GB2254024A - Cyclone sampler - Google Patents

Abstract

Particle (e.g. biological particles) laden air is drawn through a sampling orifice 28 of a sampler into the inlet 28 of a particle separating cyclone 26. An air exhaust 24 of the cyclone is connected to a driven exhaust pump, turbine, fan 4, etc., which draws air through the cyclone at a predetermined flow rate. As the air flows through the cyclone, airborne particles are separated from it and pass through a particle outlet 34 of the cyclone into a closed particle collection chamber 36. The sampling orifice of the sampler may be modified for collecting airborne particles or particles deposited on surfaces. <IMAGE>

Description

Sampler This invention relates to samplers for collecting particles including biological particles.

The quantitative and representative sampling and subsequent identification of airborne particles are important in many applications, for example in industry, medicine, occupational hygiene, and animal and crop sciences. Many industrial dusts and asbestos fibres are important health hazards, as is a wide spectrum of biological materials stretching from viruses through bacteria and fungi, to pollen grains, mites and insects.

At present, the two most common means of identification are visual recognition, often under the microscope (e.g. for pollens, fungus spores and some inert particles), and growth in culture (e.g. for bacteria, fungi, actinomycetes etc.). Less frequently, gravimetric methods may be used, for example when sampling heavily contaminated environments. Enzyme and immunological particle identification techniques are also used in a few applications: a significant increase in the use of these techniques is anticipated however.

Many types of particle collectors or samplers are known. They rely however on only a few methods of collecting particles, including most commonly either filter techniques or the use of 'adhesive' or 'adsorbent' surfaces or media to remove particles from the air in which they are carried.

Samplers using filters generally draw the air to be sampled through a single filter or a graded set of filters by means of a suction pump. Filter samplers are capable of collecting very small particles but have a number of significant drawbacks. In order to sample small particles, a fine mesh filter is high and so a powerful pump is needed. The resistance to airflow through a fine filter is needed. Such pumps tend to be bulky, noisy and if electrically driven need either large batteries or mains power supplies. Filter samplers are therefore not usually portable, which is a severe disadvantage in many applications.

Fine mesh filters become blocked very rapidly in use, and so their sampling time is disadvantageously short, and the volume of air sampled is rather small. The number of particles that can be collected is similarly limited, which can iead to problems of particle identification. Sampling time can be increased by the use of a graded set of filters so that large particles are removed before the air being sampled passes through finer filters. Graded filters lead however to further increased resistance to airflow.

Adhesive or adsorbent collecting media include many types, ranging from an agar medium in a simple exposed petri dish to more complex systems in which, for example, a predetermined calibrated airflow impinges on a liquid or solid surface on which particles collect.

Using these collection techniques methods of sample recognition are disadvantageously limited. On inert substrates, particles can be identified visually by microscopy, and on agar, suitable particles can be cultured, but this limits the types of particles that can be identified.

The invention provides a sampler for collecting airborne particles, comprising a cyclone having an air inlet, an air exhaust and a particle outlet, the air inlet comprising a sampling orifice, the air exhaust being coupled to a driven exhaust pump means for drawing air at a predetermined flow rate through the cyclone, and the particle outlet leading to a closed particle collection chamber.

The sampler of the invention may advantageously be adapted to collect either particles which are already airborne or particles deposited on surfaces, principally by altering the construction of the sampling orifice or of a nozzle connected thereto and by selecting the airspeed through the orifice or nozzle.

For collecting particles which are already airborne it may in many applications be advantageous to use a relatively large nozzle and a low nozzle airspeed so that a wide range of particle sizes may be collected. In addition it may be advantageous to orient the nozzle perpendicular to any ambient airflow near the sampler in order to reduce any effect of the ambient airflow on the flow through the nozzle.

For collecting particles deposited on a surface it is necessary to draw the particles away from the surface and make them airborne so that they may be drawn into the sampler and collected by the cyclone. In such applications it may therefore be advantageous to use a relatively small orifice or nozzle and a high nozzle airspeed in order to tear particles away from the surface.

