Cleanrooms and associated controlled environments - Part 1: Classification of air cleanliness (ISO 14644-1:1999)

This Part of this European Standard specifies the classification of particulate cleanliness for cleanrooms and clean air controlled spaces in three possible occupancy states according to the number concentration of airborne particulate matter present.

Reinräume und zugehörige Reinraumbereiche - Teil 1: Klassifizierung der Luftreinheit (ISO 14644-1:1999)

Dieser Teil der Internationalen Norm ISO 14644 enthält die Klassifizierung der Luftreinheit in Reinräumen und zugehörigen Reinraumbereichen. Die Ausführungen und Festlegungen der Klassifizierung nach dieser Norm beziehen sich ausschließlich auf die Konzentration luftgetragener Partikel. Desweiteren werden für Klassifizierungßwecke nur Partikelgruppen in Betracht gezogen, deren Summenhäufigkeitsverteilung zwischen den kritischen Partikelgrößen ( untere Grenze) 0,1 um un 5 um basiert.

Salles propres et environnements maîtrisés apparentés - Partie 1: Classification de la propreté de l'air (ISO 14644-1:1999)

La présente partie de l'ISO 14644 comprend la classification de la propreté de l'air des salles propres et environnements maîtrisés apparentés exclusivement en termes de concentration des particules en suspension dans l'air. Pour l'application de cette classification, on ne considère que les populations de particules présentant une distribution cumulée dont le seuil inférieur de sensibilité se situe dans l'étendue granulométrique de 0,1 µm à 5 µm. La présente partie de l'ISO 14644 ne donne pas la classification des populations de particules sortant de l'étendue granulométrique de référence de 0,1 µm à 5 µm. Les concentrations de particules ultrafines (plus petites que 0,1 µm) et de macroparticules (plus grandes que 5 µm) peuvent être utilisées pour quantifier ces populations en terme de descripteurs U et M. La présente partie de l'ISO 14644 n'est pas applicable pour caractériser la nature physique, chimique, radiologique ou viable des particules en suspension dans l'air.
NOTE La distribution granulométrique réelle de particules par taille à l'intérieur de l'étendue de référence n'est pas habituellement prévisible et est typiquement variable avec le temps.

Cleanrooms and associated controlled environments - Part 1: Classification of air cleanliness (ISO 14644-1:1999)

General Information

Status
Withdrawn
Publication Date
30-Apr-1999
Withdrawal Date
22-Dec-2015
Current Stage
9960 - Withdrawal effective - Withdrawal
Completion Date
23-Dec-2015

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SLOVENSKI STANDARD
SIST EN ISO 14644-1:2000
01-december-2000

Cleanrooms and associated controlled environments - Part 1: Classification of air

cleanliness (ISO 14644-1:1999)

Cleanrooms and associated controlled environments - Part 1: Classification of air

cleanliness (ISO 14644-1:1999)

Reinräume und zugehörige Reinraumbereiche - Teil 1: Klassifizierung der Luftreinheit

(ISO 14644-1:1999)

Salles propres et environnements maîtrisés apparentés - Partie 1: Classification de la

propreté de l'air (ISO 14644-1:1999)
Ta slovenski standard je istoveten z: EN ISO 14644-1:1999
ICS:
13.040.35 Brezprašni prostori in Cleanrooms and associated
povezana nadzorovana controlled environments
okolja
SIST EN ISO 14644-1:2000 en

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO 14644-1:2000
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SIST EN ISO 14644-1:2000
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SIST EN ISO 14644-1:2000
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SIST EN ISO 14644-1:2000
INTERNATIONAL ISO
STANDARD 14644-1
First edition
1999-05-01
Cleanrooms and associated controlled
environments —
Part 1:
Classification of air cleanliness
Salles propres et environnements maîtrisés apparentés —
Partie 1: Classification de la propreté de l'air
Reference number
ISO 14644-1:1999(E)
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SIST EN ISO 14644-1:2000
ISO 14644-1:1999(E) © ISO
Contents
Page

