Clothes washing machines for household use - Method for measuring the microbial contamination reduction

IEC PAS 62958:2015(E) specifies a test method for measuring the reduction of microbial contamination in clothes washing machines and of the possible cross contamination to uncontaminated load. This PAS applies to clothes washing machines for household use, with or without heating devices utilising cold and/or hot water supply. It also covers washing machines which specify the use of no detergent for normal use. This PAS applies also to washing machines for communal use in blocks of flats or in launderettes. This PAS does not deal with professional washing machines nor with commercial laundry operations associated with food service, hospital linens or other non-residential applications. It also does not address the needs of persons with specific health conditions requiring special sanitization and/or disinfection techniques. This PAS does not specify safety requirements and does not deal with performance of washing machines measured under IEC 60456 nor with effects on fabrics.

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27-Feb-2022
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IEC PAS 62958
Edition 1.0 2015-03
PUBLICLY AVAILABLE
SPECIFICATION
PRE-STANDARD
Clothes washing machines for household use – Method for measuring the
microbial contamination reduction
IEC PAS 62958:2015-03(en)
---------------------- Page: 1 ----------------------
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IEC PAS 62958
Edition 1.0 2015-03
PUBLICLY AVAILABLE
SPECIFICATION
PRE-STANDARD
Clothes washing machines for household use – Method for measuring the
microbial contamination reduction
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 97.060 ISBN 978-2-8322-2478-6

Warning! Make sure that you obtained this publication from an authorized distributor.

® Registered trademark of the International Electrotechnical Commission
---------------------- Page: 3 ----------------------
– 2 – IEC PAS 62958:2015 © IEC 2015
CONTENTS

FOREWORD ........................................................................................................................... 5

INTRODUCTION ..................................................................................................................... 7

1 Scope .............................................................................................................................. 8

2 Normative references ...................................................................................................... 8

3 Terms, definitions and symbols........................................................................................ 9

3.1 Terms and definitions .............................................................................................. 9

3.2 Symbols .................................................................................................................. 9

4 Requirements ................................................................................................................ 10

5 Test conditions, materials, equipment and instrumentation ............................................ 10

5.1 Test conditions ..................................................................................................... 10

5.2 Materials and reagents ......................................................................................... 10

5.2.1 Microorganisms for test purposes .................................................................. 10

5.2.2 Culture media and solutions .......................................................................... 10

5.2.3 Detergent ...................................................................................................... 13

5.3 Equipment ............................................................................................................ 14

5.3.1 General ......................................................................................................... 14

5.3.2 Incubator ....................................................................................................... 14

5.3.3 Autoclave ...................................................................................................... 14

5.3.4 Microorganism carrier .................................................................................... 14

5.3.5 Pipettes ......................................................................................................... 14

5.3.6 Electromechanical agitator............................................................................. 14

5.3.7 Centrifuge, centrifuge tubes ........................................................................... 14

5.3.8 Base load ...................................................................................................... 14

5.3.9 Measuring equipment for assessing temperature profile ................................ 15

5.3.10 Measuring equipment for water consumption ................................................. 15

6 Tests ............................................................................................................................. 15

6.1 Test method principles .......................................................................................... 15

6.2 Preparation of test washing machine ..................................................................... 15

6.3 Preparation of test microorganisms and bio monitors ............................................ 15

6.3.1 Cultures ......................................................................................................... 15

6.3.2 Bio monitors .................................................................................................. 17

6.4 Main test ............................................................................................................... 18

6.4.1 General ......................................................................................................... 18

6.4.2 Evidence of test microorganisms ................................................................... 18

6.5 Validation .............................................................................................................. 18

6.5.1 Enumeration of microorganisms before exposition N (bio monitor

reference) ...................................................................................................... 18

6.5.2 Negative control (cross contamination) .......................................................... 18

6.5.3 Determination of water quality ....................................................................... 19

6.5.4 Determination of water quantity in the main wash .......................................... 19

7 Evaluation ..................................................................................................................... 19

