ASTM F50-21

Standard Practice for Continuous Sizing and Counting of Airborne Particles in Dust-Controlled Areas and Clean Rooms Using Instruments Capable of Detecting Single Sub-Micrometre and Larger Particles

SIGNIFICANCE AND USE
5.1 The primary purpose of this practice is to describe a procedure for collecting near real-time data on airborne particle concentration and size distribution in clean areas as indicated by single particle counting techniques. Implementation of some government and industry specifications requires acquisition of particle size and concentration data using an SPC.  
5.2 The processing requirements of many products manufactured in a clean room involves environmental cleanliness levels so low that a single particle counter with capability for detecting very small particles is required to characterize clean room air. Real-time information on concentration of airborne particles in size ranges from less than 0.1 μm to 5 μm and greater can be obtained only with an SPC. Definition of particles larger than approximately 0.05 μm may be carried out with direct measurement of light scattering from individual particles; other techniques may be required for smaller particles, such as preliminary growth by condensation before particle measurement.  
5.3 Particle size data are referenced to the particle system used to calibrate the SPC. Differences in detection, electronic and sample handling systems among the various SPCs may contribute to differences in particle characterization. Care must be exercised in attempting to compare data from particles that vary significantly in composition or shape from the calibration base material. Variations may also occur between instruments using similar particle sensing systems with different operating parameters. These effects should be recognized and minimized by using standard methods for SPC calibration and operation.  
5.4 In applying this practice, the fundamental assumption is made that the particles in the sample passing through the SPC are representative of the particles in the entire dust-controlled area being analyzed. Care is required that good sampling procedures are used and that no artifacts are produced at any point in the samp...
SCOPE
1.1 This practice covers the determination of the particle concentration, by number, and the size distribution of airborne particles in dust-controlled areas and clean rooms, for particles in the size range of approximately 0.01 to 5.0 μm. Particle concentrations not exceeding 3.5 × 106 particles/m 3 (100 000/ft3) are covered for all particles equal to and larger than the minimum size measured.  
1.2 This practice uses an airborne single particle counting device (SPC) whose operation is based on measuring the signal produced by an individual particle passing through the sensing zone. The signal must be directly or indirectly related to particle size.  
Note 1: The SPC type is not specified here. The SPC can be a conventional optical particle counter (OPC), an aerodynamic particle sizer, a condensation nucleus counter (CNC) operating in conjunction with a diffusion battery or differential mobility analyzer, or any other device capable of counting and sizing single particles in the size range of concern and of sampling in a cleanroom environment.  
1.3 Individuals performing tests in accordance with this practice shall be trained in use of the SPC and shall understand its operation.  
1.4 Since the concentration and the particle size distribution of airborne particles are subject to continuous variations, the choice of sampling probe configuration, locations, and sampling times will affect sampling results. Further, the differences in the physical measurement, electronic, and sample handling systems between the various SPCs and the differences in physical properties of the various particles being measured can contribute to variations in the test results. These differences should be recognized and minimized by using a standard method of primary calibration and by minimizing variability of sample acquisition procedures.  
1.5 Sample acquisition procedures and equipment may be selected for specific applications based on ...

General Information

• Status: Published
• Publication Date: 31-Mar-2021
• ICS: 13.040.30 - Workplace atmospheres
• Technical Committee: E21 - Space Simulation and Applications of Space Technology
• Drafting Committee: E21.05 - Contamination

Relations

• Refers: ASTM D1356-20a - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 01-Sep-2020
• Refers: ASTM D1356-20 - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 15-Mar-2020
• Refers: ASTM D1356-15a - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 15-Oct-2015
• Refers: ASTM D1356-15 - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 01-Jul-2015
• Refers: ASTM D1356-14b - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 01-Dec-2014
• Refers: ASTM D1356-14a - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 01-May-2014
• Refers: ASTM D1356-14 - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 15-Jan-2014
• Refers: ASTM D1356-05(2010) - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 01-Apr-2010
• Refers: ASTM F658-00a(2006) - Standard Practice for Calibration of a Liquid-Borne Particle Counter Using an Optical System Based Upon Light Extinction (Withdrawn 2007)
• Effective Date: 01-Apr-2006
• Refers: ASTM D1356-05 - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 01-May-2005
• Refers: ASTM F649-01 - Standard Practice for Secondary Calibration of Airborne Particle Counter Using Comparison Procedures (Withdrawn 2007)
• Effective Date: 10-May-2001
• Refers: ASTM F649-80(1999) - Standard Practice for Secondary Calibration of Airborne Particle Counter Using Comparison Procedures
• Effective Date: 10-May-2001
• Refers: ASTM D1356-00a - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 10-Nov-2000
• Refers: ASTM F658-00 - Standard Practice for Calibration of a Liquid-Borne Particle Counter Using an Optical System Based Upon Light Extinction
• Effective Date: 10-Oct-2000
• Refers: ASTM F658-00a - Standard Practice for Calibration of a Liquid-Borne Particle Counter Using an Optical System Based Upon Light Extinction
• Effective Date: 10-Oct-2000

