Apparatus and method for sampling of airborne asbestos and other particles released from a surface

A sampling apparatus includes a housing defining a test chamber with an opening for contacting a test surface to expose at least a portion the test surface to the test chamber. A movable agitator within the test chamber contacts the test surface and agitates the test surface to release material from the test surface. The apparatus further includes an inlet and an outlet communicating with the test chamber and defining an air flow path through the chamber. At least one sample cassette may be supported near the outlet to collect a sample from the air flow, including material released from the surface into the test chamber.

TECHNICAL FIELD

The present invention relates generally to environmental test devices, and more particularly to apparatus and methods for sampling of airborne particles released from a surface.

BACKGROUND

Asbestos is a naturally occurring fibrous material that has been mined and incorporated into more than 3,000 commercial products, including building materials and non-building related products. Asbestos and other mineral fibers may be present as introduced contamination in soils, or as settled dust on various horizontal surfaces in buildings. Exposure to asbestos fibers from natural sources or from activities using asbestos-containing materials can produce debilitating health effects in humans. Asbestos aerosolization, or releasability, is the potential for fibrous asbestos structures that are present in a material or on a solid surface to become airborne when the source is disturbed by human activities or natural forces. The magnitude of the airborne concentration that can be generated from the release of asbestos is a function of the concentration of asbestos at the source, certain properties of the source matrix, the nature of the activity causing the source to be disturbed, and local environmental conditions.

Conventional testing methods for repeatable and representative measurement of asbestos or other particle aerosolization from materials (e.g., soil) are not suitable for field use. These conventional methods require removal and transport of the source matrix (e.g., soil), thereby potentially altering the physical characteristics of the matrix and subsequent aerosolization.

It is desirable to be able to determine repeatable and representative asbestos or other particle aerosolization concentrations from soil in-situ. Risk management decisions would be greatly enhanced by knowing the level of airborne asbestos or other particles that are expected when asbestos-containing sources are disturbed by specific human activities or natural forces under defined environmental conditions.

SUMMARY

The present invention provides a sampling apparatus and methods for sampling asbestos or other particles released from a material or a surface that overcome drawbacks of prior apparatus and methods for sampling particles released from a material or a surface, such as those described above. In one embodiment, an apparatus for sampling asbestos or other particles released from a surface includes a housing having at least one sidewall defining a test chamber. The test chamber includes an opening that is adapted to confront a surface to be tested, so that a portion of the surface is exposed to the test chamber. The apparatus further includes a movable agitator disposed within the test chamber. The agitator contacts the test surface and thereby agitates the test surface as it moves within the test chamber.

The apparatus also includes an inlet and an outlet, both communicating with the test chamber to define an air flow path through the test chamber. As air flows through the test chamber, asbestos or other particles released from the test surface by movement of the agitator become entrained in the air flow and are moved toward the outlet. One or more sample cassettes are provided near the outlet to obtain samples of the released asbestos or other particles for subsequent analysis. The apparatus thus permits in-situ collection of a sample of asbestos or other particles released from a test surface without the need for additional processing which might otherwise affect the physical characteristics of the sample matrix, e.g., soil. In another aspect, other sampling apparatus (e.g., optical particle counters) may be used to collect and analyze particles.

In one aspect, the apparatus may further include a fan communicating with the inlet to provide a flow of air through the test chamber, between the inlet and the outlet. The speed of the fan may be adjustable to vary the flow rate of air through the test chamber.

In another aspect, the agitator may include one or more tines adapted to contact the test surface. The agitator may also be coupled to an actuator that is adapted to repeatedly move the agitator along a predetermined path within the test chamber to thereby facilitate the release of material from the test surface. In one embodiment, the actuator may include a threaded rod and a motor coupled to the threaded rod, whereby rotation of the threaded rod in opposite angular directions by the motor causes the agitator to move in opposite linear directions.

In another aspect, a method of sampling airborne asbestos or other particles released from a test surface includes exposing at least a portion of the test surface to a test chamber, agitating the portion of the test surface within the test chamber to release material of the test surface, providing a flow of air across the test surface, and collecting a sample of the air from the test chamber. In one embodiment, separate sample cassettes are used to collect samples of the air substantially simultaneously. One of the cassettes may then be examined while the test surface is still exposed to the test chamber, to evaluate the quality of the collected sample. If the collected sample is determined to be insufficient, the previously collected samples may be discarded and a new test may be run, using different test parameters if needed.

In one embodiment, the flow of air across the test surface is provided while the test surface is agitated. In another embodiment, the test surface is agitated while samples are collected.

By virtue of the foregoing, there are thus provided a sampling apparatus and methods for sampling asbestos or other particles released from a surface that overcome drawbacks of prior apparatus and methods for sampling asbestos or other particles released from a surface. These and other objects and advantages of the present invention shall be made apparent from the accompanying drawings and the description thereof.

