Abstract:
A sampling device samples gas from a gas stream flowing through a tube to means utilizing the gas to detect the presence or otherwise of particulate contaminants. The device ensures that the sampled flow has at least as many particulate contaminants/unit volume as the main flow. The device divides the flow into two parallel flows and then decelerates one flow before providing the sampled flow. The other flow passes to the utilizing means. The device is particularly useful in the sterile packaging of product to detect microorganisms and other culturable contamination.

Description:
BACKGROUND TO THE INVENTION 
     1. Field of the Invention 
     The invention relates to sampling devices and to air supply systems incorporating such devices and sterile filling apparatus including such air supply systems. 
     2. Brief Review of the Prior Art 
     There are many circumstances where gas from a gas stream is flowed through a tube from a source to means utilizing the gas and where the gas may contain unwanted particulate contamination. An example of this is sterile filling apparatus such as blow/fill/seal apparatus where the gas is air and is used to prevent contamination in the sterile packaging of articles such as sterile liquids. Plainly, the presence in the air of particulate contaminants such as micro-organisms can compromise the sterility of the packaging process and may result in packaged product being contaminated. 
     In order to remove contamination, the air supply is normally filtered through a filter (such as HEPA or 0.2 μm rated filter) having a rating sufficient to remove unwanted particulate contaminants such as micro-organisms. The filter can be inspected at the end of its life to see whether its integrity has been compromised to allow contaminants to enter the air stream supplied to the apparatus. This procedure may, however, render a large quantity of the articles unusable if it is found that the filter integrity has been compromised, since it is not possible to say when during the life of the filter the compromise occurred so making it necessary to remove all articles produced during the life of the filter. 
     In order to try and overcome this problem, it has been proposed to include in the tube a sampling port in the form of a pipe extending through a wall of the tube normal to the length of the tube. This port is connected to a unit containing a filter which filters out all particulate contaminants in a sample airstream taken from the port. At intervals, the port is closed and the unit removed so that any particulate contaminants on the filter material can be identified. In the case of biological materials, this may be done by culturing. If an unacceptable level of contaminants is present, the batch of articles produced with a contaminated airstream can be identified and removed. 
     FIG. 1 shows a sampling port of this known type inserted in a tube. Referring to FIG. 1, the tube  100  is of generally constant circular cross-section along its length and passes air from a source to apparatus utilizing the air. A sampling port  101  is inserted in the tube with the port extending normal to the axis of the tube. Air flows through the sampling port to a unit containing a filter as described above. At intervals, the port is closed and the unit removed so that any particulate contaminant on the filter material can be identified. 
     It is a problem with a sampling port of this known type that it does not always reliably identify the presence of particulate contaminants. There can be occasions when sampled air shows no contaminants but replacement of the filter element at the end of the filter element life shows the integrity of the filter to have been compromised so allowing contaminated air to pass to the article. It is then necessary to remove from production all the articles made during the life of the filter. This is plainly unsatisfactory. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the invention, there is provided a sampling device for sampling gas from a gas stream flowing from a source to means utilizing said gas to determine the presence of particulate contamination comprising a pipe through which the gas stream is flowed, a flow divider receiving the gas stream from the pipe and separating the gas stream into first and second flows, the first flow passing to said gas utilizing means and the second flow passing to a contamination detector for determination of particulate contaminants per unit volume present in the gas stream and comprising a deceleration volume disposed downstream of the flow divider and arranged to decelerate the second flow before the second flow exits for contamination detection. 
     By arranging the flows in accordance with the first aspect of the invention, a gas sample is obtained for analysis which will reveal reliably the presence of particulate contaminants. 
     According to a second aspect of the invention, there is provided a sampling device for sampling gas from a gas stream flowing from a source to means utilizing said gas to determine the presence of particulate contamination comprising an inlet tube through which the gas stream is flowed, a housing for receiving a portion of the gas flowing through the inlet tube, and an exit pipe for receiving another portion of the gas flowing through the inlet pipe, wherein the housing includes an outlet for connecting to a contamination sampling means and wherein the volume of the housing is such as to decelerate the portion of the gas received therein. 
     According to a third aspect of the invention, there is provided a sampling device for sampling gas from a gas stream flowing from a source of gas to means utilizing the gas to determine the presence of particulate contamination comprising a housing for receiving and decelerating a portion of the flow, an exit tube for conveying the remainder of the flow and a sampling tube leading from the housing for connection to contamination detection means. 
