IEC 60721-3-1:2018

Classification of environmental conditions - Part 3-1: Classification of groups of environmental parameters and their severities - Storage

IEC 60721-3-1:2018 classifies the groups of environmental parameters and their severities to which products together with their packaging, if any, are subjected when stored. The environmental conditions specified in this document are limited to those which can directly affect the products or their ultimate performance. Only environmental conditions as such are considered. No special description of the effects of these conditions on the products is given. Environmental conditions directly related to fire or explosions are not included. Conditions of stationary use, portable and non-stationary use, use in vehicles and ships, and conditions of transportation are given in other subparts of the IEC 60721-3 series. This third edition cancels and replaces the second edition, published in 1997, and constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition:
a. Clause 3: reworded and simplified.
b. Clause 4: reworded and simplified.
c. Clause 5: Annex C has been incorporated in Clause 5.
d. 5.2: all existing climate classes have been replaced by completely new classes. The new classes are divided into 3 groups. The reason for the new classes is the latest revision of IEC 60721-2-1 which incorporated new climate types.
e. 5.3: new classes for solar radiation and snow load.
f. 5.6: all existing classes for mechanically active substances have been replaced by completely new classes.
g. 5.7: all existing classes for mechanical conditions have been replaced by completely new classes.
h. Table 1: new climatic classes with new severities.
i. Table 2: new classes for solar radiation and snow load.
j. Table 5 new mechanically active substances classes.
k. Table 6: new mechanical conditions classes.
The content of the corrigendum 1 (2024-10) has been included in this copy.

Classification des conditions d'environnement - Partie 3-1: Classification des groupements des agents d’environnement et de leurs sévérités - Stockage

L’IEC 60721-3-1:2018 classifie les groupements d’agents d’environnement et leurs sévérités auxquels des produits, éventuellement emballés, sont soumis lorsqu’ils sont stockés. Les conditions d’environnement spécifiées dans le présent document se limitent à celles qui sont susceptibles d’influencer directement les produits ou leur comportement ultérieur. Seules de telles conditions sont prises en considération, aucune description particulière de leurs effets sur les produits n’étant donnée. Les conditions d’environnement directement liées aux risques d’incendie ou d’explosion ne sont pas incluses. Les conditions pour une utilisation à poste fixe ou en déplacement, à bord de véhicules ou de navires, et les conditions de transport sont données dans d’autres sous-parties de la série IEC 60721-3. Cette troisième édition annule et remplace la deuxième édition, parue en 1997. Elle constitue une révision technique. Cette édition inclut les modifications techniques majeures suivantes par rapport à l’édition précédente:
a. Article 3: reformulé et simplifié.
b. Article 4: reformulé et simplifié.
c. Article 5: l’Annexe C a été intégrée dans l’Article 5.
d. 5.2: toutes les catégories climatiques existantes ont été remplacées par des catégories complètement nouvelles. Les nouvelles catégories ont été divisées en 3 groupes. Ces catégories nouvelles ont été créées en raison de l’intégration de nouveaux types de climats dans la dernière révision de l’IEC 60721-2-1,
e. 5.3: nouvelles catégories pour le rayonnement solaire et la charge de neige.
f. 5.6: toutes les catégories existantes de substances mécaniquement actives ont été remplacées par des catégories complètement nouvelles.
g. 5.7: toutes les catégories de conditions mécaniques existantes ont été remplacées par des catégories complètement nouvelles.
h. Tableau 1: nouvelles catégories climatiques avec de nouvelles sévérités.
i. Tableau 2: nouvelles catégories pour le rayonnement solaire et la charge de neige.
j. Tableau 5: nouvelles catégories de substances mécaniquement actives.
k. Tableau 6: nouvelles catégories de conditions mécaniques.
Le contenu du corrigendum 1 (2024-10) a été pris en considération dans cet exemplaire.

General Information

• Status: Published
• Publication Date: 22-Feb-2018
• ICS: 19.040 - Environmental testing
• Technical Committee: TC 104 - Environmental conditions, classification and methods of test
• Drafting Committee: MT 19 - TC 104/MT 19
• Current Stage: PPUB - Publication issued
• Start Date: 23-Feb-2018
• Completion Date: 23-Feb-2018

Relations

• Corrected By: IEC 60721-3-1:2018/COR1:2024 - Corrigendum 1 - Classification of environmental conditions - Part 3-1: Classification of groups of environmental parameters and their severities - Storage
• Effective Date: 27-Sep-2024
• Revises: IEC 60721-3-1:1997 - Classification of environmental conditions - Part 3 Classification of groups of environmental parameters and their severities - Section 1: Storage
• Effective Date: 05-Sep-2023

Overview

IEC 60721-3-1:2018 - Classification of environmental conditions - Part 3-1: Storage - defines how to classify the groups of environmental parameters and their severities that products (together with their packaging, if any) are exposed to during storage. This edition (3.0, 2018) is a technical revision of the 1997 edition and incorporates Corrigendum 1 (2024‑10). It focuses only on environmental conditions that can directly affect product performance during storage and excludes fire/explosion, ionizing radiation and offshore locations. The standard provides a common vocabulary and environmental classification framework for storage-related design, testing and procurement.

Key topics and technical content

• Classification of environmental parameter groups and severity levels for storage scenarios.
• Main parameter groups covered:
  • Climatic conditions (K) - completely new class structure (three groups) aligned with IEC 60721-2-1 revisions.
  • Special climatic conditions (Z) - includes new classes for solar radiation and snow load.
  • Biological conditions (B).
  • Chemically active substances (C) - updated classes; Annex A provides informative details.
  • Mechanically active substances (S) - fully revised classes.
  • Mechanical conditions (M) - new mechanical condition classes and shock/vibration considerations.
• Tables and annexes: updated Table 1 (climatic classes), Table 2 (special climatic), Table 5 (mechanically active substances), Table 6 (mechanical conditions), plus sets of class combinations and explanatory annexes.
• General rules: severities are maximum/limit values with a low probability of being exceeded; combinations of parameters may increase risk; transfer during storage and handling are outside scope.

Practical applications

• Use IEC 60721-3-1:2018 to define realistic storage environment requirements for products and packaging.
• Create procurement and specification language that references standardized environmental classes and severities.
• Guide laboratory and field environmental testing and acceptance criteria for stored goods.
• Support packaging design, warehouse planning and logistics by identifying relevant climatic, chemical and mechanical stressors.
• Feed into reliability assessments, risk analyses and maintenance planning by clarifying environmental exposures during storage.

Who should use this standard

• Product designers and engineers (electrical/electronic equipment)
• Reliability and test engineers
• Packaging and supply chain professionals
• Test laboratories and conformity assessment bodies
• Procurement and warehouse managers specifying storage conditions

Related standards

• IEC 60721-1 (environmental parameters and severities)
• IEC 60721-2-1 (temperature and humidity climate types)
• Other IEC 60721-3 parts (transportation, stationary use at protected/unprotected locations)

Using IEC 60721-3-1:2018 helps organizations standardize how they classify and communicate storage environmental conditions, enabling clearer specifications, better testing, and improved product protection during storage.

