ASTM E2088-06(2021)

Standard Practice for Selecting, Preparing, Exposing, and Analyzing Witness Surfaces for Measuring Particle Deposition in Cleanrooms and Associated Controlled Environments

SIGNIFICANCE AND USE
5.1 This practice provides a standard approach to measuring particle deposition, or fallout, in cleanrooms and other controlled environments. It is based on the use of a witness surface to collect particles that deposit from the surrounding environment and subsequently sizing and counting the particles by conventional methods. Several options are introduced, with limitations and guidelines for selecting the best choice for the intended application.  
5.2 This practice is applicable across numerous industries including aerospace, microelectronics, and pharmaceuticals.
SCOPE
1.1 This practice is intended to assist in the selection, preparation, exposure, and analysis of witness surfaces for the purpose of characterizing particle deposition rates in cleanrooms and associated controlled environments, particularly for aerospace applications.  
1.2 Requirements may be defined in terms of particle size distribution and count, percent area coverage, or product performance criteria such as optical transmission or scatter. Several choices for witness surfaces are provided.  
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.4 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.  
1.5 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-Aug-2021
• ICS: 13.040.35 - Cleanrooms and associated controlled environments
• Technical Committee: E21 - Space Simulation and Applications of Space Technology
• Drafting Committee: E21.05 - Contamination

Relations

• Refers: ASTM F24-20 - Standard Test Method for Measuring and Counting Particulate Contamination on Surfaces
• Effective Date: 01-Apr-2020
• Refers: ASTM F24-09(2015) - Standard Test Method for Measuring and Counting Particulate Contamination on Surfaces
• Effective Date: 01-Oct-2015
• Refers: ASTM E1216-11 - Standard Practice for Sampling for Particulate Contamination by Tape Lift
• Effective Date: 01-Sep-2011
• Refers: ASTM F24-09 - Standard Method for Measuring and Counting Particulate Contamination on Surfaces
• Effective Date: 01-Apr-2009
• Refers: ASTM F312-08 - Standard Test Methods for Microscopical Sizing and Counting Particles from Aerospace Fluids on Membrane Filters
• Effective Date: 01-Nov-2008
• Refers: ASTM E1216-06 - Standard Practice for Sampling for Particulate Contamination by Tape Lift
• Effective Date: 01-Apr-2006
• Refers: ASTM E1216-99(2005) - Standard Practice for Sampling for Particulate Contamination by Tape Lift
• Effective Date: 01-Apr-2005
• Refers: ASTM F24-04 - Standard Method for Measuring and Counting Particulate Contamination on Surfaces
• Effective Date: 01-Sep-2004
• Refers: ASTM F24-00 - Standard Method for Measuring and Counting Particulate Contamination on Surfaces
• Effective Date: 10-May-2000
• Refers: ASTM E1216-99 - Standard Practice for Sampling for Particulate Contamination by Tape Lift
• Effective Date: 10-Oct-1999
• Refers: ASTM F312-97(2003) - Standard Test Methods for Microscopical Sizing and Counting Particles from Aerospace Fluids on Membrane Filters
• Effective Date: 10-Apr-1997
• Refers: ASTM F312-97 - Standard Test Methods for Microscopical Sizing and Counting Particles from Aerospace Fluids on Membrane Filters
• Effective Date: 01-Jan-1997

Overview

ASTM E2088-06(2021) - "Standard Practice for Selecting, Preparing, Exposing, and Analyzing Witness Surfaces for Measuring Particle Deposition in Cleanrooms and Associated Controlled Environments" - establishes a standardized methodology for characterizing particle deposition in cleanrooms and other controlled environments. The standard is especially significant for industries where surface cleanliness impacts product performance, including aerospace, microelectronics, and pharmaceuticals.

This ASTM standard outlines best practices for:

• Selecting appropriate witness surfaces to monitor particulate deposition
• Preparing and exposing these surfaces within controlled environments
• Analyzing and measuring particle accumulation rates using reliable techniques

By following this practice, organizations ensure consistent, reproducible measurements of contamination, helping maintain the required cleanliness levels for critical operations and products.

