ASTM F25/F25M-21

Standard Test Method for Sizing and Counting Airborne Particulate Contamination in Cleanrooms and Other Dust-Controlled Areas

ABSTRACT
This test method covers the apparatuses required, sampling methods, standard procedures and calculations, and test reports for counting and sizing airborne microparticulate matter, the sampling areas for which are specifically those with contamination levels typical of cleanrooms and dust-controlled areas. The test method is based on the microscopical examination of particles impinged upon a membrane filter with the aid of a vacuum. Sampling may be done in a cleanroom, clean zone, or other controlle areas, or in a duct or pipe, wherein the number of sampling points is proportional to the floor area of the enclosure to be checked. The apparatus and facilities required are typical of a laboratory for the study of macroparticle contamination. The operator must have adequate basic training in microscopy and the techniques of particle sizing and counting.
SCOPE
1.1 This test method covers counting and sizing airborne particulate matter 5 µm and larger (macroparticles). The sampling areas are specifically those with contamination levels typical of cleanrooms and dust-controlled areas.  
1.2 Units—The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system are not necessarily exact equivalents; therefore, to ensure conformance with the standard, each system shall be used independently of the other, and values from the two systems shall not be combined.  
1.3 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.4 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.

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

• Replaces: ASTM F318-06 - Standard Practice for Sampling Airborne Particulate Contamination in Cleanrooms for Handling Aerospace Fluids
• Effective Date: 11-Jun-2013
• Refers: ASTM F50-12 - 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
• Effective Date: 01-Apr-2012
• Refers: ASTM F50-07 - 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
• Effective Date: 01-Nov-2007
• Refers: ASTM F50-92(2001)e1 - 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
• Effective Date: 15-May-1992
• Refers: ASTM F50-92(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
• Effective Date: 15-May-1992

Overview

ASTM F25/F25M-21 is the international standard test method developed by ASTM International for sizing and counting airborne particulate contamination in cleanrooms and other dust-controlled areas. This methodology is vital for environments requiring stringent air purity, addressing the need to accurately collect, count, and size airborne particles 5 micrometres (µm) and larger (macroparticles). The standard outlines apparatus requirements, sampling plans, procedural steps, and reporting criteria for reliable assessment of airborne particulate contamination, supporting compliance with regulatory and process control objectives across various industries.

Key Topics

• Scope of Measurement: Covers counting and sizing airborne particulate matter of 5 µm and larger in cleanrooms, clean zones, and other controlled environments.
• Sampling Approach:
  • Employs microscopical examination of particles collected on a membrane filter using a vacuum-based apparatus.
  • Sampling points are proportional to the floor area or specific to critical zones or ducts.
• Apparatus Requirements:
  • Membrane filter holder and vacuum source
  • Flow-limiting orifice, calibrated flowmeter, and microscope with defined magnifications
  • Proper cleaning procedures and handling practices to reduce contamination
• Sampling Methods:
  • Detailed steps for both room- and duct-based particle collection
  • Emphasizes isokinetic sampling in ducts to ensure representative samples
• Microscopical Analysis:
  • Sizing and statistical counting of particulate contamination in multiple size ranges
  • Application of statistical sampling plans and background correction to ensure data reliability
• Test Reporting:
  • Specific requirements for comprehensive recording and reporting of results, including location information, test conditions, particle concentrations, and compliance statements.

Applications

The ASTM F25/F25M-21 standard is essential for any organization operating or certifying cleanrooms or dust-controlled areas. Typical uses include:

• Cleanroom Validation and Certification: Applied by testing laboratories and facilities managers during cleanroom commissioning, routine monitoring, and periodic validation.
• Process Control and Compliance: Supports compliance with manufacturing quality systems in industries like pharmaceuticals, medical device production, microelectronics, and aerospace.
• Environmental Monitoring: Utilized for ongoing risk assessments and to verify the effectiveness of air filtration, cleaning, and operational controls in critical environments.
• Research and Development: Aids in the design and optimization of cleanroom systems where airborne contamination control is required for product yield or safety.

Related Standards

For comprehensive contamination control and cleanroom classification, the following standards are commonly referenced alongside ASTM F25/F25M-21:

• ASTM F50: Practice for continuous sizing and counting of airborne particles in dust-controlled areas and cleanrooms using instruments capable of detecting single sub-micrometre and larger particles.
• ISO 14644-1: International standard for classification of air cleanliness by particle concentration in cleanrooms and associated controlled environments.
• IEST-G-CC1003: Measurement of airborne macroparticles, provides guidance on sampling plans and isokinetic sampling techniques.
• SAE ARP-743: Procedure for the determination of particulate contamination of air in dust-controlled spaces by the particle count method.