A suitably designed cyclone may collect airborne particles down to 1 micrometre diameter or less, with high capture efficiency. The sampler of the invention may therefore collect a wide range of biological and other particles. In addition, since the sampler of the invention may in principle collect particles for any length of time until the collecting chamber is full, a large volume of air or a large area of a surface can be sampled and a large number of particles collected compared with prior samplers. This is particularly advantageous for collecting uncommon or sparsely distributed particles.

Particularly though not exclusively in a sampler for collecting airborne particles, the sampler components may all be mounted on or in a housing, which may advantageously be portable. The pump means may comprise a fan mounted within the housing and preferably driven by an electric motor, which may be powered by electric storage cells mounted within the housing or may be externally powered, for example by mains electricity. In many applications, for example for air sampling in the field, it would be very advantageous if the sampler were thus self contained, including its power source, and portable.

Particularly though not exclusively in a sampler for collecting particles from surfaces the pump means may comprise a pump separate from the sampler and powered by an external power source. This is because a high sampling nozzle airspeed and a small nozzle or orifice may be required1 and a pump means, for example a fan, mounted within the sampler housing may not be able to maintain sufficient sampling airspeed. In many applications the sampler may advantageously comprise a frame or housing on which the cyclone and sampling chamber are mounted so that the sampler can be manipulated by an operator for collecting particles from surfaces, the sampler being connected by a flexible pipe to for example a vacuum pump which may not be easily portable.A critical orifice may be mounted between the air exhaust from the cyclone and the pump means to maintain a predetermined airflow through the cyclone. The critical orifice may advantageously be mounted on the frame or housing.

The cyclone of the invention may advantageously be made of a plurality of easily demountable component parts. This would be particularly advantageous in collecting biological samples as the necessary cleaning of the cyclone before and after sampling could more easily be carried out. Advantageously, for ease of cleaning, none of the cyclone components will have re-entrant, or concave, internal surfaces.

In particular, it would also be advantageous to make the components of the cyclone and collecting jar, for biological particle collection, of a material suitable for sterilisation and autoclaving.

The invention is expected to find a very wide diversity of applications in collecting airborne particles or particles from surfaces including for example seasonal pollen studies, sampling of house-dust-mite allergen, sampling dense particle concentrations in animal houses, collecting dusts from animals, industrial situations including routine sampling of surfaces to ensure hygiene and help detect deleterious contaminants, long-term gravimetric analysis, crop disease studies, collecting spores of plant pathogens and in forensic or environmental pollution applications where it may be necessary to sample substrate surfaces for microscopic contaminants. The sampler of the invention is also likely to prove much better suited than prior samplers to the collection of airborne antigens in an appropriate form and in sufficient quantity for immunological identification and assessment.

Embodiments of the invention will now be described by way of example, with reference to the accompanying drawings, in which: Figure 1 shows a sectional view of a cyclone sampler according to a first embodiment of the invention, on a reduced scale relative to figures 2 to 12 which also relate to the first embodiment; Figure 2 shows a longitudinal section of the cyclone of figure 1, sectioned on II-II; Figure 3 shows the cyclone exhaust portion of figures 1 and 2, sectioned on IA-IA and IB-IB; Figure 4 shows a side view of the cyclone inlet portion of figures 1 and 2, viewed along direction IV; Figure 5 shows a transverse section of the cyclone inlet portion of figures 1, 2 and 4, sectioned on V-V; Figure 6 shows an axial section on II-II of the cyclone cone portion of figures 1 and 2;; Figure 7 shows an axial section on II-II of the cyclone nozzle portion of figure 1; Figure 8 shows an axial section on II-II of the collection chamber lid of figure 1; Figure 9 shows an axial section on II-II of the collection chamber support of figure 1; Figure 10 shows a side view in direction X of the upper portion of the collection chamber support of figures 1 and 9; Figure 11 shows a vertical section on IA-IA and IB-IB of the cyclone exhaust portion of figures 1, 2 and 3, part of the inlet portion of figures 1,2,4 and 5, and the air inlet nozzle of figure 1; Figure 12 shows a plan view of direction XII of the cyclone portion of figure 11; Figure 13 shows a sectional view of a cyclone sampler according to a further embodiment of the invention;; Figure 14 shows a side view in direction XIV as shown in figure 13 of a portion of the cyclone of figure 13 including the sampling orifice; and Figure 15 shows a plan view in direction XV as shown in figure 13 of the base member of the cyclone of figure 13.

