Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
  • G01N15/02—Investigating particle size or size distribution
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
  • G01N15/02—Investigating particle size or size distribution
  • G01N15/0205—Investigating particle size or size distribution by optical means
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
  • G01N15/06—Investigating concentration of particle suspensions
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
  • G01N2015/0042—Investigating dispersion of solids
  • G01N2015/0046—Investigating dispersion of solids in gas, e.g. smoke
  • G01N2015/0049—Investigating dispersion of solids in gas, e.g. smoke of filaments in gas

Definitions

• This invention relates to methods and devices for estimating the concentration of airborne fibers, and particularly to devices which can decipher between respirable fibers and non-fibrous respirable fibers.
• airborne fibers are collected on a filter.
• This filter is analyzed by microscopy or chemical methods to determine the type of fibers present and to estimate airborne fiber concentration.
• This method suffers from the drawbacks of delayed availability of information, tediousness, inconvenience, high cost per sample, and lack of precision.
• identification of fibers typically is performed by visual inspection, adding uncertainty to measurements for particular species of airborne fibers.
• real-time airborne fibers concentration is determined using optical techniques, in which light, attenuated by fibers passing by a light source, is analyzed.
• optical techniques in which light, attenuated by fibers passing by a light source, is analyzed.
• most of these devices do not discriminate between different species of airborne fibers and, in particular, may not provide an accurate measurement of potentially respirable fibers, particularly small glass fibers.
• respirable fibers including, for example, glass fibers
• such methods may not be appropriate.
• an airborne fiber concentration measuring device that can accurately determine the concentration of respirable fibers suspended in an air sample, in real time, without the need for electrostatic, magnetic or hybrid electromagnetic components.
• the Lillienfeld's device is more complicated, detects only a small percentage of fibers in a given sample, and if the concentration of fibers in the sample is low or not representative of the fiber concentration in the air flow, measurement errors can result. There therefore remains a need for a fiber concentration measuring device which takes a more significant sampling of the fiber population and which is accurate at low concentration readings.
• This invention provides devices and methods for measuring the concentration of airborne fibers in a fiber-containing air sample.
• the preferred device includes flow means for providing laminar flow to at least a portion of the fibers in the air sample. These laminarly flowing fibers are then illuminated with a light source to produce scattered light. A portion of the scattered light is then sensed to produce an output from which a fiber concentration estimate can be measured. Additionally, separation devices can be used to preselect fibers having a particular size, so as to measure only respirable fibers, for example. This invention provides an inexpensive way of measuring respirable fibers in a work environment, such as a glass insulation or mat-making facility.
• a device for analyzing air having respirable fibers, and non-respirable fibers or non-fibrous particulate matter, or both.
• This device includes separation means for selectively removing respirable fibers from non-respirable fibers to produce a filtered air sample containing aligned respirable fibers. These aligned fibers are then illuminated to produce scattered light, which is collected by a light sensor to produce an electrical output.
• the device further includes processing means for providing a concentration estimate for the respirable fibers from the output of the light sensor.
• FIG 1 is an illustration of an airborne fiber concentration measuring device in accordance with the present invention.
• FIG. 2 is an illustration of one presently preferred embodiment of a sensor in accordance with the present invention.
• FIG. 3 is an illustration of another presently preferred embodiment of a sensor in accordance with the present invention.
• Figure 1 illustrates one embodiment of the airborne fiber concentration measuring device 100 according to the principles of the invention herein.
• Device 100 can include a sensor 1 for detecting fibers and separation means, for example, virtual impactor 2, for separating respirable from non-respirable fibers or non-fibrous particulate matter.
• separation means for example, virtual impactor 2
• respirable fibers means fibers which are less than about 3 ⁇ M in diameter, and preferably those with an aspect ratio of at least about 5:1 (length: diameter).
• the term "light” refers to both visible and invisible electromatic waves, including x-ray and infrared.
• FIG. 1 This device takes in fiber-containing ambient air and draws off smaller respirable fibers 20 laterally at a venturi's mouth. Larger fibers 41 , greater than about 3 ⁇ m, are drawn into the center tube of the virtual impactor 2.
• the air entering the device can have respirable fibers, non- respirable fibers, and other particulate matter mixed therein.
• Sensor 1 preferably senses aligned respirable fibers in the air but is substantially insensitive the other non-fibrous particulate matter.
• respirable fibers 20 that may be present in the air are drawn from virtual impactor 2 through hose 3 which connects virtual impactor 2 to sensor 1.
• Air is drawn through the system by a small vacuum pump 22 to outlet 4 of lower flow tube 6.
• the air flow rate, and lengths and diameter of the upper and lower flow tubes 5,6, are preferred to be such as to produce a laminar flow of air through tubes 5,6.
• Flow tubes 5,6 preferably are separated by a small gap 7 within sensor 1. Alternatively, a single tube having a pair of slots through its side wall perpendicular to its axis could work as well. This gap 7 is preferably positioned symmetrically about axis 8 of sensor 1. Flow tubes 5,6 and gap 7 constitute the "flow channel" for this embodiment of the invention.
• a light source 9 which can be a coherent light source such as, for example, a diode laser.
• Light source 9 can produce a beam 12, preferably with a preselected cross-section along the beam path. It is preferred that light source 9 produce a collimated beam of light, ideally with an elliptical cross-section directed at light sensor 14.
