than the first cross-sectional area. 
         [0029]    In accordance with a fourth aspect of the present invention, there is provided an air sampling system for a low-temperature space, the air sampling system including: 
         [0030]    an air sampling pipe that runs outside the low-temperature space for passing sampling air to an air sampling device, wherein when the sampled air is in the sampling pipe the sampled air is above a temperature that is above the freezing point of water and also above the temperature of the low-temperature space; and 
         [0031]    a sampling conduit extending from the low-temperature space to the sampling pipe, for collecting air sample from the low-temperature space; 
         [0032]    a restrictor having a characteristic flow impedance for determining a flow-rate of the sampled air through the sampling conduit, wherein the restrictor is situated between the low-temperature space and the sampling pipe, at a location sufficiently warm to prevent water vapour from causing a temperature-related blockage at the restrictor. 
         [0033]    In one embodiment the restrictor is part of the sampling conduit. In another embodiment the air sampling system further includes a connection assembly that connects the sampling conduit to the sampling pipe, wherein the restrictor is part of the connection assembly. The restrictor may be integrally formed with the sampling conduit or connection assembly. 
         [0034]    The temperature-related blocking could be blocking caused by condensation, and especially freezing, of the water vapour on the restrictor. 
         [0035]    Preferably for this and all other aspects of the invention, the low-temperature space is a space having a temperature of +4 degrees Celsius or below. Such a low-temperature space may advantageously be a refrigerated space, preferably enclosed by surrounding wails, a floor and a ceiling. 
         [0036]    In the case of the low-temperature space being a refrigerated space, the temperature of the low-temperature space is preferably between −40 degrees Celsius and +4 degrees Celsius, but generally is at or around −25 degrees Celsius. Whereby the low-temperature space is below 0 degrees Celsius, it is preferable for the restrictor to be placed in a warmer environment at a location sufficiently far from the low-temperature space so as to prevent water vapour, sampled from the low-temperature space, from freezing on the restrictor. In one embodiment, the restrictor is situated at least 30 cm from the interior of the refrigerated space. Preferably, the restrictor is situated at least 15 cm, and preferably between 15 and 25 cm, from an outside surface of a wall panel or partition that insulates the low-temperature space. In addition to the flow rate being determined by the characteristic impedance of the flow restrictor, the flow rate may also determined by a pressure controlled by a pump or fan. However, optionally, the characteristic flow impedance of the restrictor may be such that the restrictor acts a flow-limiting device. 
         [0037]    In accordance with a fifth aspect of the present invention, there is provided a kit for an air sampling system for a low-temperature space, the kit including: a sampling conduit to extend from the low-temperature space to outside the low-temperature space, the sampling conduit having an entry port and an exit port; and a connection assembly which is removably connectable with the exit port, at least one of the connection assembly and the sampling conduit having one or more apertures which are closable by the side wall(s) of the other of the connection assembly and the sampling conduit when the connection assembly is correctly connected with the sampling conduit. 
         [0038]    Any of the features described above in connection with other aspects of the invention may be applied to the fourth aspect of the invention. 
         [0039]    In accordance with a sixth aspect of the present invention, there is provided, a kit for an air sampling system for a low-temperature space, the kit including: 
         [0040]    a sampling conduit to extend from the low-temperature space to outside the low-temperature space, the sampling conduit having an entry port and an exit port; and 
         [0041]    a connection assembly which is removably connectable with the exit port for connecting the sampling conduit to a sampling pipe, the connection assembly having: (i) a restrictor for restricting flow of sampling air, the restrictor having a first characteristic flow-impedance, and (ii) a passageway between the restrictor and the sampling pipe, wherein the passageway has a second characteristic flow-impedance that is less than the first characteristic flow impedance. 
         [0042]    Preferably, restrictor has an opening having a first cross-sectional area for determining first characteristic impedance and the passageway has a minimum cross-sectional area that is greater than the first cross-sectional area, so that the second characteristic impedance is less than the first characteristic impedance 
         [0043]    In one embodiment the restrictor is a substantially closed end of the connection assembly that has a small entry port for sampling air. 