DETAILED DESCRIPTION

FIGS. 1-3depict an exemplary apparatus10for in-situ sampling of airborne material released from a surface, in accordance with the principles of the present disclosure. The apparatus10includes a housing12having first and second oppositely disposed sidewalls14,16, first and second oppositely disposed end walls18,20adjacent the first and second sidewalls14,16, and a top wall22extending between upper ends of the first and second sidewalls14,16and the first and second end walls18,20to form an enclosure. The housing12includes an open end24generally opposite the top wall22. The sidewalls14,16and end walls18,20thereby define a test chamber26proximate the open end24, and the open end24is adapted to confront a test surface28to expose the test surface28to the test chamber26. The peripheral edges of the housing12around the opening24may be provided with foam gasket material (not shown), or any other material suitable for substantially isolating the portion of the test surface28exposed to the test chamber26from the surrounding environment. In one embodiment, the test chamber26is approximately 6 inches high and approximately 6 inches wide, and has a length of approximately 24 inches.

In the embodiment shown, the first and second sidewalls14,16include windows30positioned adjacent the test chamber26to facilitate viewing the interior of the test chamber26while the apparatus10is in use. With particular reference toFIGS. 2 and 3, the housing12further includes an interior compartment40disposed between the test chamber26and the top wall22for enclosing various mechanical and/or electrical components of the sampling apparatus10, as will be described in more detail below. The boundary of the test chamber26and the compartment40is defined by an intermediate wall42disposed generally parallel to the top wall22and positioned between the opening24and the top wall22. The housing12of the exemplary embodiment is formed from 0.08 inch-thick anodized aluminum sheet that has been cut, bent, and welded or other wise fastened together to form the various features described herein. It will be appreciated, however, that the housing may be formed from various other materials and by various other methods to obtain an enclosure as described generally herein.

The apparatus10further includes an agitator50disposed within the test chamber26. The agitator50is movable within the test chamber26and contacts the test surface28during movement thereof to thereby disturb the test surface28and release material into the air within the test chamber26. Referring toFIGS. 3 and 5, the agitator50includes an agitator block52and a plurality of elongate tines54extending downwardly from the agitator block52to engage the test surface28. In this embodiment, the agitator50includes ten tines54that are spaced from one another and arranged in two generally parallel rows. It will be appreciated, however, that the agitator50may include various other configurations of tines54, or various other structure suitable for contacting the test surface28to facilitate releasing material into the air within the test chamber26.

The agitator block50is coupled to an elongate yoke56having apertures58a,58bprovided at opposite terminal ends60a,60b. The agitator50is supported by a pair of vertical rods62,64extending through the apertures60a,60bin the yoke56and having upper ends operatively coupled to the threaded rod66of an actuator assembly68disposed in the compartment40above the test chamber26. The vertical rods62,64extend through a generally elongate slot70provided in the intermediate wall42between the test chamber26and the compartment40. The threaded rod66extends generally parallel to the test chamber26and the vertical rods62,64are coupled to the threaded rod66by bushings72,74that are threadably engaged with the threaded rod66such that when the threaded rod66is rotated, the bushings72,74are caused to move along the length of the threaded rod66thereby imparting movement to the agitator50within the test chamber26. The vertical rods62,64are also threaded and the vertical position of the yoke56and agitator block52within the test chamber26may be adjusted by selectively adjusting the position of sleeves76a,76band nuts78provided on the respective vertical rods62,64and supporting the yoke56thereon.

The actuator assembly68further includes a motor80, such as gear motor part number 4FM-17 available from W.W. Grainger, Inc. of Lake Forest, Ill., disposed in the compartment40and operatively coupled to the threaded rod66. The ends66a,66bof the threaded rod66are rotatably supported in bearing blocks82,84, such as part number 5912K22 available from McMaster-Carr Supply Co. of Elmhurst, Ill. An output shaft86of the motor80is coupled to one end of the threaded rod66by a drive chain88, whereby the threaded rod66may be rotated about its longitudinal axis by the motor80to cause the agitator50to move within the test chamber26between first and second ends90,92of the test chamber26. The direction of the agitator50is determined by the rotational direction of the threaded rod66. The apparatus10further includes a speed control100, such as part number 4Z826 available from W.W. Grainger, Inc., communicating with the motor80and a current switch102operative to change the direction of current provided to the motor80. Changing the direction of the current, in turn, changes the rotational direction of the motor output shaft86and the rotational direction of the threaded rod66.