Keywords: airborne particulate contamination, cleanroom testing, particle sizing, macroparticles, dust-controlled areas, air cleanliness, ASTM F25/F25M-21, environmental monitoring, contamination control, cleanroom certification.

By following ASTM F25/F25M-21, organizations ensure robust, standardized, and internationally recognized assessment of airborne particulate contamination, facilitating regulatory compliance, product quality, and process reliability in cleanrooms and controlled environments.

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: F25/F25M − 21
Standard Test Method for
Sizing and Counting Airborne Particulate Contamination in
Cleanrooms and Other Dust-Controlled Areas
This standard is issued under the fixed designation F25/F25M; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 2.2 ISO Standard:
ISO 14644-1 Cleanrooms and Associated Controlled
1.1 This test method covers counting and sizing airborne
Environments—Part 1: Classification of Air Cleanliness
particulate matter 5 µm and larger (macroparticles). The
2.3 IEST Document:
samplingareasarespecificallythosewithcontaminationlevels
IEST-G-CC1003Measurement of Airborne Macroparticles
typical of cleanrooms and dust-controlled areas.
(1999)
1.2 Units—The values stated in either SI units or inch-
2.4 SAE Document:
pound units are to be regarded separately as standard. The
SAEAbstractARP-743, Procedure for the Determination of
values stated in each system are not necessarily exact equiva-
Particulate Contamination of Air in Dust-Controlled
lents; therefore, to ensure conformance with the standard, each
Spaces by Particle Count Method, August 1962
system shall be used independently of the other, and values
from the two systems shall not be combined. 3. Terminology
3.1 Definitions:
1.3 This standard does not purport to address all of the
3.1.1 airflow, n—
safety concerns, if any, associated with its use. It is the
3.1.1.1 unidirectional airflow, n—air flow which has a
responsibility of the user of this standard to establish appro-
singular direction of flow and may or may not contain uniform
priate safety, health, and environmental practices and deter-
velocities of air flow along parallel lines.
mine the applicability of regulatory limitations prior to use.
NOTE 1—Formerly known as laminar airflow.
1.4 This international standard was developed in accor-
dance with internationally recognized principles on standard- 3.1.1.2 non-unidirectional airflow, n—airdistributionwhere
the supply air entering the room mixes with the internal air by
ization established in the Decision on Principles for the
means of induction.
Development of International Standards, Guides and Recom-
mendations issued by the World Trade Organization Technical
3.1.2 critical pressure, n—for an orifice with a constant
Barriers to Trade (TBT) Committee.
upstream pressure, the downstream pressure at which the flow
will not increase when the downstream pressure decreases.
2. Referenced Documents
3.1.3 critical pressure ratio, n—the ratio of the critical
pressure of an orifice to the entrance pressure.
2.1 ASTM Standards:
3.1.4 customer, n—organization, or the agent thereof, re-
F50Practice for Continuous Sizing and Counting of Air-
sponsible for specifying the requirements of a cleanroom or
borne Particles in Dust-Controlled Areas and Clean
clean zone.
Rooms Using Instruments Capable of Detecting Single
Sub-Micrometre and Larger Particles
3.1.5 fiber, n—particle having an aspect (length-to-width)
ratio of 10 or more.
3.1.6 macroparticle, n—particlewithanequivalentdiameter
greater than 5 µm.
This test method 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.
Current edition approved April 1, 2021. Published April 2021. Originally
approvedin1963.Lastpreviouseditionapprovedin2015asF25/F25M–09(2015). Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
DOI: 10.1520/F0025_F0025M-21. 4th Floor, New York, NY 10036, http://www.ansi.org.
2 4
For referenced ASTM standards, visit the ASTM website, www.astm.org, or Available from Institute of Environmental Sciences and Technology (IEST),
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM 1827Walden Office Square, Suite 400, Schaumburg, IL60173, http://www.iest.org.
Standards volume information, refer to the standard’s Document Summary page on Available from Society of Automotive Engineers (SAE), 400 Commonwealth