A first embodiment of the particle sampler of the invention is shown in figure 1, and is a portable self-contained unit for sampling airborne particles. A housing or base 2 houses an exhaust fan 4 driven by an electric motor 6, powered either by cells housed within the base 2 or by an external power supply. The base comprises a control panel 7 having a control for switching the fan 4 on and off and a timer for operating the fan for a predetermined time. A control may also be provided for varying the speed of the fan. A support 8 is fixed to the upper surface of the base, and is sealed around the intake 10 to the exhaust fan 4. A first portion 12 of an exhaust tube 14 is a push fit in the support 8, and extends vertically upwards from the base 2.The upper portion of the exhaust tube 14 turns through a 180 degree bend, via two 90 degree corner portions 18,20 linked by a straight pipe portion 22, so that the intake end 16 of the exhaust tube 14 points vertically downwards towards the base 2. The joints between the straight exhaust tube portions 12,22 and the corner portions 18,20 may be demountable, but when assembled are gas tight.

The intake end 16 of the exhaust tube 14 is connected via a connector 23 to an axial air exhaust outlet 24 of a particle separating cyclone 26. The internal diameter of the exhaust tube 14 is larger than that of the cyclone exhaust 24 to minimise the drop in air pressure along the exhaust tube, and the connector 23 is of conical internal profile to provide a gradual change in internal diameter between the two. The connector 23 is joined by airtight push fits to the exhaust tube and the cyclone exhaust.

The cyclone 26 is described in more detail below but comprises the axial air exhaust 24 connected to the exhaust tube 14, a tangential air inlet 28 (the air sampling orifice) for drawing in air to be sampled, and downwardly extending frusto-conical cavity 32 ending at its lower end at a particle outlet 34. In operation air is drawn out of the cyclone exhaust 24 along the exhaust tube 14, driven by the exhaust fan 4. Air is thus drawn into the cyclone inlet, airborne particles are separated from the air by the action of the cyclone and pass down through the particle outlet 34, the air passing upwards though the air exhaust 24. The action of the cyclone causes the particles to drift radially outwards to the cyclone wall and then be driven out of the particle outlet 34. At no point do the particles impact any surfaces hard enough to damage the particles collected.

The particles outlet 34 opens into a sealed collecting chamber 36 comprising a container 38 and a lid 40 fastened thereto by a screw thread 42. The lower portion of the cyclone push fits sealingly into a recess 44 in the lid 40.

The collecting chamber 36 stands in a shallow recess 46 on a height adjustable support 48 fastened to the base 2 beside the support 8 for the exhaust pipe 14. Since the cyclone, the collecting chamber and the exhaust tube intake 16 are linked only by sealing push-fit joints, when the height adjustable support 48 is lowered, the push-fit components can be separated and removed from the base 2.

This is particularly important in collecting biological particles since the cyclone and collecting chamber can then easily be cleaned and sterilised, but improves ease of operation of the sampler for all applications.

The construction of the cyclone is shown in more detail in figures 2 to 7. The cyclone comprises four separable components which are shown assembled in figure 2 and separately in figures 3 to 7. It should be noted that none of these components comprise re-entrant, or concave, internal surfaces and so can easily be cleaned.

The first component 50 of the cyclone, at the upper end of the cyclone, comprises the air exhaust outlet 24, the upper face 52 of the cyclone chamber 32, the upper face 54 of the tangential air inlet 28, and a vortex finder 56. The vortex finder 56 is an annular wall coaxial with the cyclone exhaust and extending into the cyclone chamber 32 adjacent the tangential air inlet 28.