Key Topics

• Witness Surface Selection: Guidance is provided on how to choose surfaces that best represent those in actual use or are suitable for specific analytical methods.
• Surface Preparation & Cleaning: Recommendations for cleaning and packaging witness surfaces and holders, including precision cleaning following industry standards, are included.
• Exposure Protocols: Procedures detail correct exposure, handling, and protection to avoid external contamination during transport and in situ placement.
• Particle Measurement Methods: Several analysis techniques are supported:
  • Microscopic sizing and counting (manual or image analysis)
  • Optical monitoring via changes in reflectance, transmission, or scatter
  • Gravimetric analysis and particle fallout (PFO) methods
• Data Reporting: Results are expressed as particle count, size distribution, percent area coverage, or in relation to product performance criteria such as optical scatter. Instructions specify reporting per unit area and time, referencing baseline/control measurements.
• Control and Calibration: Proper use of controls and calibration of analysis instruments ensures measurement reliability and equivalency with standardized cleanliness levels.

Applications

This practice is widely used in contamination control to:

• Monitor particle deposition rates in cleanrooms, controlled environments, and associated zones with rigorous cleanliness requirements.
• Support aerospace manufacturing and assembly, where surface contamination can directly affect component and system reliability.
• Manage contamination in microelectronics production, minimizing particulate interference with sensitive circuitry.
• Validate cleanliness in pharmaceutical production, helping ensure product purity and compliance with regulatory standards.
• Supplement the development and maintenance of contamination control programs in any environment where airborne particles can impact product quality or research integrity.

Related Standards

• ASTM E1216 - Practice for Sampling for Particulate Contamination by Tape Lift
• ASTM F24 - Test Method for Measuring and Counting Particulate Contamination on Surfaces
• ASTM F312 - Test Methods for Microscopical Sizing and Counting Particles from Aerospace Fluids on Membrane Filters
• ISO 14644-1 - Cleanrooms and Associated Controlled Environments - Classification of Air Cleanliness
• IEST-STD-CC1246 - Product Cleanliness Levels and Contamination Control Program
• Fed-Std-209 - Airborne Particulate Cleanliness Classes in Cleanrooms and Clean Zones (historical reference)

Practical Value

Using ASTM E2088-06(2021) enables organizations to implement a consistent, validated approach to assessing particle deposition in critical environments. This supports regulatory compliance, product quality assurance, and risk management in contamination-sensitive applications. The standard can be used as part of routine environmental monitoring, process validation, and as a benchmark during facility qualification or troubleshooting contamination issues.

Keywords: ASTM E2088, witness surfaces, cleanroom contamination, particle deposition, controlled environments, particulate measurement, aerospace cleanliness, microelectronics contamination control, surface analysis.