the ASTM website. Dr., Warrendale, PA 15096-0001, http://www.sae.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F25/F25M − 21
FIG. 2 Typical Air Sampling-Filtration Apparatus
5. Apparatus
5.1 Filter Holder, aerosol open type having an effective
filtering area of 960 6 25 mm .
FIG. 1 Suitable Microscope: Inclined Binocular Body; Mechanical
5.2 Adapter.
Stage; Triple Nosepiece; Ocular-Objective Combination to Obtain
40 to 45× and 90 to 150× Magnification
5.3 Flow-Limiting Orifice, 10 L/min.
5.4 Membrane Filters, black, 0.80µm mean pore size,
47mmdiameter,withimprintedgridsquareshavingsides3.10
3.1.7 M descriptor, n—measured or specified concentration
6 0.08 mm. Pressure drop across the filter used shall be no
of macroparticles per cubic metre of air, expressed in terms of
greater than 50 torr for an air flow rate of 1 L/min·cm .
the equivalent diameter that is characteristic of the measure-
ment method used.
5.5 Forceps, with unserrated tips.
3.1.7.1 Discussion—The M descriptor may be regarded as
5.6 Vacuum Pump, capable of producing a pressure of 34
an upper limit for the averages at sampling locations (or as an
kPa [260 torr] [vacuum of 500 torr] downstream of the orifice
upper confidence limit, depending upon the number of sam-
at a flow rate of 10 L/min through the orifice.
pling locations used to characterize the cleanroom or clean
5.7 Flowmeter,calibratedandhavingacapacityinexcessof
zone). M descriptors cannot be used to define airborne particu-
late cleanliness classes, but they may be quoted independently 10 L/min.
or in conjunction with airborne particulate cleanliness classes.
5.8 Glass Microscope Slides, 50 mm by 75 mm, or 47mm
3.1.8 occupancy states, n—
plastic disposable petri dishes.
3.1.8.1 as-built, n—condition where the installation is com-
plete with all services connected and functioning but with no
The sole source of supply of the apparatus known to the committee at this time
additional equipment, materials, or personnel present.
is 47 mm Stainless Steel, Millipore XX5004710, available from MilliporeSigma
Headquarters, 400 Summit Drive, Burlington, MA 01803, https://
3.1.8.2 at-rest, n—condition where the installation is com-
www.emdmillipore.com/US/en. If you are aware of alternative suppliers, please
plete with equipment installed and operating in a manner
provide this information toASTM International Headquarters.Your comments will
agreed upon by the customer and supplier, but with no 1
receive careful consideration at a meeting of the responsible technical committee,
personnel present. which you may attend.
The sole source of supply of the apparatus known to the committee at this time
3.1.8.3 operational, n—condition where the installation is
1 3
is Luer slip to ⁄4 in. - ⁄8 in. ID hose Stainless Steel, XX6200004, available from
functioning in the specified manner, with the specified number MilliporeSigma Headquarters, 400 Summit Drive, Burlington, MA 01803, https://
www.emdmillipore.com/US/en. If you are aware of alternative suppliers, please
of personnel present and working in the manner agreed upon.
provide this information toASTM International Headquarters.Your comments will
3.1.9 particle size, n—major projected dimension of the
receive careful consideration at a meeting of the responsible technical committee,
which you may attend.
particle.
The sole source of supply of the apparatus known to the committee at this time
is Limiting Orifice Set (5 orifices including 10 L/min), XX5000000, available from
4. Summary of Test Method
MilliporeSigma Headquarters, 400 Summit Drive, Burlington, MA 01803, https://
www.emdmillipore.com/US/en. If you are aware of alternative suppliers, please
4.1 The test method is based on the microscopical exami-
provide this information toASTM International Headquarters.Your comments will
nation of particles impinged upon a membrane filter with the
receive careful consideration at a meeting of the responsible technical committee,
aid of a vacuum. The number of sampling points is propor-
which you may attend.
tional to the floor area of the enclosure to be checked. The
The sole source of supply of the apparatus known to the committee at this time
isAABG04700,BlackGrid,0.80µm,availablefromMilliporeSigmaHeadquarters,