Overview

ASTM F50-21: Standard Practice for Continuous Sizing and Counting of Airborne Particles in Dust-Controlled Areas and Clean Rooms Using Instruments Capable of Detecting Single Sub-Micrometre and Larger Particles defines procedures for the real-time measurement of airborne particle concentration and size distribution in cleanrooms and dust-controlled environments. The standard enables organizations to monitor and verify the cleanliness of air by counting and sizing particles with single particle counting (SPC) instruments, especially in critical manufacturing processes where environmental purity is paramount.

This standard is essential for industries where strict contamination controls are required, such as semiconductor manufacturing, pharmaceuticals, aerospace, and biotechnology. It incorporates best practices for sampling strategies, equipment calibration, data reporting, and ongoing monitoring, supporting compliance with industry and government regulations on air cleanliness.

Key Topics

• Scope of Particle Measurement:
  Covers determination of airborne particle concentration and size distribution for particles ranging from approximately 0.01 to 5.0 μm, with concentrations up to 3.5 × 10⁶ particles/m³.

• Instrument Requirements:
  Specifies performance and calibration requirements for single particle counting devices such as optical particle counters (OPCs), condensation nucleus counters, and aerodynamic particle sizers capable of measuring in cleanroom conditions.

• Sampling Procedures:
  Provides guidelines for the selection and preparation of sampling points, appropriate probe configurations, and sample sizes to ensure representative and accurate particle count data.

• Calibration and Standardization:
  Emphasizes the importance of using standard calibration methods and minimizing sample acquisition variability to improve data precision and comparability between instruments and environments.

• Data Reporting and Analysis:
  Outlines the necessary details to be included in monitoring reports, including cleanroom identification, equipment calibration status, particle size ranges, sampling schedules, and raw data.

Applications

ASTM F50-21 is widely implemented in:

• Semiconductor Manufacturing:
  Maintaining ultra-clean environments to prevent defects caused by micro and sub-micrometre particles.

• Pharmaceutical Cleanrooms:
  Complying with regulatory requirements for sterile production spaces by continuously monitoring airborne particle concentration.

• Aerospace and Precision Engineering:
  Reducing contamination in assembly environments to ensure high reliability and quality of components.

• Life Sciences and Biotechnology:
  Protecting sensitive cultures and experiments by ongoing assessment of airborne particulates in laboratory clean areas.

• Quality Assurance in Controlled Environments:
  Supporting certification and regular re-verification of cleanroom classes as referenced by ISO 14644-1 and other relevant standards.

Related Standards

• ISO 14644-1: Cleanrooms and associated controlled environments - Classification of air cleanliness
• ISO 14644-2: Cleanrooms and associated controlled environments - Monitoring to provide evidence of cleanroom performance related to air cleanliness by particle concentration
• ASTM D1356: Terminology relating to sampling and analysis of atmospheres
• U.S. Federal Standard 209E: (Superseded, but referenced) Cleanroom and Work Station Requirements, Controlled Environment

Practical Value

Using ASTM F50-21 provides organizations with a robust, standardized framework for continuous airborne particle counting and sizing in cleanrooms and controlled environments. Adoption of this practice:

• Ensures high confidence in cleanroom classification and product quality
• Supports regulatory compliance and internal quality programs
• Enables timely detection of contamination trends, reducing downtime and product recall risks
• Facilitates consistent and comparable data reporting across facilities and systems

