IEST G-CC1002-1999 Determination of the Concentration of Airborne Ultrafine Particles.pdf

1、INSTITUTE OF ENVIRONMENTAL SCIENCES AND TECHNOLOGY Contamination Control Division Technical Guide 102 IEST-G-C102 Determination of the Concentration of Airborne Ultrafine Particles INSTITUTE OF ENVIRONMENTAL SCIENCES AND TECHNOLOGY Arlington Place One 2340 S. Arlington Heights Road, Suite 10 Arlingt

2、on Heights, IL 6005-4516 Phone: (847) 981-010 Fax: (847) 981-4130 E-mail: iestiest.org Web: ww.iest.org 2 Copyrighted material INSTITUTE OF ENVIRONMENTAL SCIENCES AND TECHNOLOGY IEST-G-C102 This Guide is published by the INSTITUTE OF ENVIRONMENTAL SCIENCES AND TECHNOLOGY to advance contamination con

3、-trol technology and the technical and enginering sciences. Its use is entirely voluntary, and determination of its aplicability and suitability for any particular use is solely the responsibility of the user. Copyright 199 by the INSTITUTE OF ENVIRONMENTAL SCIENCES AND TECHNOLOGY ISBN 978-1-87862-7

4、5-5 No part of this publication may be copied or reproduced in any form, or by any means, including electronic, mechanical, photocopying, or otherwise, without the prior writen permision of the Institute of Environmental Sciences and Technol-ogy, 2340 S. Arlington Heights Road, Arlington Heights, IL

5、 6005-4516. INSTITUTE OF ENVIRONMENTAL SCIENCES AND TECHNOLOGY Arlington Place One 2340 S. Arlington Heights Road, Suite 10 Arlington Heights, IL 6005-4516 Phone: (847) 981-010 Fax: (847) 981-4130 E-mail: iestiest.org Web: ww.iest.org IEST-G-CC1002 INSTITUTE OF ENVIRONMENTAL SCIENCES AND TECHNOLOGY

6、Copyrighted material 3Determination of the Concentration ofAirborne Ultrafine ParticlesIEST-G-CC1002CONTENTSSECTION1 Application 52 Definitions . 53 Counting apparatus for ultrafine particles . 64 Counting procedure . 75 Data reporting . 86 References 8APPENDIXAPPENDIX A; Data Report Example 9FIGURE

7、Figure 1. Envelope of acceptable U descriptor counting efficiency . 74 Copyrighted material IEST-G-CC1002 INSTITUTE OF ENVIRONMENTAL SCIENCES AND TECHNOLOGYIEST-G-CC1002 INSTITUTE OF ENVIRONMENTAL SCIENCES AND TECHNOLOGY Copyrighted material 5INSTITUTE OF ENVIRONMENTAL SCIENCES AND TECHNOLOGYContami

8、nation Control DivisionGuide 1002Determination of the Concentration ofAirborne Ultrafine ParticlesIEST-G-CC10021 ApplicationThis guide describes standardized procedures fordetermination of the concentration of airborne par-ticles in the ultrafine size range (i.e., particles witha size distribution h

9、aving a threshold lower limitparticle size smaller than 0.1 m). The numericalvalue of the concentration of such particles, ex-pressed in terms of particles per cubic meter, is theU descriptor. This term may refer to a specifiedconcentration of ultrafine particles or to measure-ment of the concentrat

10、ion of ultrafine particles in agiven sample of air.The procedures described herein are suitable foruse in conjunction with related cleanroom stan-dards, such as ISO 14644-1 for determination ofairborne particulate cleanliness, and ISO 14644-2for monitoring. The procedures are applicable tocleanrooms

11、 and clean zones in any of three occu-pancy states, as defined in ISO 14644-1.This document is most appropriate for use withcleanroom and clean zone environments that qualifyas ISO Class 4 or cleaner, as defined in ISO 14644-1.2 Definitions2.1 condensation nucleus counter(CNC)An instrument for count

12、ing airborne particles, inthe nanometer size range and larger, by opticallydetecting droplets formed by condensation of avapor upon those particles.2.2 discrete-particle counter (DPC)An instrument, such as an optical particle counteror a modified condensation nucleus counter, ca-pable of counting an

13、d sizing individual airborneparticles within a particle population. A DPC usedfor counting ultrafine particles shall be able todiscriminate threshold sizes smaller than 0.1 mequivalent diameter.2.3 inlet deviceA size cutoff device which, when attached to thesample inlet of a DPC or CNC, will remove

14、par-ticles smaller than the defined ultrafine particlesize. The device is chosen so that its particle reten-tion by diffusion effects will meet the defined par-6 Copyrighted material IEST-G-CC1002 INSTITUTE OF ENVIRONMENTAL SCIENCES AND TECHNOLOGYticle size specification at the flow rate of the DPC