Foreword ......................................................................................................... iii

Introduction ..................................................................................................... iv

1 Scope ........................................................................................................ 1

2 Definitions .................................................................................................. 1

3 Classification ............................................................................................. 3

4 Demonstration of compliance .................................................................... 4

Annexes

Annex A (informative) Graphical illustration of the classes of Table 1 ............ 5

Annex B (normative) Determination of particulate cleanliness classification
using a discrete-particle-counting, light-scattering instrument...... 6
Annex C (normative) Statistical treatment of particle concentration data ..... 9
Annex D (informative) Worked examples of classification calculations ........ 10
Annex E (informative) Considerations for the counting and sizing of particles
outside the size range applicable for classification ..................... 13

Annex F (informative) Sequential sampling procedure ................................ 15

Bibliography ................................................................................................... 18

Figures
Figure A.1 Graphical representation of ISO-class concentration limits

for selected ISO classes ............................................................... 5

Figure F.1 Boundaries for pass or fail by the sequential sampling

procedure .................................................................................. 15

Tables
Table 1 Selected airborne particulate cleanliness classes for

cleanrooms and clean zones ........................................................ 3

Table C.1 Student’s t distribution for the 95% upper confidence limit ........... 9

Table F.1 Upper and lower limits for time at which C observed counts

should arrive ............................................................................... 16

© ISO 1999

All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic

or mechanical, including photocopying and microfilm, without permission in writing from the publisher.

International Organization for Standardization
Case Postale 56 • CH-1211 Genève 20 • Switzerland
Internet iso@iso.ch
Printed in Switzerland
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SIST EN ISO 14644-1:2000
© ISO
ISO 14644-1:1999(E)
Introduction

Cleanrooms and associated controlled environments provide for the control of airborne

particulate contamination to levels appropriate for accomplishing contamination-sensitive

activities. Products and processes that benefit from the control of airborne contamination

include those in such industries as aerospace, microelectronics, pharmaceuticals, medical

devices, food, and healthcare.

This part of ISO 14644 assigns ISO classification levels to be used for the specification of

air cleanliness in cleanrooms and associated controlled environments. It also prescribes the

standard method of testing as well as the procedure for determining the concentration of

airborne particles.

For classification purposes, this part of ISO 14644 is limited to a designated range of

considered particle sizes for determination of particle concentration limits. This part of ISO

14644 also provides standard protocols for the determination and designation of cleanli-

ness levels that are based on airborne concentrations of particles smaller or larger than the

size range designated for classification.

This part of ISO 14644 is one of a series of standards concerned with cleanrooms and

contamination control. Many factors besides airborne particulate cleanliness must be

considered in the design, specification, operation, and control of cleanrooms and other

controlled environments. These are covered in some detail in other parts of the International

Standards prepared by ISO/TC 209.

In some circumstances, relevant regulatory agencies may impose supplementary policies

or restrictions. In such situations, appropriate adaptations of the standard testing proce-

dures may be required.
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SIST EN ISO 14644-1:2000

INTERNATIONAL STANDARD © ISO ISO 14644-1:1999(E)