Keywords: airborne particle counter, cleanroom monitoring, dust-controlled areas, continuous particle sizing, SPC, calibration, ISO 14644, particle size distribution, air cleanliness standards.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: F50 − 21
Standard Practice for
Continuous Sizing and Counting of Airborne Particles in
Dust-Controlled Areas and Clean Rooms Using Instruments
Capable of Detecting Single Sub-Micrometre and Larger
Particles
ThisstandardisissuedunderthefixeddesignationF50;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginal
adoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscript
epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope should be recognized and minimized by using a standard
methodofprimarycalibrationandbyminimizingvariabilityof
1.1 This practice covers the determination of the particle
sample acquisition procedures.
concentration, by number, and the size distribution of airborne
particlesindust-controlledareasandcleanrooms,forparticles 1.5 Sample acquisition procedures and equipment may be
in the size range of approximately 0.01 to 5.0 µm. Particle selected for specific applications based on varying cleanroom
6 3
concentrations not exceeding 3.5 × 10 particles/m class levels. Firm requirements for these selections are beyond
(100000⁄ft ) are covered for all particles equal to and larger thescopeofthispractice;however,samplingpracticesshallbe
than the minimum size measured. stated that take into account potential spatial and statistical
variations of suspended particles in clean rooms.
1.2 This practice uses an airborne single particle counting
device(SPC)whoseoperationisbasedonmeasuringthesignal
NOTE 2—General references to cleanroom classifications follow Fed-
eral Standard209E, latest revision. Where airborne particles are to be
produced by an individual particle passing through the sensing
characterized in dust-controlled areas that do not meet these
zone. The signal must be directly or indirectly related to
classifications, the latest revision of the pertinent specification for these
particle size.
areas shall be used.
NOTE 1—The SPC type is not specified here. The SPC can be a
1.6 Units—The values stated in SI units are to be regarded
conventional optical particle counter (OPC), an aerodynamic particle
as standard. The values given in parentheses after SI units are
sizer,acondensationnucleuscounter(CNC)operatinginconjunctionwith
providedforinformationonlyandarenotconsideredstandard.
a diffusion battery or differential mobility analyzer, or any other device
capableofcountingandsizingsingleparticlesinthesizerangeofconcern
1.7 This standard does not purport to address all of the
and of sampling in a cleanroom environment.
safety concerns, if any, associated with its use. It is the
1.3 Individuals performing tests in accordance with this
responsibility of the user of this standard to establish appro-
practiceshallbetrainedinuseoftheSPCandshallunderstand
priate safety, health, and environmental practices and deter-
its operation.
mine the applicability of regulatory limitations prior to use.
For specific hazards statements, see Section 8.
1.4 Sincetheconcentrationandtheparticlesizedistribution
1.8 This international standard was developed in accor-
of airborne particles are subject to continuous variations, the
dance with internationally recognized principles on standard-
choice of sampling probe configuration, locations, and sam-
ization established in the Decision on Principles for the
plingtimeswillaffectsamplingresults.Further,thedifferences
Development of International Standards, Guides and Recom-
in the physical measurement, electronic, and sample handling
mendations issued by the World Trade Organization Technical
systems between the various SPCs and the differences in
Barriers to Trade (TBT) Committee.
physicalpropertiesofthevariousparticlesbeingmeasuredcan
contribute to variations in the test results. These differences
2. Referenced Documents
2.1 ASTM Standards:
This practice is under the jurisdiction of ASTM Committee E21 on Space
Simulation andApplications of SpaceTechnology and is the direct responsibility of
Subcommittee E21.05 on Contamination. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved April 1, 2021. Published April 2021. Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
approved in 1965. Last previous edition approved in 2015 as F50–12(2015). DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/F0050-21. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F50−21
D1356Terminology Relating to Sampling and Analysis of and the particle properties that affect the nucleation efficiency
Atmospheres and, for example, the diffusion coefficient, will influence
F328Practice for Calibration of anAirborne Particle Coun- reported data. The SPC instruction manual should make the
ter Using Monodisperse Spherical Particles (Withdrawn user aware of the effects of such factors on the indicated
2007) particle size data.
F649PracticeforSecondaryCalibrationofAirborneParticle
3.1.5 primary calibration, n—calibration with standard ref-
