ASTM F50-92(1996)
(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
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 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 209, 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.
1.6 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 and health practices and determine the applicability of regulatory limitations prior to use. For specific hazards statements, see Section 8.
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Designation: F 50 – 92 (Reapproved 1996)
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 F 50; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope the scope of this practice; however, sampling practices shall be
stated that take into account potential spatial and statistical
1.1 This practice covers the determination of the particle
variations of suspended particles in clean rooms.
concentration, by number, and the size distribution of airborne
particles in dust-controlled areas and clean rooms, for particles
NOTE 2—General references to cleanroom classifications follow Fed-
in the size range of approximately 0.01 to 5.0 μm. Particle
eral Standard 209, latest revision. Where airborne particles are to be
6 3
characterized in dust-controlled areas that do not meet these classifica-
concentrations not exceeding 3.5 3 10 particles/m (100 000/
tions, the latest revision of the pertinent specification for these areas shall
ft ) are covered for all particles equal to and larger than the
be used.
minimum size measured.
1.6 This standard does not purport to address all of the
1.2 This practice uses an airborne single particle counting
device (SPC) whose operation is based on measuring the signal safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
produced by an individual particle passing through the sensing
zone. The signal must be directly or indirectly related to priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use. For specific hazards
particle size.
statements, see Section 8.
NOTE 1—The SPC type is not specified here. The SPC can be a
conventional optical particle counter (OPC), an aerodynamic particle
2. Referenced Documents
sizer, a condensation nucleus counter (CNC) operating in conjunction with
2.1 ASTM Standards:
a diffusion battery or differential mobility analyzer, or any other device
capable of counting and sizing single particles in the size range of concern D 1356 Terminology Relating to Atmospheric Sampling
and of sampling in a cleanroom environment.
and Analysis
F 328 Practice for Determining Counting and Sizing Accu-
1.3 Individuals performing tests in accordance with this
racy of an Airborne Particle Counter using Near-
practice shall be trained in use of the SPC and shall understand
Monodisperse Spherical Particulate Materials
its operation.
F 649 Practice for Secondary Calibration of Airborne Par-
1.4 Since the concentration and the particle size distribution
ticle Counter using Comparison Procedures
of airborne particles are subject to continuous variations, the
F 658 Practice for Defining Size Calibration, Resolution,
choice of sampling probe configuration, locations and sam-
and Counting Accuracy of a Liquid-Borne Particle Counter
pling times will affect sampling results. Further, the differences
using Near-Monodisperse Spherical Particulate Materials
in the physical measurement, electronic and sample handling
2.2 U.S. Federal Standard:
systems between the various SPCs and the differences in
Federal Standard No. 209D, Clean Room and Work Station
physical properties of the various particles being measured can
Requirements, Controlled Environment
contribute to variations in the test results. These differences
should be recognized and minimized by using a standard
3. Terminology
method of primary calibration and by minimizing variability of
3.1 Definitions of Terms Specific to This Standard:
sample acquisition procedures.
3.1.1 dust-controlled area—a clean room or clean work
1.5 Sample acquisition procedures and equipment may be
space in which airborne and deposited particulate contamina-
selected for specific applications based on varying cleanroom
tion levels, or both, are controlled on the basis of a documented
class levels. Firm requirements for these selections are beyond
standard such as Federal Standard 209D.
This practice is under the jurisdiction of ASTM Committee E-21 on Space
Simulation and Applications of Space Technology and is the direct responsibility of Annual Book of ASTM Standards, Vol 11.03.
Subcommittee E21.05 on Contamination. Annual Book of ASTM Standards, Vol 15.03.
Current edition approved May 15, 1992. Published July 1992. Originally Available from U.S. General Services Administration, Federal Supply Service,
e1
published as F 50 – 65 T. Last previous edition F 50 – 83 (1989) Standardization Division, Washington, DC 20406.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
F50
3.1.2 dynamic range—the particle size range, expressed as a the SPC. Each particle produces a signal that can be related to
multiple of the minimum measured size, over which the SPC particle size. An electronic system sorts and counts the pulses,
can measure particles with size resolution of 10 % or less. registering the number of particles of various sizes that have
3.1.3 particle concentration—the number of individual par- passed through the sensing zone during passage of a known gas
ticles per unit volume of ambient temperature and pressure air, volume. The concentration and particle size data can be
3 3
particles/m or particles/ft . displayed, printed or otherwise processed, locally or remotely.
3.1.4 particle size—equivalent diameter of a particle de-
5. Significance and Use
tected by an SPC.
5.1 The primary purpose of this practice is to describe a
3.1.4.1 Discussion—The equivalent diameter is the diam-
procedure for collecting near real-time data on airborne particle
eter of a reference sphere of known size and physical charac-
concentration and size distribution in clean areas as indicated
teristics (for example, refractive index when using an OPC;
by single particle counting techniques. Implementation of
density when using an aerodynamic particle sizer; etc) and
some government and industry specifications requires acquisi-
generating the same response in the SPC sensing zone as the
tion of particle size and concentration data using an SPC.
particle being measured. Spherical particles are used for
5.2 The processing requirements of many products manu-
calibration of the SPCs considered here. The SPC response is
factured in a clean room involves environmental cleanliness
related to the size, shape, orientation and physical properties of
levels so low that a single particle counter with capability for
the particle passing through the SPC sensing zone. If an optical
detecting very small particles is required to characterize clean
particle counter is used, the geometry of the optical system, as
room air. Real-time information on concentration of airborne
well as the spectral distribution of the illuminating light
influences the reported particle size. If a condensation nucleus particles in size ranges from less than 0.1 μm to 5 μm and
greater can be obtained only with an SPC. Definition of
counter with a size-fractionation device is used, the SPC
operating parameters and the particle properties that affect the particles larger than approximately 0.05 μm may be carried out
with direct measurement of light scattering from individual
nucleation efficiency and, for example, the diffusion coeffi-
cient, will influence reported data. The SPC instruction manual particles; other techniques may be required for smaller par-
ticles, such as preliminary growth by condensation before
should make the user aware of the effects of such factors on the
indicated particle size data. particle measurement.