Standards Content (Sample)

IEC 60721-3-1 ®
Edition 3.0 2018-02
REDLINE VERSION
INTERNATIONAL
STANDARD
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Classification of environmental conditions –
Part 3-1: Classification of groups of environmental parameters and their
severities – Storage
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IEC 60721-3-1 ®
Edition 3.0 2018-02
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
Classification of environmental conditions –

Part 3-1: Classification of groups of environmental parameters and their

severities – Storage
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 19.040 ISBN 978-2-8322-5449-3

– 2 – IEC 60721-3-1:2018 RLV © IEC 2018
CONTENTS
FOREWORD . 3
1 Scope and object . 5
2 Normative references . 5
3 Terms and definitions. 5
4 General . 7
5 Classification of groups of environmental parameters and their severities . 7
5.1 General . 8
5.2 Climatic conditions (K) . 8
5.3 Special climatic conditions (Z) . 12
5.4 Biological conditions (B) . 13
5.5 Chemically active substances (C) . 14
5.6 Mechanically active substances (S) . 15
5.7 Mechanical conditions (M) . 15
Sets of environmental condition class combinations .
Annex Summary of conditions covered by the classes .
Annex Summary of conditions covered by the sets of class combinations .
Annex Explanation of the environmental conditions in tropical areas as specified
in classes 1K10 and 1K11 .
Annex A (informative) Chemically active substances . 25
Bibliography . 26

Figure Model shock response spectra(first order maximax shock response spectra) .

Table 1 – Classification of climatic conditions . 10
Table 2 – Classification of special climatic conditions . 13
Table 3 – Classification of biological conditions . 14
Table 4 – Classification of chemically active substances . 15
Table 5 – Classification of mechanically active substances . 16
Table 6 − Classification of mechanical conditions . 17
Table 7 Sets of environmental class combinations .

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
CLASSIFICATION OF ENVIRONMENTAL CONDITIONS –

Part 3-1: Classification of groups of environmental
parameters and their severities – Storage

FOREWORD
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– 4 – IEC 60721-3-1:2018 RLV © IEC 2018
International Standard IEC 60721-3-1 has been prepared by IEC technical committee 104:
Environmental conditions, classification, and methods of test.
This third edition cancels and replaces the second edition, published in 1997, and constitutes a
technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) Clause 3: reworded and simplified.
b) Clause 4: reworded and simplified.
c) Clause 5: Annex C has been incorporated in Clause 5.
d) 5.2: all existing climate classes have been replaced by completely new classes. The new
classes are divided into 3 groups. The reason for the new classes is the latest revision of
IEC 60721-2-1 which incorporated new climate types.
e) 5.3: new classes for solar radiation and snow load.
f) 5.6: all existing classes for mechanically active substances have been replaced by
completely new classes.
g) 5.7: all existing classes for mechanical conditions have been replaced by completely new
classes.
h) Table 1: new climatic classes with new severities.
i) Table 2: new classes for solar radiation and snow load.
j) Table 5 new mechanically active substances classes.
k) Table 6: new mechanical conditions classes.
The text of this International Standard is based on the following documents:
FDIS Report on voting
104/772/FDIS 104/782/RVD
Full information on the voting for the approval of this International Standard can be found in the
report on voting indicated in the above table.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts in the IEC 60721 series, published under the general title Classification of
environmental conditions, can be found on the IEC website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document 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 publication using a colour printer.

CLASSIFICATION OF ENVIRONMENTAL CONDITIONS –

Part 3-1: Classification of groups of environmental
parameters and their severities – Storage

1 Scope and object
This part of IEC 60721 classifies the groups of environmental parameters and their severities
to which products together with their packaging, if any, are subjected when stored.
The environmental conditions specified in this document are limited to those which may can
directly affect the products or their ultimate performance. Only environmental conditions as
such are considered. No special description of the effects of these conditions on the products
is given.
Transfer during storage is not included in the classification.
Environmental conditions directly related to fire or explosions and conditions related to ionizing
radiation are excluded are not included. Any other unforeseen incidents are also excluded.
The possibility of their occurrence should be taken into account in special cases. Offshore
locations are not included.
Conditions of stationary use, portable and non-stationary use, use in vehicles and ships, and
conditions of transportation are given in other subparts of the IEC 60721-3 series.
The object of this document is to classify environmental parameters and their severities to
which a product may can be exposed during storage. Transfer and handling during storage and
transport are addressed in IEC 60721-3-2.
A limited number of classes of environmental conditions is given, covering a broad field of
application. The user of this standard should select the lowest classification necessary for
covering the conditions of intended storage.
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.
IEC 60721-1, Classification of environmental conditions − Part 1: Environmental parameters
and their severities
IEC 721-1: 1990, Classification of environmental conditions − Part 1: Environmental
parameters and their severities
Amendment 1 (1992)
IEC 721-2-1: 1982, Classification of environmental conditions − Part 2: Environmental
conditions appearing in nature − Temperature and humidity
Amendment 1 (1987)
– 6 – IEC 60721-3-1:2018 RLV © IEC 2018
IEC 721-3-0: 1984, Classification of environmental conditions − Part 3: Classification of groups
of environmental parameters and their severities − Introduction
Amendment 1 (1987)
IEC 60721-3-2: 1997, Classification of environmental conditions − Part 3: Classification of
environmental parameters and their severities − Section 2: Transportation
IEC 721-3-3: 1994, Classification of environmental conditions − Part 3: Classification of
environmental parameters and their severities − Section 3: Stationary use at weatherprotected
locations
IEC 721-3-4: 1995, Classification of environmental conditions − Part 3: Classification of
environmental parameters and their severities − Section 4: Stationary use at non-
weatherprotected locations
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60721-1 and the
following apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
enclosed location
location or structure that is covered on all sides in such a manner as to provide a degree of
protection
3.2
non-weather-protected location
location at which the product is not protected from direct weather influences meteorological
conditions
3.3
open-air location
location that is unenclosed that provides no protection from meteorological conditions
3.4
storage
The product is placed at a certain site for long periods, but not intended for use during these
periods
a product kept in a place when not being operated
3.5
sheltered location
location or structure that provides limited protection from direct meteorological conditions such
as rain and wind
3.6
weather-protected location
location at which the product is protected from weather influences meteorological conditions
− totally weatherprotected location: direct weather influences are totally excluded;
(enclosed location)
− partially weatherprotected location: direct weather influences are not completely
(sheltered location) excluded.
4 General
For further general guidance, see IEC 721-3-0.
The severities specified are those which will have a low probability of being exceeded. All
specified values are maximum or limit values. These values may be reached, but do not occur
permanently. Depending on the local situation, there may be different frequencies of
occurrence related to a certain period of time. Such frequencies of occurrence have not been
included in this standard, but should be considered for any environmental parameter.
They should additionally be specified, if applicable. Information on the duration and frequency
of occurrence is given, as clause 6, in amendment 1 to IEC 721-3-0.
Attention is drawn to the fact that combinations of the environmental parameters given may
increase the effect on a product. This applies especially to the presence of high relative
humidity in addition to biological conditions, or to the presence of chemically or mechanically
active substances.
A product may be subjected to a range of environmental conditions during its lifetime. These
conditions have been separated into classes described in IEC 60721-3-0. The classes given
may be used for defining the maximum short-term environmental stresses of a product.
However, they do not provide information regarding the long-term or total lifetime
environmental stresses a product may experience. This means that no reliability or lifetime
assessment is possible based on these classes alone. Refer to IEC 60721-2 (all parts) and
applicable technical reports (IEC TR 62130 and IEC TR 62131-5) for further information on
actual environmental conditions.
A product will be simultaneously exposed to a number of environmental parameters. For
example, solar radiation and temperature, temperature and humidity, as well as vibration and
temperature change. Combinations of the environmental parameters given may increase the
effect on a product. Therefore, combined conditions should be considered in the design and
evaluation of a product.
Products should be designed to survive and operate in different environments. Basically, they
will be affected by the environmental influences in two ways:
• by the effects of short-term extreme environmental conditions which may directly cause
malfunction or destroy the product;
• by the effect of long-term subjection to non-extreme environmental stresses which may
slowly degrade the product and finally cause malfunction or destruction of the product.
Short-term extreme environmental conditions may occur at any time in the product's life. A
product may be unaffected by an extreme condition when it is new but fail when it is subjected
to the same condition after being used for a long period of time due to the effect of ageing. The
order in which the environmental conditions are applied may affect the results of an evaluation.
It is important for the product specification, when referring to a certain class in
IEC 60721-3 (all parts), to define whether the product is required to be capable of operating or
only to survive without permanent damage when being exposed to the conditions described by
the class.
The environmental classes may be used as a basis for the selection of design and test
severities with respect to the consequence of failure. Information contained in
IEC 60721-3 (all parts) may be used as a means to help establish expected requirements for
use, storage, transportation, etc., and in the development of relevant specifications. The