apparatus and facilities required are typical of a laboratory for
400 Summit Drive, Burlington, MA 01803, https://www.emdmillipore.com/US/en.
the study of macroparticle contamination. The operator must
If you are aware of alternative suppliers, please provide this information toASTM
have adequate basic training in microscopy and the techniques
International Headquarters. Your comments will receive careful consideration at a
of particle sizing and counting. meeting of the responsible technical committee, which you may attend.
F25/F25M − 21
5.9 Binocular Microscope, (Fig. 1) with ocular-objective 7.2 The filter surface may be vertical or horizontal with
combinations to obtain 40 to 45× and 90 to 150× magnifica- respect to the floor.
tions. Latter objective shall have numerical aperture of 0.15 7.2.1 The orientation of the filter depends on airflow direc-
min. tion for unidirectional airflow areas.
10 7.2.1.1 Samplinginaunidirectionalairflowshallbeasclose
5.10 Normal Counter, (2 gang) or equivalent.
to isokinetic as is possible.
5.11 Microscope Lamp, 6 V, 5 A, high-intensity.
7.2.1.2 IEST-G-CC1003 provides additional information on
5.12 Ocular Micrometer Scale, 5mm linear scale with 100 isokinetic sampling.
7.2.2 For nonunidirectional airflow areas, the customer may
divisions.
specify an orientation or the process being monitored in the
5.13 Stage Micrometer, standard 0.01mm to 0.1mm scale.
cleanroom may indicate which orientation would be preferred.
7.2.2.1 In nonunidirectional airflow, airflow directions and
6. Sampling Apparatus
velocities vary with location and time.
6.1 The airborne particles shall be collected, with the aid of
7.2.2.2 IEST G-CC1003 recommends a sample inlet probe,
a vacuum source, on a membrane filter of 960mm effective
with an inlet diameter of at least 20 mm, facing upward. This
filtering area.
will collect larger particles that tend to settle out of the air.
6.2 Theapparatusspecifiedin5.1,5.2,and5.3orequivalent
7.3 The standard sample for this test method shall be 300 L
shall be used.
[10 ft ].
6.3 Fig. 2 is picture of a typical sampler.
7.3.1 The sample size may be adjusted for specific condi-
tions.
6.4 Fig. 3 is a drawing of a typical sampler assembly.
7.3.2 The number of particles sampled shall meet statistical
6.5 Sampler airflow is maintained using the vacuum pump,
criteria of ISO 14644-1 or other accepted statistical sampling
specified in 5.6, connected to the sampler and either a
criteria.
flowmeter to measure flow or a calibrated orifice to control
7.4 The sample shall be taken at waist level (0.9 to 1.0 m
flow.
[36 to 40 in.] from the floor), at bench level, or at other points
6.5.1 The flow rate may be adjusted using a flowmeter and
as specified by the customer. The sample points may be
valvedownstreamofthesamplerwithfilterandotherelements
selectedforrelevancetoandsensitivityoftheoperationsbeing
installed.
performed in the cleanroom.
6.5.2 A calibrated orifice, 5.3, may be used to control the
airflow rate. The specified flow rate for the orifice depends on
7.5 The number and location of sampling points shall be as
critical pressure ratio of less than 0.53 for air at room
designated in the sampling plan.
temperature and pressure. The limiting orifice shall be cali-
7.5.1 The minimum number of sample locations, as speci-
brated with the pump, filter holder, and filter used for this test
fied in ISO 14644-1, Annex B, may be used:
method. The required flow rate is 10 6 0.5 L/min.
N 5 =A (1)
L
6.6 Inspect the sampler, including the orifice, to ensure that
where:
itisfreeofrestrictingmatterbeforeeachtest.Cleanifrequired.
N = minimumnumberofsamplinglocations(roundedupto
L
7. Sampling in a Cleanroom, Clean Zone, or Other
a whole number), and
Controlled Areas
A = area of the cleanroom or clean zone in square metres.
7.1 Sampling Plan:
7.1.1 A sampling plan shall be provided.
In the case of unidirectional horizontal airflow, the area A
7.1.2 ISO 14644-1 and IEST-G-CC1003 may be used as
may be considered as the cross section of the moving air
guides for the plan.
perpendicular to the direction of the airflow.
7.5.2 The nature of the operations or the customer may
select the number of sampling points.
Thesolesourceofsupplyoftheapparatusknowntothecommitteeatthistime
is the Veeder-Root counter, available from Veeder-Root, 25 Powder Forest Drive,
