EN ISO 14644-17:2021

SLOVENSKI STANDARD
01-april-2021
Čiste sobe in podobna nadzorovana okolja - 17. del: Aplikacije glede hitrosti
usedanja delcev (ISO 14644-17:2021)
Cleanrooms and associated controlled environments - Part 17: Particle deposition rate
applications (ISO 14644-17:2021)
Reinräume und zugehörige Reinraumbereiche - Teil 17: Anwendungen zur
Partikelabscheidungsrate (ISO 14644-17:2021)
Salles propres et environnements maîtrisés apparentés - Partie 17: Applications de taux
de dépôt de particules (ISO 14644-17:2021)
Ta slovenski standard je istoveten z: EN ISO 14644-17:2021
ICS:
13.040.35 Brezprašni prostori in Cleanrooms and associated
povezana nadzorovana controlled environments
okolja
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 14644-17
EUROPEAN STANDARD
NORME EUROPÉENNE
February 2021
EUROPÄISCHE NORM
ICS 13.040.35
English Version
Cleanrooms and associated controlled environments - Part
17: Particle deposition rate applications (ISO 14644-
17:2021)
Salles propres et environnements maîtrisés apparentés Reinräume und zugehörige Reinraumbereiche - Teil
- Partie 17: Applications de taux de dépôt de particules 17: Anwendungen zur Partikelabscheidungsrate (ISO
(ISO 14644-17:2021) 14644-17:2021)
This European Standard was approved by CEN on 6 January 2021.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2021 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 14644-17:2021 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 14644-17:2021) has been prepared by Technical Committee ISO/TC 209
"Cleanrooms and associated controlled environments" in collaboration with Technical Committee
CEN/TC 243 “Cleanroom technology” the secretariat of which is held by BSI.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by August 2021, and conflicting national standards shall
be withdrawn at the latest by August 2021.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the
United Kingdom.
Endorsement notice
The text of ISO 14644-17:2021 has been approved by CEN as EN ISO 14644-17:2021 without any
modification.
INTERNATIONAL ISO
STANDARD 14644-17
First edition
2021-02
Cleanrooms and associated controlled
environments —
Part 17:
Particle deposition rate applications
Salles propres et environnements maîtrisés apparentés —
Partie 17: Applications de taux de dépôt de particules
Reference number
ISO 14644-17:2021(E)
©
ISO 2021
ISO 14644-17:2021(E)
© ISO 2021
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2021 – All rights reserved

ISO 14644-17:2021(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols . 3
5 Particle deposition rate methodology . 4
5.1 General . 4
5.2 Establishing the particle deposition rate required for control of particle deposition
on vulnerable surfaces . 4
5.3 Particle deposition rate for demonstrating control of particle contamination . 5
6 Measurement of particle deposition rate . 5
7 Particle deposition rate level . 6
8 Documentation . 7
Annex A (informative) Measurement of particle deposition rate . 8
Annex B (informative) Examples of particle deposition rate measurements .12
Annex C (informative) Measurement of the particle obscuration .16
Annex D (informative) Relationship between particle deposition rate and airborne
concentration of particles .19
Annex E (informative) Assessment and control of particle deposition .20
Bibliography .25
ISO 14644-17:2021(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/
iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 209, Cleanrooms and associated controlled
environments, in collaboration with the European Committee for Standardization (CEN) Technical
Committee CEN/TC 243, Cleanroom technology, in accordance with the Agreement on technical
cooperation between ISO and CEN (Vienna Agreement).
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
A list of all parts in the ISO 14644 series can be found on the ISO website.
iv © ISO 2021 – All rights reserved

ISO 14644-17:2021(E)
Introduction
Cleanrooms and associated controlled environments are used to control contamination to levels
appropriate for accomplishing contamination-sensitive activities. Products and processes that benefit
from the control of contamination include those in industries such as aerospace, microelectronics,
optics, nuclear, food, healthcare, pharmaceuticals, and medical devices.