Cleanrooms and associated controlled environments —
Part 1:
Classification of air cleanliness
1 Scope cles inside the room, and in which other relevant parameters,
e.g. temperature, humidity, and pressure, are controlled as
This part of ISO 14644 covers the classification of air cleanli-
necessary
ness in cleanrooms and associated controlled environments
exclusively in terms of concentration of airborne particles. 2.1.2
Only particle populations having cumulative distributions based
clean zone
on threshold (lower limit) sizes ranging from 0,1 μm to 5 μm are
dedicated space in which the concentration of airborne parti-
considered for classification purposes.
cles is controlled, and which is constructed and used in a
manner to minimize the introduction, generation, and retention
This part of ISO 14644 does not provide for classification of
of particles inside the zone, and in which other relevant
particle populations that are outside of the specified particle
parameters, e.g. temperature, humidity, and pressure, are
size range, 0,1 μm to 5 μm. Concentrations of ultrafine particles
controlled as necessary
(particles smaller than 0,1 μm) and macroparticles (particles
larger than 5 μm) may be used to quantify these populations in
NOTE This zone may be open or enclosed and may or may not be
terms of U descriptors and M descriptors, respectively.
located within a cleanroom.
This part of ISO 14644 cannot be used to characterize the
2.1.3
physical, chemical, radiological, or viable nature of airborne
installation
particles.
cleanroom or one or more clean zones, together with all
NOTE The actual distribution of particle concentrations within incre-
associated structures, air-treatment systems, services, and
mental size ranges normally is not predictable and typically is variable
utilities
over time.
2.1.4
classification
level (or the process of specifying or determining the level) of
2 Definitions
airborne particulate cleanliness applicable to a cleanroom or
For the purposes of this part of ISO 14644, the following
clean zone, expressed in terms of an ISO Class N, which
definitions apply. represents maximum allowable concentrations (in particles
per cubic metre of air) for considered sizes of particles
NOTE 1 The concentrations are determined by using equation (1)
2.1 General
in 3.2.
2.1.1
NOTE 2 Classification in accordance with this International Stan-
cleanroom
dard is limited to the range extending from ISO Class 1 through ISO
room in which the concentration of airborne particles is con-
Class 9.
trolled, and which is constructed and used in a manner to
NOTE 3 The considered particle sizes (lower threshold values)
minimize the introduction, generation, and retention of parti-
applicable for classification in accordance with this International
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SIST EN ISO 14644-1:2000
ISO 14644-1:1999(E) © ISO
Standard are limited to the range from 0,1 μm through 5 μm. Air 2.3 Descriptors
cleanliness may be described and specified (but not classified) in
2.3.1
terms of U descriptors or M descriptors (see 2.3.1 or 2.3.2) for
considered threshold particle sizes that are outside of the range
U descriptor
covered by classification.
measured or specified concentration, of particles per cubic
metre of air, including the ultrafine particles
NOTE 4 Intermediate ISO classification numbers may be speci-
fied, with 0,1 the smallest permitted increment; i.e., the range of
NOTE The U descriptor may be regarded as an upper limit for the
intermediate ISO classes extends from ISO Class 1,1 through ISO
averages at sampling locations (or as an upper confidence limit,
Class 8,9.
depending upon the number of sampling locations used to character-
ize the cleanroom or clean zone). U descriptors cannot be used to
NOTE 5 Classification may be specified or accomplished in any of
define airborne particulate cleanliness classes, but they may be
three occupancy states (see 2.4).
quoted independently or in conjunction with airborne particulate
cleanliness classes.
2.2 Airborne particles
2.3.2
2.2.1
M descriptor
particle
measured or specified concentration of macroparticles per
solid or liquid object which, for purposes of classification of air
cubic metre of air, expressed in terms of the equivalent
cleanliness, falls within a cumulative distribution that is based
diameter that is characteristic of the measurement method
upon a threshold (lower limit) size in the range from 0,1 μm to
used
5 μm
NOTE The M descriptor may be regarded as an upper limit for the
2.2.2 averages at sampling locations (or as an upper confidence limit,
depending upon the number of sampling locations used to character-
particle size
ize the cleanroom or clean zone). M descriptors cannot be used to
diameter of a sphere that produces a response, by a given
define airborne particulate cleanliness classes, but they may be
particle-sizing instrument, that is equivalent to the response
quoted independently or in conjunction with airborne particulate
produced by the particle being measured
cleanliness classes.
NOTE For discrete-particle-counting, light-scattering instruments,
the equivalent optical diameter is used.
2.4 Occupancy states
2.2.3
2.4.1
particle concentration
as-built
number of individual particles per unit volume of air
condition where the installation is complete with all services
connected and functioning but with no production equipment,
2.2.4
materials, or personnel present
particle size distribution
cumulative distribution of particle concentration as a function of
2.4.2
particle size
at-rest
condition where the installation is complete with equipment
2.2.5
installed and operating in a manner agreed upon by the
ultrafine particle
customer and supplier, but with no personnel present
particle with an equivalent diameter less than 0,1 μm
2.4.3
2.2.6
operational
macroparticle
condition where the installation is functioning in the specified
particle with an equivalent diameter greater than 5 μm
manner, with the specified number of personnel present and
working in the manner agreed upon
2.2.7
fibre
particle having an aspect (length-to-width) ratio of 10 or more
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SIST EN ISO 14644-1:2000
© ISO ISO 14644-1:1999(E)