– 8 – IEC 60721-3-1:2018 RLV © IEC 2018
selected severities used for testing should attempt to produce the effects of the actual
environment.
EXAMPLE 1 A high temperature test on a heat dissipating product is designed to simulate the thermal effect of
subjecting a product to conditions of high air temperature, solar radiation and other possible heat sources
dependent on the application;
EXAMPLE 2 In a mechanical shock test, the product can be subjected to mechanical shocks of simple pulse
shapes (e.g., half-sine), while the actual conditions cannot be described by such simple pulses.
It is recognized that extreme or special environmental conditions may exist which require
consideration of severities that are not addressed by this document. Specifications for products
to be stored under such special conditions are a matter of negotiation between supplier and
user.
5 Classification of groups of environmental parameters and their severities
5.1 General
A number of classes for climatic conditions (K), special climatic conditions (Z), biological
conditions (B), chemically active substances (C), mechanically active substances (S), and
mechanical conditions (M) are specified.
This classification allows a number of possible combinations of environmental conditions which
bear upon products wherever stored. It represents the real situation concerning worldwide
conditions of storage, for example, due to local influences of open-air climate, etc.
For certain environmental parameters, it has not yet been possible to specify quantitative
severities.
For a given location or product, reference should be made to the total set of classes, for
example:
1K2/1Z1/1B1/1C2/1S1/1M3
1K21/1Z1/1B1/1C2/1S10/1M10
See also clause 6.
Annex A contains a summary of the conditions covered by each class.
5.2 Climatic conditions (K)
NOTE All old classes have been replaced with new classes. The new classes were chosen to reflect 3 different
storage condition: enclosed, sheltered and open-air locations.
The climatic conditions specified for classes 1K1 to 1K11 1K20 to 1K29 refer to the conditions
of storage of products. These conditions have been experienced worldwide over a long period
of time taking into account all the parameters that can influence them such as external (open-
air) climatic conditions, type of building construction, temperature/humidity controlling systems,
and internal conditions, for example heat dissipation from other equipment and presence of
humans, etc. The conditions should cover all normal cases, but not exceptional events.
Climatic conditions in tropical areas, as specified in classes 1K10 and 1K11, are explained in
annex C.
When selecting appropriate classes, attention should be paid to the fact that the climatic
conditions inside buildings may depend on the outside (open-air) conditions, especially air
temperature and solar radiation, and the type of building construction. Walls with good thermal

insulation or high thermal capacity can consistently smooth the peaks of outside air
temperature variations between day and night, or, exceptionally, those produced over a longer
period of time. Walls with poor thermal insulation or low thermal capacity cannot have this
effect, and peaks can be magnified due to the effect of solar radiation during the day, and to
the effect of building radiation at night. The effect of solar radiation can be increased by either
heat-trap or greenhouse effects.
At non-weather-protected locations, the influence from special climatic conditions constitutes a
more significant share of the effects bearing upon a product and its functional parts than at
weatherprotected locations. The effects of temperature change, solar radiation, precipitation,
air velocity and wind-chill should be particularly considered in this respect.
The severity of these effects may be influenced, for example by constructional details (type and
thickness of material, colour of surfaces, sealing or breathing of casings, etc.), and by storage
details (selection of storage site, consideration of degrees of exposure to prevailing wind and
weather, etc.).
Enclosed storage
1K20 applies to fully air conditioned enclosed storage locations. Air temperature and
humidity control is used continuously to maintain the required conditions.
1K21 applies to enclosed storage locations with limited temperature control and no humidity
control.
1K22 applies to enclosed storage locations having no temperature or humidity control.
Sheltered storage
1K23 applies to sheltered storage locations in tropical, arid, temperate, and cold climatic
classification with the thermal effects from solar radiation encompassed in the
temperature.
1K24 applies to sheltered storage locations in the polar climate type with the thermal effects
from solar radiation encompassed in the temperature.
Open-air storage
1K25 applies to open-air storage in the tropical climatic classification.
1K26 applies to open-air storage in the arid and temperate climatic classifications.
1K27 applies to open-air storage in the cold and polar climatic classifications.
These conditions are specified in Table 1.