ISO 14644-1:2015 considers airborne particles in cleanrooms and classifies cleanroom cleanliness
by maximum permitted concentrations, and both ISO 14644-9:2012 and IEST -STD -CC1246E: 2013
consider the concentration of surface particles. This document considers the rate of particle deposition
[5]
onto cleanroom surfaces and is based on VCCN Guideline 9 . The particle deposition rate is important,
as the probability of contamination by airborne particles onto contamination sensitive, vulnerable
surfaces, such as manufactured products, is directly related to the particle deposition rate.
ISO 14644-3:2019 gives an overview of methods for the determination of deposition of particles, larger
or equal to 0,1 µm. In this document, the focus is on the rate that macroparticles larger than 5 µm
deposit on surfaces, and the application of this information to controlling contamination in cleanrooms.
Various sizes of particles are generated in cleanrooms by personnel, machinery, tools, and processes,
and distributed by air moving about the cleanroom. According to ISO 14644-1, cleanrooms and
controlled environments with a particle class of the ISO 5 series, or cleaner, contain zero or very low
concentrations of airborne particles larger than 5 µm. However, in operating cleanrooms, many more
particles in the size range of 5 µm to 500 µm, and greater, are found on surfaces than suggested by the
classification limits of the size of particles given in ISO 14644-1. The main reason for this is that the
largest particles in the range of sizes of macroparticles are not counted by particle counters because
of deposition losses in sampling tubes, and at the entry to and within particle counters. Also, for the
same reason, only a proportion of the smaller particles in the range of sizes is measured. In many cases,
large particles cause contamination problems and their presence and potential for deposition onto
contamination sensitive, vulnerable surfaces is best determined by measuring the particle deposition
rate onto surfaces.
Particles smaller than 5 µm are most likely to be removed from the cleanroom air by the ventilation
system but, for particles above 10 µm, more than 50 % is removed from the air by surface deposition.
Above 40 µm, more than 90 % is deposited (see Reference [6]). The dominant deposition mechanism of
this size of particles has been shown to be gravitational but air turbulence and electrostatic attraction
can also cause deposition (see Reference [7]). These deposited particles can be re-dispersed by walking
and cleaning actions, but not by air velocities associated with the cleanroom air. It is important that
these particles are removed by cleaning.
The presence and redistribution of particles >5 µm in cleanrooms is mostly related to human or
mechanical activity. In a cleanroom "at rest", there is likely to be little activity and dispersion of
particles, and the concentration of particles larger than 5 µm is close to zero with no significant particle
deposition. Therefore, it is only in the "operational" occupancy state that the particle deposition rate
should be considered.
The particle deposition rate is an attribute of a cleanroom or clean zone that determines the likely rate
of deposition of airborne particles onto cleanroom surfaces, such as product or process area. Using a
risk assessment, the acceptable amount of contamination of a vulnerable surface can be defined, and
the particle deposition rate can then be obtained that ensures that this amount of contamination is not
exceeded.
Methods of measuring the particle deposition rate in a cleanroom or clean zone are given in this
document. These are used during the operation of the cleanroom to ensure that the required particle
deposition rate is obtained, and for monitoring the cleanroom and clean zones to demonstrate
continuous control of airborne contamination. Monitoring the particle deposition rate also enables
PDR peaks to be correlated with activities so as to detect sources of contamination, and indicate what
changes are required to working procedures to reduce the contamination risk.
ISO 14644-17:2021(E)
The particle deposition rate is the rate of deposition of particles onto surfaces over time, and can be
calculated as the change of particle surface concentration per m during the time of exposure in hours
and can be expressed as Formula (1):
CC−
fi
DD
R = (1)
D
tt−
fi
where
R is the deposition rate of particles equal to, or larger than D (µm) per m per hour;
D
C is the final particle surface concentration (number per m ) for particles equal to and larger
f
D
than D (µm);
C is the initial particle surface concentration (number per m ) for particles equal to and larger
i
D
than D (µm);
t is the final time of exposure (h);
f
t is the initial time of exposure (h).
i
If the particle deposition rate is determined on, or in close proximity to, a vulnerable surface, such as
product, then an estimate of the deposition of airborne particles onto the surface can be obtained by
applying Formula (2):
NR =⋅ta⋅ (2)
DD
where
N number of deposited particles larger than or equal to particle size D (µm);
D
t is the time the surface is exposed to particle deposition (h);
a is the surface area exposed to airborne contamination (m ).