Table 1 — Selected airborne particulate cleanliness classes for cleanrooms and clean zones

Maximum concentration limits (particles/m of air) for particles equal to and larger

ISO
than the considered sizes shown below (concentration limits are calculated in
classification
accordance with equation (1) in 3.2)
number (N)
0,1 μm20, μm30, μm50, μm1 μm5 μm
I0SO Class 1 12
I0SO Class 2 140 2014
I0SO Class 3 1700 223 150 38
I0SO Class 4100 00 2037 1202 335 8
I0SO Class 51000 00203 70100 20 3252 893 2
I0SO Class 610000 002037 001002 00305 20 8332 29
I0SO Class 7 3052 00803 20 2 93
I0SO Class 8 30520 008032 00 29 30
I0SO Class 9 305 200 0080320 00 293 00

NOTE Uncertainties related to the measurement process require that concentration data with no more

than three significant figures be used in determining the classification level
2.5 Roles 3.2 Classification number
Airborne particulate cleanliness shall be designated by a
2.5.1
classification number, N. The maximum permitted concentra-
customer
tion of particles, C , for each considered particle size, D, is
organization, or the agent thereof, responsible for specifying
determined from the equation:
the requirements of a cleanroom or clean zone
20, 8
01,
 
2.5.2 N
C=×10
 
(1)
 
supplier
organization engaged to satisfy the specified requirements of
where
a cleanroom or clean zone
C is the maximum permitted concentration (in parti-
cles per cubic metre of air) of airborne particles that
are equal to or larger than the considered particle
size. C is rounded to the nearest whole number,
3 Classification
using no more than three significant figures.
N is the ISO classification number, which shall not
3.1 Occupancy state(s)
exceed a value of 9. Intermediate ISO classification
numbers may be specified, with 0,1 the smallest
The particulate cleanliness of air in a cleanroom or clean zone
permitted increment of
shall be defined in one or more of three occupancy states, viz.
“as-built”, “at-rest”, or “operational” (see 2.4).
D is the considered particle size, in micrometres.
NOTE It should be recognized that the “as-built” state is applicable
0,1 is a constant, with a dimension of micrometres.
to newly completed or newly modified cleanrooms or clean zones.
Table 1 presents selected airborne particulate cleanliness
Once testing in the “as-built” state is completed, further testing for
classes and the corresponding particle concentrations for
compliance will be performed in the “at-rest” or the “operational” state,
particles equal to and larger than the considered sizes shown.
or both.
Figure A.1 (see annex A) provides a representation of the
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SIST EN ISO 14644-1:2000
ISO 14644-1:1999(E) © ISO

selected classes in graphical form. In case of dispute, the (when applicable) shall be calculated using equations shown

