WO2018130808A1

WO2018130808A1 - Personal aerosol sampling device

Info

Publication number: WO2018130808A1
Application number: PCT/GB2018/000007
Authority: WO
Inventors: Pramukh Nalaka Jayasekera; Paul Henry Kaye
Original assignee: The Secretary Of State For Defence
Priority date: 2017-01-16
Filing date: 2018-01-16
Publication date: 2018-07-19
Also published as: GB201800658D0; GB2560611A; GB201700695D0; GB2560611B

Abstract

The present invention provides personal aerosol sampling devices, in particular personal bio-aerosol sampling devices, and methods of use thereof to sample air in any working environment, such as in a hospital environment, or a manufacturing facility.

Description

Personal Aerosol Sampling Device

The present invention is concerned with personal aerosol sampling devices, and especially bio- aerosol sampling devices for sampling for biological particles, such as bacteria.

Personal sampling technologies are used in the occupational health sector for monitoring exposure to airborne industrial hazards including nuisance dusts. The majority of these technologies are bulky and modular and have features which while tolerated by the wearers in occupational health situations, are still not optimal or desirable. These features may include for example a tube across the wearer's chest to connect the sampling head located in the breathing zone to a separate large pump worn at the waist.

It remains a problem to provide an 'all-in-one' (i.e. all features within the same unit; integral) simple miniature device with a low burden, low power requirement, and which is capable of collecting particles for a reasonable length of time, such as up to 8 hours, especially for biological particles.

The present application is thus concerned with providing such a device, especially an 'all-in one' personal sampler to eliminate these shortcomings, and more particularly an 'all-in-one' personal bio- aerosol sampling device.

Accordingly, in a first aspect, the present invention provides a personal aerosol sampling device comprising a filter material, a blower or fan for creating an air flow through the filter material, and a power source for the blower/fan.

The filter may be any suitable material, but preferably is a filter material of low impedance (low pressure drop) to enable the power requirement of the blower, and subsequently the device, to be kept low. The pressure drop of the filter material is preferably 300 Pa or less, which may be 200 Pa or less, such as between 100 Pa to 200 Pa for a low/medium impedance material, or less than 100 Pa for some filter materials, such as needle felt materials. The pressure drop could be measured, for example, at an air velocity of 5.3 cm s-1. Such a device is then not only low power, but consequently also compact, and all-in-one (i.e. it is not modular, and in particular does not require use of a separate pump, which is often bulky and has a relatively high power requirement).The filter material may be a HEPA (high efficiency particulate air) filter material, or a glass filter, especially for detection of a broad range of particle sizes, such as ranging from deep sub-micron, to tens of microns, which has been found to be especially applicable to collecting chemical particles from chemical aerosols.

In one preferred embodiment the filter material is a needle felt material.

The Applicant has recognised that needle felt materials are of particularly low impedance (often less than 100 Pa) and that such filter materials are especially suitable for use as filter materials for particles of about 1 micron and above, and thus especially for bio-aerosols (i.e. for collecting biological particles from bio-aerosols). This recognition by the Applicant has led to the development of a personal aerosol sampling system, in particular a bio-aerosol sampling system, that

consequently only requires a low power blower or fan (rather than a pump, and especially a separate pump) to provide a suitable air flow for such a device, such as 4 1 min-l, 2 I min-l, or 0.5 I min-l, which could then collect for a sufficient period of time such as 4 hours (half a working day), or 8 hours (a working day) with use of only a very small battery, such as an alkaline coin cell battery. Such a device is low power, compact, and all-in-one (i.e. it is not modular, and in particular does not require use of a separate pump, which is often bulky and has a relatively high power requirement).

The device is most likely wearable, for example through use of a clip, in the vicinity of the breathing zone of the wearer.

Needle felt materials are materials produced by a felting technique known as needle felting which uses barbed needles to push fibres through a top fabric to lock into a base fabric.

The needle felt material may comprise polypropylene, or may be polypropylene needle felt. The needle felt material may also comprise polyester, or any other suitable polymer from which biological particles can be extracted to enable detection. The needle felt material provides a low pressure drop filter with a good collection capability for biological particles. Such materials have not previously been used for collection of biological particles, and moreover have not been used in personal sampling devices. Since the needle felt material functions as a low pressure drop filter it places a reduced demand on the supporting air- mover (blower or fan) and battery compared to commonly deployed high efficiency filters used in the personal sampling devices in the art.