Counter Using Comparison Procedures (Withdrawn
erenceparticlesforparticlesizeand(optionally)concentration.
2007)
Initially carried out by the SPC manufacturer.
F658Practice for Calibration of a Liquid-Borne Particle
3.1.6 resolution, n—the capability of the SPC to differenti-
Counter Using an Optical System Based Upon Light
ate between particles with small difference in size.
Extinction (Withdrawn 2007)
3.1.6.1 Discussion—It can be quantified as the ratio of the
4,5
2.2 U.S. Federal Standard:
square root of the difference between the measured and actual
Federal Standard No. 209E,Clean Room and Work Station
variances of a monosized particle size distribution to the mean
Requirements, Controlled Environment
diameter of those monosize particles, using procedures as
2.3 ISO Standards:
shown in Practice F658.
ISO 14644-1 Cleanrooms and Associated Controlled
3.1.7 standardization, n—secondary calibration of elec-
Environments, Classification of air cleanliness
tronic system voltage and signal response threshold levels
ISO 14644-2 Cleanrooms and Associated Controlled
using the reference system built into the SPC.
Environments,Specificationsfortestingandmonitoringto
3.1.7.1 Discussion—TheSPCshouldbecapableofcarrying
prove continued compliance with ISO 14644-1
out this procedure with a simple, rapid manual operation or by
internal timed or microprocessor controlled components.
3. Terminology
3.2 For definitions of other terms used in this practice, see
3.1 Definitions of Terms Specific to This Standard:
Terminology D1356 and (Federal Standard209E).
3.1.1 dust-controlled area, n—a clean room or clean work
space in which airborne and deposited particulate contamina-
4. Summary of Practice
tionlevels,orboth,arecontrolledonthebasisofadocumented
standard such as Federal Standard209E.
4.1 Satisfactory primary calibration within the manufactur-
er’s recommended time period and routine standardization
3.1.2 dynamic range, n—the particle size range, expressed
should be verified as a first step.
as a multiple of the minimum measured size, over which the
SPCcanmeasureparticleswithsizeresolutionof10%orless.
4.2 Asampleacquisitionprogramisestablishedonthebasis
of the cleanliness level that is to be verified or monitored.This
3.1.3 particle concentration, n—the number of individual
program will include sample point identification, sample size
particles per unit volume of ambient temperature and pressure
3 3
definitions and sampling frequency, specification of the sam-
air, particles/m or particles/ft .
plerinletandsampletransportsystem,definitionoftheparticle
3.1.4 particle size, n—equivalent diameter of a particle
size ranges to be measured, and any other parameters of
detected by an SPC.
concern in the dust-controlled area or clean room.
3.1.4.1 Discussion—Theequivalentdiameteristhediameter
ofareferencesphereofknownsizeandphysicalcharacteristics
4.3 AirsamplesarepassedthroughtheSPCandtheparticle
(for example, refractive index when using an OPC; density content of each sample is defined by the SPC. Particles
when using an aerodynamic particle sizer; etc) and generating
contained in the sampled air pass through the sensing zone of
thesameresponseintheSPCsensingzoneastheparticlebeing the SPC. Each particle produces a signal that can be related to
measured. Spherical particles are used for calibration of the
particle size.An electronic system sorts and counts the pulses,
SPCs considered here.The SPC response is related to the size, registering the number of particles of various sizes that have
shape, orientation, and physical properties of the particle
passedthroughthesensingzoneduringpassageofaknowngas
passing through the SPC sensing zone. If an optical particle volume. The concentration and particle size data can be
counter is used, the geometry of the optical system, as well as displayed, printed or otherwise processed, locally or remotely.
the spectral distribution of the illuminating light influences the
reported particle size. If a condensation nucleus counter with a 5. Significance and Use
size-fractionationdeviceisused,theSPCoperatingparameters
5.1 The primary purpose of this practice is to describe a
procedureforcollectingnearreal-timedataonairborneparticle
concentration and size distribution in clean areas as indicated
The last approved version of this historical standard is referenced on
by single particle counting techniques. Implementation of
www.astm.org.
Available from U.S. General ServicesAdministration, Federal Supply Service,
some government and industry specifications requires acquisi-
Standardization Division, Washington, DC 20406, http://www.gsa.gov.
tion of particle size and concentration data using an SPC.
Fed-Std-209EhasbeenreplacedbyISO/DIS14644-1and-2,butmaycontinue
to be used by mutual agreement.
5.2 The processing requirements of many products manu-
Available from Institute of Environmental Sciences and Technology (IEST),
factured in a clean room involves environmental cleanliness
1827Walden Office Square, Suite 400, Schaumburg, IL60173, http://www.iest.org;