Some industries use cleanrooms to manufacture optical instruments and components, such as mirrors,
lenses, and solar panels used in aerospace. The quality of these products is related to the amount of
light absorbed or reflected by particles on the surface. Therefore, this document also considers particle
obscuration rate of test surfaces exposed in cleanrooms in Annex C. Using the particle deposition rate
of various particle sizes, the particle obscuration rate of airborne particles depositing onto a surface
and obscuring light can be calculated and used in a similar way to the particle deposition rate to reduce
the risk of surface contamination.
vi © ISO 2021 – All rights reserved

INTERNATIONAL STANDARD ISO 14644-17:2021(E)
Cleanrooms and associated controlled environments —
Part 17:
Particle deposition rate applications
1 Scope
This document gives direction on the interpretation and application of the results of the measurement
of particle deposition rate on one or more vulnerable surfaces in a cleanroom as part of a contamination
control programme. It provides some instructions on how to influence the particle deposition rate and
reduce the risk of particle contamination on vulnerable surfaces.
This document gives information on how a cleanroom user can use the particle deposition rate
measurements to determine limits that can be set for macroparticles on vulnerable surfaces. It also
gives a risk assessment method by which an acceptable risk of deposition of particles onto vulnerable
surfaces in a cleanroom can be established and, when this is not achieved, methods that can be used to
reduce the particle deposition rate.
An alternative to the particle deposition rate is the particle obscuration rate which determines the rate
of increase of coverage of particles onto an area of surface over time. The particle obscuration rate can
be used in an analogous way to the particle deposition rate and the required particle obscuration rate
for a specified surface can be calculated and the risk from deposited particles reduced.
This document does not:
— provide a method to classify a cleanroom with respect to particle deposition rate or particle
obscuration rate;
— directly consider the deposition of microbe-carrying particles, although they can be treated as
particles;
— give any consideration to surface deposition by contact as, for example, when personnel touch a
product and contamination is transferred.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 14644-3:2019, Cleanrooms and associated controlled environments — Part 3: Test methods
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
ISO 14644-17:2021(E)
3.1
cleanroom
room within which the number concentration of airborne particles is controlled and classified, and
which is designed, constructed and operated in a manner to control the introduction, generation and
retention of particles inside the room
Note 1 to entry: The class of airborne particle concentration is specified.
Note 2 to entry: Levels of other cleanliness attributes such as chemical, viable or nanoscale concentrations in the
air, and also surface cleanliness in terms of particle, nanoscale, chemical and viable concentrations might also be
specified and controlled.
Note 3 to entry: Other relevant physical parameters might also be controlled as required, e.g. temperature,
humidity, pressure, vibration and electrostatic.
[SOURCE: ISO 14644-1:2015, 3.1.1]
3.2
clean zone
defined space within which the number concentration of airborne particles is controlled and classified,
and which is constructed and operated in a manner to control the introduction, generation, and
retention of contaminants inside the space
Note 1 to entry: The class of airborne particle concentration is specified.
Note 2 to entry: Levels of other cleanliness attributes such as chemical, viable or nanoscale concentrations in the
air, and also surface cleanliness in terms of particle, nanoscale, chemical and viable concentrations might also be
specified and controlled.
Note 3 to entry: A clean zone(s) can be a defined space within a cleanroom (3.1) or might be achieved by a
separative device. Such a device can be located inside or outside a cleanroom.
Note 4 to entry: Other relevant physical parameters might also be controlled as required, e.g. temperature,
humidity, pressure, vibration and electrostatic.