7.1 Log reduction ........................................................................................................ 19

7.2 Cross contamination ............................................................................................. 19

8 Test report ..................................................................................................................... 19

Annex A (informative) Microorganism reduction in household washing machines with

risk class 1 test microorganisms for internal development purpose ...................................... 21

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IEC PAS 62958:2015 © IEC 2015 – 3 –

A.1 Scope ................................................................................................................... 21

A.2 General recommendation ...................................................................................... 21

A.3 Material and reagents ........................................................................................... 21

A.3.1 Microorganisms on bio monitors .................................................................... 21

A.3.2 Water for culture media and solutions ............................................................ 21

A.3.3 Culture media and solutions .......................................................................... 21

A.3.4 Detergent ...................................................................................................... 23

A.4 Equipment ............................................................................................................ 23

A.4.1 Incubator ....................................................................................................... 23

A.4.2 Autoclave ...................................................................................................... 23

A.4.3 Microorganism carrier .................................................................................... 23

A.4.4 Pipettes ......................................................................................................... 23

A.4.5 Electromechanical agitator............................................................................. 23

A.4.6 Centrifuge ...................................................................................................... 23

A.4.7 Base load ...................................................................................................... 23

A.4.8 Measuring equipment for assessing temperature profile ................................ 23

A.4.9 Measuring equipment for water consumption ................................................. 23

A.5 Tests .................................................................................................................... 23

A.5.1 Test method principles ................................................................................... 23

A.5.2 Preparation of washing machine .................................................................... 24

A.5.3 Preparation of test organisms and bio monitors ............................................. 24

A.5.4 Main test ....................................................................................................... 25

A.5.5 Validation ...................................................................................................... 26

A.6 Evaluation ............................................................................................................. 26

A.6.1 Plate counts per bio monitor .......................................................................... 26

A.6.2 Log reductions ............................................................................................... 27

A.6.3 Cross contamination ...................................................................................... 27

A.7 Test report ............................................................................................................ 27

Annex B (informative) Sources of materials and supplies ..................................................... 28

B.1 Disclaimer ............................................................................................................. 28

B.2 Microorganism carriers ......................................................................................... 28

B.3 Electromechanical agitator .................................................................................... 28

B.4 Ready-to-use bio monitors .................................................................................... 28

B.5 Nonionic surfactant and emulsifier ........................................................................ 28

Bibliography .......................................................................................................................... 29

Figure A.1 – Scheme for preparing a dilution series .............................................................. 25

Table 1 – Composition of Tryptone Soy Agar (TSA) .............................................................. 11

Table 2 – Composition of Sabouraud Dextrose Agar with Chloramphenicol .......................... 11

Table 3 – Composition of Cetrimide Agar .............................................................................. 11

Table 4 – Composition of Baird-Parker Agar ......................................................................... 12

Table 5 – Composition of Malt Extract Agar (MEA) ................................................................ 12

Table 6 – Composition of Tryptone Soy Broth (TSB) ............................................................. 12

Table 7 – Composition of diluting agent ................................................................................ 13

Table 8 – Composition of recommended neutralisation solution ............................................ 13

Table 9 – Specifications for temperature logger .................................................................... 15

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– 4 – IEC PAS 62958:2015 © IEC 2015

Table A.1 – Composition of Sabouraud Dextrose Agar .......................................................... 22

Table A.2 – Composition of Columbia CNA Agar ................................................................... 22

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IEC PAS 62958:2015 © IEC 2015 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
CLOTHES WASHING MACHINES FOR HOUSEHOLD USE –
METHOD FOR MEASURING THE MICROBIAL
CONTAMINATION REDUCTION
FOREWORD

1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising

all national electrotechnical committees (IEC National Committees). The object of IEC is to promote

international co-operation on all questions concerning standardization in the electrical and electronic fields. To

this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,

Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC

Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested

in the subject dealt with may participate in this preparatory work. International, governmental and non-

governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely

with the International Organization for Standardization (ISO) in accordance with conditions determined by

agreement between the two organizations.