8. Sampling in a Duct or Pipe
PO Box 2003, Simsbury, CT 06070, https://www.veeder.com. If you are aware of
8.1 The sampling of a moving gas stream in a duct or
alternative suppliers, please provide this information to ASTM International
Headquarters.Your comments will receive careful consideration at a meeting of the
pipeline requires isokinetic sampling.
responsible technical committee, which you may attend.
FIG. 3 Typical Aerosol Monitor Sampling System
F25/F25M − 21
8.2 Often by reason of the total flow, the allowable pressure
drop, or the physical dimensions of the system (as, for
example, an air conditioning air duct), it is impracticable to
sample the entire flow.
8.3 Becauseofthelowviscosityofgas,movinggasstreams
present several special sampling problems, which may disturb
FIG. 5 Faulty Sample from a Rapid-Ducted Gas Stream
the results unless care is taken.
8.4 To collect a representative sample of particulate con-
8.10 Sampling rate and probe dimensions shall be carefully
tamination from a ducted air stream, insert a probe (as shown
adjusted to match duct and probe air velocities.
in Fig. 4) coupled to the sampling apparatus described in 5.1,
5.2, and 5.3.
9. Preparation of Apparatus
8.5 Achievingaccurateisokineticsamplingrequiresthatthe
9.1 Before sampling, remove dirt and dust from the filter
gas linear velocity at the probe opening match that in the duct.
holder by washing in a free-rinsing detergent, ketone-free
Equalvelocitiesmaybeachievedbyaproperratiobetweenthe
isopropyl alcohol, submicron-filtered reagent grade petroleum
probe opening and the limiting orifice dimensions, for ex-
ether (boiling range 30 to 60°C) or trichloromonofluorometh-
ample:
ane or trichlorotrifluoroethane.
flowinduct ~L/min! samplingrate ~L/min!
5 (2) 9.2 The clean laboratory equipment used for counting and
ductcross 2 sectionalarea probeopeningarea
sizing the collected particles shall be in a HEPA-filtered clean
8.6 Failuretomatchtheprobeandductvelocitieswillcause
bench or equivalent clean area.
adistortionofresultsfavoringeitherlargeparticlesiftheprobe
9.3 Plastic microscope hoods shall be installed on the
velocitylowerthanductvelocityorsmallparticlesiftheprobe
microscope to minimize particle deposition on the filter being
velocity higher than duct velocity.
counted.
8.7 Fig. 5 shows an open-type holder installed in a duct.
9.4 Personnel performing sizing and counting operations
Some large particles are diverted from the filter by airflow
shall be equipped with cleanroom garments consistent with
around the filter holder. Most small particles are diverted.
good practice.
8.8 Probes shall have thin walls, sharp edges, as large an
9.5 Cleanandpreparemicroscopeslidesandpetridishesfor
inside diameter as is practicable, but with a minimum inside
preserving the membrane filter and specimen. Lens tissue
diameter of 6.4 mm [0.25 in.].
properly used is satisfactory for this operation.
8.8.1 Practice F50 provides some guidelines for sample
9.6 Handle hazardous chemicals used in the method with
probe tubing.
recognized precautions.
8.8.1.1 Sampletransittubesshouldbeconfiguredsothatthe
flow Reynolds number is maintained in the range 5000 to
9.7 Establish a background count on membrane filters by
25000.
examiningeachfilterusedforrefereepurposes.Examinationat
8.8.1.2 For particles in the size range 0.1 µm to approxi-
40 to 50× magnifications through the microscope will reveal
mately 2 µm in diameter and a flow rate of 30 L/min [1
low or high background count.
ft /min], a transit tube up to 30 m long can be used.
9.8 For routine work, a background count on two filters per
8.8.1.3 For particles in the size range approximately 2 to 10
boxof100isadequateunderpresentrigidproductionmethods.
µm, a maximum transit tube length of 3 m can be used.
9.9 Make a background count, following the microscopical
8.8.1.4 If a flexible transit tube is to be used, then no radius
methods outlined in this method.
of curvature below 150 mm shall be used.
8.8.2 Tubing diameter, length, and bend radius shall be
9.10 A background is required upon any filter with a
selectedtomaximizethetransportofparticlesofthemaximum
contamination level approximating 10% or greater of the
size to be measured.
estimated test sample. This count will be subtracted from the
total count (Pt) obtained for each size rang
...