– 10 – IEC 60721-3-1:2018 RLV © IEC 2018
Table 1 – Classification of climatic conditions
10)
Class
Environmental
parameter Unit 1K1 1K2 1K3 1K4 1K5 1K6 1K7 1K8 1K9 1K10 1K11
11) 11)
6)
a) Low air °C +20 +5 +5
−5 −25 −40 −55 −20 −33 −65 −20
temperature
6)
°C +25 +40 +45 +55 +70 +70 +35 +40 +55 +40 +55
b) High air
temperature
c) Low relative % 20 5 5 10 10 10 20 15 4 30 4
1)
humidity
d) High relative % 75 85 95 100 100 100 100 100 100 100 100
1)
humidity
e) Low absolute g/m 4 1 1 0,5 0,1 0,02 0,9 0,26 0,003 6 0,9
1)
humidity
f) High absolute g/m 15 25 29 29 35 35 22 25 36 36 27
1)
humidity
g) Rate of °C/min 0,1 0,5 0,5 0,5 1,0 1,0 0,5 0,5 0,5 0,5 0,5
change of
2)
temperature
kPa 70 70 70 70 70 70 70 70 70 70 70
h) Low air
3)
pressure
i) High air kPa 106 106 106 106 106 106 106 106 106 106 106
3)
pressure
j) Solar W/m 500 700 700 1120 1120 1120 1120 1120 1120 1120 1120
radiation
7) 7) 7) 7) 7) 7) 7) 7) 7) 7)
k) Heat None No
radiation
8) 8) 8)
8) 8) 8) 8) 8) 8)
l) Movement of m/s 0,5 1,0 1,0 1,0 5,0 5,0 50
surrounding air
4)
m) Condensation None No No Yes Yes Yes Yes Yes Yes Yes Yes Yes
9) 9) 9)
n) Precipitation None No No No Yes Yes Yes Yes Yes Yes Yes Yes
(rain, snow,
hail, etc.)
o) Rain intensity None None None 15 15
mm/min None None None 6 6 15
9) 9) 9)
p) Low rain °C None None None
None None None +5 +5 +5 +5 +5
9) 9) 9)
5)
temperature
7) 7) 7) 7) 7) 7) 7) 7) 7)
q) Water from None No No
sources other
than rain
r) Formation of None No No Yes Yes Yes Yes Yes Yes Yes No Yes
ice and frost
Enclosed Sheltered Open-air
Environmental Parameter
Unit 1K20 1K21 1K22 1K23 1K24 1K25 1K26 1K27
6)
a) Low air temperature
°C +20 +5 +5 -50
−25 −45 −50 −20
6) 11) 11) 11)
b) High air temperature
°C +25 +40 +55 +70 +70 +45 +50 +45
1)
c) Low relative humidity
% 20 5 10 4 4 30 4 10
1)
d) High relative humidity
% 75 85 100 100 100 100 100 100
1)
e) Low absolute humidity
g/m 4 1 0,5 0,2 0,003 6 0,1 0,003
1)
f) High absolute humidity
g/m 15 25 29 35 20 35 30 25
g) Rate of change of
°C/min 0,1 0,5 0,5 1,0 1,0 1,0 1,0 1,0
2)
temperature
3)
h) Low air pressure
kPa 70 70 70 70 70 70 70 70
3)
i) High air pressure
kPa 106 106 106 106 106 106 106 106
j) Solar radiation
W/m 7) 7) 10) 10) 10) 1090 1090 1090
Not
No No No No
7) 7) 7) 7)
k) Heat radiation
specified
8) 8)
l) Movement of surrounding air
8)
m/s 0,5 1,0 1,0 5,0 5,0
8) 8)
4)
Not
No No Yes Yes Yes Yes Yes Yes
m) Condensation
specified
n) Precipitation (rain, snow,
Not 9) 9)
No No No Yes Yes Yes
Yes Yes
specified
hail, etc.)
9) 9)
o) Rain intensity
mm/min
None None None None None 15 15 15
p) Driving rain
m/s None None None None None 18 18 18
q Snow load
8) 8)
kg/m None None None None None None
5)
9) 9)
r) Low rain temperature
°C None None None None None +5 +5 +5
s) Water from sources other
Dripping Dripping Dripping 12) 12) 12)
L/m²/min No No
Water Water Water
than rain
t) Formation of ice and frost
Not
No No Yes Yes Yes No Yes Yes
specified
(including freeze-thaw)
– 12 – IEC 60721-3-1:2018 RLV © IEC 2018
Notes to Table 1
1) The low and high relative humidities humidity levels are limited by the low and high absolute humidities, so
that, for example, for environmental parameters a) and c), or b) and d), the severities given in Table 1 do not
occur simultaneously.
2) Averaged over a period of time of 5 min.
3) The value of 70 kPa represents a limit for open-air conditions, normally at an altitude of 3 000 m. In some
geographical areas, open-air conditions may occur at higher altitudes. Conditions in mines are not
considered.
4) A cooling system based on non-assisted convection may be disturbed by adverse movement of surrounding
air.
5) This rain temperature should be considered together with high air temperature b) and solar radiation j). The
cooling effect of the rain has to be considered in connection with the surface temperature of the product.
6) These are air-conditioned locations with a tolerance of ±2 °C on stated temperature value.
7) Conditions occurring at the location concerned to be selected from Table 2.
8) If applicable, a special value may be selected from Table 2.
9) Applies only to wind-driven precipitation at partially weather protected sheltered locations.
10) The classes of climatic conditions of this standard include the classes of IEC 721-3-3 and IEC 721-3-4 as
follows:
1K1 covers 3K1 1K3 covers 3K5 1K5 covers 3K7 1K7 covers 4K1 1K9 covers 4K4 1K11 covers 4K6
1K2 covers 3K3 1K4 covers 3K6 1K6 covers 3K8 1K8 covers 4K2 1K10 covers 4K5
10) Thermal effect of solar radiation is included in the temperature.
11) Thermal effect of solar radiation is not included in the temperature.
12) Sources of water other than rain are encompassed by driving rain.

5.3 Special climatic conditions (Z)
As, in practice, Parameters such as heat radiation, movement of the surrounding air, solar
radiation, snow load, and water from sources other than rain may occur with any severity in
combination with any of the other climatic conditions. These special conditions are specified in
Table 2. In those cases, an assumption of the coincidence of events of increasing severity
would lead to unnecessary overdesign.

Table 2 – Classification of special climatic conditions
3)
Environmental parameter Class Unit Special condition Z
1Z1 None Negligible
k) Heat radiation
Conditions of heat radiation, e.g. in the
1Z2 None
vicinity of room heating systems
1Z3 m/s 30
1)
l) Movement of surrounding air
1Z4 m/s 50
1Z5 None Dripping water
2)
qs) Water from sources other than rain 1Z6 None Water jets
1Z7 None Water waves
1Z8 W/m 500
j) Solar radiation
1Z9 W/m 700
1Z10 kg/m 100 (single snow storm)
q) Snow load
1Z11 kg/m 240 (whole season)
1)
A cooling system based on non-assisted convection may be disturbed by adverse movement of surrounding
air.
2)
Underwater conditions are not considered.
3)
The classes of special climatic conditions of this standard include the classes of IEC 721-3-3 and IEC 721-3-
4 as follows:
1Z1 covers 3Z1 1Z3 covers 3Z6 and 4Z4 1Z5 covers 3Z7 1Z7 covers 4Z9
1Z2 covers 3Z2         1Z4 covers 4Z5          1Z6 covers 3Z10 and 4Z8

5.4 Biological conditions (B)
No quantitative severity has been specified for these conditions. The specified parameters of
Table 3 are typical, but may not be complete.
1B1 applies to storage locations with environmental controls in place to prevent the growth
of mould and physical controls to prevent attack by animals.
1B2 applies to storage locations without environmental or physical controls in place to
prevent mould growth or attacks by animals, except termites.
1B3 applies to locations where attacks by termites may occur.