A flange 58 around the circumference of the first component 50 seats on the top surface of the second cyclone component 60, shown in figures 4 and 5, which comprises a circular cylindrical wall within which a cylndrical upper portion 62 of the cyclone chamber 32 is defined. In addition this second component 60 defines the sides and bottom of the rectangular, tangential air inlet or sampling orifice, 28.

The first component 50 seats sealingly on the second 60, though they are not fastened. A locating pin in one seating surface locates in a recess in the other to ensure correct orientation. An axially extending, curved flange 64 on the first component locates within the bore of the second component and defines a curved annular channel which forms the upper surface 52 of the cyclone chamber 32.

A third component 66 of the cyclone, in figure 6, locates beneath the second component and defines a first frusto-conical portion 68 of the cyclone chamber 32. Circular, axially extending flanges 70,72 sealingly interconnect the second and third cyclone components 60,66. These components are not fastened, and need no locating pin as the third component 66 is rotationally symmetrical.

The inner surface of the lower end of the third component 66 defines a cylindrical recess 74 into which a fourth cyclone component 76 fits. The fourth component defines at its inner surface a frusto-conical nozzle 78 matching and of the same cone angle as the frusto-conical interior of the third component 66.

The nozzle ends at its lower end at a sharp edge 80.

The outer surface of the third component 66 is cylindrical and at its lower end fits sealingly within the cylindrical recess 44 in the lid 40 of the collectin chamber 36. When the nozzle 76 is located in the recess in the thrid component 66, an annular step 82 on the outer surface of the nozzle 76 seats on a corresponding flange 84 in the lid 40 and the nozzle end 80 extends through a hole 86 in the lid 44 into the collecting chamber.

When the adjustable height support 48 is raised, all of the push-fit components of the cyclone 26 are gently loaded against each other and thus held in place.

In the embodiment all components of the cyclone 26 are of an aluminium alloy but may be made of any appropriate material which can be formed sufficiently accurately to produce substantially airtight joints between the components and which can be sterilised, and preferably autoclaved, for biological use. The collection container may be for example of glass or aluminium.

The inner surfaces of the cyclone are highly polished to improve airflow in the cyclone chamber 32 and enhance particle separation, especially for small particles and low density particles.

The sealing at the joints between the cyclone components may be improved in an alternative embodiment by the use of 0-ring seals.

The shape of the cyclone chamber and the airflow rate are crucial to the performance of the particle sampler. The dimensions of the cyclone chamber of the embodiment are given in Table 1, expressed in terms of the diameter of the cylindrical cyclone portion, i.e.

the internal diameter of the second cyclone component 60. The cyclone chamber may be changed in size without adversely affecting performance as long as its shape and the necessary air flow rate are retained. The preferred demension D is 23.9mm.

Table 1 Internal diameter of second component 60: D Internal diameter of air exhaust outlet 24: 0.411 D External diameter of vortex finder 56: 0.500 D Length of vortex finder 56: 0.643 D Length of cylindrical cyclone chamber portion 62: 1.532 D Height of air inlet (sampling orifice) 28: 0.376 D Width of air inlet (sampling orifice) 28: 0.125 D Vertex angle of conical cyclone chamber portion 68,78: 16.4" In the embodiment the air flow rate is fixed by controlling the speed of the exhaust fan 4. The air speed through the cyclone inlet is preferably 9.7 m.s-l, giving an air sampling rate through the inlet of 16.5 l.min-1 for the preferred cyclone size.

The particle outlet diameter can be chosen by the operator by using different nozzles 76. This can affect the particle distribution collected in the collection chamber 36. Experimental data are given in Table 2 from tests conducted using the sampler as described to sample air containing predetermined particle types ranging from 1 micrometre diameter to 25-30 micrometre diameter.

For the tests a filter membrane was included in the sampler at the base of the exhaust tube 14 to prevent any particles from escaping and so to check the particle capture rate of the cyclone for each particle type. Such a membrane could usefully be incorporated in the sampler in non-experimental use, depending on the type of particles being collected.

Table 2 Distribution of particles within cyclone and escape fraction expressed as percentage of particles collected.