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: F25/F25M − 09 (Reapproved 2015) F25/F25M − 21
Standard Test Method for
Sizing and Counting Airborne Particulate Contamination in
Cleanrooms and Other Dust-Controlled Areas
This standard is issued under the fixed designation F25/F25M; 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 test method covers counting and sizing airborne particulate matter 5 μm and larger (macroparticles). The sampling areas
are specifically those with contamination levels typical of cleanrooms and dust-controlled areas.
1.2 Units—The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in
each system mayare not benecessarily exact equivalents; therefore, to ensure conformance with the standard, each system shall be
used independently of the other. Combiningother, and values from the two systems may result in non-conformance with the
standard.shall not be combined.
1.3 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 requirementslimitations prior to use.
1.4 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:
F50 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
2.2 ISO Standard:
ISO 14644-1 Cleanrooms and Associated Controlled Environments—Part 1: Classification of Air Cleanliness
2.3 IEST Document:
IEST-G-CC1003 Measurement of Airborne Macroparticles (1999)
2.4 SAE Document:
SAE Abstract ARP-743, Procedure for the Determination of Particulate Contamination of Air in Dust-Controlled Spaces by
Particle Count Method, August 1962
This test method 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 1963. Last previous edition approved in 20092015 as
F25 – 09.F25/F25M – 09(2015). DOI: 10.1520/F0025_F0025M-09R15.10.1520/F0025_F0025M-21.
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.
Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http://www.ansi.org.
Available from Institute of Environmental Sciences and Technology (IEST), Arlington Place One, 2340 S. Arlington Heights Rd., Suite 100, Arlington Heights, IL
60005-4516,1827 Walden Office Square, Suite 400, Schaumburg, IL 60173, http://www.iest.org.
Available from Society of Automotive Engineers (SAE), 400 Commonwealth Dr., Warrendale, PA 15096-0001, http://www.sae.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F25/F25M − 21
3. Terminology
3.1 Definitions:
3.1.1 airflow:airflow, n—
3.1.1.1 unidirectional airflow—airflow, n—air flow which has a singular direction of flow and may or may not contain uniform
velocities of air flow along parallel lines.
NOTE 1—Formerly known as laminar airflow.
3.1.1.2 non-unidirectional airflow—airflow, n—air distribution where the supply air entering the room mixes with the internal
air by means of induction.
3.1.2 critical pressure—pressure, n—for an orifice,orifice with a constant upstream pressure, the downstream pressure at which the
flow will not increase when the downstream pressure decreases.
3.1.3 critical pressure ratio—ratio, n—the ratio of the critical pressure of an orifice to the entrance pressure.
3.1.4 customer—customer, n—organization, or the agent thereof, responsible for specifying the requirements of a cleanroom or
clean zone.
3.1.5 fiber—fiber, n—particle having an aspect (length-to-width) ratio of 10 or more.
3.1.6 macroparticle—macroparticle, n—particle with an equivalent diameter greater than 5 μm.
3.1.7 M descriptor—descriptor, n—measured or specified concentration of macroparticles per cubic metre of air, expressed in
terms of the equivalent diameter that is characteristic of the measurement method used.
3.1.7.1 Discussion—
The M descriptor may be regarded as an upper limit for the averages at sampling locations (or as an upper confidence limit,
depending upon the number of sampling locations used to characterize the cleanroom or clean zone). M descriptors cannot be used
to define airborne particulate cleanliness classes, but they may be quoted independently or in conjunction with airborne particulate
cleanliness classes.
3.1.8 occupancy states:states, n—
FIG. 1 Suitable Microscope: Inclined Binocular Body; Mechanical Stage; Triple Nosepiece; Ocular-Objective Combination to Obtain 40
to 45× and 90 to 150× Magnification
F25/F25M − 21
3.1.8.1 as-built—as-built, n—condition where the installation is complete with all services connected and functioning but with
no additional equipment, materials, or personnel present.
3.1.8.2 at-rest—at-rest, n—condition where the installation is complete with equipment installed and operating in a manner
agreed upon by the customer and supplier, but with no personnel present.
3.1.8.3 operational—operational, n—condition where the installation is functioning in the specified manner, with the specified
number of personnel present and working in the manner agreed upon.
3.1.9 particle size—size, n—major projected dimension of the particle.
FIG. 2 Typical Air Sampling-Filtration Apparatus
4. Summary of Test Method
4.1 The test method is based on the microscopical examination of particles impinged upon a membrane filter with the aid of a
vacuum. The number of sampling points is proportional to the floor area of the enclosure to be checked. The apparatus and facilities
required are typical of a laboratory for the study of macroparticle contamination. The operator must have adequate basic training
in microscopy and the techniques of particle sizing and counting.
5. Apparatus
6 2
5.1 Filter Holder, aerosol aerosol open type having an effective filtering area of 960 6 25 mm .
5.2 Adapter.