15、orCNC to which it is attached.2.4 ultrafine particleA particle with an equivalent diameter less than 0.1m, as specified by agreement between the cus-tomer and the supplier.2.5 U descriptorThe cumulative measured or specified concentra-tion in particles per cubic meter of air, including theultrafine

16、particles.2.6 zero count rateThe maximum count indicated by a discrete-par-ticle counter (DPC) within a specified period oftime, while sampling air that is free of particleslarger than the lower sizing limit of the DPC. Alsoreferred to as false count rate or background noise level.NOTE: For further

17、definitions and explanations ofother terms used in this document, see IEST-RD-CC011.3 Counting apparatus for ultrafineparticlesDeterminations of U descriptors are accomplishedby measurement with a discrete-particle counter(DPC), as described in reference 6a, or a condensa-tion nucleus counter (CNC),

18、 as described in refer-ence 6b. Suitable configurations of such instru-ments and their required characteristics are de-scribed below:a) DPC, with the following features: Counting efficiency of 50% at the specifiedultrafine particle threshold size (in accordancewith reference 6a). Capability for dyna

19、mic size range definition ex-tending from the specified threshold size (de-fined in accordance with Figure 1) up to at least0.1 m.b) DPC or CNC, with the following features: Capability to detect particles that are as small asor smaller than the specified ultrafine particlethreshold size. Accessory i

20、nlet device, with known particle-sizepenetration performance as described in section3.2, for the DPC or CNC with particle-size mea-surement capability for particles smaller than thespecified ultrafine particle size.3.1 Counting efficiencyThe counting efficiency of a DPC or CNC is deter-mined by comp

21、arison with the response of a refer-ence instrument having a counting efficiency of100(10)% for ultrafine particles (see reference 6c).The response of the instrument being characterizedis compared with that of the reference instrumentby measuring and reporting the concentrations of aseries of refere

22、nce particle suspensions simulta-neously with both instruments. The counting effi-ciency of the DPC or CNC being characterized isderived from the ratio of its reported concentrationdata to the concentration data from the referenceinstrument. Detailed information on the proce-dures for determination

23、of the counting efficiencyshould be available on request from the supplier ofthe DPC or CNC.The counting efficiency characteristic of the DPCor CNC used to define or verify a U descriptor mustfall within the diagonally marked envelope of Fig-ure 1. This region of acceptable performance cen-ters on a

24、 counting efficiency of 50% at the specifiedultrafine particle size, shown at size U on Figure 1.It includes a tolerance band of 10% of the ultrafineparticle size, shown at sizes 0.9 U and 1.1 U onFigure 1. The minimum and maximum countingefficiencies that are acceptable for particles aboveand below

25、 the 10% size tolerance band are basedon the calculated penetration of a diffusion elementhaving at least 40% penetration efficiency for par-ticles 10% larger than the defined ultrafine particlesize U and at least 60% penetration efficiency forparticles 10% smaller than U.A DPC or CNC having a count

26、ing efficiencycurve that falls to the right of the diagonally markedenvelope of Figure 1 cannot be used to measure orverify the U descriptor. If the curve falls to the leftof the diagonally marked envelope, the instrumentscounting efficiency can be suitably decreased bymodifying it with an accessory

27、 size cutoff inletdevice as described in section 3.2. In this case, thecounting efficiency of the modified DPC or CNC isthe product of the counting efficiency of the un-modified DPC or CNC and the fractional penetra-tion of the size cutoff inlet device.3.2 Inlet device for particle size cutoffTo ach

28、ieve the desired counting efficiency charac-teristic required to measure or verify a U descrip-tor, a size cutoff device can be attached to theIEST-G-CC1002 INSTITUTE OF ENVIRONMENTAL SCIENCES AND TECHNOLOGY Copyrighted material 7sample inlet of the DPC or CNC whose countingefficiency curve falls to

29、 the left of the diagonallymarked envelope of Figure 1. The resulting count-ing efficiency curve of the combined DPC or CNC,sample inlet, and cutoff device will then fall withinthe required shaded envelope of Figure 1.Cutoff devices remove small particles from thesampled airstream by diffusional cap

30、ture, thus re-ducing penetration of particles smaller than theagreed-upon ultrafine particle size of section 2.4 ina well-defined and reproducible manner. The re-quired penetration characteristic is achievedthrough diffusional capture of small particles onthe surfaces of small-diameter tubing, perfo

31、ratedplates, or fine-mesh screen through which thesampled air passes. Penetration is a function of theparticle diffusion constant, the configuration of thecutoff device, and the volumetric flow rate of thesample through the device. A wide variety of sizesand configurations of inlet devices is possib

32、le andacceptable, provided that they produce the requiredpenetration characteristics.Care is required with all cutoff devices that theybe used only at the flow rates for which they weredesigned, and that they are installed so as to avoidaccumulation of electrostatic charge. Charge accu-mulation can

33、be minimized by ensuring that thecutoff device is suitably grounded electrically. Inaddition, the initial determination of the countingefficiency of the system should be carried out withan aerosol suspension that is as close to electricalneutrality as possible.4 Counting procedureSet up the sample i