Collection Particle Cyclone Air Exhaust Membrane Nozzle Chamber 36 Outlet 76 Chamber Outlet Tube 76 60,66 50 14 Diameter/ mm Lycopodium, 25-30um, Spore washings.

97.26 2.01 0.73 7.00 97.18 2.13 0.70 5.00 97.25 2.15 0.61 3.00 Penicillium spores, 2-3 um, Spore washings.

58.93 2.88 26.41 10.71 0.74 0.34 7.00 61.82 4.14 26.15 5.71 1.55 0.63 5.00 58.66 7.74 26.34 4.62 1.93 0.70 3.00 Actinomycete lum, Spore washings.

31.74 10.57 31.62 16.08 6.18 3.81 7.00 32.57 13.65 29.37 14.28 7.09 3.04 5.00 30.62 14.46 29.85 15.78 7.21 2.08 3.00 Actinomycete culture forming unit. Nutrient agar 25 & 55 "C.

63.99 3.22 26.42 4.06 1.21 0.09 7.00 47.41 4.33 40.16 5.11 2.87 0.12 5.00 38.90 7.45 40.93 9.96 2.30 0.45 3.00 Note: All lycopodium spores were expected to be retained in the cyclone so the escape fraction was not measured. These particles are dry surfaced and almost monodispersed.

As shown in table 2, particles, especially small particles, are not all collected in the collection chamber 36 but adhere to the cyclone walls and to some extent the exhaust tube walls. It is clearly advantageous therefore that the cyclone may be dismantled and these particles collected by washing the cyclone components.

The ease of use of the sampler of the invention for collecting biological particles may be improved by providing a biological shield to protect at least the cyclone and the collection chamber from contamination during use.

In an alternative embodiment, more than one cyclone may be connected in series to improve the particle capture characteristics of the sampler.

For example the air exhaust outlet of an axial flow cyclone may be connected to the air sampling inlet of the cyclone of figure 1 to remove larger particles from the sampled air. If only the smaller airborne particles were of interest for a particular application then this would usefully concentrate these smaller particles in the collecting chamber at the output of the second cyclone in the series. The designs of the two (or more) cyclones in such a series could be chosen in order to tailor their particle capture characteristics as required for any given application of the sampler.

The Adjustable Height Support The mechanism of the adjustable height support 48 is shown in figures 9 and 10. An annular base 90 fastened to the sampler base 2, and a ring 92 located in an annular recess in the upper, outer corner of the annular base for rotation relative thereto. The ring 92 is retained on the annular base 90 by a circular plate 94 fastened to its upper surface by screws 96. A cylindrical cover 98 is a close sliding fit over the annular base 90, and is slidable vertically with respect to the base but is restrained from rotation relative thereto by a locating pin. The cover 98 has a circular, flat upper surface 100 with a flange 102 around its edge.

The collection chamber 38 is supported on the upper surface 100 within the flange 102.

The cylindrical wall of the cover 98 is formed with an angled slot 104 through which a handle 106 protrudes, the shaft 108 of the handle extending through the slot 104 and being fastened by a screw thread into the rotatable ring 92. Movement of the handle 106 rotates the ring 92 about the base 90, and moves the shaft 108 of the handle 106 along the angled slot 104. The cover 98 is thus raised and lowered relative to the base 90.

More than one angled slot, e.g. three, may be spaced around the cylindrical wall of the cover 98 and engage with shafts extending from the rotatable ring 92 to ensure that the cover is maintained horizontal at all times, even under load. The further shafts need not have handles.

The angled slot 104 has at one end, corresponding to the fully raised cover position, a level slot portion 106. When the handle and shaft lie in this slot portion, the cover is locked in position and cannot be lowered by excessive vertical loading.

The Non-Directional Sampling Orifice The tangential air inlet 28 to the cyclone 30 as shown in figure 2 is a highly directional sampling orifice. In some sampling applications this is adequate but in many applications it is desirable to use a non-directional sampling orifice which is not affected by, for example, ambient wind speed or direction. Such an orifice is shown fastened to the tangential air inlet 28 in figure 1 and in more detail in figures 11 and 12.

