ASTM F50-92(2001)e1
(Practice)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
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
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.
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.
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.
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 ana...
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 [mu]m. Particle concentrations not exceeding 3.5 X 106 particles/m3 (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 varying...
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Designation: F 50 – 92 (Reapproved 2001)
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
ThisstandardisissuedunderthefixeddesignationF 50;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginal
adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.Asuperscript
epsilon (e) indicates an editorial change since the last revision or reapproval.
e NOTE—Keywords were added editorially in July 2001.
1. Scope method of primary calibration and by minimizing variability of
sample acquisition procedures.
1.1 This practice covers the determination of the particle
1.5 Sample acquisition procedures and equipment may be
concentration, by number, and the size distribution of airborne
selected for specific applications based on varying cleanroom
particles in dust-controlled areas and clean rooms, for particles
class levels. Firm requirements for these selections are beyond
in the size range of approximately 0.01 to 5.0 µm. Particle
6 3
the scope of this practice; however, sampling practices shall be
concentrations not exceeding 3.5 3 10 particles/m (100 000/
stated that take into account potential spatial and statistical
ft ) are covered for all particles equal to and larger than the
variations of suspended particles in clean rooms.
minimum size measured.
1.2 This practice uses an airborne single particle counting
NOTE 2—General references to cleanroom classifications follow Fed-
device(SPC)whoseoperationisbasedonmeasuringthesignal
eral Standard 209, latest revision. Where airborne particles are to be
characterized in dust-controlled areas that do not meet these classifica-
produced by an individual particle passing through the sensing
tions, the latest revision of the pertinent specification for these areas shall
zone. The signal must be directly or indirectly related to
be used.
particle size.
1.6 This standard does not purport to address all of the
NOTE 1—The SPC type is not specified here. The SPC can be a
safety concerns, if any, associated with its use. It is the
conventional optical particle counter (OPC), an aerodynamic particle
responsibility of the user of this standard to establish appro-
sizer,acondensationnucleuscounter(CNC)operatinginconjunctionwith
priate safety and health practices and determine the applica-
a diffusion battery or differential mobility analyzer, or any other device
capable of counting and sizing single particles in the size range of concern bility of regulatory limitations prior to use.Forspecifichazards
and of sampling in a cleanroom environment.
statements, see Section 8.
1.3 Individuals performing tests in accordance with this
2. Referenced Documents
practice shall be trained in use of the SPC and shall understand
2.1 ASTM Standards:
its operation.
D 1356 Terminology Relating to Sampling and Analysis of
1.4 Since the concentration and the particle size distribution
Atmospheres
of airborne particles are subject to continuous variations, the
F 328 Practice for Calibration of an Airborne Particle
choice of sampling probe configuration, locations and sam-
Counter using Monodisperse Spherical Particles
pling times will affect sampling results. Further, the differences
F 649 Practice for Secondary Calibration of Airborne Par-
in the physical measurement, electronic and sample handling
ticle Counter using Comparison Procedures
systems between the various SPCs and the differences in
F 658 Practice for Calibration of a Liquid-Borne Particle
physical properties of the various particles being measured can
Counter using an Optical System Based Upon Light
contribute to variations in the test results. These differences
Extinction
should be recognized and minimized by using a standard
2.2 U.S. Federal Standard:
Federal Standard No. 209D, Clean Room and Work Station
This practice is under the jurisdiction of ASTM Committee E21 on Space
Simulation andApplications of Space Technology and is the direct responsibility of
Subcommittee E21.05 on Contamination.
Current edition approved May 15, 1992. Published July 1992. Originally Annual Book of ASTM Standards, Vol 11.03.
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published as F 50 – 65 T. Last previous edition F 50 – 83 (1989) Annual Book of ASTM Standards, Vol 15.03.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
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F 50 – 92 (2001)
Requirements, Controlled Environment 4. Summary of Practice
4.1 Satisfactory primary calibration within the manufactur-
3. Terminology
er’s recommended time period and routine standardization
should be verified as a first step.
3.1 Definitions of Terms Specific to This Standard:
4.2 Asampleacquisitionprogramisestablishedonthebasis
3.1.1 dust-controlled area—a clean room or clean work
of the cleanliness level that is to be verified or monitored. This
space in which airborne and deposited particulate contamina-
program will include sample point identification, sample size
tionlevels,orboth,arecontrolledonthebasisofadocumented
definitions and sampling frequency, specification of the sam-
standard such as Federal Standard 209D.
plerinletandsampletransportsystem,definitionoftheparticle
3.1.2 dynamic range—theparticlesizerange,expressedasa
size ranges to be measured, and any other parameters of
multiple of the minimum measured size, over which the SPC
concern in the dust-controlled area or clean room.
can measure particles with size resolution of 10 % or less.