– 14 – IEC 60721-3-1:2018 RLV © IEC 2018
Table 3 – Classification of biological conditions
1)
Unit Class
Environmental
parameter
1B1 1B2 1B3
None Negligible Presence of mould, fungus, etc.
a) Flora
b) Fauna None Negligible Presence of rodents and other animals
harmful to products
excluding termites including termites
1)
The classes of biological conditions of this standard include the classes of IEC 721-3-3 and IEC 721-3-4 as
follows:
1B1 covers 3B1 1B2 covers 3B2 and 4B1 1B3 covers 3B3 and 4B2

Class
Units
1B1 1B2 1B3
Presence of mould, fungus, etc.
None Negligible
Presence of rodents and other animals harmful to products
excluding termites including termites

5.5 Chemically active substances (C)
The contamination of the natural atmosphere is mainly caused by chemical emissions from
industrial activities, motor-driven vehicles, and heating systems. A further chemical influence is
caused by aerosols of sea and road salts. Contamination may affect the function and materials
of products. These conditions are specified in Table 4.
The values given in this classification have been taken from surveys over several years.
Maximum values are given, because direct influence of higher concentrations over a short
period of time normally causes more damage to material, which cannot regenerate. Mean
values are given additionally, because their influence may be important for the long-term effect
on internal parts of the products.
In practice, not all contaminants (parameters) classified in this standard are present
simultaneously. Furthermore, the probability is low that the concentrations of those
contaminants actually present increase simultaneously and homogeneously. Depending on the
local situation, there are often higher values of one contaminant only. The values specified for
class 1C1 will normally be experienced in rural areas and areas with low industrial activity. The
values specified for class 1C2 are experienced in urban areas. Therefore the severity of each
of these two classes shall be considered as the requirements for the combined effect of all
parameters stated. The severities of class 1C3, however, cannot be combined as the
requirement for the combined effect of all parameters stated in order to avoid any
uneconomical overdesign. For that class, it is possible to select only the severities of those
single parameters which might be relevant in the case of application. If single parameters of
class 1C3 are selected for the description of the chemically active substances present at a
location, the severities of class 1C2 are valid for all other parameters which are not specially
named.
NOTE − Chemically active liquids and chemically active solids other than sea salts or road salts are not considered
in this standard.
See Annex A for additional information.
1C1 applies to locations in rural and some urban areas, with low industrial activity and
moderate traffic. In winter, heating methods in concentrated urban areas may cause
increased contamination.
1C2 applies to locations with normal levels of contaminants as experienced in urban areas
with industrial activity scattered over the whole area, or with heavy traffic. Salt mist is
present in coastal areas.
1C3 applies to locations in the immediate vicinity of industrial sources, with chemical
emissions. Salt mist is present in coastal areas.
Table 4 – Classification of chemically active substances
5)
Class
1) 3)
Unit 1C1L 1C1 1C2 1C3
Environmental
parameter
Maximum Maximum Mean value Maximum Mean value Maximum
2) 2)
value value value value
4)
a) Salt mist to None No No Salt mist Yes Salt mist Yes
include Sea and
road salts
b) Sulphur dioxide mg/m 0,1 0,1 0,3 1,0 5,0 10
3 3
cm /m 0,037 0,037 0,11 0,37 1,85 3,7
c) Hydrogen mg/m 0,01 0,01 0,1 0,5 3,0 10
sulphide
3 3
cm /m 0,0071 0,0071 0,071 0,36 2,1 7,1
d) Chlorine mg/m 0,01 0,1 0,1 0,3 0,3 1
3 3
cm /m 0,0034 0,034 0,034 0,1 0,1 0,34
e) Hydrogen mg/m 0,01 0,1 0,1 0,5 1,0 5,0
chloride
3 3
cm /m 0,0066 0,066 0,066 0,33 0,66 3,3
f) Hydrogen mg/m 0,003 0,003 0,01 0,03 0,1 2,0
fluoride
3 3
cm /m 0,0036  0,0036 0,012 0,036 0,12 2,4
g) Ammonia mg/m 0,3 0,3 1,0 3,0 10 35
3 3
cm /m 0,42 0,42 1,4 4,2 14 49
h) Ozone mg/m 0,01 0,01 0,05 0,1 0,1 0,3
3 3
cm /m 0,005 0,005 0,025 0,05 0,05 0,15
i) Nitrogen oxides mg/m 0,1 0,1 0,5 1,0 3,0 9,0
(expressed in
3 3
cm /m 0,052 0,052 0,26 0,52 1,56 4,68
equivalent values
of nitrogen
dioxide)
1) 3 3 3
The values given in cm /m have been calculated from the values given in mg/m , and refer to a temperature
of 20 °C and a pressure of 101,3 kPa. The table uses round values.
2)
Mean values are expected long-term values. Maximum values are limit or peak values, occurring over a period
of time of not more than 30 min per day.
3)
It is not mandatory to consider class 1C3 as a requirement for the combined effect of all parameters stated. If
applicable, the values of single parameters may be selected from this class. In that case, the severities of class
1C2 are valid for all parameters not especially named.
4)
Salt mist may be present in sheltered locations of coastal areas.
5)
The classes of chemically active substances of this standard include the classes of IEC 721-3-3 and IEC 721-3-4
as follows:
1C1L covers 3C1L 1C1 covers 3C1 and 4C1 1C2 covers 3C2 and 4C2 1C3 covers 3C3 and 4C3

5.6 Mechanically active substances (S)
NOTE All old classes have been replaced with new classes. The new classes were chosen to reflect 3 different
storage conditions; enclosed, sheltered and open-air locations.
Dust and sand are classified together, as the effects caused by these environmental conditions
are similar.
– 16 – IEC 60721-3-1:2018 RLV © IEC 2018
1S10 applies to enclosed storage locations where precautions have been taken to minimize
the presence of dust and sand.
1S11 applies to enclosed storage locations not situated in proximity to dust or sand sources
and with no precautions to minimize the ingress of dust or sand. Such enclosed storage
locations could include shipping containers.
1S12 applies to enclosed storage locations in close proximity to sand or dust sources,
including urban area and with no precautions to minimize the ingress of dust or sand. It
also applies to exposed storage locations situated in areas not subject to natural dust
storms or significant industrial activity.
1S13 applies to exposed storage locations which may be exposed to wind-driven dust and
sand either due to natural conditions or due to industrial activity producing blown sand
or dust.
These conditions are specified in Table 5.
Table 5 – Classification of mechanically active substances
1)
Environmental parameter Unit Class
1S1 1S2 1S3 1S4
a) Sand mg/m None 30 300 1000
b) Dust (suspension)   mg/m 0,01 0,2 5,0 15
c) Dust (sedimentation) 0,4 1,5 20 40
mg/(m ⋅h)
1) The classes of mechanically active substances of this standard include the classes of IEC 721-3-3 and
IEC 721-3-4 as follows:
1S1 covers 3S1 1S1 covers 3S2 1S3 covers 4S2 1S4 covers 4S3

Class
Environmental parameter Unit
1S10 1S11 1S12 1S13
Setting (sedimentary) dust mg/(m ⋅d) None 6 Note 1 Note 2
Turbulent (suspended) dust None None 600 Note 2
mg/(m ⋅h)
Windblown dust mg/m 18
None None None
m/s 13
NOTE 1 Encompassed within turbulent (suspended) dust.
NOTE 2 Encompassed within windblown dust.

5.7 Mechanical conditions (M)
The conditions of vibration (sinusoidal) are classified by severity levels of acceleration, and
displacement amplitudes in high and low frequency range, respectively.
Random vibration is not considered in this standard. It may be included when sufficient
information is available.
Non-stationary vibration including shock is classified by using the first order undamped
maximax shock response spectrum (see figure 1).
NOTE All old classes have been replaced with new classes. The new classes based on IEC TR 62131-5.
Mechanical conditions relate to the levels of vibration and shock that may exist at a storage
location, for example as a result of normal operations, nearby vehicular movement, etc. These
conditions are specified in Table 6.