The flow rate may be at least 0.5 I min-1, or may be at least 1 1 min-1, 2 I min-1 or 4 I min-1. A flow rate of 7 I min-1 is possible through a 25 mm diameter needle felt filter in such a device for a short duration sampling (of about 1 hour) with a low power blower, and between 4 and 5 I min-1 for a much longer duration (about 3 hours) with the same 25 mm filter.

The device includes any circuitry which may be required for it to function, such as to provide power to the blower/fan, for charging of the battery, for switching of the device on/off, or to provide different air flow rates.

One embodiment of the first aspect of the invention may comprise a 25 mm diameter filter material (needle felt material), wherein the dimensions of the consequent device could measure about 30 mm wide, 50 mm long, and 25 mm depth, as a result of use of a low power blower and a suitable coin battery. The weight of the device may be less than 20g, or less than 30 g, or less than 40 g, or less than 50 g (including the battery). This is clearly a lightweight, compact, miniature device as compared to prior art devices.

The device of the first aspect may comprise additional detection elements, such as a particle counter, fluorescence detection unit, or additional chemical detector (e.g. a carbon monoxide detector; especially for a sampler directed to detecting chemical particles), depending on the utility of the device. The device may also comprise a removable cartridge element, comprising the filter material, to allow the filter material to be transported to a second device for controlled removal of particles from the filter material. The controlled removal of the particles could be through washing, shaking, and/or by foam extraction.

In a second aspect, the present invention provides for use of the device of the first aspect for sampling air with a flow rate of at least 0.5 I min-1, for a period of at least 4 hours.

The device could sample air in any working environment, such as in a hospital environment, or a manufacturing facility.

The flow rate may be much higher than 0.5 I min-1, such as 2 I min-1, which is the flow rate commonly used in personal sampling devices, or 4 1 min-1, or even higher (such as 7 I min-1 for a short duration). Such a device may be able to sample for a period of approximately 8 hours, or even more.

The present invention will now be described with reference to the following non-limiting examples and drawings in which

Figure 1 illustrates one embodiment of the device of the first aspect of the invention; and

Figure 2 illustrates an exploded view of one embodiment of the device of the first aspect of the invention.

Examples '25mm' Personal Aerosol Sampler (PAS) with needle felt filter

The 25mm PAS development involved modelling of possible designs to achieve the most compact solution for the Sampler body shell whilst also achieving the required sample airflow through the 25mm diameter needle felt filter, of 0.5 litres/minute over a 4 hour sampling period.

Key components:

• 25 mm diameter needle felt filter (polypropylene; Fiberlox™)

• Blower

The specific blower used was a Sunon miniature blower (UB3-H3-700). These ultra-compact blowers offer a higher static pressure drop than fans of equivalent size and are both inexpensive and low- power consumption. This blower offered the best compromise between static pressure drop (40 Pa) and power consumption (nominally 37 mA at 3V operation) and, at a size of just 17 mm x 17mm x 3mm would fit within the nominal 25mm diameter required for the Sampler.

• Battery

Battery technology is developing rapidly and achievable energy densities are increasing. After a review of existing options, the ulticomp™ Lithium-Ion rechargeable battery (LIR2450) was selected as the best compromise of price, performance, reliability and availability (other higher capacity batteries are available but have drawbacks such as relatively high leakage discharge rates and/or complex charging conditions). This battery is 24.5 mm diameter and 5mm thick and provides an output voltage of 3.6v, matching the maximum permitted operating voltage of the blower. It offered a nominal capacity of 120 mA.

• Control and Charging Circuitry The PAS was designed so that the voltage applied to the blower is switchable so that the user could operate the PAS for a shorter time period at high flow rate or a longer time period at a lower flow rate. The option of 'High' and 'Low' flowrate settings were implemented.

A PCB (printed circuit board) was designed and fabricated to accommodate the flow-rate switching circuitry and the battery charging circuitry.