5.3 Flow-Limiting Orifice, 10 10 L/min.
5.4 Membrane Filters, black, 0.80-μm black, 0.80 μm mean pore size, 47-mm47 mm diameter, with imprinted grid squares
having sides 3.10 6 0.08 mm. Pressure drop across the filter used shall be no greater than 50 torr for an air flow rate of 1
L/min·cm .
The sole source of supply of the apparatus known to the committee at this time is 47 mm Stainless Steel, Millipore XX5004710, available from Millipore Corporation,
290 Concord Rd., Billerica, MA 01821. MilliporeSigma Headquarters, 400 Summit Drive, Burlington, MA 01803, https://www.emdmillipore.com/US/en. If you are aware
of alternative suppliers, please provide this information to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of the responsible
technical committee, which you may attend.
1 3
The sole source of supply of the apparatus known to the committee at this time is Luer slip to ⁄4 in. - ⁄8 in. ID hose Stainless Steel, XX6200004, available from Millipore
Corporation, 290 Concord Rd., Billerica, MA 01821. MilliporeSigma Headquarters, 400 Summit Drive, Burlington, MA 01803, https://www.emdmillipore.com/US/en. If you
are aware of alternative suppliers, please provide this information to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of
the responsible technical committee, which you may attend.
The sole source of supply of the apparatus known to the committee at this time is Limiting Orifice Set (5 orifices including 10 L/min), XX5000000, available from
Millipore Corporation, 290 Concord Rd., Billerica, MA 01821. MilliporeSigma Headquarters, 400 Summit Drive, Burlington, MA 01803, https://www.emdmillipore.com/
US/en. If you are aware of alternative suppliers, please provide this information to ASTM International Headquarters. Your comments will receive careful consideration at
a meeting of the responsible technical committee, which you may attend.
The sole source of supply of the apparatus known to the committee at this time is AABG04700, Black Grid, 0.80 μm, available from Millipore Corporation, 290 Concord
Rd., Billerica, MA 01821. MilliporeSigma Headquarters, 400 Summit Drive, Burlington, MA 01803, https://www.emdmillipore.com/US/en. If you are aware of alternative
suppliers, please provide this information to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of the responsible technical
committee, which you may attend.
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5.5 Forceps, with unserrated tips.
5.6 Vacuum Pump, capable of producing a pressure of 34 kPa (260 torr) (vacuum[260 torr] [vacuum of 500 torr)torr] downstream
of the orifice at a flow rate of 10 L/min through the orifice.
5.7 Flowmeter, calibrated and having a capacity in excess of 10 L/min.
5.8 Glass Microscope Slides, 50 mm by 75 mm, or 47-mm47 mm plastic disposable petri dishes.
5.9 Binocular Microscope, (Fig. 1) with ocular-objective combinations to obtain 40 to 45× and 90 to 150× magnifications. Latter
objective shall have numerical aperture of 0.15 min.
5.10 Normal Counter, (2 (2 gang) or equivalent.
5.11 Microscope Lamp, 6 V, 5 A, high-intensity.
5.12 Ocular Micrometer Scale, 5-mm5 mm linear scale with 100 divisions.
5.13 Stage Micrometer, standard 0.01-mm0.01 mm to 0.1-mm0.1 mm scale.
6. Sampling Apparatus
6.1 The airborne particles shall be collected, with the aid of a vacuum source, on a membrane filter of 960-mm960 mm effective
filtering area.
6.2 The apparatus specified in 5.1, 5.2, and 5.3 or equivalent shall be used.
6.3 Fig. 2 is picture of a typical sampler.
6.4 Fig. 3 is a drawing of a typical sampler assembly.
6.5 Sampler airflow is maintained using the vacuum pump, specified in 5.6, connected to the sampler and either a flowmeter to
measure flow or a calibrated orifice to control flow.
6.5.1 The flow rate may be adjusted using a flowmeter and valve downstream of the sampler with filter and other elements
installed.
6.5.2 A calibrated orifice, 5.3, may be used to control the airflow rate. The specified flow rate for the orifice depends on critical
pressure ratio of less than 0.53 for air at room temperature and pressure. The limiting orifice shall be calibrated with the pump,
filter holder, and filter used for this test method. The required flow rate is 10 6 0.5 L/min.
FIG. 3 Typical Aerosol Monitor Sampling System
The sole source of supply of the apparatus known to the committee at this time is the Veeder-Root counter, available from Veeder-Root, 6th Ave. & Burns Xing, Altoona,
PA 16602. 25 Powder Forest Drive, PO Box 2003, Simsbury, CT 06070, https://www.veeder.com. If you are aware of alternative suppliers, please provide this information
to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of the responsible technical committee, which you may attend.
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6.6 Inspect the sampler, including the orifice, to ensure that it is free of restricting matter before each test. Clean if required.
7. Sampling in a Cleanroom, Clean Zone, or otherOther Controlled Areas
7.1 Sampling Plan:
7.1.1 A sampling plan shall be provided.
7.1.2 ISO 14644-1 and IEST-G-CC1003 may be used as guides for the plan.
7.2 The filter surface may be vertical or horizontal with respect to the floor.
7.2.1 The orientation of the filter depends on airflow direction for unidirectional airflow areas.
7.2.1.1 Sampling in a unidirectional airflow shall be as close to isokinetic as is possible.
7.2.1.2 IEST-G-CC1003 provides additional information on isokinetic sampling.