• Light sensor 14 is preferred to be a photodetector. Beam 12 can be aimed along axis 8 of sensor 1 with the major axis of the ellipse of light preferably being substantially parallel to gap 8 between flow tubes 5,6. The width of beam 12 need not be as wide as the diameter of flow tubes 5,6.
• a suitable light source for this embodiment can be, for example, a model LPM 03(670-5) laser diode from Power Technology, Inc., Little Rock, Arkansas.
• a suitable photodetector is, for example, Devar Model 509-1, Bridgeport, Connecticut.
• a skilled artisan could employ other suitable light sources and light sensors to provide and detect light signals indicative of the presence of respirable fiber.
• Figure 2 presents a cross-sectional view of a preferred sensor 1 , which is positioned generally perpendicular to the airflow.
• beam 12 After passing through gap 7, beam 12 enters an optical lens assembly 10.
• Lens assembly 10 can be a pair of condensing lenses, for example. This combination of lenses tends to have a short focal length, permitting a portion 23 of beam 12 to be directed to the back surface 24 of the second lens 25.
• Beam block 11 can be used to substantially block the collimated light 23 from being sensed by photodetector 14. It is preferred that the beam block 11 be umbrageously situated relative to photodetector 14 so that beam block 11 can shield photodetector 14 from light not indicative of the presence of a sensed fiber.
• the Reynolds number should be less than about 2000 and there must be sufficient distance for the flow to become laminar.
• a flow of about 4 liters/min. and a fiber diameter of .44 in. (1.1 cm) produces a Reynolds number of about 500, which is well into the laminar flow regime.
• the length of the flow tube before the fibers reach the laser beam is about 5-50 in. (12.7-127 cm), preferably about 10 in. (25.4 cm) which is more than 22 times the fiber diameter. Since laminar flow should develop within 10 diameters from the entrance of the tube the flow in the device should have ample time to assume a laminar condition.
• a visual confirmation of the alignment of fibers during the transition between turbulent flow and laminar flow can be made. It can be seen that: in the case of glass fibers in a turbulent flow, the diffracted laser beam is dispersed into separated spots of light in random directions; while in the case of glass fibers in a laminar flow, the diffracted laser beam is concentrated in approximately one direction (area), thus showing that the fibers are aligned in a direction substantially parallel to the fiow.
• Light that is scattered in a forward direction 13 can be collected by lens assembly 10 and focused on photodetector 14. Because this light typically is not collimated when it enters the lens assembly 10, it can be focused to a point some distance beyond lens assembly 10, thereby passing around beam block 11. Thus, while both the beam 12 and scattered light 26 enter lens assembly 10, beam 12 typically is blocked from impinging on photodetector 14 while scattered light 26 is, for the most part, focused onto the photodetector 14. Overall, only a small fraction of scattered light 26 is blocked by beam block 11.
• photodetector 14 have a sensing region with a finite width which is wide enough to receive the scattered light 26. Within this width, it will respond to light scattered by fibers 20 that are some distance to either side of, as well as in front and in back of, axis 30 of flow tubes 5,6. Therefore, fibers 20 are not required to pass through beam 12 single-file or closely aligned with axis 30.
• beam 12 is scattered by fiber 20, it is focussed though lens assembly 10 to impinge upon photodetector 14, thus generating a brief electrical pulse therefrom. In general, the amplitude of this pulse is preferred to be proportional to the amount of light scattered by the fiber.
• the resultant pulse can be sent to an appropriate electronic measurement circuit 31 where the pulse is recorded. Using other quantitative information, such as, the flow rate of the air through sensor 1, and determining the rate at which the pulses are received, the concentration of respirable fibers in the air can be determined.
• sensor 1 be substantially insensitive to non-fibrous particulate matter.
• Presently preferred embodiment of the current invention accomplish this selectivity by analyzing, for example, the optical differences between the typically cylindrical respirable fibers, and particulate matter having other shapes. That is, if a spherical or irregularly-shaped dust particle is drawn into sensor 1 , the particulate matter will also scatter light from beam 12. However, such a particle tends to scatter light into a spherical volume. Much of this scattered light will impinge on, and be absorbed by the walls of flow tubes 5,6.
• circuit 31 receiving pulses from the photodetector 14, can be designed to ignore low amplitude pulses resulting from particulate matter. Therefore, device 100 can be made to respond only to respirable fibers while ignoring other non-fibrous particulate matter that may be present. Unlike prior art devices, the invention herein does not require the use of electrostatic or electromagnetic components to induce movement in the matter suspended in the air in order to determine whether or not the matter is a respirable fiber.
• the ability of device 100 to discriminate between respirable fibers and other particles could optionally use the following principles.
• Second, the remaining fibers tend to be aligned with flow tube axis 30 by the laminar flow of air through tubes 5,6.
• light scattered by fibers 20 tends to be scattered in a plane which passes between the ends of flow tubes 5,6, and a portion of the scattered light is focused onto photodetector 14.
• Fifth, light scattered by other particles tends to be scattered more omni-directionally than is the case with cylinders.
• device 100 can discriminate between fibers and other particles.
• lens assembly 10 and photodetector 14 are shown as being substantially in-line with, or in opposition to, beam 12.
• lens assembly 10 and photodetector 14 may be placed anywhere around axis 30 of flow tubes 5,6, as long as they are still in the plane of light scattered from fibers 20.
• sensor 1 can discriminate between respirable fibers and other particles even with these alternative configurations.
• the components of device 100 are substantially the same as those in Figures 1 and 2, with the exception that lens assembly 10 and photodetector 14 have been rotated in orientation by 90 degrees. Also in Figure 3, beam block 11 seen in Figures 1 and 2, may be eliminated because beam path 12 no longer is in-line with, or in opposition to, photodetector 14.