         [0044]    In a seventh aspect of the present invention, there is provided a kit for an air sampling system for a low-temperature space, the kit including: 
         [0045]    a sampling conduit to extend from the low-temperature space to outside the low-temperature space, the sampling conduit having an entry port and an exit port; and 
         [0046]    a connection assembly which is removably connectable with the exit port for connecting the sampling conduit to a sampling pipe, the connection assembly having: (i) a restrictor having an opening having a first cross-sectional area for restricting flow of sampling air, and (ii) a passageway between the restrictor and the sampling pipe, wherein the passageway has a minimum cross-sectional area that is greater than the first cross-sectional area. 
         [0047]    It will be appreciated that any of the first to seventh aspects of the invention may also include a mounting system for mounting the sampling conduit through a side wall, floor or ceiling that insulates the refrigerated space. 
         [0048]    In an eighth aspect of the present invention, there is provided a method of evaluating assembly of an air sampling network in an network portion between (a) a sampling point for sampling air from a space being or to be monitored by an air sampling device, and (b) a sampling pipe outside the space, wherein the method comprises: 
         [0049]    measuring a flow parameter; 
         [0050]    determining, based on the flow parameter, the presence or absence of a flow restrictor component of the network portion; and
       indicating a condition of assembly based on the determined presence or absence of the flow restrictor.       
 
         [0052]    Preferably, the sampling device is a particle detector. 
         [0053]    Preferably, when the measured flow parameter is above a predetermined threshold, the method determines a fault condition. In one embodiment, the predetermined threshold is between a first flow rate that is normal for the network portion being correctly assembled, and a second flow rate that is expected for the network being assembled without the flow restrictor component. In another embodiment, the predetermined threshold is between a first flow rate that is normal for the network portion being correctly assembled, and a second flow rate that is expected when the sampling point is disconnected from the sampling pipe. 
         [0054]    In one embodiment, the method evaluates the assembly between (a) the sampling pipe, the sampling pipe being configured for passing air from the connection assembly toward the particle detector, and (b) an exit port of a sampling conduit, the sampling conduit being configured for passing air from the monitored space to the connection assembly, wherein in correct assembly of the sampling network, the flow restrictor component forms part of the connection assembly. 
         [0055]    Preferably, the method includes comparing a measured flow parameter with a threshold flow value that is selected to be greater than an expected rate when the restrictor is connected. In one embodiment, the threshold flow value is additionally selected to be less than an expected flow rate when the air sampling pipe and sampling conduit are connected, but without a restrictor in the connection. 
         [0056]    Advantageously, this provides the method with a sensitivity to detect that the connection has been made but that the restrictor is absent. The threshold may be derived empirically or may be calculated from the known characteristic flow-impedances of the respective sampling conduit, restrictor and sampling pipe. 
         [0057]    Preferably, the connection is provided by a connection assembly in accordance with any of the other aspects of the invention. 
         [0058]    As would be understood by a person skilled in the art, the characteristic flow impedance of the restrictor is preferably selected to be greater than the characteristic impedance of the sampling conduit and all portions of the connection assembly other than at the restrictor. In this manner, it is easy to measure the restrictor&#39;s effect on the overall impendence of the sampling conduit and connection assembly, and the consequential sample air flow. 
         [0059]    In a ninth aspect of the present invention, there is provided a computing system having: a memory for storing a set of instructions that are executable by a processing system; and a processing system configured to read and execute the instructions, wherein upon executing the instructions the computing system performs the method according to the eighth aspect of the present invention. Preferably the flow sensor is an ultrasonic flow sensor, but other types of flow sensors may be used, e.g. a thermal flow sensor, an anemometer or the like. 
         [0060]    In a tenth aspect of the present invention, there is provided an air sampling device having a computing system in accordance with the ninth aspect of the present invention. Preferably, the air sampling device is (or includes) a particle detector, more preferably a smoke detector. 
         [0061]    In an eleventh aspect of the present invention there is provided an air monitoring system, having and an air sampling system in accordance with any one of the first, second, third or fourth aspects of the present invention, wherein the air sampling system feeds into said sampling device. Preferably the particle detector is a particle detector in accordance with the tenth aspect of the present invention. Preferably, the air monitoring system is a particle detection system, more preferably a smoke detection system. 
         [0062]    It will be understood that the invention disclosed and defined in this specification extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention. 