levels so low that a single particle counter with capability for
andfromInternationalOrganizationforStandardization(ISO),ChemindeBlandon-
net 8 CP 401, 1214 Vernier, Geneva, Switzerland, http://www.iso.org. detecting very small particles is required to characterize clean
F50−21
room air. Real-time information on concentration of airborne particles less than 0.05 µm, a CNC in combination with a
particles in size ranges from less than 0.1 µm to 5 µm and diffusion battery, a differential mobility analyzer, or an equiva-
greater can be obtained only with an SPC. Definition of lent SPC can be used.
particleslargerthanapproximately0.05µmmaybecarriedout
7.1.1 Sample Air Flow System, consists of an intake tube,
with direct measurement of light scattering from individual
the particle sensing/measurement chamber, an air flow meter-
particles; other techniques may be required for smaller
ing or control system, and an exhaust system. No abrupt
particles, such as preliminary growth by condensation before
transitions in dimension should occur within the air flow
particle measurement.
system. The inlet tube should consist of a sharp-edged inlet
nozzle connected to a tube that will transport the sample air to
5.3 Particle size data are referenced to the particle system
the particle characterization system. The sample inlet nozzle
used to calibrate the SPC. Differences in detection, electronic
should have a cross-sectional area equivalent to that of a circle
and sample handling systems among the various SPCs may
of diameter at least 2 mm. The nozzle can be attached to a
contributetodifferencesinparticlecharacterization.Caremust
transit tube with dimensions so that residence time in the tube
be exercised in attempting to compare data from particles that
willnotexceed10s.Sampletubesshouldbeconfiguredsothat
vary significantly in composition or shape from the calibration
the flow Reynolds number is maintained in the range 5000 to
base material. Variations may also occur between instruments
25000. For particles in the size range 0.1 µm to ≈2µmin
using similar particle sensing systems with different operating
3 3
diameter and a SPC flow rate of 0.028 m /min (1 ft /min), a
parameters.These effects should be recognized and minimized
transit tube up to 30 m long can be used. For particles in the
by using standard methods for SPC calibration and operation.
size range ≈ 2 µm to 10 µm, a maximum transit tube length of
5.4 In applying this practice, the fundamental assumption is
3 m can be used. If a flexible transit tube is to be used, then no
made that the particles in the sample passing through the SPC
radius of curvature below 15 cm shall be used.
are representative of the particles in the entire dust-controlled
7.1.2 Particle Sensing/Measurement Chamber—Defined by
area being analyzed. Care is required that good sampling
the nature of the SPC that is used. It should be verified that
procedures are used and that no artifacts are produced at any
minimum recirculation and recounting of particles occurs in
point in the sample handling and analysis process; these
that chamber. If the particle characterization system includes
precautions are necessary both in verification and in operation
any particle manipulation (for example, diffusion battery or
of the SPC.
nucleation chamber, etc) before particle sensing occurs, then
the SPC element that manipulates the particles shall not result
6. Interferences
in significant particle number change during that process.
6.1 Since the SPC is typically a high sensitivity device, its
7.1.3 Air Flow Metering of Control System, shall be located
response may be affected by internally or externally generated
after the particle sensing/measurement chamber so as to
noise. The SPC should not be operated at a sensitivity level so
minimize particle losses or artifact generation before measure-
high that internal noise produces more than 5% of the data
ment occurs.
signals.
7.1.4 Exhaust System, may consist of either a built-in
6.2 Precautions should also be taken to ensure that the test
vacuum source or an external vacuum supply. If the built-in
area environment does not exceed the radio frequency or
vacuum source is used, then the exhaust stream from that
electromagnetic interference capabilities of the SPC.
sourceshallbesuitablyfilteredsothatparticlessampledbyand
internallygeneratedbytheSPC,orboth,arenotreturnedtothe
6.3 Operation at acceptably low levels of internal noise can
dust-controlled area.
be verified by drawing a sample into the SPC through a filter
orothergascleaningdevicethatwillpositivelyremoveatleast
7.2 Particle Characterization System, shall be capable of
99.97% of all particles of size equal to and greater than that
both detecting and sizing the particles that are sampled by the
which the SPC will measure.After a short stabilization period,
SPC. The characterization system particle sizing resolution,
any signals reported by the SPC can be assumed to arise from
expressed as a percentage, shall not exceed 10% over the
internal or external noise sources.
operating dynamic range.The SPC specifications shall include