     According to a fourth aspect of the invention, there is provided an air supply system comprising a source of air, a filter supplied with air from said source, an outlet passage for conveying filtered air from the filter to means utilizing said air, the outlet passage including a sampling device according to the first, second or third aspects of the invention. 
     According to a fifth aspect of the invention, there is provided a sterile packaging apparatus for packaging articles comprising an air supply system according to the fourth aspect of the invention, the outlet passage leading to a filling and sealing station of the apparatus. 
     According to a sixth aspect of the invention, there is provided a method of sampling an air stream to test for the presence of particulate contaminants comprising dividing the air stream into first and second flows, decelerating the first flow, passing decelerated first flow to contamination detection means and passing the second flow for utilization. 
     The following is a more detailed description of some embodiments of the invention, by way of example, reference being made to the accompanying drawings in which: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-section of a sampling port inserted in a tube, 
     FIG. 2 is a schematic view of a sterile packaging apparatus incorporating a sampling device, 
     FIG. 3 is a cross section of a first form of sampling device for use in the apparatus of FIG. 2, 
     FIG. 4 is a perspective view from one end of a second form of sampling device for use in the apparatus of FIG. 2, 
     FIG. 5 is an end elevation of the sampling device of FIG. 4, 
     FIG. 6 is a side elevation of the sampling device of FIG. 5, 
     FIG. 7 is a schematic view of a test rig for testing the efficiency of the sampling port of FIG.  1  and the sampling device of FIGS. 4 to  6 , 
     FIG. 8 is a bar chart showing the efficiency of collection of three (BS, BM, SP) different sizes and types of particulate contaminants with a total air flow of 1.3 m 3 min −1  and an air flow of 11 dm 3 min −1  to the sampling port of FIG.  1  and the sampling device of FIGS. 4 to  6 , and 
     FIG. 9 is a bar chart showing the efficiency of collection of 3 (BS,BM,SP) different sizes and types of particulate contaminants with a total air flow of 1.8 m 3 min −1  and an air flow of 11 dm 3 min −1  to the sampling port of FIG.  1  and the sampling device of FIGS. 4 to  6 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring first to FIG. 2, the sampling device will be described in the context of its use in a sterile packaging apparatus in the form of a blow/fill/seal apparatus. It will be appreciated, however, that the sampling device can be used in other apparatus and the following description is by way of example only. 
     Referring to FIG. 2, the blow/fill/seal apparatus includes a supply  10  of product to be packaged which may typically be a sterile liquid. The product is fed to a packaging station  11  where a plastics material is blown into an appropriately shaped packaging, product is fed to the packaging and is then sealed in the packaging. For example, a bottle for receiving liquid may be blown at the packaging station  11 , sterile liquid placed in the bottle and the bottle sealed. 
     The blowing, filling and sealing must take place in a sterile atmosphere and, for this purpose, air is supplied to the packing station  11  from an air supply  12 . Air from the supply  12  is fed to an appropriately rated filter  13  which removes particulate contaminants in the air. For example, the filter may have an absolute rating of 0.2 μm. From the filter  13 , filtered air is supplied through a pipe  14  to the packing station  11 . 
     A sampling device  15 , examples of which will be described below, is inserted in the pipe  14  and feeds a sample of the air to a contamination monitor  16 , again to be described in detail below. A collection device from the contamination monitor  16  is taken to a testing station  17  to test for the presence of contamination. 
     Testing takes place at predetermined time intervals which are correlated with the production of packaged articles from the packaging station  11  so that if contamination appears, it is known which batch of articles has been packaged using contaminated air. 
     Referring next to FIG. 3, the first form of sampling device  15  comprises an inlet tube  18  of constant circular cross section along its length. This connects to an aperture in a first end wall  19  of a circular cross-section tube forming a housing  20  whose axis is coaxial with the axis of the inlet tube  18 . The opposite second end wall  22  of the housing  20  carries an exit tube  23 . The second end wall  22  is provided with reinforcing plate to mount the exit tube  23 . The exit tube  23  has an outlet portion  24  of constant circular cross-section along its length and extending through the second end wall  22  of the housing  20 . This leads to an inlet portion which is of reducing circular cross section as it extends away from the outlet portion  24  to terminate in an inlet  26 . The exit tube  23  is coaxial with the axes of the inlet tube  18  and the housing  20  and, as seen in FIG. 2, the inlet  26  and the associated inlet portion form an inner tube lying within the inlet tube  18 . 