• 3D Printed Parts

These could be injection moulded parts or even machined metal parts. However, this specific example used a Dimension Elite™ 3D printer that is capable of producing robust ABS plastic parts in relatively short timescales. For some of the required parts, however, the resolution of the ABS process (0.27mm) was insufficient to achieve the accuracy required and for those parts a stereo- lithographic processes (0.05mm resolution) was used.

Implementation:

Having regard to Figure 1, the personal aerosol sampling device produced measures 29 mm width by 49 mm length, with a depth of 22 mm. It weighs 16 g (including the battery). The device has a filter inlet 1, a high/low flow rate switch 2, a clip attachment point 3, a sample flow vent 4, a micro-USB charger point 5, and an on/off switch 6.

Having regard to Figure 2, the order in which the elements of this device are combined to make the final device are shown. The device comprises filter cap 7, which was 3D stereo printed, the 25 mm needle felt filter 8, a filter standoff 9, again 3D stereo printed , the body shell 10, 3D printed ABS, the Sunon blower 11, PCB material 12, the battery standoff 13 (3D printed ABS), the Li-ion rechargeable battery 14. And the base unit 15 (3D printed ABS). This is all designed to clip together for ease of assembly (no screws are required). Since the unit has a rechargeable Li-ion battery which is charged by connecting a standard micro- USB cable from a laptop or mains-USB there is no need to access the battery except for replacement after at least 300 charge-discharge cycles.

A dual-colour LED has also been included with the charging circuitry, and is visible from the side of the unit, to indicate when the battery is charging (LED is red) or when it is fully charged (LED is green).

The device is designed to accept a 25mm diameter needle felt filter. However, standard 25mm diameter glass fibre AE filters could also be used with an additional 1.6mm thick o-ring (which could be provided with the unit), though the flow rate possible with the device would be reduced with this higher impedance filter. The glass fibre filter should be placed on the Filter standoff and the o-ring placed between it and the filter cap to ensure a good seal at the filter edges. The filter could also be a low or medium impedance HEPA filter.

A modified filter cap was also produced which allows a pre-filter to be fitted upstream of the normal sampling filter to remove oversized particles.

Testing:

Initial testing of the device was carried out using a Gilian™ Bubble Flowmeter. An adapter piece was made that fitted tightly over the filter head, thus allowing the PAS to pull air through the Bubble Flowmeter.

NB: Although the Bubble Flowmeter offers very low flow impedance it is still significant compared with the pressure drop being created by the PAS blower (approximately 40 Pa). The result is that the flow rate measured by the Bubble Flowmeter is an underestimate of the actual flow rate that would be achieved if the device was operating in 'free air⁷ and not connected to the Bubble Flowmeter. Therefore, the flow rate figures measured are likely to be an underestimate of the actual flow rate through the filter.

The results are shown in Table 1 are for use of the 25mm diameter needle felt filter fitted within the device. Data are the average of 10 Bubble Flowmeter measurements in each case.

Table 1: Flowrate measurements of five identical devices with needle felt filters fitted.

As can be seen from Table 1, the mean flowrate exhibited by the five units was 1018 ml/min +/- 4% in the High setting and 369 ml/min+/-10% in the Low setting.

If correction for the loading effect of the Bubble Flowmeter is made, the flowrate would almost certainly exceed 500 ml/min in the Low flow setting.

These experiments, with needle felt filter, were then compared with a glass fibre filter fitted instead, to assess whether there was any improvement in flow rate seen with a needle felt material, over a filter commonly used in personal sampling devices, and if so what the extent of that difference was. A 25mm diameter glass fibre AE filter was used, and the flowrates were again as measured by the Bubble flowmeter.

Table 2: Flowrate measurements of a single device with glass fibre filter fitted.

The higher impedance of the glass fibre filter clearly results in far lower flow rates (almost a ten-fold difference) than the needle felt.

The operational runtimes for the device was measured starting with fully charged batteries. The mean duration values were as shown in Table 3.

Table 3: The operational run times for the device in the High and Low flow setting.

During runtime, the output voltage of the battery was maintained at 3.5v or above until the capacity had fallen to 20% of maximum, after which the voltage fell rapidly to zero volts. In the High flow setting the blower was connected directly to the battery voltage, stopping when the battery dropped to below 2v (the minimum operational voltage for the blower). In the Low flow setting, the blower was connected to the battery via a 2.2v regulator and maintained its speed until the battery dropped to approx. 2.4v.