4.3 Air samples are passed through the SPC and the particle
3.1.3 particle concentration—the number of individual par-
content of each sample is defined by the SPC. Particles
ticles per unit volume of ambient temperature and pressure air,
contained in the sampled air pass through the sensing zone of
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particles/m or particles/ft .
the SPC. Each particle produces a signal that can be related to
3.1.4 particle size—equivalent diameter of a particle de-
particle size.An electronic system sorts and counts the pulses,
tected by an SPC.
registering the number of particles of various sizes that have
3.1.4.1 Discussion—The equivalent diameter is the diam-
passedthroughthesensingzoneduringpassageofaknowngas
eter of a reference sphere of known size and physical charac-
volume. The concentration and particle size data can be
teristics (for example, refractive index when using an OPC;
displayed, printed or otherwise processed, locally or remotely.
density when using an aerodynamic particle sizer; etc) and
generating the same response in the SPC sensing zone as the
5. Significance and Use
particle being measured. Spherical particles are used for
5.1 The primary purpose of this practice is to describe a
calibration of the SPCs considered here. The SPC response is
procedureforcollectingnearreal-timedataonairborneparticle
related to the size, shape, orientation and physical properties of
concentration and size distribution in clean areas as indicated
the particle passing through the SPC sensing zone. If an optical
by single particle counting techniques. Implementation of
particle counter is used, the geometry of the optical system, as
some government and industry specifications requires acquisi-
well as the spectral distribution of the illuminating light
tion of particle size and concentration data using an SPC.
influences the reported particle size. If a condensation nucleus
5.2 The processing requirements of many products manu-
counter with a size-fractionation device is used, the SPC
factured in a clean room involves environmental cleanliness
operating parameters and the particle properties that affect the
levels so low that a single particle counter with capability for
nucleation efficiency and, for example, the diffusion coeffi-
detecting very small particles is required to characterize clean
cient, will influence reported data.The SPC instruction manual
room air. Real-time information on concentration of airborne
shouldmaketheuserawareoftheeffectsofsuchfactorsonthe
particles in size ranges from less than 0.1 µm to 5 µm and
indicated particle size data.
greater can be obtained only with an SPC. Definition of
3.1.5 primary calibration—calibration with standard refer-
particles larger than approximately 0.05 µm may be carried out
ence particles for particle size and (optionally) concentration.
with direct measurement of light scattering from individual
Initially carried out by the SPC manufacturer.
particles; other techniques may be required for smaller par-
3.1.6 resolution—the capability of the SPC to differentiate
ticles, such as preliminary growth by condensation before
between particles with small difference in size.
particle measurement.
5.3 Particle size data are referenced to the particle system
3.1.6.1 Discussion—It can be quantified as the ratio of the
square root of the difference between the measured and actual used to calibrate the SPC. Differences in detection, electronic
and sample handling systems among the various SPCs may
variances of a monosized particle size distribution to the mean
diameter of those monosize particles, using procedures as contribute to differences in particle characterization. Care must
shown in Practice F 658. be exercised in attempting to compare data from particles that
vary significantly in composition or shape from the calibration
3.1.7 standardization—secondary calibration of electronic
base material. Variations may also occur between instruments
system voltage and signal response threshold levels using the
using similar particle sensing systems with different operating
reference system built into the SPC.
parameters. These effects should be recognized and minimized
3.1.7.1 Discussion—The SPC should be capable of carrying
by using standard methods for SPC calibration and operation.
out this procedure with a simple, rapid manual operation or by
5.4 In applying this practice, the fundamental assumption is
internal timed or microprocessor controlled components.
made that the particles in the sample passing through the SPC
3.2 For definitions of other terms used in this practice, see
are representative of the particles in the entire dust-controlled
Terminology D 1356 and Federal Standard 209D.
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
Available from U.S. General ServicesAdministration, Federal Supply Service,
Standardization Division, Washington, DC 20406. of the SPC.
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F 50 – 92 (2001)
6. Interferences the SPC element that manipulates the particles shall not result
in significant particle number change during that process.
6.1 Since the SPC is typically a high sensitivity device, it’s
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
6.3 Operation at acceptably low levels of internal noise can
internallygeneratedbytheSPC,orboth,arenotreturnedtothe
be verified by drawing a sample into the SPC through a filter
dust-controlled area.
or other gas cleaning device that will positively remove at least
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 before coincidence error > 10 % of the indicated
7.1 SPC—The apparatus shall consist of a SPC, selected on
particle count, occurs in the detection process. The specifica-
the basis of its ability to count and size single particles in the
tions shall also define the pulse rate where the data processing
required size range. The SPC shall include a sample air flow
system becomes saturated and can no longer produce accurate
system, a particle characterization system, and a data process-
pulse size and frequency information.
ing system. The minimum measurable particle size shall be
NOTE 3—Dynamic range for SPCs will frequently vary with particle
selected from the clean area definition stated in Table I of
size sensitivity. For an SPC operating solely in the size range < 1 µm, a
Federal Standard 209D, or from a different specification of
dynamic range of 20 to 1 is typical. For an SPC used for particle
clean-area airborne particle concentration at a stated minimum
measurement > 1 µm, a dynamic range of 20 to 40 is typical.The dynamic
particle size. For classification levels based on measurement of
range limitations occur as a consequence of both typical particle size
particles larger than 0.05 µm, an optical particle counter
distributions in clean areas and of data processing system gain limitations.
(OPC), an aerodynamic particle sizer or an equivalent SPC can
7.3 Particle Data Processing System, shall include compo-
be used. For classification levels based on particles less than
nents for counting and sizing data signals from particles
0.05 µm, a CNC in combination with a diffusion battery, a
observed by the SPC, a means of converting data signal level
differential mobility analyzer or an equivalent SPC can be
to particle size information, sufficient data processing capabil-
used.
ity to relate particle count and air flow data to particle
7.1.1 Sample Air Flow System, consists of an intake tube,
concentration information, and internal monitoring capability
the particle sensing/measurement chamber, an air flow meter-
to verify that critical SPC components are operating correctly.
ing or control system, and an exhaust system.
...
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