1M10 applies to storage locations experiencing insignificant levels of vibration and shock.
1M11 applies to storage locations experiencing low levels of vibration and shock, such as
those transmitted from air conditioning, machines or passing vehicles in the vicinity,
etc.
1M12 applies to storage locations experiencing significant levels vibration and shock, such
as those close to heavy machines and conveyor belts.
Table 6 − Classification of mechanical conditions
2)
Environmental parameter Unit Class
1M1 1M2 1M3 1M4
a) Stationary vibration, sinusoidal:
displacement amplitude mm 0,3 1,5 3,0 7,0
acceleration amplitude m/s 1 5 10 20
frequency range Hz 2-9 9-200 2-9 9-200 2-9 9-200 2-9 9-200
b) Non-stationary vibration, including
shock:
shock response spectrum type L m/s 40 40 None None
1)
peak acceleration â
shock response spectrum type I m/s None None 100 None
1)
peak acceleration â
shock response spectrum type II m/s None None None 250
1)
peak acceleration â
c) Static load kPa 5 5 5 5
1) See figure 1.
2) The classes of mechanical conditions of this standard (except static load) include the classes of IEC 721-3-3
and IEC 721-3-4 as follows:
1M1 covers 3M1 1M2 covers 3M2 1M3 covers 3M4 1M4 covers 3M6 and 4M6.

Class
Environmental parameter Unit
1M10 1M11 1M12
2 2
Stationary vibration, random: (m/s ) /Hz 0,01 0,1
None
acceleration spectral density
Hz 5 to 200 Hz 5 to 200 Hz
6 Sets of environmental condition class combinations
As indicated in clause 5, the classification allows a number of possible combinations of
environmental conditions bearing on products wherever used. The number of possibilities, and
thus the flexibility, is therefore very great. In practice, however, this flexibility is not always an
advantage when, for instance, environmental co
...

IEC 60721-3-1 ®
Edition 3.0 2018-02
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Classification of environmental conditions –
Part 3-1: Classification of groups of environmental parameters and their
severities – Storage
Classification des conditions d’environnement –
Partie 3-1: Classification des groupements des agents d’environnement et de
leurs sévérités – Stockage
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IEC 60721-3-1 ®
Edition 3.0 2018-02
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Classification of environmental conditions –

Part 3-1: Classification of groups of environmental parameters and their

severities – Storage
Classification des conditions d’environnement –

Partie 3-1: Classification des groupements des agents d’environnement et de

leurs sévérités – Stockage
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 19.040 ISBN 978-2-8322-5375-5

– 2 – IEC 60721-3-1:2018 © IEC 2018
CONTENTS
FOREWORD . 3
1 Scope and object . 5
2 Normative references . 5
3 Terms and definitions. 5
4 General . 6
5 Classification of groups of environmental parameters and their severities . 7
5.1 General . 7
5.2 Climatic conditions (K) . 7
5.3 Special climatic conditions (Z) . 10
5.4 Biological conditions (B) . 10
5.5 Chemically active substances (C) . 11
5.6 Mechanically active substances (S) . 12
5.7 Mechanical conditions (M) . 12
Annex A (informative) Chemically active substances . 13
Bibliography . 14

Table 1 – Classification of climatic conditions . 9
Table 2 – Classification of special climatic conditions . 10
Table 3 – Classification of biological conditions . 11
Table 4 – Classification of chemically active substances . 11
Table 5 – Classification of mechanically active substances . 12
Table 6 − Classification of mechanical conditions . 12

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
CLASSIFICATION OF ENVIRONMENTAL CONDITIONS –

Part 3-1: Classification of groups of environmental
parameters and their severities – Storage

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
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6) All users should ensure that they have the latest edition of this publication.
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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.
International Standard IEC 60721-3-1 has been prepared by IEC technical committee 104:
Environmental conditions, classification, and methods of test.
This third edition cancels and replaces the second edition, published in 1997, and constitutes a
technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) Clause 3: reworded and simplified.
b) Clause 4: reworded and simplified.
c) Clause 5: Annex C has been incorporated in Clause 5.

– 4 – IEC 60721-3-1:2018 © IEC 2018
d) 5.2: all existing climate classes have been replaced by completely new classes. The new
classes are divided into 3 groups. The reason for the new classes is the latest revision of
IEC 60721-2-1 which incorporated new climate types.
e) 5.3: new classes for solar radiation and snow load.
f) 5.6: all existing classes for mechanically active substances have been replaced by
completely new classes.
g) 5.7: all existing classes for mechanical conditions have been replaced by completely new
classes.
h) Table 1: new climatic classes with new severities.
i) Table 2: new classes for solar radiation and snow load.
j) Table 5 new mechanically active substances classes.
k) Table 6: new mechanical conditions classes.
The text of this International Standard is based on the following documents:
FDIS Report on voting
104/772/FDIS 104/782/RVD
Full information on the voting for the approval of this International Standard can be found in the
report on voting indicated in the above table.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts in the IEC 60721 series, published under the general title Classification of
environmental conditions, can be found on the IEC website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
CLASSIFICATION OF ENVIRONMENTAL CONDITIONS –

Part 3-1: Classification of groups of environmental
parameters and their severities – Storage