information as to the maximum particle concentration that can
7. Apparatus
be measured bef
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: F50 − 12 (Reapproved 2015) F50 − 21
Standard Practice for
Continuous Sizing and Counting of Airborne Particles in
Dust-Controlled Areas and Clean Rooms Using Instruments
Capable of Detecting Single Sub-Micrometre and Larger
Particles
This standard is issued under the fixed designation F50; the number immediately following the designation indicates the year of original
adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript
epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This practice covers the determination of the particle concentration, by number, and the size distribution of airborne particles
in dust-controlled areas and clean rooms, for particles in the size range of approximately 0.01 to 5.0 μm. Particle concentrations
6 3 3
not exceeding 3.5 × 10 particles/m (100 000 ⁄ft ) are covered for all particles equal to and larger than the minimum size measured.
1.2 This practice uses an airborne single particle counting device (SPC) whose operation is based on measuring the signal
produced by an individual particle passing through the sensing zone. The signal must be directly or indirectly related to particle
size.
NOTE 1—The SPC type is not specified here. The SPC can be a conventional optical particle counter (OPC), an aerodynamic particle sizer, a condensation
nucleus counter (CNC) operating in conjunction with a diffusion battery or differential mobility analyzer, or any other device capable of counting and
sizing single particles in the size range of concern and of sampling in a cleanroom environment.
1.3 Individuals performing tests in accordance with this practice shall be trained in use of the SPC and shall understand its
operation.
1.4 Since the concentration and the particle size distribution of airborne particles are subject to continuous variations, the choice
of sampling probe configuration, locations, and sampling times will affect sampling results. Further, the differences in the physical
measurement, electronic, and sample handling systems between the various SPCs and the differences in physical properties of the
various particles being measured can contribute to variations in the test results. These differences should be recognized and
minimized by using a standard method of primary calibration and by minimizing variability of sample acquisition procedures.
1.5 Sample acquisition procedures and equipment may be selected for specific applications based on varying cleanroom class
levels. Firm requirements for these selections are beyond the scope of this practice; however, sampling practices shall be stated
that take into account potential spatial and statistical variations of suspended particles in clean rooms.
NOTE 2—General references to cleanroom classifications follow Federal Standard 209E, latest revision. Where airborne particles are to be characterized
in dust-controlled areas that do not meet these classifications, the latest revision of the pertinent specification for these areas shall be used.
This practice is under the jurisdiction of ASTM Committee E21 on Space Simulation and Applications of Space Technology and is the direct responsibility of
Subcommittee E21.05 on Contamination.
Current edition approved Oct. 1, 2015April 1, 2021. Published November 2015April 2021. Originally approved in 1965. Last previous edition approved in 20122015 as
F50 – 12.F50 – 12(2015). DOI: 10.1520/F0050-12R15.10.1520/F0050-21.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F50 − 21
1.6 Units—The values stated in SI units are to be regarded as the standard. The values given in parentheses after SI units are
provided for information only and are not considered standard.
1.7 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use. For specific hazards statements, see Section 8.
1.8 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D1356 Terminology Relating to Sampling and Analysis of Atmospheres
F328 Practice for Calibration of an Airborne Particle Counter Using Monodisperse Spherical Particles (Withdrawn 2007)
F649 Practice for Secondary Calibration of Airborne Particle Counter Using Comparison Procedures (Withdrawn 2007)
F658 Practice for Calibration of a Liquid-Borne Particle Counter Using an Optical System Based Upon Light Extinction
(Withdrawn 2007)
4,5
2.2 U.S. Federal Standard:
,
Federal Standard No. 209E, Clean Room and Work Station Requirements, Controlled Environment
2.3 Other Documents:ISO Standards:
ISO 14644-1 Cleanrooms and Associated Controlled Environments, Classification of air cleanliness
ISO 14644-2 Cleanrooms and Associated Controlled Environments, Specifications for testing and monitoring to prove continued
compliance with ISO 14644-1
3. Terminology
3.1 Definitions of Terms Specific to This Standard:
3.1.1 dust-controlled area—area, n—a clean room or clean work space in which airborne and deposited particulate contamination
levels, or both, are controlled on the basis of a documented standard such as Federal Standard 209E.