concentration C as derived from equation (1) shall serve as in annex C.
the standard value.
Average particle concentration(s), calculated in accordance
with equation (C.1), shall not exceed the concentration
limit(s) determined by use of equation (1) in 3.2, as specified
3.3 Designation
[3.3 c)] for the considered size(s).
The designation of airborne particulate cleanliness for clean-
In addition, for situations in which the number of sampling
rooms and clean zones shall include:
locations involved is at least two but not more than nine, the
a) the classification number, expressed as “ISO Class N ”;
calculation of 95% upper confidence limits in accordance with
b) the occupancy state to which the classification applies;
C.3 shall not exceed the concentration limits established
c) the considered particle size(s), and the related concen-
above.
tration(s), as determined by the classification equation (1)
NOTE Worked examples of classification calculations are provided
where each considered threshold particle size is in the range
in annex D.
from 0,1 μm through 5 μm.
Particle concentrations used for determination of conformance
Example designation:
to classification limits shall be measured by the same method
ISO Class 4; operational state; considered sizes:
for all considered particle sizes.
3 3
0,2 μm (2 370 particles/m ), 1 μm (83 particles/m )
4.4 Test report
The considered particle size(s) for which the concentra-
tion(s) will be measured shall be agreed upon by the custom-
The results from testing each cleanroom or clean zone shall
er and the supplier.
be recorded and submitted as a comprehensive report, along
with a statement of compliance or noncompliance with the
If measurements are to be made at more than one considered
specified designation of airborne particulate cleanliness clas-
particle size, each larger particle diameter (e.g., D ) shall be at
sification.
least 1,5 times the next smaller particle diameter (e.g., D ).
The test report shall include the following:
e.g.: D ≥ 1,5 x D
2 1
a) the name and address of the testing organization, and the
date on which the test was performed;
b) the number and year of publication of this part of ISO
4 Demonstration of compliance
14644, i.e., ISO 14644-1: date of current issue;
c) a clear identification of the physical location of the clean-
4.1 Principle room or clean zone tested (including reference to adjacent
areas if necessary), and specific designations for coordinates
Compliance with air cleanliness (ISO class) requirements
of all sampling locations;
specified by the customer is verified by performing specified
d) the specified designation criteria for the cleanroom or clean
testing procedures and by providing specified documentation
zone, including the ISO classification, the relevant occupancy
of the results and conditions of testing, as agreed upon by the
state(s), and the considered particle size(s);
customer and the supplier.
e) details of the test method used, with any special conditions
relating to the test or departures from the test method, and
4.2 Testing
identification of the test instrument and its current calibration
The reference test method for demonstrating compliance is
certificate;
given in annex B. An alternative method having comparable
f) the test results, including particle concentration data for all
accuracy may be specified, although if no method is specified
sampling location coordinates.
or agreed upon, the reference method shall be used.
NOTE If concentrations of ultrafine particles or macroparticles are
Tests performed to demonstrate compliance shall be con-
quantified, as described in annex E, the pertinent information should
ducted using calibrated instruments.
be included with the test report.
4.3 Airborne particle concentration
limits
Upon completion of testing in accordance with 4.2, average
particle concentrations and the 95% upper confidence limit
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SIST EN ISO 14644-1:2000
ISO ISO 14664-1:1999(E)
Annex A
(informative)
Graphical illustration of the classes of Table 1

Figure A.1 depicts the air cleanliness classes of Table 1 in The classification lines shown on the graph may not be

graphical form, for illustration purposes only. The ISO classes extrapolated beyond the solid circle symbols, which

of Table 1 are shown as lines representing the class indicate the minimum and maximum particle size limits

concentration limits for the considered threshold particle sizes. acceptable for each of the ISO classes shown.

They are based on calculations using equation (1) of 3.2 As
The classification lines do not represent actual particle size
the lines only approximate the class limits, they are not to be

used to define the limits. Such determinations are made in distributions found in cleanrooms and clean zones.

accordance with equation (1).