     The housing  20  is also provided with a sampling tube  27 . The sampling tube  27  extends from the curved outer surface of the housing  20  and is located closer to the second end wall  22  of the housing. The sampling tube  27  is of circular cross-section with its axis normal to the axis of the housing  20 . 
     The free end of the inlet tube  18  and the outlet portion  24  of the exit tube  23  are provided with respective flanges  28 , 29  to allow them to be connected in the pipe  14  between the filter  13  and the packaging station  11 . The sampling device  15  may be made of stainless steel to allow it to be steam sterilized in situ. 
     In use, the sampling device  15  of FIG. 2 is inserted in the pipe  14  utilizing the flanges  28 , 29 . Air from the filter  13  passes to the inlet tube  18  and the inlet tube  26  acts as a flow divider to divide the air with a first portion of the air taken from the centre of the pipe  14  flowing into the exit tube  23  and a second portion of the air taken from adjacent the wall of the pipe flowing into the housing  20 . As will be seen, the division is such that the flows are initially parallel. It will be appreciated that the proportion of air flowing into the housing  12  as compared with the proportion of air flowing to the exit tube  23  is determined by the relative cross sections of the inlet tube  18 , the inlet  26  to the exit tube  23  and the sampling tube  27  and so, in turn, depend on the diameter (D) of the inlet tube  18 , the diameter (a) of the inlet  26  of the exit tube  23 , and the diameter (d) of the sampling tube  27 . It has been found that satisfactory sampling can be achieved when the air flow between the sampling tube is between 1×10 −2  and 2×10 −2  of the air flow through the inlet tube  18 . For example, typical air flows through the inlet tube  18  may be 1.3 m 3 min −1  and 1.8 m 3 mm −1  with a flow through the sampling tube of 11 dm 3 mm −1 . 
     The second flow of air enters the housing  20  and, because of the larger volume of the housing  20 , is decelerated so causing contaminants in the air flow also to be decelerated. The air/contaminants in the housing  20  then pass to the sampling tube  27 . The sampling tube  27  is connected to the contamination monitor  16 . This may comprise, in known fashion, a filter material (not shown) through which the air from the sampling tube  27  passes. After a predetermined period of time, the sampling tube  27  is closed, the filter material removed from the contamination monitor  16  (with care being taken not to contaminate the material) and the material taken to the testing station  17  for analysis. There, the filter material is used as a culture medium and any contamination in the form of microorganisms or other culturable biological material present is cultured and examined. If contamination has occurred, then the apparatus is stopped until the source of the contamination is discovered and those articles packaged between the last negative test and the positive test are removed for destruction. 
     An alternative form of the sampling device will now be described with reference to FIGS. 4 to  6 . In FIGS. 4 to  6 , parts common to FIG. 3, on the one hand, and to FIGS. 4 to  6 , on the other hand, are given the same reference numerals and will not be described in detail. 
     Referring now to FIGS. 4 to  6 , the second form of sampling device has an inlet tube  18  of constant circular cross-section along its length with a flange  28  at its free end. The housing  20  is, however, frusto-conical with a smaller diameter end  31  leading from the inlet tube  18  and a larger diameter end being closed by a wall  33  lying in a plane angled to the axis of the housing  20 . An outlet portion  24  of an exit tube  23  passes through this wall  33  and terminates at its outer end in a flange  29 . The outlet portion  24  is of circular cross-section along its length and leads to an inlet portion  25  of frusto-conical shape and an inlet  26 . The inlet  26  and the associated inlet portion  25  form an inner tube within the outer tube  18 . The cone angle of both the housing  20  and the inlet portion  25  is about 13° in order to maintain laminar flow across these surfaces. 
     A sampling tube  27  leads from the wall  33  and has its axis parallel to but spaced from the intersection with the housing  20  of a plane including the housing axis and the sampling pipe axis. The sampling tube  27  terminates in a flange  34 . 
     The sampling device of FIGS. 4 to  6  is used in the same way as the sampling device of FIG.  3 . The sampling tube  27  is connected to the contamination monitor  16  by a pipe attached to the sampling tube  27  utilizing the flange  34 . 
     The sampling device of FIGS. 4 to  6  may also be made of stainless steel so that it can be steam sterilized in situ. 
     As indicated above, the purpose of sampling the air is to detect the presence in the air of contamination, particularly microorganisms. It is therefore a requirement of the sampling device  15  that air passing through the sampling tube  27  has at least the same amount of contaminants per unit volume as the air leaving through the exit tube  23 . 