3.1.2 dynamic range—range, n—the particle size range, expressed as a multiple of the minimum measured size, over which the
SPC can measure particles with size resolution of 10 % or less.
3.1.3 particle concentration—concentration, n—the number of individual particles per unit volume of ambient temperature and
3 3
pressure air, particles/m or particles/ft .
3.1.4 particle size—size, n—equivalent diameter of a particle detected by an SPC.
3.1.4.1 Discussion—
The equivalent diameter is the diameter of a reference sphere of known size and physical characteristics (for example, refractive
index when using an OPC; density when using an aerodynamic particle sizer; etc) and generating the same response in the SPC
sensing zone as the particle being measured. Spherical particles are used for calibration of the SPCs considered here. The SPC
response is related to the size, shape, orientation, and physical properties of the particle passing through the SPC sensing zone.
If an optical particle counter is used, the geometry of the optical system, as well as the spectral distribution of the illuminating light
influences the reported particle size. If a condensation nucleus counter with a size-fractionation device is used, the SPC operating
parameters and the particle properties that affect the nucleation efficiency and, for example, the diffusion coefficient, will influence
reported data. The SPC instruction manual should make the user aware of the effects of such factors on the indicated particle size
data.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
The last approved version of this historical standard is referenced on www.astm.org.
Available from U.S. General Services Administration, Federal Supply Service, Standardization Division, Washington, DC 20406, http://www.gsa.gov.
Fed-Std-209E has been replaced by ISO/DIS 14644-1 and -2, but may continue to be used by mutual agreement.
Available from Institute of Environmental Sciences and Technology (IEST), Arlington Place One, 2340 S. Arlington Heights Rd., Suite 100, Arlington Heights, IL
60005-4516, http://www.iest.org,1827 Walden Office Square, Suite 400, Schaumburg, IL 60173, http://www.iest.org; and from International Organization for Standardization
(ISO), 1, ch. de la Voie-Creuse, CP 56, CH-1211 Geneva 20,Chemin de Blandonnet 8 CP 401, 1214 Vernier, Geneva, Switzerland, http://www.iso.org.
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3.1.5 primary calibration—calibration, n—calibration with standard reference particles for particle size and (optionally)
concentration. Initially carried out by the SPC manufacturer.
3.1.6 resolution—resolution, n—the capability of the SPC to differentiate between particles with small difference in size.
3.1.6.1 Discussion—
It can be quantified as the ratio of the square root of the difference between the measured and actual variances of a monosized
particle size distribution to the mean diameter of those monosize particles, using procedures as shown in Practice F658.
3.1.7 standardization—standardization, n—secondary calibration of electronic system voltage and signal response threshold levels
using the reference system built into the SPC.
3.1.7.1 Discussion—
The SPC should be capable of carrying out this procedure with a simple, rapid manual operation or by internal timed or
microprocessor controlled components.
3.2 For definitions of other terms used in this practice, see Terminology D1356 and (Federal Standard 209E).
4. Summary of Practice
4.1 Satisfactory primary calibration within the manufacturer’s recommended time period and routine standardization should be
verified as a first step.
4.2 A sample acquisition program is established on the basis of the cleanliness level that is to be verified or monitored. This
program will include sample point identification, sample size definitions and sampling frequency, specification of the sampler inlet
and sample transport system, definition of the particle size ranges to be measured, and any other parameters of concern in the
dust-controlled area or clean room.
4.3 Air samples are passed through the SPC and the particle content of each sample is defined by the SPC. Particles contained
in the sampled air pass through the sensing zone of the SPC. Each particle produces a signal that can be related to particle size.
An electronic system sorts and counts the pulses, registering the number of particles of various sizes that have passed through the
sensing zone during passage of a known gas volume. The concentration and particle size data can be displayed, printed or otherwise
processed, locally or remotely.
5. Significance and Use
5.1 The primary purpose of this practice is to describe a procedure for collecting near real-time data on airborne particle
concentration and size distribution in clean areas as indicated by single particle counting techniques. Implementation of some
government and industry specifications requires acquisition of particle size and concentration data using an SPC.