Figure A.1 — Graphical representation of ISO-class concentration limits for selected

ISO classes

NOTE 1 C represents the maximum permitted concentration (in particles per cubic metre of air) of

airborne particles equal to and larger than the considered particle size.
NOTE 2 N represents the specified ISO class number.
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SIST EN ISO 14644-1:2000
ISO 14644-1:1999(E) © ISO
Annex B
(normative)
Determination of particulate cleanliness classification using a
discrete-particle-counting, light-scattering instrument
B.1 Principle B.4 Sampling
A discrete-particle-counting, light-scattering instrument is used
B.4.1 Establishment of sampling
to determine the concentration of airborne particles, equal to
locations
and larger than the specified sizes, at designated sampling
locations.
B.4.1.1
Derive the minimum number of sampling point locations from
equation (B.1):
B.2 Apparatus requirements
(B.1)
N = A
B.2.1 Particle-counting instrument
where
Discrete-particle counter (DPC), a light-scattering device hav-
N is the minimum number of sampling locations
ing a means of displaying or recording the count and size of L
(rounded up to a whole number).
discrete particles in air with a size discrimination capability to
detect the total particle concentration in the appropriate par-
A is the area of the cleanroom or clean zone in square
ticle size ranges for the class under consideration, and a
metres.
suitable sampling system.
NOTE In the case of unidirectional horizontal airflow, the area A may
be considered as the cross section of the moving air perpendicular to
B.2.2 Instrument calibration
the direction of the airflow.
The instrument shall have a valid calibration certificate; the
frequency and method of calibration should be based on
B.4.1.2
current accepted practice.
Ensure that the sampling locations are evenly distributed
throughout the area of the cleanroom or clean zone and
positioned at the height of the work activity.
B.3 Pretest conditions
If the customer specifies additional sampling locations, their
B.3.1 Preparation for testing number and positions shall also be specified.
Prior to testing, verify that all aspects of the cleanroom or clean
NOTE Such additional locations may be those considered critical,
zone that contribute to its operational integrity are complete
based on a risk analysis.
and functioning in accordance with its performance specifica-
tion.
B.4.2 Establishment of single sample
volume per location
Such pretesting may include, for example:
a) airflow volume or velocity tests; B.4.2.1
At each sampling location, sample a sufficient volume of air
b) air pressure difference test;
that a minimum of 20 particles would be detected if the particle
c) containment leakage test;
concentration for the largest considered particle size were at
d) installed filter leakage test.
the class limit for the designated ISO class.
The single sample volume V per location is determined by
B.3.2 Pretest equipment setup s
using equation (B.2):
Perform equipment setup and pretest calibration of the instru-
ment in accordance with the manufacturer’s instructions.
V=× 1 000
(B.2)
nm,
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SIST EN ISO 14644-1:2000
© ISO ISO 14644-1:1999(E)
where B.5.1.2
When only one sampling location is used, calculate and record
V is the minimum single sample volume per location,
the average value of the sample data (B.4.3.4) for each
expressed in litres (except see B.4.2.2).
considered particle size.
C is the class limit (number of particles per cubic
n,m
metre) for the largest considered particle size spec-
B.5.1.3
ified for the relevant class.
When two or more single sample volumes are taken at a
location, compute the average particle concentration for each
20 is the defined number of particles that could be
considered particle size from the individual sample particle
counted if the particle concentration were at the
concentrations (B.5.1.1), according to the procedure given in
class limit.
C.2, and record the results.
NOTE When V is very large, the time required for sampling can be
substantial. By using the sequential sampling procedure (see annex
B.5.2 Requirement for computing the
F), both the required sample volume and the time required to obtain
95% upper confidence limit (UCL)
samples may be reduced.
B.5.2.1
B.4.2.2
When the number of locations sampled is more than one and
The volume sampled at each location shall be at least 2 litres,
less than ten, compute the overall mean of the averages,
with a minimum sampling time at each location of 1 min.
standard deviation, and 95% upper confidence limit from the
average particle concentrations for all locations (B.5.1) follow-
B.4.3 Sampling procedure
ing the procedure described in C.3.
B.4.3.1
B.5.2.2
Set up the particle counter (B.2.1) in accordance with the
When only a single location is sampled, or when more than
manufacturer’s instructions and in compliance with the instru-
nine are sampled, computing the 95% upper confidence limit
ment calibration certificate.
is not applicable.
B.4.3.2
The sampling probe shall be positioned pointing into the
B.6 Interpretation of results
airflow. If the direction of the airflow being sampled is not
controlled or predictable (e.g., nonunidirectional airflow), the
B.6.1 Classification requirements
inlet of the sampling probe shall be directed vertically upward.
The cleanroom or clean zone is deemed to have met the
specified air cleanliness classification if the averages of the
B.4.3.3
particle concentrations measured at each of the locations and,
Sample the volume of air determined in B.4.2, as a minimum,
when applicable, the 95% upper confidence limit calculated
at each sampling location.
according to B.5.2, do not exceed the concentration limits
determined in accordance with equation (1) of 3.2.
B.4.3.4
Where only one sampling location is required (B.4.1), take a
If the results of testing fail to meet the specified air cleanliness
minimum of three single sample volumes (B.4.2) at that loca-
classification, testing may be performed at additional, evenly
tion.
distributed sampling locations. The results of recalculation,
including data from the added locations, shall be definitive.
B.5 Recording of results
B.6.2 Treatment of outliers
The result of the 95% UCL calculation may fail to meet the
B.5.1 Average concentration of
specified ISO class designation. If the noncompliance is
particles at each sampling location
caused by a single, nonrandom “outlier” value resulting from an
B.5.1.1
erroneous measurement (due to procedural error or equip-
Record the result of each sample measurement as the concen-
ment malfunction) or from an unusually low particle concentra-
tration of each of the considered particle size(s) (3.3) appropri-
tion (due to exceptionally clean air), the outlier may be ex-