[SOURCE: ISO 14644-1:2015, 3.1.2]
3.3
critical particle size
smallest particle size (3.7) that negatively impacts on product or process quality
3.4
critical location
location where a vulnerable surface (3.12) is exposed to particle contamination
3.5
operational
agreed condition where the cleanroom (3.1) or clean zone (3.2) is functioning in the specified manner,
with equipment operating and with the specified number of personnel present
[SOURCE: ISO 14644-1:2015, 3.3.3]
3.6
particle
minute piece of matter with defined physical boundaries
[SOURCE: ISO 14644-1:2015, 3.2.1]
2 © ISO 2021 – All rights reserved

ISO 14644-17:2021(E)
3.7
particle size
diameter of a sphere or the diameter of a sphere (circle) that encompasses a non-spherical particle, or
an equivalent diameter
Note 1 to entry: The definition should be stated in relation to the measurement method.
Note 2 to entry: In ISO 14644-1, light scattering based detection is used. Other measurement methods yield
different size definitions (see A.1).
3.8
particle deposition rate
PDR
number of particles depositing onto a known surface area during a known time of exposure
Note 1 to entry: It is expressed in number per m per hour.
3.9
particle deposition rate level
PDRL
level of particle deposition rates (3.8) for a range of particle sizes (3.7)
3.10
particle obscuration rate
POR
rate of change of particle area coverage of a surface during time of exposure
3.11
test surface
surface of specific area and known surface cleanliness used to collect particles that deposit from the air
in a specified time
Note 1 to entry: A test surface is used in this document to determine the particle deposition rate (3.8).
Note 2 to entry: A test surface can be a witness plate or an integral part of a measuring instrument.
3.12
vulnerable surface
surface whose functionality diminishes when particles larger than the critical size are present
3.13
witness plate
clean flat plate of a specified surface area used to collect particles that deposit from the air in a
specified time
Note 1 to entry: A witness plate is exposed adjacent to a vulnerable surface (3.12) to obtain the particle deposition
rate that occurs at that location.
Note 2 to entry: A witness plate is not normally part of a measuring instrument and, after exposure, the witness
plate is taken to a measuring instrument for the counting and sizing of the particles deposited.
4 Symbols
a product area in m
A area of the silhouette of the observed particles (mm )
C particle concentration in number of particles ≥D µm per m
D
D particle size in micrometres
ISO 14644-17:2021(E)
F particle obscuration rate
L particle deposition rate level
N number of particles ≥D µm deposited onto a surface
D
η efficiency of detection method
2 -2
O particle obscuration factor (in mm ·m )
R particle deposition rate in number of particles ≥D µm per m ·h
D
t time of exposure
5 Particle deposition rate methodology
5.1 General
Particle deposition rate data obtained in a cleanroom can be used to establish the probability of
airborne particles depositing onto a vulnerable surface during exposure and provide a methodology
that supports the required quality of a cleanroom during operation. The information in 5.2 and 5.3 gives
a method that can be used to establish the correct particle deposition rate cleanliness conditions in a
cleanroom and associated controlled environments. This information is used to demonstrate continued
control of these cleanliness conditions. ISO 14644-2 shall be considered as a guide for the development
and application of a monitoring plan.
5.2 Establishing the particle deposition rate required for control of particle deposition
on vulnerable surfaces
Establishing control of macroparticles in the controlled environment through use of the particle
deposition rate is required when a new facility is designed, or when cleanliness requirements are
changed in existing facilities. An assessment shall be made of the product attributes and the process
activities performed in the cleanroom. Based on this assessment, the required degree of control of
particle contamination shall be established using the following steps.
1) The surfaces in the cleanroom or associated controlled environments that are vulnerable to particle
deposition shall be identified. This can be done by considering the manufacturing carried out in
the cleanroom, the status of the technical installations, production equipment, and operational
procedures.
2) The smallest particle size that impacts on product or production quality on each vulnerable surface
(critical particle size) shall be determined.
NOTE 1 Differences in particle type (metallic vs non-metallic, transparent vs opaque, microbial vs non-
microbial) can lead to a particle-specific approach.
3) The maximum number of particles of the critical size that contaminates each vulnerable surface
considered shall be determined.
4) Knowing the maximum number of particles of a critical size that is acceptable on each surface, the
particle deposition rate or particle deposition rate level (see Table 1) at the critical particle size
shall be determined.
5) The critical surface with the tightest requirements on particle deposition rate and particle
deposition rate level will determine the particle deposition rate and particle deposition rate level
for the critical area.
