IEC 60721-2-1:2013

IEC 60721-2-1 ®
Edition 2.0 2013-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Classification of environmental conditions –
Part 2-1: Environmental conditions appearing in nature – Temperature and
humidity
Classification des conditions d'environnement –
Partie 2-1: Conditions d'environnement présentes dans la nature – Température
et humidité
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IEC 60721-2-1 ®
Edition 2.0 2013-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Classification of environmental conditions –

Part 2-1: Environmental conditions appearing in nature – Temperature and

humidity
Classification des conditions d'environnement –

Partie 2-1: Conditions d'environnement présentes dans la nature – Température

et humidité
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX L
ICS 19.040 ISBN 978-2-83220-899-1

– 2 – 60721-2-1 © IEC:2013
CONTENTS
FOREWORD . 3
INTRODUCTION . 5
1 Scope . 6
2 Normative references . 6
3 Terms and definitions, abbreviations, quantities and units . 6
4 General information regarding data collection and analysis . 6
5 General validation process . 7
6 Open air climates . 8
6.1 General . 8
6.2 Environmental parameters . 8
6.3 Identification of statistical open-air climates . 8
6.4 Map of open-air climates . 9
Annex A (informative) Map of climate classification . 10
Bibliography . 11

Figure A.1 – Climate classifications . 10

Table 1 – Climate classifications . 7
Table 2 – Climate classification definitions . 7
Table 3 – Classification of climates by extreme daily mean values . 8
Table 4 – Classification of climates by annual extreme values . 8
Table 5 – Classification of climates by absolute extreme value . 9

60721-2-1 © IEC:2013 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
CLASSIFICATION OF ENVIRONMENTAL CONDITIONS –

Part 2-1: Environmental conditions appearing in nature –
Temperature and humidity
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
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
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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.
International Standard IEC 60721-2-1 has been prepared by IEC technical committee 104:
Environmental conditions, classification and methods of test.
This second edition cancels and replaces the first edition published in 1982 and its
amendment 1 (1987), and constitutes a technical revision.
The main changes with respect to the previous edition are in the definitions of climate types.

– 4 – 60721-2-1 © IEC:2013
The text of this standard is based on the following documents:
FDIS Report on voting
104/610/FDIS 104/617/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all the parts in the IEC 60068 series, under the general title Classification of
environmental conditions, can be found on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
60721-2-1 © IEC:2013 – 5 –
INTRODUCTION
Electrotechnical products are used in almost all areas of the world under varying climatic
conditions and have to meet the stresses imposed by these climatic conditions with the
necessary reliability. A detailed knowledge of the climatic conditions to which the product will
be subjected is necessary in the design stage to ensure that reliability is met.
Data on open-air temperature and humidity have been collected and statistically processed for
many years throughout the world. Such data is represented in this part of IEC 60721.
In addition to open-air temperature, temperature stresses on a product depend on a number
of other environmental parameters, for example solar radiation, air velocity or heating from
adjacent equipment.
The effects of humidity depend on temperature, temperature changes and impurities in the
humid air.
In many cases the extremes of temperature and humidity are of great importance even if they
occur for a short time. In other cases, where large time constants for heat or water
penetration are involved, the mean values of temperature and humidity over a certain period
may be more important.
It has therefore been considered useful to present here both the mean value over many years
of the annual extreme values of temperature and humidity, which will occur only for short
periods (a few hours), and the mean value over many years of the extreme daily mean values
of temperature and humidity, which will occur for longer periods.
In order to cover cases where rare events need to be taken into account, the absolute
extreme temperatures and humidity levels, observed over a period of many years, have also
been presented.
– 6 – 60721-2-1 © IEC:2013
CLASSIFICATION OF ENVIRONMENTAL CONDITIONS –