ate to the relevant classification of air cleanliness. cluded from the calculation, provided that:

NOTE Consideration should be given to the requirements of B.6.1
a) the calculation is repeated, including all remaining sam-
before proceeding with the calculation of the 95% upper confidence
pling locations;
limit.
b) at least three measurement values remain in the calcula-
tion;
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SIST EN ISO 14644-1:2000
ISO 14644-1:1999(E) © ISO
c) no more than one measurement value is excluded from the
calculation;
d) the suspected cause of the erroneous measurement or low
particle concentration is documented and accepted by both the
customer and supplier.
NOTE Widely divergent values for particle concentrations among
the locations sampled may be reasonable and even intentional,
depending on the nature of the application of the clean installation
under test.
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SIST EN ISO 14644-1:2000
© ISO ISO 14644-1:1999(E)
Annex C
(normative)
Statistical treatment of particle concentration data
m is the number of individual location averages.
C.1 Rationale
This statistical analysis considers only random errors (lack of
All individual location averages are equally weighted, regard-
precision), not errors of a nonrandom nature (e.g. bias associ-
less of the number of samples taken at any given location.
ated with erroneous calibration).
C.3.3 Standard deviation of the
location averages (s)
C.2 Algorithm for computation of
Using equation (C.3), determine the standard deviation of the
average particle concentration at a
location averages.
———
location (x )
When multiple samples are taken at a location, equation (C.1) 2 22
xx––+x x ++K... x–x
(ii,,1 ) ( 2 ) (i,m )
shall be used to determine the average particle concentration
(C.3)
s =
at the location. Calculation of the average particle concentra- (m – 1)
tion shall be performed for each sampling location at which two
where
or more samples have been taken.
s is the standard deviation of the location averages.
xx++ ...K+x
ii,,12 i,n
x =
(C.1)
C.3.4 95% upper confidence limit (UCL)
for the overall mean
where
– Using equation (C.4), determine the 95% upper confidence
x is the average particle concentration at location i,
limit for the overall mean.
representing any location.
x to x are the particle concentrations of the indi-
i,1 i,n
 s 
95% UCL=+xt
(C.4)
vidual samples. 09,. 5  
 
n is the number of samples taken at loc
...

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