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: E2088 − 06 (Reapproved 2021)
Standard Practice for
Selecting, Preparing, Exposing, and Analyzing Witness
Surfaces for Measuring Particle Deposition in Cleanrooms
and Associated Controlled Environments
This standard is issued under the fixed designation E2088; 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 Contamination on Surfaces
F312 Test Methods for Microscopical Sizing and Counting
1.1 This practice is intended to assist in the selection,
Particles from Aerospace Fluids on Membrane Filters
preparation, exposure, and analysis of witness surfaces for the
purpose of characterizing particle deposition rates in clean- 2.2 ISO Standard:
ISO 14644-1 Cleanrooms and Associated Controlled
rooms and associated controlled environments, particularly for
aerospace applications. Environments—Part 1: Classification of Air Cleanliness
2.3 Government Standards:
1.2 Requirements may be defined in terms of particle size
Fed-Std-209 Airborne Particulate Cleanliness Classes in
distribution and count, percent area coverage, or product
Cleanrooms and Clean Zones
performance criteria such as optical transmission or scatter.
IEST-STD-CC1246 Product Cleanliness Levels and Con-
Several choices for witness surfaces are provided.
tamination Control Program
1.3 The values stated in SI units are to be regarded as
standard. No other units of measurement are included in this NOTE 1—The Institute of Environmental Sciences and Technology has
several Recommended Practices which may also be useful.
standard.
1.4 This standard does not purport to address all of the
3. Terminology
safety concerns, if any, associated with its use. It is the
3.1 Definitions:
responsibility of the user of this standard to establish appro-
3.1.1 bidirectional reflectance distribution function
priate safety, health, and environmental practices and deter-
(BRDF)—the scattering properties of light reflected off
mine the applicability of regulatory limitations prior to use.
surfaces, expressed as the ratio of differential outputs of
1.5 This international standard was developed in accor-
radiance divided by differential inputs of radiance. Surface
dance with internationally recognized principles on standard-
contaminants scatter the incident radiation in all directions and
ization established in the Decision on Principles for the
withvariableintensities.TheBRDFisamethodtoquantifythe
Development of International Standards, Guides and Recom-
spatial distribution of the scattered energy.
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee. 3.1.2 cleanliness level—an established maximum allowable
amount of contamination in a given area or volume, or on a
2. Referenced Documents (Note 1)
component.
2.1 ASTM Standards:
3.1.3 cleanroom—an environmentally conditioned area in
E1216 Practice for Sampling for Particulate Contamination
which temperature, humidity, and airborne contaminants are
by Tape Lift
controlled by design and operation. High-efficiency particulate
F24 Test Method for Measuring and Counting Particulate
air (HEPA) filters or better are usually required to achieve the
air cleanliness level. Air particulate cleanliness is classified in
accordance with Fed-Std-209 or ISO 14644-1.
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 Sept. 1, 2021. Published October 2021. Originally Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
approved in 2000. Last previous edition approved in 2015 as E2088 – 06(2015). 4th Floor, New York, NY 10036, http://www.ansi.org.
DOI: 10.1520/E2088-06R21. Although Fed-Std-209 has been cancelled, it still may be used and designations
For referenced ASTM standards, visit the ASTM website, www.astm.org, or in Fed-Std-209 may be used in addition to the ISO designations.
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Available from Institute of Environmental Sciences and Technology (IEST),
Standards volume information, refer to the standard’s Document Summary page on Arlington Place One, 2340 South Arlington Heights Road, Suite 100, Arlington
the ASTM website. Heights, IL 60005-4516, http://www.iest.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2088 − 06 (2021)
3.1.4 contaminant—unwanted molecular and particulate particle detected by automatic instrumentation. The equivalent
matter that could affect or degrade the performance of the diameter is the diameter of a reference sphere having known
components upon which they reside. properties and producing the same response in the sensing
instrument as the particle being measured; (3) the diameter of
3.1.5 contamination—a process of contaminating.
a circle having the same area as the projected area of a particle,
3.1.6 contamination control—organized action to control
intheplaneofobservation,observedbyimageanalysis;(4)the
the level of contamination.
size defined by the measurement technique and calibration
3.1.7 controlled area—an environmentally controlled area,
procedure.
operated as a cleanroom, but without the final stage of HEPA
3.1.18 particulate contamination—discrete mass of solid
(or better) filters used in cleanrooms.
matter, size often measured in micrometres (µm), which
3.1.8 critical surface—any surface of an item or product
adversely affects critical surfaces of component and hence
which is required to meet established cleanliness level require-
system performance.
ments.
3.1.19 percent area coverage(PAC)—fractionofthesurface
3.1.9 demonstrated equivalence—the condition in which a
that is covered by particles, reported in percent as total particle
method of measurement has passed a series of tests to show
projected area divided by total area of the surface.
that it gives equivalent results to those of a standard measure-
3.1.20 precision cleaning—cleaning of hardware surfaces
ment.
approved by established facility methods or methods specified
3.1.10 environmentally controlled area—cleanrooms, con-
or provided by the customer with verification to a specified
trolled areas, good housekeeping areas, and other enclosures
cleanliness level.
that are designed to protect hardware from contamination.
3.1.21 visibly clean—absence of particulate or molecular
Cleanliness is achieved by controlling air purity, temperature,