The apparatus10further includes sensors104,106disposed proximate the respective first and second ends90,92of the test chamber26to facilitate changing the direction of motion of the agitator50within the test chamber26. In the embodiment shown, the sensors104,106comprise limit switches, such as part number 6X289 available from W.W. Grainger, Inc., in electrical communication with the current switch102and the control100. As the agitator50is driven by the threaded rod66toward one of the first and second ends90,92of the test chamber26, one of the vertical rods62,64will eventually engage one of the sensors104,106. In response, the respective sensor104,106sends a signal to the current switch102and the control100which in turn respond to change the rotational direction of the motor80and the threaded rod66, thereby causing the agitator50to move in the opposite direction. The agitator50will continue moving in the opposite direction, toward the other end of the test chamber until a threaded rod90,92contacts the other sensor104,106, and the direction is again reversed. The agitator will continue moving back and forth between the first and second ends90,92of the test chamber26during the collection of a test sample.

While the agitator50has been shown and described herein as including tines54that are moved in a substantially linear motion, it will be appreciated that the agitator may alternatively comprise various other structure suitable for agitating the surface and/or may utilize various other types of motion, such as rotational motion, non-periodic or random motion, compaction-type motion, or any other type of motion that facilitates the release of material from a test surface28.

With continued reference toFIGS. 1-3, the test chamber26includes an air inlet110at the first end90of the test chamber26for providing a flow of air through the test chamber26. The air flows over the test surface28and exits through an outlet112at the second end92of the test chamber26. In the embodiment shown, air is drawn through an air inlet114and into an inlet conduit116by a fan118provided near the first end90of the test chamber26. The air passes through a High Efficiency Particulate Air (HEPA) filter120, such as part number 506510 available from Labconco Corporation of Kansas City, Mo., to prevent asbestos or other airborne particles outside the apparatus10from entering the test chamber26. The air is directed through an arcuate elbow122and a diffuser124having tapered sidewalls126to the inlet110of the test chamber26. The speed of the fan118may be adjustable, such as by a selectively adjustable power supply119, to vary the flow rate of air through the test chamber26. In the embodiment shown, the inlet conduit116and elbow122may be formed from 6-inch diameter PVC pipe, such as reducing coupling part number 4511K86 available from McMaster-Carr Supply Co. and 90-degree elbow part number 1WKV4 available from W.W. Grainger, Inc. The fan118may be an in-line centrifugal duct fan, part number 19135K65, available from McMaster-Carr Supply Co.

FIG. 4depicts the diffuser124used in this exemplary embodiment. The diffuser124has a generally rectangular first end130with mounting flanges132for coupling to the first end90of the test chamber26, and a generally circular second end134for coupling to the elbow122. The diffuser124includes flow-straightening vanes128aligned with a longitudinal direction of the test chamber26to create a laminar flow of air through the test chamber26from the inlet110to the outlet112. As seen inFIG. 4, the flow straightening vanes128are spaced approximately 1.5 inches apart and include a plurality of generally horizontal vanes128aand a plurality of generally vertical vanes128b.

With particular reference toFIGS. 1,3, and6, the outlet112at the second end92of the test chamber26includes a generally rectangular opening formed in the second end wall20to permit air flowing through the test chamber26to exit the second end92of the test chamber26. One or more sample cassettes140are provided adjacent the outlet112for collecting samples of the air passing through the outlet112of the test chamber26. In the embodiment shown, three sample cassettes140are used to simultaneously collect samples of the air flowing through the outlet112. The cassettes140are supported on a mounting bar142extending across the outlet112and are held in position by respective clamps144attached to the mounting bar142, by fasteners146. In the embodiment shown, the sample cassettes140are 25 mm-diameter, mixed cellulose ester (MCE) filters having 0.8 μm pore size adapted to collect particulate material in the air flowing through the test chamber26. An exemplary sample cassette140is part number 225-321 available from SKC, Inc. of Eighty-Four, Pa.

The sample cassettes140are positioned a distance above the test surface28that facilitates collecting airborne material released from the test surface28. In one embodiment, the sample cassettes140may be positioned with their centerlines approximately 1.5 inches above the test surface28. In this embodiment, two sample cassettes140are positioned with their centerlines approximately 1.5 inches from the respective sidewalls14,16, and a third sample cassette is positioned with its centerline approximately 3 inches from either sidewall14,16. The leading edges148of the sample cassettes140are positioned approximately 2 inches from the outlet112. It will be appreciated, however, that various other types and sizes of sample cassettes140may alternatively be used and/or the sample cassettes140may be positioned and arranged in various other configurations to facilitate collecting samples of the released material from within the test chamber26.