34、nlet probe of the DPC or CNC(with the appropriate cutoff device, if required) ata specified sampling location. Sample the requiredvolume of air, as determined by application of ISO14644-1 or by agreement between the customer andthe supplier.Repeat the procedure at all remaining samplingpoints. Their

35、 number and locations may be deter-mined in accordance with ISO 14644-1 or by agree-ment between the customer and the supplier.When the U descriptor data are collected for thepurpose of monitoring the cleanroom or clean zone,such as directed by ISO 14644-2, the number andlocations of sampling points

36、 are selected and agreedupon by the customer and the supplier. Specialregard in the selection of locations may be based onthe positions of critical processes, equipment, andoperations in the cleanroom or clean zone.Note: Where information is required to determinethe stability of ultrafine particle p

37、resence in thecleanroom or clean zone, three or more addi-Figure 1. Envelope of acceptable U descriptor counting efficiency1008060402000.01 0.9 U 1.1 U 0.1U, 50%Particle Diameter (m)Counting Efficiency (%)8 Copyrighted material IEST-G-CC1002 INSTITUTE OF ENVIRONMENTAL SCIENCES AND TECHNOLOGYtional m

38、easurements should be made at selectedlocations over a specified time interval, as agreedupon between the customer and the supplier.NOTE: When the cleanliness of air is to be measuredas the air comes from a potential contaminatingsource, or as contaminated air approaches apotential target, an approp

39、riate procedure shouldbe selected from ASTM F 50-00, reported, andfollowed.Calculate the U descriptor concentrations basedupon the specified ultrafine particle size threshold,as agreed upon between customer and supplier,and report the data as shown in section 5 andAppendix A.5 Data reportingReport t

40、he following information, as specified, forclassification or testing of each cleanroom or cleanzone:a) Identification and location of the cleanroom orclean area.b) Identification of the DPC or CNC and its calibra-tion status.c) Zero count rate for the DPC.d) Date and time when DPC or CNC data wereco

41、llected, and operator identification.e) Cleanroom or clean area status: as-built, at-rest,or operational.f) Type of testing: characterization of air flowingfrom potential source(s) of contamination or airflowing toward specified target areas of concern; ormonitoring.g) Classification level and U des

42、criptor (target level,if initial measurement).h) Particle size threshold for the U-descriptor data.i) DPC or CNC inlet sample flow and sensingvolume sample flow rate.j) Location of sampling point.k) Sampling schedule for classification or sam-pling protocol for testing.l) Raw data for each measureme

43、nt, if required.An example of a data report is shown in Appendix A.6 Referencesa) ASTM F 50, Continuous Sizing and Counting ofAirborne Particles in Dust-Controlled Areas andCleanrooms Using Instruments Capable of Detect-ing Single Sub-micrometer and Larger Particles.West Conshohocken, Pennsylvania:

44、American Soci-ety for Testing and Materials.b) Stolzenburg, M. R., and P. H. McMurry. A Theo-retical Model for an Ultrafine Aerosol Conden-sation Nucleus Counter. In Aerosols. B. Y. H.Liu, et al., Editors. New York: Elsevier, 1984, pp.59-62.c) Liu, B. Y. H., and D. Y. H. Pui. A SubmicronAerosol Stan

45、dard and the Primary, AbsoluteCalibration of the Condensation Nuclei Counter.Journal of Colloid and Interface Science, Vol. 47,No. 1 (1974), pp. 155-171.d) ISO 14644-1, Cleanrooms and associated controlledenvironments Part 1: Classification of air cleanli-ness. Geneva, Switzerland: ISO, Internationa

46、lOrganization for Standardization.e) ISO 14644-2, Cleanrooms and associated controlledenvironments Part 2: Specifications for testing andmonitoring cleanrooms and clean zones to provecontinued compliance with ISO 14644-1. Geneva,Switzerland: ISO, International Organization forStandardization.f) IEST

47、-RD-CC011, A Glossary of Terms and Defini-tions Relating to Contamination Control. MountProspect, Illinois: Institute of EnvironmentalSciences and Technology.IEST-G-CC1002 INSTITUTE OF ENVIRONMENTAL SCIENCES AND TECHNOLOGY Copyrighted material 9Ultrafine Particle Count Data ReportCleanroom identific

48、ation Company _Dept. _ Room _DPC/CNC identification Mfr. _ Model _ SN _Zero count rate _ counts/minData collection information Date _ /_ /_ Time _ Operator _Area status As-built a73 At-rest a73 Operational a73Type of testing Measurement of airborne contaminant from source a73,or toward target a73 Mo

49、nitoring a73Area air cleanliness classification ISO Class _Area U descriptor _ ultrafine particles/m3Ultrafine particle size threshold 0._ mCounter sample flow rate Inlet _ m3/sec; Sensor _ m3/secSampling point (probe) location Equipment or grid designation _Sampling schedule, as specified Operation or equipment step _Sampling frequency _