     In this regard, it will be appreciated that there is no significant disadvantage in the air passing through the sampling tube  27  having a higher amount of contamination per unit volume than the air in the exit tube  23 . Indeed, this could be an advantage in making it easier to determine the presence of such contamination, particularly when levels are low. 
     In order to test the effectiveness of the sampling device of FIGS. 4 to  6  in this regard, use was made of the test rig shown in FIG.  7 . 
     Referring now to FIG. 7, the test rig comprises a dispersion chamber  36  having an inlet  37  connected to a Collison nebulizer. The nebulizer is of a known kind and is not illustrated or described in further detail. The nebulizer produces in the chamber a mist from a liquid containing in suspension a known microorganism, described in more detail below. 
     The chamber  36  has a first outlet line  38  connected to an air sampler (not shown) which measures the number of microorganisms per unit volume in air taken from the chamber  36 . The second outlet line  39  leads to an air sampler, which may be either the sampling device  15  described above with reference to FIGS. 4 to  6  or the sampling port of FIG.  1 . The exit tube  23  of the sampling device of FIGS. 4 to  6  or the tube  100  of the sampling port leads to a blower  40  whose output is controlled by a control valve  41  connected to a return pipe  42  leading to the chamber  36 . A baffle plate  43  is located opposite the end of the return pipe  42  in the chamber  36  so that incoming air impinges on the baffle plate  43 . 
     An air outlet  44  is connected to the atmosphere via a high efficiency filter (not shown) to ensure that air exhausting from the chamber  36  is free of microorganisms. 
     The following Examples use the test rig of FIG.  7 . 
     EXAMPLE 1 
     A sampling device  15  as described above with reference to FIGS. 4 to  6  was connected to the second outlet line  39  of the chamber  36 . 
     The Collison nebulizer was charged with an aqueous suspension of the bacterial endospore  Bacilllus subtilis  var.niger (BS) having an aerodynamic size of about 1.3 μm. This was nebulized by the Collison nebulizer and fed into the chamber  36 . The control valve  41  was adjusted to give an air flow through the second outlet line  39  of about 1.3 m 3 min −1 . At the same time, air was passed to the sampler and a count made of the number of viable organisms of BS per unit volume (N s ). The second outlet line  39  and the proportions of the inlet tube  18 , the inlet  26  and the sampling tube  27  were such as to provide a sampling rate air flow through the sampling tube  27  of about 11 dm 3 min −1 . The number of viable organisms of BS per unit volume (N ST ) of the sampled air was then counted. The efficiency of the sampling device  15  was then calculated as            N   ST       N   s       ×   100      %                          
     This was repeated a number of times and average efficiency (E SD ) calculated. 
     The sampling device  15  was then replaced with the sampling port  100  of FIG. 1 and a similar average efficiency (E SP ) derived as described above. 
     FIG. 8 is a bar chart showing above the designation BS E SD  (plain bar) and E SP  (shaded bar) using BS at the air flow of about 11 dm 3 min −1 . Also shown as a straight vertical line at the top of each bar is an indication of the range of efficiencies measured. 
     EXAMPLE 2 
     As Example 1 but using the bacterial endospore  Bacillus megaterium  KM (BM) having an aerodynamic size of about 1.6 μm. The measured average efficiencies are E SD  and E ST  shown as bars on FIG. 8 above the designation BM with the range of efficiencies being shown by vertical lines. 
     EXAMPLE 3 
     As Example 1 but using the yeast cell  Schizosaccharomyces pombe  (SP) having an aerodynamic size of about 6.7 μm. The measured average efficiencies are E SD  and E SP  shown as bars on FIG. 8 above the designation SP with the range of efficiencies being shown by vertical lines. 
     EXAMPLE 4 
     As Example 1 but with a flow through the second outlet line  39  of 1.8 m 3 min −3 . The results are shown in FIG. 9 in a similar way to FIG. 8 as bars (E SD -plain bar, E SP -shaded bar) together with vertical lines indicating the range of efficiencies measured. 
     EXAMPLE 5 
     As Example 2 but with a flow through the second outlet line  39  of 1.8 m 3 min −1 . The measured average efficiencies are E SD  and E SP  shown as bars on FIG. 9 with the range of efficiencies being shown by vertical lines. 
     EXAMPLE 6 
     As Example 3 but with a flow through the second outlet line  39  of 1.8 m 3 min −1 . The measured average efficiencies are E SD  and E SP  shown as bars on FIG. 9 with the range of efficiencies being shown by vertical lines. 
     The results of these Examples will now be discussed. 