         [0063]    As used herein, except where the context requires otherwise, the term “comprise” and variations of the term, such as “comprising”, “comprises” and “comprised”, are not intended to exclude further additives, components, integers or steps. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0064]    In order that the invention may be more fully understood, one embodiment will now be described by way of example, with reference to the figures in which: 
           [0065]      FIG. 1  is a schematic illustration of a particle detection system having an air sampling system according to an embodiment of the present invention; 
           [0066]      FIG. 2  is a detailed view of part of the air sampling system of  FIG. 1 ; 
           [0067]      FIG. 3  is a detail of an alternative embodiment of the air sampling system illustrated in  FIG. 1 ; 
           [0068]      FIG. 4  is a perspective view of another part of the air sampling system of  FIG. 1 , corresponding to the view shown in  FIG. 3 ; and 
           [0069]      FIG. 5  is a detailed view of an end piece, corresponding to the embodiment illustrated in  FIG. 2 ; 
           [0070]      FIG. 6  is an illustration of a portion of an air sampling system in accordance with another embodiment of the present invention; 
           [0071]      FIG. 7  is a longitudinal sectional view through the air sampling system illustrated in  FIG. 6 ; 
           [0072]      FIG. 8  is an enlarged view of a restriction fitting illustrated in the air sampling system of  FIGS. 6 and 7 ; and 
           [0073]      FIG. 9  is a schematic illustration of an air sampling system according to another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0074]    The exemplary embodiments of the invention are described hereinafter with reference to use for a refrigerated space. However, the present invention may alternatively be applied to other low-temperature environments, such as cold outdoor environments. 
         [0075]    The exemplary embodiments are also described with reference to a particle detection system in which monitoring of sampled air is performed by an air sampling device that is a particle detector. However, the air monitoring system or sampling device may additionally or alternatively be adapted to analyse and/or detect other characteristics or components of the air. For example the air monitoring system or sampling device may be a gas detector or other device capable of detecting the presence and or concentration of one or more target gasses. An example of such an air sampling device is sold by Xtralis Technologies Ltd under the product name Vesda Eco. 
         [0076]      FIG. 1  illustrates an air monitoring system in the form of a particle detection system  1  for a refrigerated space  12 . The refrigerated space  12  is typically enclosed by a floor, walls and a ceiling including ceiling panel  14 . The ceiling and the walls may be insulating partitions or of an insulated sandwiched construction, as is known in the prior art. Typically, however, the sandwiched construction includes internal and external metallic panels  4  and  5 , respectively, with foam insulation  6  between the metallic panels  4 ,  5 . 
         [0077]    The particle detection system  1  includes a particle detector  2  in the form of an aspirating smoke detector, and an air sampling system  10  for drawing air from the refrigerated space  12 . Thus, externally of the refrigerated space  12  is a network of sampling pipes  16 , two of which are shown in  FIG. 1 . The sampling pipes connect to a sampling device—in this case, the aspirating smoke detector  2 —above the ceiling panel  14 . The sampling pipes  16  run along the outside of the refrigerated space  12  to connect to the sampling device  2 , either directly or via a manifold (not shown) proximate the sampling device  2 . A fan  8  may be provided within the aspirating smoke detector unit or elsewhere in the sample pipe network to draw air from the refrigerated space  12 , through the sampling system  10 , to the smoke detector  2 . Additionally, it is also possible for the outlet of the smoke detector unit to feed back into the refrigerated space  12  to create a closed loop system (not shown) to avoid the introduction of warm and humid air into the refrigerated space  12  when the detector unit is powered down for any reason. 
         [0078]    Each sampling pipe  16  may include a number of sampling points  18  at spaced locations within the refrigerated space  12 . Each of the sampling points exists at an entry port of a corresponding sampling conduit  20  which is connected to the sampling pipe  16  by means of a connector assembly  22 . The connection assembly  22  includes a flexible connector pipe  23  intermediate a restriction fitting  40 , that fits to the sampling conduit  20 , and a T-junction fitting  24  that fits to the sampling pipe  16 . Thus, the connection assembly forms a branch that stems from the sampling pipe, the branch including the sampling conduit. 
         [0079]    There may be a number of such T-junctions  24  along a single length of sampling pipe  16 , thereby providing a number of sample points  18  along a single length of sampling pipe  16 . Furthermore, it will be appreciated that a number of lengths of sampling pipe  16  can be arranged side by side to create a grid (or other geometry) of sampling points  18 . 