6) After the maximum particle deposition rate or particle deposition rate level requirements are
defined for the critical area, the measurement method shall be chosen and put into operation. The
4 © ISO 2021 – All rights reserved

ISO 14644-17:2021(E)
method can be selected based on sensitivity, required measurement frequency, and other factors
such as ease of use. ISO 14644-3 can be consulted for information on measurement methods.
NOTE 2 Examples of the method described above are given in Annex E.
5.3 Particle deposition rate for demonstrating control of particle contamination
Demonstrating control of the particle deposition rate in a cleanroom over time is important to ensure
that the quality of the facility remains constant. It is necessary to demonstrate control of the particle
deposition rate by demonstrating that the required particle deposition rate limits are still achieved.
Monitoring shall be carried out where the most vulnerable surfaces are located, or at a location that is
in close proximity and representative of the location of the vulnerable surface.
The required frequency of monitoring shall be determined by the criticality of the product being
manufactured and the measuring equipment available (see Clause 6).
Failure to achieve the required particle deposition rate limit may require an investigation to understand
the cause of the failure. Depending on the failure cause, improvements to working, cleaning, and
maintenance procedures may be required. If needed, changes in manufacturing equipment, or
cleanroom design and ventilation can be implemented. Methods of reducing the risk of airborne
contamination are discussed in Annex E.
6 Measurement of particle deposition rate
The method for measuring the particle deposition rate is based on the collection of particles onto a
test surface of a known surface area over a known time period. The particle deposition rate is then
calculated by using Formula (1).
The particle deposition rate shall be measured on, or in close proximity to, a vulnerable surface
during the manufacturing carried out in the cleanroom. If required, the particle deposition rate can be
measured at several locations. The result of the measurement can then be used to check whether the
location complies with a specified maximum particle deposition rate, or maximum particle deposition
rate level, for certain cumulative particle sizes.
The methods for collecting airborne particles onto a surface, sizing and counting these particles, shall
be chosen with reference to ISO 14644-3. Additional information is available in ASTM E2088, ASTM 25
and ASTM F50. When choosing the counting and sizing apparatus, consideration shall be given to the
detection of particles in the relevant size range. The area of the test surface also needs consideration,
particularly if the particle deposition rate is to be measured within a restricted time.
The witness plate, or measuring instrument, shall be placed in the same plane, and as close as possible
to the vulnerable surface. The test surface shall be at the same electrical potential. Particles collected
on the test surface are counted and sized to obtain reproducible data and are used to obtain the particle
deposition rate adjacent to the vulnerable surface being investigated.
NOTE Be aware that measurement equipment and witness plates can interfere with process activities.
Therefore, the location for monitoring needs to be selected carefully.
Sampling shall only be carried out during manufacturing when the product or process is exposed to
airborne contamination. The minimum expected count for the largest critical particle size under
consideration shall not be less than 1, but desirably 5. If insufficient particles have been counted, the
time for measuring the particle deposition rate during the manufacturing of products or process shall
be extended to obtain a higher number of particles. It can be necessary to measure more than one
manufacturing period. A method of calculating the sample time is given in A.3.3. If a suitable sample is
not feasible, alternative measurement techniques shall be considered.
ISO 14644-17:2021(E)
7 Particle deposition rate level
For a defined range of particle sizes, the particle deposition rate can be expressed as a particle
deposition rate level, L. The particle deposition rate level expresses the particle deposition rate over
a range of particle sizes, in a similar way to that used in ISO 14644-9 to expresses surface particle
concentration. This allows the concentration of particles at one size to be converted to a concentration
at another size, and it can be used, for example, when the particle deposition rate is measured at one
particle size but the critical particle size is different.
The particle deposition rate level is obtained using typical size distributions found in cleanroom that
show the particle deposition rate is in direct proportion to the cumulative particle size. A typical size
distribution is shown later in Figure B.3. The particle deposition rate levels are calculated by means of
Formula 3 by assuming a linear distribution and a reference particle size of 10µm.
RD·
D
L= (3)
Table 1 gives examples of L over a range of different cleanliness levels in orders of magnitude.