Part 2-1: Environmental conditions appearing in nature –
Temperature and humidity
1 Scope
This part of IEC 60721 presents classifications of open-air climates in terms of temperature
and humidity. It is intended to be used as part of the background material when selecting
appropriate temperature and humidity severities for product testing and application.
The climates cover all areas of the world, excluding the central Antarctic and high altitudes
(above 5 000 m).
This presentation may be used as background material when issuing climatic environmental
classes for product applications.
This standard defines a limited number of open-air climate classifications, in terms of
temperature and humidity, which represent the conditions most frequently met by products
while being transported, stored, installed and used.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60721-1:1990, Classification of environmental conditions – Part 1: Environmental
parameters and their severities
IEC/TR 62130, Climatic field data including validation
MIL210 Extreme and Percentile Environmental Reference Tables (ExPERT) database
(Version 1.0 July 1997)
PEARCE, E.A., and SMITH, C.G., The Hutchinson World Weather Guide by Helicon
Publishing Ltd (ISBN 1-85986-342-6, 2000)
KOTTEK, M., GRIESER, J., BECK, C., RUDOLF, B. and RUBEL, F., World Map of the
Köppen-Geiger climate classification updated: 2006, Meteorol. Z., 15, 259-263
3 Terms and definitions, abbreviations, quantities and units
Terms and definitions are defined, in context, throughout the present standard.
4 General information regarding data collection and analysis
Climatic data was collected and validated in IEC/TR 62130. The two principle data sources
were the MIL210 ExPERT and The Hutchinson World Weather Guide.

60721-2-1 © IEC:2013 – 7 –
The MIL210 ExPERT database contained daily temperature and humidity data that were
collected during 1973–1992. Measurement locations were mainly from airports and major
cities worldwide. The total number of sites/stations was 289. The uncertainty of
measurements was not documented and the data source contained no data about highest
temperature with relative humidity (RH) >95 %.
The Hutchinson World Weather Guide used data provided by the British Meteorological Office.
The length of the measured period differed from location to location varying from 2 years to
105 years. Detailed locations and uncertainty of measurement were not documented in the
book and there were no data relating to highest temperature with RH >95 %.
As stated in IEC 60721-1, other references were used for comparison purposes of both the
climatic classes and the map of climatic classes.
5 General validation process
The high level process for validating the data used to update this standard is given in Figure 4
of IEC 60721-1:1990.
The process has three main phases:
– identify and collect data;
– analyse data and compare to current values;
– update data as appropriate.
As a result of the data collection and analysis, open-air climates have been simplified and
revised as shown in Table 1.
Table 1 – Climate classifications
New Previous IEC 60721-2-1 classes when combined
classifications
Tropical Warm damp and Warm damp, Equable
Arid Mild warm dry and Extremely warm dry
Temperate Warm temperate and Warm dry
Cold Cold temperate
Polar Extremely cold and Cold
Further details regarding each climate classification are provided in Table 2.
Table 2 – Climate classification definitions
Climate Definition
classification
Tropical Tropical rain climates where the mean temperature of the coldest month exceeds +18 °C
Arid Arid climates with rainfall less than 500 mm
Temperate rain climates where the mean temperature of the coldest month is between –3 °C
Temperate
and +18 °C
Boreal forest and snow climates. Mean temperature of the warmest month exceeding 10 °C
Cold
and a mean temperature of the coldest month below –3 °C
Polar Cold snow climates. Mean temperature of the warmest month below 10 °C

– 8 – 60721-2-1 © IEC:2013
6 Open air climates
6.1 General
The different open-air temperature and humidity conditions of the world are presented by
defining a limited number of climate classifications, hereinafter referred to as "open-air
climates". For the application of a product in a geographical area, the open-air temperature
and humidity can be taken from climatic data for that area. This helps ensure that the product
is designed for application in this climate.
6.2 Environmental parameters
For this standard, open-air climates are defined by the air temperature and relative humidity
values. The relative humidity at a certain temperature is defined as the ratio between the
actual vapour pressure and the saturation vapour pressure at the same temperature. The
absolute air humidity is defined as the mass of water vapour per cubic meter of air.
The annual extreme value of low temperature normally occurs for a period of approximately
10 h, while the annual extreme value of high temperature normally occurs for approximately
5 h.
6.3 Identification of statistical open-air climates
The following tables present the climate classifications defined as open-air climates.
In Table 3 the mean value of the annual extreme daily mean values of temperature and
humidity is given for each climate classification. Table 4 provides the mean value of annual
extreme values of temperature and humidity is given for each classification. In Table 5, the
absolute extreme value of temperature and humidity is given for each climate classification.
Table 3 – Classification of climates by extreme daily mean values
Mean value of the annual extreme daily mean values of temperature and humidity
Climate
Low temperature High temperature Highest absolute humidity
classification
–3
°C °C g × m
Tropical 10 40 30
Arid 0 45 25
Temperate –15 40 25
Cold –25 35 25
Polar –40 25 15
Table 4 – Classification of climates by annual extreme values
Mean value of the annual extreme values of temperature and humidity
Climate
Low temperature High temperature Highest absolute humidi
...