         [0080]    The sampling conduit  20  is of a sufficient length to extend across the width of the ceiling panel  14  or a wall panel, as the case may be. The sampling conduit  20  extends from the inside of the refrigerated space to outside the refrigerated space as most clearly illustrated in  FIGS. 2 and 3 . As shown in  FIG. 1 , the inside end (entry port) of the sampling conduit  20  may be provided with a bell-shaped sample nozzle  26 . 
         [0081]    At the other end of the sampling conduit  20 , the connection assembly  22  is received in the exit port  30  of the sampling conduit  20 . In  FIGS. 3 and 4 , the flexible connection assembly  22  has an integral end construction, such that the end portion  29  of the flexible connector pipe  23  acts like the restriction fitting  40 . The restriction fitting  29  in this embodiment includes a small entry port  32 , to restrict sample flow, and two relatively larger side apertures  34 . The small entry port  32  is disposed in a central location in a substantially closed end  36  of the restriction fitting  29 . The two larger apertures  34  are disposed in the side walls of the restriction fitting  29 . As will be understood from  FIG. 3 , when the end of the restriction fitting  29  is inserted correctly into the exit port  30  of the sampling conduit  20 , the large apertures  34  will be closed by sealing against the inside surface of the wall of the sampling conduit  20 . However, as will be understood from  FIG. 4 , if the restriction fitting  29  of the connection assembly  22  is not properly inserted back into the sampling conduit  20  then the large apertures  34  are able to draw in a large quantity of air, sufficient to trigger a fault within the detector unit  2 . 
         [0082]    Preferably the leakage through the large apertures  34  approximates the leakage of a broken pipe. Thus, aperture  34  may be of a similar sectional area as the pipe  16 . 
         [0083]      FIGS. 2 and 5  illustrate an alternative embodiment whereby the connection assembly  22  is comprised of multiple component parts which preferably are separable from each other. One of the components is a connector pipe  23 . In this embodiment, the connector pipe is advantageously flexible, but it is appreciated that a rigid connector pipe may be used. Attached to one end of the connector pipe  23  is a restriction fitting  40  in the form of an adaptor. The restriction fitting  40  constitutes a second component of the connection assembly  22 , and fits the flexible pipe  23  to the sampling conduit  20 . Thus, the restriction fitting  40  acts as an end piece of the connection assembly  22 . The restriction fitting  40  includes the small entry port  32  at the substantially closed end  36 , with two diametrically opposed, relatively larger apertures  34 , all of which serve a similar purpose as described above. Additionally, the restriction fitting  40  includes a peripheral flange  42  which serves to locate the restriction fitting  40  in its properly installed position within the sampling conduit  20 . The restriction fitting  40 , including the flange  42 , peripheral side wall and substantially closed end  36  is preferably of one piece, integral construction. The restriction fitting  40  may be an integrally moulded piece. It will be appreciated that the provision of a separate restriction fitting  40  is a simpler construction than machining or forming the small entry port  32  and apertures  34  into the end of a flexible pipe  22 . 
         [0084]    An embodiment of an alternative air sampling system  110  is illustrated in  FIG. 6 . The air sampling system  110  uses an alternative connection assembly  122  which is similar to, and may be used interchangeably with, the connection assembly  22  in air sampling system  10 . In this embodiment, the connector pipe  123  includes a flexible pipe segment  123   a  terminated with upstream and downstream rigid pipe pieces  125   a  and  125   b , respectively. It is, however, appreciated, that the pipe  123  may be interchanged with a pipe that is either flexible or rigid across its entire length or for any portion thereof, as desired. Connection assembly  122  includes an alternative restriction fitting  140  for fitting the connection assembly  122  to the sampling conduit  120 . 
         [0085]      FIG. 7  illustrates a longitudinal sectional view through the connection assembly  122  and sampling conduit  120 . The connection assembly  122  may alternatively be attached to the sampling conduit  20  of  FIGS. 1 to 3 . 