5.3 Particle size data are referenced to the particle system
3.1.5 primary calibration—calibration with standard refer-
used to calibrate the SPC. Differences in detection, electronic
ence particles for particle size and (optionally) concentration.
and sample handling systems among the various SPCs may
Initially carried out by the SPC manufacturer.
contribute to differences in particle characterization. Care must
3.1.6 resolution—the capability of the SPC to differentiate
be exercised in attempting to compare data from particles that
between particles with small difference in size.
vary significantly in composition or shape from the calibration
3.1.6.1 Discussion—It can be quantified as the ratio of the
base material. Variations may also occur between instruments
square root of the difference between the measured and actual
using similar particle sensing systems with different operating
variances of a monosized particle size distribution to the mean
parameters. These effects should be recognized and minimized
diameter of those monosize particles, using procedures as
by using standard methods for SPC calibration and operation.
shown in Practice F 658.
5.4 In applying this practice, the fundamental assumption is
3.1.7 standardization—secondary calibration of electronic
made that the particles in the sample passing through the SPC
system voltage and signal response threshold levels using the
are representative of the particles in the entire dust-controlled
reference system built into the SPC.
area being analyzed. Care is required that good sampling
3.1.7.1 Discussion—The SPC should be capable of carrying
out this procedure with a simple, rapid manual operation or by procedures are used and that no artifacts are produced at any
point in the sample handling and analysis process; these
internal timed or microprocessor controlled components.
3.2 For definitions of other terms used in this practice, see precautions are necessary both in verification and in operation
of the SPC.
Terminology D 1356 and Federal Standard 209D.
4. Summary of Practice 6. Interferences
4.1 Satisfactory primary calibration within the manufactur- 6.1 Since the SPC is typically a high sensitivity device, it’s
er’s recommended time period and routine standardization response may be affected by internally or externally generated
should be verified as a first step. noise. The SPC should not be operated at a sensitivity level so
4.2 A sample acquisition program is established on the basis high that internal noise produces more than 5 % of the data
of the cleanliness level that is to be verified or monitored. This signals.
program will include sample point identification, sample size 6.2 Precautions should also be taken to ensure that the test
definitions and sampling frequency, specification of the sam- area environment does not exceed the radio frequency or
pler inlet and sample transport system, definition of the particle electromagnetic interference capabilities of the SPC.
size ranges to be measured, and any other parameters of 6.3 Operation at acceptably low levels of internal noise can
concern in the dust-controlled area or clean room. be verified by drawing a sample into the SPC through a filter
4.3 Air samples are passed through the SPC and the particle or other gas cleaning device that will positively remove at least
content of each sample is defined by the SPC. Particles 99.97 % of all particles of size equal to and greater than that
contained in the sampled air pass through the sensing zone of which the SPC will measure. After a short stabilization period,
F50
any signals reported by the SPC can be assumed to arise from operating dynamic range. The SPC specifications shall include
internal or external noise sources. information as to the maximum particle concentration that can
be measured before coincidence error > 10 % of the indicated
7. Apparatus
particle count, occurs in the detection process. The specifica-
7.1 SPC—The apparatus shall consist of a SPC, selected on
tions shall also define the pulse rate where the data processing
the basis of its ability to count and size single particles in the
system becomes saturated and can no longer produce accurate
required size range. The SPC shall include a sample air flow
pulse size and frequency information.
system, a particle characterization system, and a data process-
NOTE 3—Dynamic range for SPCs will frequently vary with particle
ing system. The minimum measurable particle size shall be
size sensitivity. For an SPC operating solely in the size range < 1 μm, a
selected from the clean area definition stated in Table I of
dynamic range of 20 to 1 is typical. For an SPC used for particle
Federal Standard 209D, or from a different specification of
measurement > 1 μm, a dynamic range of 20 to 40 is typical. The dynamic
clean-area airborne particle concentration at a stated minimum
range limitations occur as a consequence of both typical particle size
particle size. For classification levels based on measurement of distributions in clean areas and of data processing system gain limitations.
particles larger than 0.05 μm, an optical particle counter
7.3 Particle Data Processing System, shall include compo-
(OPC), an aerodynamic particle sizer or an equivalent SPC can
nents for counting and sizing data signals from particles
be used. For classification levels based on particles less than
observed by the SPC, a means of converting data signal level
0.05 μm, a CNC in combination with a diffusion battery, a
to particle size information, sufficient data processing capabil-
differential mobility analyzer or an equivalent SPC can be
ity to relate particle count and air flow data to particle
used.
concentration information, and internal monitoring capability
7.1.1 Sample Air Flow System, consists of an intake tube,
to verify that critical SPC components are operating correctly.
the particle sensing/measurement chamber, an air flow meter-
Data shall be available as front-panel display, convenient
ing or control system, and an exhaust system. No abrupt
on-board hard-copy format or as signals that can be transmitted
transitions in dimension should occur within the air flow
to a remote data reception device in a format that will allow
system. The inlet tube should consist of a sharp-edged inlet
either direct storage or further processing. The particle data
nozzle connected to a tube that will transport the sample air to
processing system shall also include the necessary components
the particle characterization system. The sample inlet nozzle
to carry out standardization of the SPC. The standardization
should have a cross-sectional area equivalent to that of a circle
may be done either manually or by internal SPC control.
of diameter a
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