5.2 The processing requirements of many products manufactured in a clean room involves environmental cleanliness levels so low
that a single particle counter with capability for detecting very small particles is required to characterize clean room air. Real-time
information on concentration of airborne particles in size ranges from less than 0.1 μm to 5 μm and greater can be obtained only
with an SPC. Definition of particles larger than approximately 0.05 μm may be carried out with direct measurement of light
scattering from individual particles; other techniques may be required for smaller particles, such as preliminary growth by
condensation before particle measurement.
5.3 Particle size data are referenced to the particle system used to calibrate the SPC. Differences in detection, electronic and
sample handling systems among the various SPCs may contribute to differences in particle characterization. Care must be exercised
in attempting to compare data from particles that vary significantly in composition or shape from the calibration base material.
Variations may also occur between instruments using similar particle sensing systems with different operating parameters. These
effects should be recognized and minimized by using standard methods for SPC calibration and operation.
5.4 In applying this practice, the fundamental assumption is made that the particles in the sample passing through the SPC are
representative of the particles in the entire dust-controlled area being analyzed. Care is required that good sampling procedures are
used and that no artifacts are produced at any point in the sample handling and analysis process; these precautions are necessary
both in verification and in operation of the SPC.
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6. Interferences
6.1 Since the SPC is typically a high sensitivity device, it’sits response may be affected by internally or externally generated noise.
The SPC should not be operated at a sensitivity level so high that internal noise produces more than 5 % of the data signals.
6.2 Precautions should also be taken to ensure that the test area environment does not exceed the radio frequency or
electromagnetic interference capabilities of the SPC.
6.3 Operation at acceptably low levels of internal noise can be verified by drawing a sample into the SPC through a filter or other
gas cleaning device that will positively remove at least 99.97 % of all particles of size equal to and greater than that which the SPC
will measure. After a short stabilization period, any signals reported by the SPC can be assumed to arise from internal or external
noise sources.
7. Apparatus
7.1 SPC—The apparatus shall consist of a SPC, selected on the basis of its ability to count and size single particles in the required
size range. The SPC shall include a sample air flow system, a particle characterization system, and a data processing system. The
minimum measurable particle size shall be selected from the clean area definition stated in ISO 14644-1 (Table I of Federal
Standard 209E), or from a different specification of clean-area airborne particle concentration at a stated minimum particle size.
For classification levels based on measurement of particles larger than 0.05 μm, an optical particle counter (OPC), an aerodynamic
particle sizer, or an equivalent SPC can be used. For classification levels based on particles less than 0.05 μm, a CNC in
combination with a diffusion battery, a differential mobility analyzer, or an equivalent SPC can be used.
7.1.1 Sample Air Flow System, consists of an intake tube, the particle sensing/measurement chamber, an air flow metering or
control system, and an exhaust system. No abrupt transitions in dimension should occur within the air flow system. The inlet tube
should consist of a sharp-edged inlet nozzle connected to a tube that will transport the sample air to the particle characterization
system. The sample inlet nozzle should have a cross-sectional area equivalent to that of a circle of diameter at least 2 mm. The
nozzle can be attached to a transit tube with dimensions so that residence time in the tube will not exceed 10 s. Sample tubes should
be configured so that the flow Reynolds number is maintained in the range 5 0005000 to 25 000. For particles in the size range
3 3
0.1 μm to ≈ 2 μm in diameter and a SPC flow rate of 0.028 m /min (1 ft /min), a transit tube up to 30 m long can be used. For
particles in the size range ≈ 2 μm to 10 μm, a maximum transit tube length of 3 m can be used. If a flexible transit tube is to be
used, then no radius of curvature below 15 cm shall be used.
7.1.2 Particle Sensing/Measurement Chamber—Defined by the nature of the SPC that is used. It should be verified that minimum
recirculation and recounting of particles occurs in that chamber. If the particle characterization system includes any particle
manipulation (for example, diffusion battery or nucleation chamber, etc) before particle sensing occurs, then the SPC element that
manipulates the part
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