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• Chemical & Material Sciences (AREA)
• Biochemistry (AREA)
• Physics & Mathematics (AREA)
• Health & Medical Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Analytical Chemistry (AREA)
• General Health & Medical Sciences (AREA)
• General Physics & Mathematics (AREA)
• Immunology (AREA)
• Pathology (AREA)
• Dispersion Chemistry (AREA)
• Investigating Or Analysing Materials By Optical Means (AREA)
• Treatment Of Fiber Materials (AREA)

Applications Claiming Priority (5)

Publications (2)

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• 1997
  • 1997-03-11 TR TR1998/01215T patent/TR199801215T1/xx unknown
  • 1997-11-03 BR BR9706914-0A patent/BR9706914A/pt unknown
  • 1997-11-03 CZ CZ981880A patent/CZ188098A3/cs unknown
  • 1997-11-03 PL PL97327503A patent/PL327503A1/xx unknown
  • 1997-11-03 AU AU51658/98A patent/AU736174B2/en not_active Ceased
  • 1997-11-03 HU HU0001651A patent/HUP0001651A3/hu unknown
  • 1997-11-03 JP JP10521689A patent/JP2000503405A/ja active Pending
  • 1997-11-03 KR KR1019980704548A patent/KR19990072187A/ko not_active Application Discontinuation
  • 1997-11-03 EP EP97946502A patent/EP0882223A1/en not_active Withdrawn
  • 1997-11-03 CA CA002239857A patent/CA2239857A1/en not_active Abandoned
  • 1997-11-03 WO PCT/US1997/020047 patent/WO1998020320A1/en not_active Application Discontinuation
• 1998
  • 1998-07-02 NO NO983075A patent/NO983075L/no not_active Application Discontinuation

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