         [0086]    An enlarged view of the restriction fitting  140  joined to the sampling conduit  120  and connector pipe  123  is illustrated in  FIG. 8 . Restriction fitting  140  includes a fitting portion in the form of a union fitting having a first component  150 , which is in this case configured to seal with the sampling conduit  120 , and a second component  152 , which is in this case configured to seal with a connector pipe  123 . It is appreciated, however, that the orientation of the restriction fitting may be reversed so the first component  150  and second component  152  mate with the connector pipe  123  and sampling conduit  120 , respectively. 
         [0087]    The first component  150  (in this case the upstream component) includes collar  154  having a tight fit with the sampling conduit  120 . The top (downstream end) of the collar has an inner flange  156  for sitting on the edge  158  of the sampling conduit  120 . The top of the collar  150  also includes an outward flange  160  for interferingly abutting with a bottom inner flange  161  of a fastening member  162 . This prevents the fastening member  162  from being removed from the sampling conduit  129  when the first component  150  is attached to the sampling conduit  120 . Extending upwardly from the fastening member&#39;s inner flange  161  is a fastening ring  163  having an inner thread  166 , which can be screwed onto thread  168  on the bottom outside surface of the second component  152  to tighten the second component  152  towards the first component  150  and to create a seal therebetween. The second component has an inner flange collar  170  having a tight fit with the connector pipe  123  and an inner flange  172  to sit beneath and abut the bottom edge  174  of the connector pipe  123 . 
         [0088]    Between the first and second components  150 ,  152  is a restrictor  132  in the form of an orifice plate. However, the restrictor  132  is also shaped to fit on the sampling conduit in a self-locating manner. This is achieved by a central portion  134  of the restrictor  132  being sunken from the restrictor&#39;s periphery  135 . In this embodiment the restrictor is metallic, but in other embodiments non-metallic materials, such as plastic or rubber, may be used. 
         [0089]    A seal is created between the first and second components  150 ,  152  by a rubber O-ring seals  136  and a ring-shaped self-adhesive foam seal  137  on the respective sides of the restrictor  132 . This creates seals between the first component  150  and the restrictor  132 , and between the restrictor  132  and the second component  152 . 
         [0090]    The restrictor has an inner diameter (i.e. the diameter of the O-ring hole  133 ) which is less than the inner diameter of the downstream flow path to the sampling pipe  16 . Thus, the diameter of hole  133  is less than the inner diameter of the second component  152  and also less than the inner diameter of the connector pipe  123 . The diameter of hole  133  is similarly less than the inner diameter of the entire sampling conduit (including the sampling point at the end of the sampling conduit). The precise diameter of the hole  133  is selected to provide a desired flow-restriction that is dictated by the dimensions and configuration of the sampling system  10  and detector  2 , and the characteristics of the fan  8 . The diameter can be determined in any known fashion including using software that has been specialised for this purpose, such as Xtralis Technologies Ltd&#39;s VESDA ASPIRE2 pipe network design software. Typically, the hole has a diameter of between 2 mm and 10 mm. As would be appreciated by a person skilled in the art, restrictor  132  may allow restrictive flow of air by having a plurality of holes, rather than a single hole  132 . In this case, the combined cross section of all the restrictor&#39;s holes is the same as cross section of the single hole  132 . By comparison the respective minimum (and in this case constant) inside diameters of the sampling conduit and connector pipe are both 25 mm. 
         [0091]    By this design, the characteristic flow-impedance of the restrictor  132  dominates the overall impedance to flow of air sampled from the refrigerated space to the sampling pipe  16 . Accordingly, if the restrictor  132  is absent (for example if the sampling system  110  is not correctly assembled), there will be an increase in flow rate through the sampling network  110 . The flow rate is measured by a flow-rate meter having a transducer (not shown) either at the particle detector  2  or elsewhere in the sampling system  110 . In one arrangement, the flow is measured in either the sampling conduit  120  or the connection assembly  122 , but preferably at a downstream end of the connection assembly. Alternatively, an accurate measurement can be acquired by including flow measurement transducers in the sampling pipe  16 , upstream and downstream from the sampling conduit  122 . The difference in flow between the two transducer measurements is attributable to the flow through the sampling conduit  120  and connection assembly  122 . In this embodiment, flow is measured by an ultrasonic transducer, but in other embodiments other types of flow sensor may be used, e.g. a thermal flow sensor. 