1 Scope and object
This part of IEC 60721 classifies the groups of environmental parameters and their severities
to which products together with their packaging, if any, are subjected when stored.
The environmental conditions specified in this document are limited to those which can directly
affect the products or their ultimate performance. Only environmental conditions as such are
considered. No special description of the effects of these conditions on the products is given.
Environmental conditions directly related to fire or explosions are not included.
Conditions of stationary use, portable and non-stationary use, use in vehicles and ships, and
conditions of transportation are given in other subparts of the IEC 60721-3 series.
The object of this document is to classify environmental parameters and their severities to
which a product can be exposed during storage. Transfer and handling during storage and
transport are addressed in IEC 60721-3-2.
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.
IEC 60721-1, Classification of environmental conditions − Part 1: Environmental parameters
and their severities
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60721-1 and the
following apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
enclosed location
location or structure that is covered on all sides in such a manner as to provide a degree of
protection
– 6 – IEC 60721-3-1:2018 © IEC 2018
3.2
non-weather-protected location
location at which the product is not protected from direct meteorological conditions
3.3
open-air location
location that is unenclosed that provides no protection from meteorological conditions
3.4
storage
a product kept in a place when not being operated
3.5
sheltered location
location or structure that provides limited protection from direct meteorological conditions such
as rain and wind
3.6
weather-protected location
location at which the product is protected from meteorological conditions
4 General
A product may be subjected to a range of environmental conditions during its lifetime. These
conditions have been separated into classes described in IEC 60721-3-0. The classes given
may be used for defining the maximum short-term environmental stresses of a product.
However, they do not provide information regarding the long-term or total lifetime
environmental stresses a product may experience. This means that no reliability or lifetime
assessment is possible based on these classes alone. Refer to IEC 60721-2 (all parts) and
applicable technical reports (IEC TR 62130 and IEC TR 62131-5) for further information on
actual environmental conditions.
A product will be simultaneously exposed to a number of environmental parameters. For
example, solar radiation and temperature, temperature and humidity, as well as vibration and
temperature change. Combinations of the environmental parameters given may increase the
effect on a product. Therefore, combined conditions should be considered in the design and
evaluation of a product.
Products should be designed to survive and operate in different environments. Basically, they
will be affected by the environmental influences in two ways:
• by the effects of short-term extreme environmental conditions which may directly cause
malfunction or destroy the product;
• by the effect of long-term subjection to non-extreme environmental stresses which may
slowly degrade the product and finally cause malfunction or destruction of the product.
Short-term extreme environmental conditions may occur at any time in the product's life. A
product may be unaffected by an extreme condition when it is new but fail when it is subjected
to the same condition after being used for a long period of time due to the effect of ageing. The
order in which the environmental conditions are applied may affect the results of an evaluation.
It is important for the product specification, when referring to a certain class in
IEC 60721-3 (all parts), to define whether the product is required to be capable of operating or
only to survive without permanent damage when being exposed to the conditions described by
the class.
The environmental classes may be used as a basis for the selection of design and test
severities with respect to the consequence of failure. Information contained in
IEC 60721-3 (all parts) may be used as a means to help establish expected requirements for
use, storage, transportation, etc., and in the development of relevant specifications. The
selected severities used for testing should attempt to produce the effects of the actual
environment.
EXAMPLE 1 A high temperature test on a heat dissipating product is designed to simulate the thermal effect of
subjecting a product to conditions of high air temperature, solar radiation and other possible heat sources
dependent on the application;
EXAMPLE 2 In a mechanical shock test, the product can be subjected to mechanical shocks of simple pulse
shapes (e.g., half-sine), while the actual conditions cannot be described by such simple pulses.
It is recognized that extreme or special environmental conditions may exist which require
consideration of severities that are not addressed by this document.
5 Classification of groups of environmental parameters and their severities
5.1 General
A number of classes for climatic conditions (K), special climatic conditions (Z), biological
conditions (B), chemically active substances (C), mechanically active substances (S), and
mechanical conditions (M) are specified.
This classification allows a number of possible combinations of environmental conditions which
bear upon products wherever stored. It represents the real situation concerning worldwide
conditions of storage, for example, due to local influences of open-air climate.
For certain environmental parameters, it has not yet been possible to specify quantitative
severities.
For a given location or product, reference should be made to the total set of classes, for
example:
1K21/1Z1/1B1/1C2/1S10/1M10
5.2 Climatic conditions (K)
NOTE All old classes have been replaced with new classes. The new classes were chosen to reflect 3 different
storage condition: enclosed, sheltered and open-air locations.
The climatic conditions specified for classes 1K20 to 1K29 refer to the conditions of storage of
products. These conditions have been experienced worldwide over a long period of time taking
into account all the parameters that can influence them such as open-air climatic conditions,
type of building construction, temperature/humidity controlling systems, and internal conditions,
for example heat dissipation from other equipment and presence of humans. The conditions
should cover all normal cases, but not exceptional events.
When selecting appropriate classes, attention should be paid to the fact that the climatic
conditions inside buildings may depend on the outside (open-air) conditions, especially air
temperature and solar radiation, and the type of building construction. Walls with good thermal
insulation or high thermal capacity can consistently smooth the peaks of outside air
temperature variations between day and night, or, exceptionally, those produced over a longer
period of time. Walls with poor thermal insulation or low thermal capacity cannot have this
effect, and peaks can be magnified due to the effect of solar radiation during the day, and to
the effect of building radiation at night. The effect of solar radiation can be increased by either
heat-trap or greenhouse effects.

– 8 – IEC 60721-3-1:2018 © IEC 2018
At non-weather-protected locations, the influence from special climatic conditions constitutes a
more significant share of the effects bearing upon a product than at weather-protected
locations. The effects of temperature change, solar radiation, precipitation, air velocity and
wind-chill should be particularly considered.
The severity of these effects may be influenced, for example by constructional details (type and
thickness of material, colour of surfaces, sealing or breathing of casings, etc.), and by storage
details (selection of storage site, consideration of degrees of exposure to prevailing wind and
weather, etc.).
Enclosed storage
1K20 applies to fully air conditioned enclosed storage locations. Air temperature and
humidity control is used continuously to maintain the required conditions.
1K21 applies to enclosed storage locations with limited temperature control and no humidity
control.
1K22 applies to enclosed storage locations having no temperature or humidity control.
Sheltered storage
1K23 applies to sheltered storage locations in tropical, arid, temperate, and cold climatic
classification with the thermal effects from solar radiation encompassed in the
temperature.
1K24 applies to sheltered storage locations in the polar climate type with the thermal effects
from solar radiation encompassed in the temperature.
Open-air storage
1K25 applies to open-air storage in the tropical climatic classification.
1K26 applies to open-air storage in the arid and temperate climatic classifications.
1K27 applies to open-air storage in the cold and polar climatic classifications.
These conditions are specified in Table 1.

Table 1 – Classification of climatic conditions
Enclosed Sheltered Open-air
Environmental Parameter
Unit 1K20 1K21 1K22 1K23 1K24 1K25 1K26 1K27
6)
a) Low air temperature
°C +20 +5 +5 -50
−25 −45 −50 −20
6) 11) 11) 11)
b) High air temperature
°C +25 +40 +55 +70 +70 +45 +50 +45
1)
c) Low relative humidity
% 20 5 10 4 4 30 4 10
1)
d) High relative humidity
% 75 85 100 100 100 100 100 100
1)
e) Low absolute humidity
g/m 4 1 0,5 0,2 0,003 6 0,1 0,003
1)
f) High absolute humidity
g/m 15 25 29 35 20 35 30 25
g) Rate of change of
°C/min 0,1 0,5 0,5 1,0 1,0 1,0 1,0 1,0
2)
temperature
3)
h) Low air pressure
kPa 70 70 70 70 70 70 70 70
3)
i) High air pressure
kPa 106 106 106 106 106 106 106 106
j) Solar radiation
7) 7) 10) 10) 10)
W/m 1090 1090 1090
Not
No No No No
7) 7) 7) 7)
k) Heat radiation
specified
8) 8)
l) Movement of surrounding air
8)
m/s 0,5 1,0 1,0 5,0 5,0
8) 8)
4)
Not
No No Yes Yes Yes Yes Yes Yes
m) Condensation
specified
n) Precipitation (rain, snow,
Not 9) 9)
No No No Yes Yes Yes
Yes Yes
specified
hail, etc.)
9) 9)
o) Rain intensity
mm/min
None None None None None 15 15 15
p) Driving rain
m/s None None None None None 18 18 18
q Snow load
8) 8)
kg/m None None None None None None
5)
9) 9)
r) Low rain temperature
°C None None None None None +5 +5 +5
s) Water from sources other
Dripping Dripping Dripping 12) 12) 12)
L/m²/min No No
Water Water Water
than rain
t) Formation of ice and frost
Not
No No Yes Yes Yes No Yes Yes
specified
(including freeze-thaw)
– 10 – IEC 60721-3-1:2018 © IEC 2018
Notes to Table 1
1) The low and high relative humidity levels are limited by the low and high absolute humidities, so that, for
example, for environmental parameters a) and c), or b) and d), the severities given in Table 1 do not occur
simultaneously.
2) Averaged over a period of time of 5 min.
3) The value of 70 kPa represents a limit for open-air conditions, normally at an altitude of 3 000 m. In some
geographical areas, open-air conditions may occur at higher altitudes. Conditions in mines are not
considered.
4) A cooling system based on non-assisted convection may be disturbed by adverse movement of surrounding
air.
5) This rain temperature should be considered together with high air temperature b) and solar radiation j). The
cooling effect of the rain has to be considered in connection with the surface temperature of the product.
6) These are air-conditioned locations with a tolerance of ±2 °C on stated temperature value.
7) Conditions occurring at the location concerned to be selected from Table 2.
8) If applicable, a special value may be selected from Table 2.
9) Applies only to wind-driven precipitation at sheltered locations.
10) Thermal effect of solar radiation is included in the temperature.
11) Thermal effect of solar radiation is not included in the temperature.
12) Sources of water other than rain are encompassed by driving rain.