The sampling orifice 110 comprises a relatively large, circular, horizontal orifice 112 (with its axis vertical), with a rounded edge 114.

This is joined by a curved, convergent passage 116 to the tangential cyclone inlet 28. The horizontal, circular orifice 112 reduces the sensitivity of the sampler to ambient air movement, which is usually horizontal, and reduces the sampling airspeed, reducing the sensitivity of the sampler to particle size and velocity.

Sampling Particles from Surfaces A further embodiment of the sampler of the invention, designed for collecting particles from surfaces is shown in figure 13. The sampler 200 is designed to be hand-held, using the handle 202. The sampler is mounted on a frame comprising a rigid member 204, shown also in figure 15. A first portion 212 of an exhaust tube 214 is located in a hole 206 defined near one end of the base member 204 and extends upwardly therefrom within the handle 202. An upper portion of the exhaust tube 214 comprises two right angled exhaust tube portions 218 and 220 sealingly linked by an intermediate straight tube portion 222. The first right angled portion 218 fits sealingly onto the upper end of the first tube portion 216 so that the exhaust tube 214 turns through 180 degrees.The exhaust tube components 212 to 222 correspond to components 12 to 22 of the first embodiment described above. The first tube portion 212 is joined at its lower end to a fitting 208 for coupling to a flexible pipe leading to a vacuum pump separate from the sampler 200. In the first tube portion 212 is mounted a critical orifice 223 for limiting the airflow drawn by the vacuum pump along the exhaust tube to a predetermined constant flow rate.

The end of the second right angled exhaust tube portion 220 fits sealingly via a connector 223 to an axial air exhaust outlet 224 of a particle separating cyclone 226. The cyclone 226 is of similar construction to the cyclone 26 of the first embodiment of the invention as described above.

A particle outlet 230 at the base 232 of the cyclone opens into a particle collecting jar 234 of glass, plastic or metal. The base 232 of the cyclone is formed with a circumferential groove 238 in which an O-ring 236 is located for sealing against the inner surface of the jar 234 and a circumferential flange 240 supporting a second O-ring 241 against which the upper edge of the jar abuts.

The base of the jar 234 is located in a shaped recess 242 in the top of a spring-loaded plunger 244. The plunger 244 is slidably located in a hole 246 formed at the opposite end of the base member 204 from that for mounting the exhaust tube 216. The plunger 244 is biased upwardly from the base 204 by a helical spring 248 surrounding a shaft portion 250 of the plunger and located at its ends in annular recesses 252 and 254 in the plunger and base member respectively. The plunger is retained in the hole 246 by a crossbar 256 located in a hole 258 formed transversely through the shaft portion 250 of the plunger. A handle 260 is fastened to the lower end of the shaft portion 250 by a grub screw 262. The lower end of the hole 246 in the base member 204 is formed with two opposite radial extensions 259 into which the crossbar can be received.The plunger can be located in two axial positions, one with the crossbar abutting the lower surface of the base member 204 and one with it received in the extensions 259. These positions can be selected by axial rotation of the plunger by means of the handle 260.

The particle collecting jar can easily be inserted or removed from the sampler by withdrawing the plunger by means of the handle 260 against the bias of the spring 248. The plunger can be locked in the withdrawn position by turning the plunger as described. If required, a jar can then be removed and sealed appropriately, a replacement jar pushed onto the base of the cyclone and the plunger released so that the jar is loaded gently by the bias of the spring against the base of the cyclone. In use of the sampler this allows convenient replacement of collecting jars.

Also, as in the first embodiment, the cyclone itself can be removed and dismantled for example for cleaning.

As in the sampler of the first embodiment, the sampling orifice 228 of the cyclone 226 extends tangentially from the upper end of the cyclone. It is therefore directed away from the handle 202 of the hand-held sampler 200 conveniently for collecting particles from surfaces. In order to achieve the required sampling orifice airspeed for drawing particles away from surfaces while retaining the optimum airflow rate for particle separation in the cyclone, a smaller sampling orifice 228 than that of the airborne particle sampler of the first embodiment is advantageous. The area of the rectangular sampling orifice 228 of the present embodiment, shown in figure 14, is lmm by 9mm compared with 3mm by 9mm for the first embodiment.So that common cyclone components can be used in a variety of sampler types, the orifice area reduction can be achieved by inserting a constriction into the 'standard' orifice of the cyclone of the first embodiment.