2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international

consensus of opinion on the relevant subjects since each technical committee has representation from all

interested IEC National Committees.

3) IEC Publications have the form of recommendations for international use and are accepted by IEC National

Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC

Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any

misinterpretation by any end user.

4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications

transparently to the maximum extent possible in their national and regional publications. Any divergence

between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in

the latter.

5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity

assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any

services carried out by independent certification bodies.

6) All users should ensure that they have the latest edition of this publication.

7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and

members of its technical committees and IEC National Committees for any personal injury, property damage or

other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and

expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC

Publications.

8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is

indispensable for the correct application of this publication.

9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of

patent rights. IEC shall not be held responsible for identifying any or all such patent rights.

A PAS is a technical specification not fulfilling the requirements for a standard, but made

available to the public.

IEC PAS 62958 has been processed by subcommittee 59D: Performance of household and

similar electrical laundry appliances, of IEC technical committee 59:
The text of this PAS is based on the This PAS was approved for publication
following document: by the P-members of the committee
concerned as indicated in the following
document
Draft PAS Report on voting
59D/423/PAS 59D/427/RVD

Following publication of this PAS, which is a pre-standard publication, the technical committee

or subcommittee concerned may transform it into an International Standard.
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– 6 – IEC PAS 62958:2015 © IEC 2015

This PAS shall remain valid for an initial maximum period of 3 years starting from the

publication date. The validity may be extended for a single period up to a maximum of

3 years, at the end of which it shall be published as another type of normative document, or

shall be withdrawn.
A bilingual version of this publication may be issued at a later date.
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IEC PAS 62958:2015 © IEC 2015 – 7 –
INTRODUCTION

SC 59D decided to address the measurement of the microbial contamination reduction in

washing machines by developing a globally acceptable Publicly Available Specification to

respond to the increase in consumer complaints regarding odour from washing machines and

washed laundry caused by presence of microorganisms.
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– 8 – IEC PAS 62958:2015 © IEC 2015
CLOTHES WASHING MACHINES FOR HOUSEHOLD USE –
METHOD FOR MEASURING THE MICROBIAL
CONTAMINATION REDUCTION
1 Scope

This Publicly Available Specification (PAS) specifies a test method for measuring the

reduction of microbial contamination in clothes washing machines and of the possible cross

contamination to uncontaminated load.

NOTE A significant differentiation in microorganism contamination reduction capability of washing machines can

be expected at wash temperature not higher than 40 °C.

This PAS applies to clothes washing machines for household use, with or without heating

devices utilising cold and/or hot water supply. It also covers washing machines which specify

the use of no detergent for normal use. This PAS applies also to washing machines for

communal use in blocks of flats or in launderettes.

This PAS does not deal with professional washing machines nor with commercial laundry

operations associated with food service, hospital linens or other non-residential applications.

It also does not address the needs of persons with specific health conditions requiring special

sanitization and/or disinfection techniques.

This PAS does not specify safety requirements and does not deal with performance of

washing machines measured under IEC 60456 nor with effects on fabrics.
2 Normative references

IEC 60456:2010, Clothes washing machines for household use − Methods for measuring the

performance

ISO 2267, Surface active agents – Evaluation of certain effects of laundering – Methods of

preparation and use of unsoiled cotton control cloth

EN 1276, Chemical disinfectants and antiseptics. Quantitative suspension test for the

evaluation of bactericidal activity of chemical disinfectants and antiseptics used in food,

industrial, domestic and institutional areas. Test method and requirements (phase 2, step 1)

EN 1650, Chemical disinfectants and antiseptics. Quantitative suspension test for the

evaluation of fungicidal or yeasticidal activity of chemical disinfectants and antiseptics used in

food, industrial, domestic and institutional areas. Test method and requirements (phase 2,

step 1)