         [0092]    It is appreciated that part of the restriction fitting may be integrally formed or permanently connected with the sampling conduit  120 . However, the restrictor component  133  should preferably, even in this case, still be removable (or at least displaceable) from the sampling conduit  120 , so as to provide good access to the sampling conduit for cleaning. To account for such variations, as used herein the term “sampling conduit” is intended to mean the part of the sampling network from the refrigerated space up to, but not including, the restrictor. The restrictor itself is part of the “restriction fitting”, which is a separate integer from the sampling conduit, even in cases where the sampling conduit  120  includes a portion, part or parts which interact with the restrictor to enable its removal, displacement, placement or fastening. 
         [0093]    In another embodiment of the invention, or as an additional feature of the embodiments hereinbefore described, the restrictor is positioned in the sampling network at a location sufficiently downstream from the sampling point so as to be at a temperature above the freezing point of water, i.e. above 0 degrees Celsius. In such an arrangement, it is not necessary that the restrictor be part of the connection assembly. An embodiment of such an arrangement is illustrated in  FIG. 9 , which shows restrictor fitting  240  being removable from a first opening  250  in the sampling conduit  220 . The sampling conduit has a second opening  252  which forms the sampling conduit&#39;s output to the sampling pipe, and fluidly connects to the connection assembly  222 . The restriction fitting restricts the sample flow between the sampling point  254  of the conduit  222  and the output at the second opening  252 . 
         [0094]    It is appreciated that the restriction fitting  250  may alternatively be located at other locations between the sampling conduit&#39;s sampling point  254  and output  252 . While it is advantageous for the restriction fitting  250  to be removable from the sampling conduit  220 , in some embodiments a restrictor is permanently fixed to or integrally formed with the sampling conduit  220 . The placement of the restrictor is nonetheless advantageous by being placed at a location where the sampled air (and the temperature of the sampling conduit) has sufficiently been warmed by the ambient environment so as to be above the freezing point of water. Thus the restrictor does not become clogged with ice. This can reduce the need or regularity for servicing of the sampling network. 
         [0095]    For embodiments in which the restrictor may be mistakenly omitted during initial assembly of the sampling pipe network, or during reassembly after servicing, a method may be employed to evaluate the assembly. The method comprises measuring a flow parameter and indicating a condition of assembly that is determinant of the presence or absence of the flow restrictor  40 ,  140 ,  240  in an evaluated portion of the network. The method evaluates the assembly at the portion of the air sampling network between (a) the sampling point  18 ,  118 ,  254  and (b) a sampling pipe  16  outside the space. In the embodiments of  FIGS. 1 to 7 , the restrictor forms part of a connection assembly between the sampling conduit  20 ,  120  and the sampling pipe  16 . Thus, the method is used to evaluate the assembly of the connection between the sampling conduit  10 ,  120  and the sampling pipe  16 . 
         [0096]    Details of various embodiments of the sampling conduit and its mount to the ceiling  14  are now described.  FIGS. 7 and 9  illustrate a sampling conduit  120  mounted to ceiling panel  14 . The sampling conduit  120  is held on the metal panel  4  on the top side of the ceiling  14  by top flange assembly  184 . The flange assembly  184  has upstanding sprung fingers  185  which retain the sampling conduit  120  in position during and after installation. A lower end  186  of sampling conduit  120  defines the sampling point hole  118 . The bottom portion the sampling conduit flanges outwardly from the sampling point  118  and then downwardly to form a dome-shaped cover  187  for the sampling point  118 . In the illustrated embodiment this bottom portion of the sampling conduit is formed as a separate part from the main pipe  188  of the sampling conduit. This bottom portion or lower flange  187  locks onto mount  189  which is held onto the bottom metal panel  4  of the ceiling  14  by screws  190 . During assembly, sealant is placed between the top and bottom flanges and their corresponding ceiling panel to provide an air-tight seal, avoid leakage at each sampling point and thus prevent air leakage from the refrigerated space  12  through the ceiling  14 . Similarly, in the embodiment of  FIG. 1 , the sampling conduit  20  is preferably surrounded by a suitable sealant within the ceiling panel  14  to eliminate leakage. A sealing grommet  44  may also surround the sampling conduit  20  where it exits the ceiling panel  14 . 
         [0097]    The foregoing describes only exemplary embodiments of the present invention and modifications may be made thereto without departing from the scope of the invention.