For the same cyclone dimensions as in the first embodiment, the optimum airflow rate through the cyclone for particle separation is 16.5 litres per minute. To maintain this flow rate through the smaller sampling orifice of the surface particle sampler a pressure of at least 180mm Hg below atmospheric pressure must be maintained immediately downstream of the critical orifice 223. For this reason, as described above, it may be advantageous to use a separate pump connected by a flexible pipe to the sampler as the electric fan used in the sampler of the first embodiment may not be sufficiently powerful to maintain the required airflow through the smaller sampling orifice, particularly when in use of the surface sampler it is likely that close proximity of the nozzle to surfaces being sampled may further restrict the nozzle.

As in the first embodiment, it may in certain applications be advantageous to filter the exhaust airflow from the cyclone, for example through a filter located in the exhaust tube portion 222, to collect any particles for example too small or of too low density to be collected in the cyclone.

In various applications of the sampler, for example in collecting different particles from different surfaces or under different conditions, it may be advantageous to fit purpose-designed sampling nozzles of a variety of types onto the sampling orifice of the cyclone.

Claims (18)

CLAIMS:

1. A sampler for collecting airborne particles, comprising a cyclone having an air inlet, an air exhaust and a particle outlet, the air inlet comprising a sampling orifice, the air exhaust being coupled to a driven exhaust pump means for drawing air at a predetermined flow rate through the cyclone, and the particle outlet leading to a closed particle collection chamber.

2. A sampler according to claim 1, in which the cyclone comprises a plurality of separable components and can be dismantled for cleaning.

3. A sampler according to claim 2, in which the cyclone components and the collecting chamber are made of materials suitable for sterilisation and/or autoclaving.

4. A sampler according to any preceding claim, comprising a biological shield shielding at least the exterior of the cyclone and collecting chamber from biological contamination.

5. A sampler according to any preceding claim, in which the sampling orifice opens into air to be sampled.

6. A sampler according to any preceding claim, in which the cyclone and the collecting chamber are mounted on a housing and the pump means comprises a fan or turbine mounted within the housing and drivable by an electric motor powered either by storage cells mounted within the housing or an external power source, optionally a switch and/or a timer being provided on the housing for controlling the motor.

7. A sampler according to claim 6, in which the housing and the components assembled thereon form a self-contained, portable sampler.

8. A sampler according to any preceding claim, in which the sampling orifice has a vertical axis.

9. A sampler according to any preceding claim, in which the sampling orifice is of larger area than the air inlet to the cyclone so that the air velocity at the sampling orifice is less than that at the air inlet.

10. A sampler according to any of claims 1 to 4, comprising a frame or housing on which are mounted the cyclone, the collecting chamber and a coupling for connecting the air exhaust to the pump means, the sampler further comprising a critical orifice for controlling the air flow rate through the cyclone.

11. A sampler according to claim 10, in which the pump means comprises a vacuum pump.

12. A sampler according to claim 10 or 11 in which the critical orifice is mounted on the frame or housing, downstream from the air exhaust of the cyclone.

13. A sampler according to any of claims 10, 11 or 12, in which the sampling orifice and the air flow rate through the sampling orifice are adapted for making airborne and collecting particles from surfaces.

14. A sampler according to any of claims 10 to 13, in which the frame or housing with the components mounted thereon is adapted to be hand held and is separate from the pump means, being connected to the pump means by a flexible pipe.

15. A sampler according to any of claims 10 to 14, comprising a filter downstream of the air exhaust.

16. A method of sampling particles using a sampler as defined in any preceding claim.

17. A sampler substantially as described herein with reference to figures 1 to 12.

18. A sampler substantially as described herein with reference to figures 13 to 15.