EN 12353, Chemical disinfectants and antiseptics. Preservation of test organisms used for the

determination of bactericidal (including Legionella), mycobactericidal, sporicidal, fungicidal

and virucidal (including bacteriophages) activity
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IEC PAS 62958:2015 © IEC 2015 – 9 –
3 Terms, definitions and symbols
3.1 Terms and definitions
3.1.1
washing machine

appliance for cleaning and rinsing of textiles using water which may also have a means of

extracting excess water from the textiles
3.1.2
test washing machine

washing machine that is subjected to part or all of the requirements in this PAS in order to

determine its performance
3.1.3
test run
single performance assessment
3.1.4
programme

series of operations which are pre-defined within the washing machine and which are

declared by the manufacturer as suitable for washing certain textile types
3.1.5
base load
textile load used for testing not including the bio monitors
3.1.6
cross contamination
transfer of microorganisms from fabrics to fabrics during one test run
3.1.7
inoculum
quantity of cells to be inoculated in culture medium
3.1.8
bio monitor

microorganism carrier inoculated with microorganisms to be used to monitor the reduction of

microbial contamination
3.1.9
temperature profile

time–temperature data representing the water temperature in the washing machine during

the test run
3.2 Symbols
N average value of microorganism amount of the two positive controls, before
exposition to the test programme (cfu/bio monitor)
N average value of microorganism amount per 5 bio monitors, after exposition to
the test programme (cfu/bio monitor)
log(N /N) reduction factor per microorganism type
v microorganism amount in a 10 times diluted solution
v microorganism amount in a 100 times diluted solution
SD standard deviation of N
initial 0
SD standard deviation of N
washed
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– 10 – IEC PAS 62958:2015 © IEC 2015
SD standard deviation of the reduction factor per microorganism type
total
4 Requirements

This Publicly Available Specification specifies a test method for measuring the reduction of

microbial contamination in clothes washing machines and of the possible cross
contamination in subsequent washed loads.

This PAS does not specify safety requirements and does not deal with performance of

washing machines measured under IEC 60456 nor with effects on fabrics.
5 Test conditions, materials, equipment and instrumentation
5.1 Test conditions

For all requirements regarding ambient conditions (electricity supply, water supply, ambient

temperature and humidity) and base load, see IEC 60456:2010.

Additionally, the water supplied to the test washing machine shall not contain more than

100 cfu/ml. Microorganisms for test purposes as listed in 5.2.1 shall not be present in the

water.

The micribiological quality of the water supplied to the test washing machine is determined

according to 5.2.3.2 and 6.5.3
5.2 Materials and reagents
5.2.1 Microorganisms for test purposes

For test purposes the following microorganisms, the first two bacteria strains and the last one

a yeast strain, shall be used:
• Pseudomonas putida (ATCC 11172 / DSM 6521)
• Staphylococcus aureus (ATCC 6538 / DSM 799)
• Candida albicans (ATCC 10231 / DSM 1386)

NOTE Additional microorganisms may be used. For internal development purpose and pre-evaluation of

microorganism contamination reduction in clothes washing machines, a protocol with risk class 1 test

microorganisms may be performed as described in Annex A.
5.2.2 Culture media and solutions
5.2.2.1 Culture media

All media and solutions shall be of microbiology grade and sterilized appropriately prior to

use. It is recommended to use commercially available and/or water-free dry materials for the

culture media. The specifications in the following clauses refer to water-free products.