Table 1 — Particle deposition rate levels in orders of magnitude
Particle dep- Number of particles per m per hour
osition rate
≥5 µm ≥10 µm ≥20 µm ≥50 µm ≥100 µm ≥200 µm ≥500 µm
level
1 2,0 1,0 0,5 0,2 0,1 0,05 0,02
10 20 10 5 2 1 0,5 0,2
100 200 100 50 20 10 5 2
1 000 2 000 1 000 500 200 100 50 20
10 000 20 000 10 000 5 000 2 000 1 000 500 200
100 000 200 000 100 000 50 000 20 000 10 000 5 000 2 000
1 000 000 2 000 000 1 000 000 500 000 200 000 100 000 50 000 20 000
If the particle deposition rate for different size of particles at intermediate levels of L is required,
Formula (4) can be used:
10L
R = (4)
D
D
If the particle deposition rate is required for another particle size at the same PDRL, Formula (5) can
be used:
D
O
RR=⋅ (5)
DD
NO
D
N
where
R is the original particle deposition rate at particle size D ;
O
D
O
R is the new particle deposition rate at particle size D ;
N
D
N
D is the original cumulative particle size (µm);
O
D is the new cumulative particle size (µm).
N
The particle deposition rate level depends on the rate of airborne dispersion of particles from sources of
contamination, and the particle removal efficiency of the ventilation system. The PDRL can be reduced
by removing or reducing particle sources and/or by improving the removal efficiency of the ventilation
system. However, the removal efficiency reduces for increasing particle size (see Reference [6]).
6 © ISO 2021 – All rights reserved

ISO 14644-17:2021(E)
To establish and maintain control of the particle contamination by surface deposition required for
vulnerable surfaces, it is necessary to set particle deposition rate limits that shall not be exceeded.
The particle deposition rate limit depends on the acceptable surface contamination, which can be
determined by a risk assessment, the vulnerable surface area, the critical particle size and the expected
time of exposure (see A.3.3 for an example).
8 Documentation
By agreement between customer and supplier, the following information and data shall be recorded:
a) name and address of the testing organization, and the date on which the measurement was
performed;
b) type of measurements and measuring conditions;
c) a reference to this document (i.e. ISO 14644-17);
d) clear identification of the physical location of the cleanroom or clean zone tested (including
reference to adjacent areas if necessary), and coordinates of all sampling locations;
e) specified designation criteria of the cleanroom or clean zone, including the ISO 14644-1
classification, and the relevant activities in the occupied state;
f) details of the measurement instrument used to determine the particle deposition rate, including
the identification of the measurement instrument, information on its current calibration certificate,
and any special conditions relating to the measurement method;
g) details of the type of test surface used with witness plate or measuring instrument;
h) initial counts of surface cleanliness on test surface(s) in the case of witness plates method;
i) details of time of exposure;
j) a log of scheduled and unscheduled activities and incidents during exposure;
k) cumulative particle size(s) that are measured;
l) test results with background counts, or previous counts, subtracted;
m) statement regarding compliance with the claimed particle deposition rate level designation;
n) any other specific requirements that are relevant to the particle deposition rate and particle
deposition rate level.
ISO 14644-17:2021(E)
Annex A
(informative)
Measurement of particle deposition rate
A.1 General
The basic principle of particle deposition rate measurement is the collection of particles on a witness
plate or a test surface of an instrument, where the particles are counted and measured.
A witness plate method is usually accompanied by an off-line particle analysis technique. Measurement
instruments containing a cleanable or replaceable test surface have a test surface and measurement
technique integrated into one sensor unit. This enables it to measure the surface cleanliness on-line at
frequent intervals.
A.2 Particle size
A particle is a 3-dimensional object, and its exact size can be determined by its diameter only if it is
spherical. The size of particles measured on a witness plate or by an instrument varies according to
the method used. The particle size is normally measured by microscopy or by an equivalent optical
measurement system. In both systems, a 2-dimensional silhouette (projected surface area) of the
particle is observed.