7.2.2 For nonunidirectional airflow areas, the customer may specify an orientation or the process being monitored in the cleanroom
may indicate which orientation would be preferred.
7.2.2.1 In nonunidirectional airflow, airflow directions and velocities vary with location and time.
7.2.2.2 IEST G-CC1003 recommends a sample inlet probe, with an inlet diameter of at least 20 mm, facing upward. This will
collect larger particles that tend to settle out of the air.
7.3 The standard sample for this test method shall be 300 L (10[10 ft ).].
7.3.1 The sample size may be adjusted for specific conditions.
7.3.2 The number of particles sampled shall meet statistical criteria of ISO 14644-1 or other accepted statistical sampling criteria.
7.4 The sample shall be taken at waist level [0.9(0.9 to 1.0 m (36[36 to 40 in.)]in.] from the floor), at bench level, or at other points
as specified by the customer. The sample points may be selected for relevance to and sensitivity of the operations being performed
in the cleanroom.
7.5 The number and location of sampling points shall be as designated in the sampling plan.
7.5.1 The minimum number of sample locations, as specified in ISO 14644-1, Annex B, may be used:
N 5=A (1)
L
where:
N = minimum number of sampling locations (rounded up to a whole number), and
L
A = area of the cleanroom or clean zone in square metres.
In the case of unidirectional horizontal airflow, the area A may be considered as the cross section of the moving air perpendicular
to the direction of the airflow.
7.5.2 The nature of the operations or the customer may select the number of sampling points.
8. Sampling in a Duct or Pipe
8.1 The sampling of a moving gas stream in a duct or pipeline requires isokinetic sampling.
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8.2 Often by reason of the total flow, the allowable pressure drop, or the physical dimensions of the system (as(as, for example,
an air conditioning air duct), it is impracticable to sample the entire flow.
8.3 Because of the low viscosity of gas, moving gas streams present several special sampling problems, which may disturb the
results unless care is taken.
8.4 To collect a representative sample of particulate contamination from a ducted air stream, insert a probe (as shown in Fig. 4)
coupled to the sampling apparatus described in 5.1, 5.2, and 5.3.
8.5 Achieving accurate isokinetic sampling requires that the gas linear velocity at the probe opening match that in the duct. Equal
velocities may be achieved by a proper ratio between the probe opening and the limiting orifice dimensions, for example:
flow in duct ~L/min! sampling rate ~L/min!
5 (2)
duct cross 2 sectional area probe opening area
8.6 Failure to match the probe and duct velocities will cause a distortion of results favoring either large particles if the probe
velocity lower than duct velocity or small particles if the probe velocity higher than duct velocity.
8.7 Fig. 5 shows an open-type holder installed in a duct. Some large particles are diverted from the filter by airflow around the
filter holder. Most small particles are diverted.
8.8 Probes shall have thin walls, sharp edges, as large an inside diameter as is practicable, but with a minimum inside diameter
of 6.4 mm (0.25 in.).[0.25 in.].
8.8.1 Practice F50 provides some guidelines for sample probe tubing.
8.8.1.1 Sample transit tubes should be configured so that the flow Reynolds number is maintained in the range 5000 to 25 000.
8.8.1.2 For particles in the size range 0.1 μm to approximately 2 μm in diameter and a flow rate of 30 L/min (1[1 ft /min),/min],
a transit tube up to 30 m long can be used.
8.8.1.3 For particles in the size range approximately 2 to 10 μm, a maximum transit tube length of 3 m can be used.
8.8.1.4 If a flexible transit tube is to be used, then no radius of curvature below 150 mm shall be used.
8.8.2 Tubing diameter, length, and bend radius shall be selected to maximize the transport of particles of the maximum size to be
measured.
8.9 Probes shall head directly up stream.
8.10 Sampling rate and probe dimensions shall be carefully adjusted to match duct and probe air velocities.
FIG. 4 Isokinetic Sampling from a Duct
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FIG. 5 Faulty Sample from a Rapid-Ducted Gas Stream
9. Preparation of Apparatus
9.1 Before sampling, remove dirt and dust from the filter holder by washing in a free-rinsing detergent, ketone-free isopropyl
alcohol, submicron-filtered reagent grade petroleum ether (boiling range 30 to 60°C)60 °C) or trichloromonofluoromethane or
trichlorotrifluoroethane.
9.2 The clean laboratory equipment used for counting and sizing the collected particles shall be in a HEPA-filtered clean bench
or equivalent clean area.
9.3 Plastic microscope hoods shall be installed on the microscope to minimize particle deposition on the filter being counted.
9.4 Personnel performing sizing and counting operations shall be equipped with cleanroom garments consistent with good
practice.
9.5 Clean and prepare microscope slides and petri dishes for preserving the membrane filter and specimen. Lens tissue properly
used is satisfactory for this operation.
9.6 Handle hazardous chemicals used in the method with recognized precautions.
9.7 Establish a background count on membrane filters by examining each filter used for referee purposes. Examination at 40 to
50× magnifications through the microscope will re
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