5.2.2.1.1 Tryptone Soy Agar (TSA)
The composition of Tryptone Soy Agar (TSA) shall be according to Table 1.
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IEC PAS 62958:2015 © IEC 2015 – 11 –
Table 1 – Composition of Tryptone Soy Agar (TSA)
Description Specification
Casein peptone (pancreatic digest) 15,0 g/l
Soy peptone (papaic digest) 5,0 g/l
Sodium chloride 5,0 g/l
Agar 15,0 g/l
Final pH
7,3 ± 0,2
5.2.2.1.2 Sabouraud Dextrose Agar with Chloramphenicol

The composition of Sabouraud Dextrose Agar with Chloramphenicol shall be according to

Table 2.
Table 2 – Composition of Sabouraud Dextrose Agar
with Chloramphenicol
Description Specification
Pancreatic digest of casein 5,0 g/l
Peptic digest of animal tissue 5,0 g/l
Dextrose monohydrate 40,0 g/l
Chloramphenicol 0,05 g/l
Agar 15,0 g/l
Final pH
5,6 ± 0,2
5.2.2.1.3 Cetrimide Agar
The composition of Cetrimide Agar shall be according to Table 3.
Table 3 – Composition of Cetrimide Agar
Description Specification
Pancreatic digest of gelatine 20,0 g/l
Magnesium chloride 1,4 g/l
Potassium sulphate 10,0 g/l
Glycerine 10,0 ml/l
Cetrimide 0,2 g/l
Agar 14,0 g/l
Final pH
7,1 ± 0,2
5.2.2.1.4 Baird-Parker Agar
The composition of Baird-Parker Agar shall be according to Table 4.
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– 12 – IEC PAS 62958:2015 © IEC 2015
Table 4 – Composition of Baird-Parker Agar
Description Specification
Casein peptone (pancreatic digest) 10,0 g/l
Beef extract 5,0 g/l
Yeast extract 1,0 g/l
Lithium chloride 5,0 g/l
Glycine 12,0 g/l
Sodium pyruvate 10,0 g/l
Agar 20,0 g/l
Sodium tellurite 0,1 g/l
Egg yolk emulsion 50,0 ml/l
Final pH 6,8 ± 0,2
5.2.2.1.5 Malt Extract Agar (MEA)
The composition of Malt Extract Agar (MEA) shall be according to Table 5.
Table 5 – Composition of Malt Extract Agar (MEA)
Description Specification
Malt extract 30,0 g/l
Soy-peptone, which is digested with papain 3,0 g/l
from soybeans
Agar 15,0 g/l
Final pH
5,6 ± 0,2
5.2.2.1.6 Tryptone Soy Broth (TSB)
The composition of Tryptone Soy Broth (TSB) shall be according to Table 6.
Table 6 – Composition of Tryptone Soy Broth (TSB)
Description Specification
Tryptone, pancreatic digest of casein 17,0 g/l
Soy peptone, papaic digest of soybean meal 3,0 g/l
Sodium chloride (NaCl) 5,0 g/l
Dipotassium hygrogen phosphate (K HPO ) 2,5 g/l
2 4
Glucose 2,5 g/l
Final pH
7,3 ± 0,2
5.2.2.2 Water for culture media and solutions

Bi-distilled or demineralised water can be used. However, demineralised water shall be

sterilised prior to use.
5.2.2.3 Diluting agent
The composition of the diluting agent shall be as in Table 7.
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IEC PAS 62958:2015 © IEC 2015 – 13 –
Table 7 – Composition of diluting agent
Description Specification
Tryptone, pancreatic digest of casein 1,0 g/l
Sodium chloride (NaCl) 8,5 g/l
Polysorbate 80 (0,05 %)
Final pH 7,0 ± 0,2
5.2.2.4 Neutralisation solution

For microorganisms growth neutralisation solution shall be used in combination with

appropriate nutrition media.
The composition of a recommended neutralisation solution is given in Table 8.
Table 8 – Composition of recommended neutralisation solution
Description Specification
Polysorbate 80 30,0 g/l
Lecithine 3,0 g/l
L-histidine 1,0 g/l
Natriumthiosulphate 5,0 g/l

Other neutralisation solutions may be used if it can be shown that they give the same results.

5.2.3 Detergent
5.2.3.1 General
The detergent shall be IEC A* base powder according to IEC 60456.
5.2.3.2 Pre test fo
...

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