Each sample cassette140is coupled to a respective vacuum pump150a,150b,150cby a vacuum conduit152. The vacuum pumps150a,150b,150cdraw air flowing through the test chamber outlet112into the respective sample cassettes140. In the embodiment shown, the pumps150a,150b,150care 1/10 HP rotary vane oil-less vacuum pumps, model number 1532-101, available from Gast Manufacturing, Inc. of Benton Harbor, Mich. The pumps150a,150b,150cmay be placed on top of the housing12to help keep the apparatus10stable during test, or may be positioned in various other locations. Each pump150a,150b,150cincludes a gauge154a,154b,154c, such as in-line flow control meter part number MMF-24-TMV available from Dwyer Instruments, Inc. of Michigan City, Ind., or any other suitable device for indicating the vacuum pressure developed by each pump150a,150b,150cso that the air flow drawn into the respective sample cassettes140may be carefully and uniformly controlled.

In use, the apparatus10is positioned directly on a test surface28at a desired test site. Before sampling at the desired test location, each of the pumps150a,150b,150cshould be calibrated with a representative sample cassette140. The total sample air volume to be collected will be determined by site conditions and properties of the test matrix. Accordingly, prior to collection of actual samples, trial samples should be collected to determine the maximum air volume that will yield an acceptable filter loading of the sample cassettes140, as determined by on-site optical examination of the trial sample cassettes140. In one embodiment, samples may be collected at a target air flow rate of approximately 14 liters-per-minute for a period of approximately 5 to 30 minutes, to achieve a target air volume of approximately 70 to 420 liters. Before the apparatus10is placed at the location to be tested, the apparatus10should be decontaminated to reduce or eliminate the possibility of cross contamination from previous test sites. After decontaminating the apparatus10, an equipment blank sample should be collected to demonstrate the cleanliness of the instrument and to ensure that no cross-contamination occurs between samples. The sample site should also be selected to be devoid of vegetation and large rocks. For example, any rock greater than ½ inch in diameter should be removed from the test area.

Prior to conducting a test, the position of the agitator yoke56on the vertical rods62,64should be adjusted by rotating the respective nuts78on the vertical rods62,64to move the sleeves76a,76bto positions that allow the tines54of the agitator50to freely contact the test surface28. The apparatus10may then be positioned over the test surface28with the open end24confronting the test surface28to expose a portion of the test surface28to the test chamber26. Anchors, such as tent stakes (not shown), may be used to secure the apparatus10to the test surface28. The vacuum pumps150a,150b,150cmay also be placed atop the housing12to weigh down the apparatus10at the test surface28and prevent movement of the apparatus10during the test.

With the apparatus10in place, the sample cassettes140may be positioned within their respective clamps144and the vacuum conduits152may be coupled to the respective sample cassettes140, such as at outlet tips141(FIG. 6). The opposite ends of the vacuum conduits152are coupled to the respective vacuum pumps150a,150b,150c. The vacuum pumps150a,150b,150care started to begin drawing air through the sample cassettes140and power is provided to the fan118to draw air from the environment through the air inlet114of the inlet conduit116. In one embodiment, the speed of the fan118may be adjusted to achieve a flow velocity of approximately 264 to 440 feet per minute within the test chamber26. The velocity of the air flow within the test chamber26may be verified using a hot wire anemometer or any other device suitable for measuring air velocity. Power is then provided to the actuator motor80to cause the agitator50to move within the test chamber26as described above.

As the agitator50moves over the test surface28to release asbestos or other material into the air flowing through the test chamber26, the vacuum pumps150a,150b,150cdraw air from the test chamber26into the sample cassettes140. At the conclusion of a test, power to the actuator motor180is terminated to stop the movement of the agitator50. Power is then terminated to the fan118to stop the flow of air through the test chamber26, and the pumps150a,150b,150care then stopped to terminate the collection of air samples by the sample cassettes140.

In one embodiment, one of the collected sample cassettes140may be examined onsite using a phase contrast microscope to determine the quality of the collected sample while the apparatus10is still in position on the previously sampled test surface28. If it is determined that the quality of the collected sample is inadequate, such as if the sample cassette140is overloaded, for example, the previously collected samples may be discarded and the test may be conducted using an adjusted flow rate until acceptable samples are obtained.

To facilitate obtaining acceptable samples, the apparatus10may further include a wind direction indicator160to aid in properly orienting the apparatus10with the predominant wind. In the embodiment shown, the wind indicator160includes a stand162for mounting the device to the housing12or other convenient surface. The apparatus10may be oriented such that the outlet112of the test chamber26is in the same direction as the predominant wind at the test site. The apparatus10may further include a wind break164or other structure which may be placed adjacent the outlet112of the test chamber26, to prevent ambient wind from disturbing the collection of test samples. To facilitate transporting the apparatus10and to facilitate positioning the apparatus10at a desired test site, handles170a,170bmay be provided on housing12, such as adjacent end walls18,20, as shown inFIGS. 1 and 2.

While the present invention has been illustrated by the description of an embodiment thereof, and while the embodiment has been described in considerable detail, it is not intended to restrict or in any way limit the scope of the appended claims to such detail. The various features discussed herein may be used alone or in any combination. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and method and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the scope or spirit of the general inventive concept.