Following further optimisation of the 25 mm (needle felt material) PAS device, flow rates of above 4 I min-1 were achieved for long duration sampling (of up to 3 hours), and 7 I min-1 for short duration sampling (of about 1 hour).

Clearly larger, or potentially smaller, devices can be manufactured depending on the specific sampling requirements, whilst retaining all the advantages provided, especially through use of a needle felt material based filter, and still be all-in-one, compact, and of low power consumption.

Testing Collection Efficiency of Needle Felt Material

The collection efficiency of a polypropylene needle felt material (Fiberlox™) filter was tested over a range of air flow rates (1, 2, 5, 6, and 14 1 min-1) for a variety of particle sizes (1 to 10 μπι, to encompass the size range of most micro-organisms). The particle size distribution of aerosol drawn through the filter was measured using a TSI aerosol particle sizer.

Generally the penetration of particles through the material decreased (and thus collection increased) with increasing particle size and increasing flow rate, this is because the likely capture mechanism for larger particles and high flow rates is impaction of particles onto the fibres of the filter as a result of their higher inertia.

For smaller particles, the material performed best at high flow rates (14 1 min-1; collection of 63% of Ιμηι particles, and 98% of particles 2μητι and above). At lower flow rates, the material was poorer at capturing 1 μη particles (5 I min-1, collection of 26%; 1 1 min-1, collection of 20%), but the collection increased significantly for 2 μιη particles (5 I min-1, 75%; 1 1 min-1, 43%)), and for particles >3μηι (5 I min-1, 99%; 1 1 min-1, 66%). The needle felt material is thus a good candidate for use as a filter in personal aerosol sampling devices for biological particles, such as micro-organisms.

For detection purposes, the needle felt material may be a polypropylene based needle felt, polyester based needle felt or any other suitable polymer which would offer opportunity of producing samples for analysis, for example by vigorous shaking in aqueous media, which may include a detergent, or by foam extraction.

'37 mm' Personal Aerosol Sampler (PAS) with HEPA filter for sampling/collection of chemical species from workplace or chemical agent aerosols

A second device was designed and built to be especially applicable for collection of chemical particles, which were shown to be more difficult to collect using the needle felt material, since they are often sub-micron in diameter.

A HEPA filter was used in this device. The HEPA filter was a Temish^® air-filter, purchased from Nitto Denko Corporation. The filter was the NTF9314 - H14 filter which had a pressure drop of 140 Pa (measured at 5.3 cm s-1). The NTF9310 H-13 filter could also be used, which had a pressure drop of 100 Pa (measured at 5.3 cm s-1).

The diameter of the filter material (HEPA) was increased (over that of the needle felt material filter) to 37 mm in order to achieve the desired and industrial standard flow rate of 2 I min-1 (the HEPA filter used is of low/moderate impedance, as compared to the low impedance of the needle felt material, though significantly of much lower impedance than the standard glass fibre filter traditionally used in personal aerosol sampling devices), which could run for a period of about 4 hours, whilst retaining the advantages that result from using a low power consumption blower, and small power source, such as an alkaline coin cell battery, and which consequently results in a compact 'all-in-one' personal aerosol sampling device for chemical particles.

Claims

1. A personal bio-aerosol sampling device comprising a filter material, a blower or fan for creating an air flow through the filter material, and a power source for the blower/fan, wherein the filter material is a needle felt material.

2. A personal bio-aerosol sampling device according to Claim 1, wherein the needle felt material comprises polypropylene.

3. A personal bio-aerosol sampling device according to Claim 1 or Claim 2, wherein the device is capable of sampling air for at least 4 hours at a flow rate of at least 0.5 I min-1.

4. A personal bio-aerosol sampling device according to Claims 1 to 3, wherein the power source is an alkaline coin cell battery.

5. An all-in-one personal aerosol sampling device comprising a filter material, a blower or fan for creating an air flow through the filter material, and a power source for the blower/fan.

6. An all-in-one personal aerosol sampling device according to Claim 5, wherein the filter material is a HEPA filter material.

7. An all-in-one personal aerosol sampling device according to Claim 5, wherein the filter material is a needle felt material.