8 © ISO 2021 – All rights reserved

ISO 14644-17:2021(E)
Key
S silhouette of particle
d equivalent diameter
F Feret diameter
D length of the particle
A equal area circle
W width
Figure A.1 — Dimensions used to measure particle size
Alternative methods of sizing are shown in Figure A.1 and described as follows.
— Equivalent diameter, D: This is normally based on the physical properties measured, such as light
scattering, where the amount of light scattered by a particle is related to the size of the particle.
Alternatively, the equivalent diameter can be calculated from the measured surface area, A, by
Formula (A.1):
2A
D=2 (A.1)
4π
where
D is the equivalent particle diameter (µm);
A is the area of the silhouette of the observed particle (µm ).
If the particles are sized microscopically by a person, the particle size can be obtained by comparing
it to a series of circles on a calibrated eyepiece. Another approach is to measure the smallest inner
and largest outer circles that contain the particle dimensions, and use the average as the equivalent
diameter.
— Largest dimension.
ISO 14644-17:2021(E)
— Feret diameter (calliper diameter), which is the largest dimension in a horizontal or vertical
direction.
The selection of the particle size that is measured is mainly determined by the type of instrument used.
In monitoring, it is important to use the same method for all measurements.
The particle area can be calculated from the equivalent diameter, or the length and width of the particle,
or by measurement of the number of (sub)pixels of a detector that can fit into the silhouette of the
particle.
A.3 Particle deposition rate measurements
A.3.1 Measuring efficiency
If the detection efficiency of the applied measurement method is not 100 % as indicated in Formula 2,
the formula can be modified to account for the efficiency of the detection method by the insertion of η,
as shown in Formula (A.2), correcting for the failure to count particles, or to count particles that are
not there.
NR=η··ta· (A.2)
DD
If a witness plate is used with a microscope, it is likely that the detection efficiency is close to 100 %.
Similarly, instruments have a high efficiency and Formula (A.2) can normally be used without the
addition of η. However, if the measuring efficiency is known, this can be added to Formula (A.2) to
increase its accuracy.
Another point to be considered is the accuracy of the sizing, which in the case of an instrument is
affected by the pixel size of the digital imaging system used to determine the particle size. However,
this is only the case for the smallest sizes of particles that are measured and this impact is reduced by
the cumulative size approach.
A.3.2 Particle deposition measurement instruments and witness plates
Particle deposition rate can be determined by measuring and counting particles deposited on a witness
plate or test surface during exposure for a known time. A witness plate can be analysed under a
microscope by a person, or with a microscope equipped for particle analysis by scanning and image
processing. Particle deposition rate measurement is the measurement of macroparticles (particles
≥5 µm) and is normally presented as cumulative sizes.
Particle deposition measurement instruments can measure macroparticles with a lower size of particles
that are equal to, and greater than, 5 μm, 10 μm, 15 μm or 20 μm. Measurement instruments should be
considered with respect to their minimal particle size, measurement interval and measurable area of
the test surface. A description of typical examples of these instruments is given in References [11], [12]
and [13].
Particle obscuration (rate) of particles (see Annex C) can be determined by measuring the area
covered by particles deposited on a witness plate or test surface of a measuring instrument during
exposure for a known time. Particle obscuration is expressed as the ratio of the total particle surface
area to the measured sample area in parts per million (ppm), or percentage area coverage. Alternative
2 -2 2 2
measurement units are µm ·mm , with µm for the total particle surface area, and mm for the area
sampled.
10 © ISO 2021 – All rights reserved

ISO 14644-17:2021(E)
A.3.3 Required measurement time of particle deposition rate
A sufficiently large sample should be taken to ensure the count of the required size of particle is
accurate. To ensure this, a count of at least 1, but desirably 5, should be obtained. The example below
shows how this can be done.
EXAMPLE A product is exposed during assembly to airborne contamination for 12 min per product. The
particle deposition rate is measured by an instrument with a test area of 25 cm at a particle size ≥20 µm.
The particle deposition rate level required to control airborne contamination is 2 000 particles ≥10 µm
per m per hour, which, as calculated by Formula (5), is equivalent to an intermediate particle deposition
rate o
...