contaminants when viewed from a specified distance with
humidity, materials, garments, and personnel activities.
normal (or corrected to normal) vision with a specified
3.1.11 fiber—a particle >100 µm in length with a length to
illumination level.
diameter ratio of ten or more.
3.1.22 witness surface (WS)—a contamination-sensitive
3.1.12 image analysis—the measurement of size, shape,
material used instead of direct evaluation of a specific surface
number, position, orientation, brightness, and other parameters
when that surface is either inaccessible or is too sensitive to be
of small objects using the combination of a microscope, an
handled.
imaging sensor, and a dedicated computer system. Image
3.1.22.1 optical witness surface (OWS)—witness surface
analysis can be used to perform particle counts or measure
fromwhichcontaminantsmaybeanalyzedbyopticalmethods.
particle dimensions automatically, with far greater accuracy
3.1.22.2 particle witness surface (PWS)—witness surface
than manual techniques.
from which particulate contaminants may be analyzed by
3.1.13 micrometre (µm)—a unit of measurement equal to
standard optical or electron microscopic methods.
one millionth of a metre, or approximately 39 millionths of an
inch, for example, 25 µm is approximately 0.001 in. The term
4. Summary of Practice
“micron” has been used but is not a recommended SI unit.
4.1 Particle deposition in controlled environments is deter-
3.1.14 nonvolatile residue(NVR)—solublematerialremain-
mined by collecting particles on a clean witness surface for a
ing after evaporation of a filtered volatile fluid or precipitate
specified period of time or operational activity, then retrieving
from a gas phase, usually reported in milligrams per unit area
the witness surface and quantifying the particle population
(or volume).
collected.
3.1.15 particle deposition—the settling of airborne particles
4.2 Witness surfaces (WS) are typically surfaces that lend
onto surfaces resulting from electrostatic or dynamic
themselves to traditional microscopic or image analysis tech-
conditions, or both, in cleanrooms or other controlled environ-
niquesforsizingandcountingparticlesonthesurface,butmay
ments.
be an optical surface that is evaluated on the basis of the
3.1.16 particle fallout(PFO)—astandardparticledeposition
changeinitsopticalpropertiesormaybeawitnesssurfacethat
method used by the European aerospace community that uses
best represents the surface material of interest which is
black glass witness surfaces and measures particle scatter in
subsequentlyevaluatedbyextractingasamplefromthesurface
parts per million.
and sizing and counting particles removed from the witness
surface.
3.1.17 particle size—(1) the apparent maximum linear di-
mension of a particle in the plane of observation, as observed
4.3 This practice does not address real time particle depo-
with an optical microscope; (2 ) the equivalent diameter of a
sition measurements involving particle counters on site with
continuous recording over a specified period of time.
The Euramark Model 255 PFO photometer has been found to be satisfactory.
5. Significance and Use
The sole source of supply of the apparatus known to the committee at this time is
Euramark, 834 East Rand Rd., Unit 6, Box 823, Mt. Prospect, IL 60056. If you are
5.1 Thispracticeprovidesastandardapproachtomeasuring
aware of alternative suppliers, please provide this information to ASTM Interna-
particle deposition, or fallout, in cleanrooms and other con-
tional Headquarters.Your comments will receive careful consideration at a meeting
of the responsible technical committee, which you may attend. trolledenvironments.Itisbasedontheuseofawitnesssurface
E2088 − 06 (2021)
to collect particles that deposit from the surrounding environ- 6.3.1 The PFO instrument uses a smooth black glass plate
ment and subsequently sizing and counting the particles by 40 by 45 mm protected from unintentional sedimentation by a
conventional methods. Several options are introduced, with plate holder. The effective sampling surface is circular with a
diameter of 25 mm.
limitations and guidelines for selecting the best choice for the
intended application.
6.3.2 Silicon wafers or disks shall be selected for image
analysis or other surface scanning methods.
5.2 This practice is applicable across numerous industries
including aerospace, microelectronics, and pharmaceuticals.
6.4 Optical Witness Surfaces, (that is, mirrors or lenses)
shall be selected to best represent the critical surface of interest
6. Selecting Witness Surfaces in the environment being evaluated. Reflectance or transmis-
sion measurements shall be made in the wavelengths of
6.1 ConsiderationsforselectingWSincludeavailablemeth-
interest, and the OWS must be the correct size and shape for
ods of analysis, precision and accuracy required, size of
the instrumentation planned for use.
particles of concern, actual material of critical surfaces of
concern, and cost. Preferably, the WS should be a surface 6.5 Gravimetric Methods—A gravimetric method can also
be used, whereby a large witness surface is rinsed with solvent
material which best represents the actual critical surface and
should be analyzed using the method which best represents the to extract the particles, filtered onto a dry, preweighed mem-
brane filter, and then dried and reweighed on a laboratory
actual performance characteristics of interest. Additionally,
balance with a resolution of 0.01 mg. The difference in weight
certain surfaces may become charged, especially in dry
can be a relative quantitative analysis of deposition based on
environments, and this charging can effect the particle deposi-
weight. Note, the efficiency of the extraction method must be
tion. IfWS are to monitor a vacuum environment they must be
known or estimated.Apreweighed membrane filter could also
made of low-outgassing, vacuum-compatible materials and
be used as the witness surface thus eliminating the extraction
held securely in vacuum-compatible, low-particle shedding
step.Additionally, a quartz crystal microbalance with adhesive
holders.
surfaces can measure accumulated mass in situ.
6.2 Microscopic Evaluation—When microscopic sizing and
counting of particles is the planned method of analysis,
...