     At a sampling rate of 11 dm 3 min −1 , the sampling link  15  gave average efficiencies consistently above 100%. This means that, for all three contaminants, the sampling air contained at least as much contaminant per unit volume as the air flow through the sampling device. This means that any detection of contaminants from the sampled air will represent the presence of contaminants in the air flow through the exit pipe  23 . 
     In contrast, the sampling port  101  provided efficiencies of greater than 100% only with the BS and BM bacterial endospores. When the size of the contaminant increased with the yeast cell SP, the sampling port  101  gave an efficiency of significantly less than 100%. At an air flow of 1.8 m 3 min −1 , the efficiency was very significantly below 100%. This means, that when used to sample contaminants in air, this sampling port may indicate that no contamination is present when, in fact, significant contamination is present. This may lead to the sale of products which are not packed in a sterile fashion or, if when the filter is changed it is seen to be compromised, it may require the destruction of very significant amounts of a possibly non-sterile product. 
     This finding is more significant as a result of a study of particles including microorganisms in air. This found a mean aerodynamic size of around 19 μm. Accordingly, many of the particles to be detected by the sampling device will be at least 6.7 μm in size and plainly it is the ability to detect such larger particles that is important. Thus the sampling port  101  of FIG. 1 can be expected to produce unreliable results in normal usage. 
     Although not certain, it is believed at the present time that this may be due to the fact that, in the sampling port  101  of FIG. 1, it is necessary for particles flowing through the pipe  100  to turn through 90° if they are to enter the sampling tube  101 . Larger particles, in particular, will have an inertia which will tend to cause them to continue travelling along the pipe  100  even if the airstream which is conveying them is turning to exit through the sampling tube  101 . Accordingly, air entering the sampling tube  101  does not contain a representative volume of such larger particles. 
     In the sampling device of FIGS. 4 to  6 , on the other hand, the particles are not diverted as they leave the entry pipe. Indeed, due to the flow patterns provided by the location of the inlet  26  of the exit tube  24  within the inlet tube  18 , while the majority of the air may pass into the exit pipe  23 , at least as many particulate contaminants per unit volume are present in the air passing into the housing  20  as are present in the first flow of air passing through the exit tube  24 . Once in the housing  20 , the velocity of the particles decreases significantly and so inertia has less effect on the particles. This means that air leaving through the sampling tube  27  contains at least as many particulate contaminants per unit volume as the air in the housing  20 . 
     It will be seen from FIGS. 8 and 9 that the sampling device of FIGS. 4 to  6  increases its efficiency as the particle size increases with an air flow of 1.3 m 3 min −1 . This may be evidence that, as particle sizes increase further, the efficiency will rise even higher. This may be important when the amount of contaminant per unit volume is low to make detection more certain. 
     The sampling port  101  of FIG. 1 requires suction in order to draw air from the pipe  100 . As described above, the sampling port  101  must be closed in order for a test to be conducted for particulate contaminants. When this is done, if there is any leak around the sample port  101 , air flowing through the pipe  100  may create a Venturi effect which will draw air into the pipe  100  through the leak. In this way, contaminated air may be drawn into the pipe  100  and will not be detected in air taken from the sampling port  101 . 
     In the sampling devices  15  of FIGS. 3 to  6 , there is always a positive pressure in the housing  20  even when the sampling tube  27  is closed. This positive pressure ensures that no air is drawn into the housing  20  if there is any leak in the sampling tube  27  or its couplings. 
     As shown in FIG. 1, it is preferred to have the sampling tube  27  leading vertically downwardly to the contamination monitor  16 . This ensures that contaminants in the air flow freely to the contamination monitor  16  and do not get trapped in bends and junctions. 
     It will be appreciated that the embodiments of the sampling device  15  shown in FIGS. 3 to  6  are examples of the way in which the sampling device  15  may be embodied in accordance with the principles of the invention. Both sampling devices described above with reference to FIGS. 2 to  5  show a portion of the air in the inlet tube  18  in a path parallel to the exit tube  23  before sampling. This may be achieved in ways other than as described above. The various tubes and pipes are described as being of circular cross-section, this need not necessarily be the case. 
     In addition, they provide a housing which decelerates the sampled air before passing it to the sampling tube. This ensures that inertial effects in larger particles do not distort the air taken by the sampling tube  27  for analysis. 
     Another example of sterile packaging apparatus in which the sampling device  15  may be used is form/fill/seal apparatus where sterile solid products such as powders, pills, dressings and medical devices are packaged into plastics trays formed at the packing station  11  and then sealed.