5.3 Special climatic conditions (Z)
Parameters such as heat radiation, movement of the surrounding air, solar radiation, snow
load, and water from sources other than rain may occur with any severity in combination with
any of the other climatic conditions. These conditions are specified in Table 2.
Table 2 – Classification of special climatic conditions
Environmental parameter Class Unit Special condition Z
1Z1 None Negligible
k) Heat radiation
Conditions of heat radiation, e.g. in the
1Z2 None
vicinity of room heating systems
1Z3 m/s 30
l) Movement of surrounding air
1Z4 m/s 50
s) Water from sources other than rain 1Z5 None Dripping water
1Z8 W/m 500
j) Solar radiation
1Z9 W/m 700
1Z10 kg/m 100 (single snow storm)
q) Snow load
1Z11 kg/m 240 (whole season)
5.4 Biological conditions (B)
No quantitative severity has been specified for these conditions. The specified parameters of
Table 3 are typical, but may not be complete.
1B1 applies to storage locations with environmental controls in place to prevent the growth
of mould and physical controls to prevent attack by animals.
1B2 applies to storage locations without environmental or physical controls in place to
prevent mould growth or attacks by animals, except termites.
1B3 applies to locations where attacks by termites may occur.

Table 3 – Classification of biological conditions
Class
Units
1B1 1B2 1B3
Presence of mould, fungus, etc.
None Negligible
Presence of rodents and other animals harmful to products
excluding termites including termites

5.5 Chemically active substances (C)
The contamination of the natural atmosphere is mainly caused by chemical emissions from
industrial activities, motor-driven vehicles, and heating systems. A further chemical influence is
caused by aerosols of sea and road salts. Contamination may affect the function and materials
of products. These conditions are specified in Table 4.
See Annex A for additional information.
1C1 applies to locations in rural and some urban areas, with low industrial activity and
moderate traffic. In winter, heating methods in concentrated urban areas may cause
increased contamination.
1C2 applies to locations with normal levels of contaminants as experienced in urban areas
with industrial activity scattered over the whole area, or with heavy traffic. Salt mist is
present in coastal areas.
1C3 applies to locations in the immediate vicinity of industrial sources, with chemical
emissions. Salt mist is present in coastal areas.
Table 4 – Classification of chemically active substances
Classification
Environmental 1C1 1C2 1C3
Unit
parameter
Maximum Maximum Maximum
Mean value Mean value
value value value
a) Salt mist to
include sea and None No Yes Yes
road salts
b) Sulphur dioxide mg/m 0,1 0,3 1,0 5,0 10
3 3
cm /m 0,037 0,11 0,37 1,85 3,7
c) Hydrogen mg/m 0,01 0,1 0,5 3,0 10
sulphide
3 3
cm /m 0,0071 0,071 0,36 2,1 7,1
d) Chlorine mg/m 0,1 0,1 0,3 0,3 1
3 3
cm /m 0,034 0,034 0,1 0,1 0,34
e) Hydrogen mg/m 0,1 0,1 0,5 1,0 5,0
chloride
3 3
cm /m 0,066 0,066 0,33 0,66 3,3
f) Hydrogen fluoride mg/m 0,003 0,01 0,03 0,1 2,0
3 3
cm /m 0,0036 0,012 0,036 0,12 2,4
g) Ammonia mg/m 0,3 1,0 3,0 10 35
3 3
cm /m 0,42 1,4 4,2 14 49
h) Ozone mg/m 0,01 0,05 0,1 0,1 0,3
3 3
cm /m 0,005 0,025 0,05 0,05 0,15
i) Nitrogen oxides
(expressed in 3
mg/m 0,1 0,5 1,0 3,0 9,0
equivalent values
3 3
cm /m 0,052 0,26 0,52 1,56 4,68
of nitrogen
dioxide)
– 12 – IEC 60721-3-1:2018 © IEC 2018
5.6 Mechanically active substances (S)
NOTE All old classes have been replaced with new classes. The new classes were chosen to reflect 3 different
storage conditions; enclosed, sheltered and open-air locations.
Dust and sand are classified together, as the effects caused by these environmental conditions
are similar.
1S10 applies to enclosed storage locations where precautions have been taken to minimize
the presence of dust and sand.
1S11 applies to enclosed storage locations not situated in proximity to dust or sand sources
and with no precautions to minimize the ingress of dust or sand. Such enclosed storage
locations could include shipping containers.
1S12 applies to enclosed storage locations in close proximity to sand or dust sources,
including urban area and with no precautions to minimize the ingress of dust or sand. It
also applies to exposed storage locations situated in areas not subject to natural dust
storms or significant industrial activity.
1S13 applies to exposed storage locations which may be exposed to wind-driven dust and
sand either due to natural conditions or due to industrial activity producing blown sand
or dust.
These conditions are specified in Table 5.
Table 5 – Classification of mechanically active substances
Class
Environmental parameter Unit
1S10 1S11 1S12 1S13
Setting (sedimentary) dust mg/(m⋅d) None 6 Note 1 Note 2
Turbulent (suspended) dust None None 600 Note 2
mg/(m⋅h)
Windblown dust mg/m 18
None None None
m/s 13
NOTE 1 Encompassed within turbulent (suspended) dust.
NOTE 2 Encompassed within windblown dust.

5.7 Mechanical conditions (M)
NOTE All old classes have been replaced with new classes. The new classes based on IEC TR 62131-5.
Mechanical conditions relate to the levels of vibration and shock that may exist at a storage
location, for example as a result of normal operations, nearby vehicular movement, etc. These
conditions are specified in Table 6.
1M10 applies to storage locations experiencing insignificant levels of vibration and shock.
1M11 applies to storage locations experiencing low levels of vibration and shock, such as
those transmitted from air conditioning, machines or passing vehicles in the vicinity,
etc.
1M12 applies to storage locations experiencing significant levels vibration and shock, such
as those close to heavy machines and conveyor belts.
Table 6 − Classification of mechanical conditions
Class
Environmental parameter Unit
1M10 1M11 1M12
2 2
Stationary vibration, random: (m/s ) /Hz 0,01 0,1
None
acceleration spectral density
Hz 5 to 200 Hz 5 to 200 Hz
Annex A
(informative)
Chemically active substances
The values given in this classification have been taken from surveys over several years.
Maximum values are given, because direct influence of higher concentrations over a short
period of time normally causes more damage to material which cannot regenerate. Mean
values are given additionally, because their influence may be important for the long-term effect
on internal parts of the products.
In practice, not all contaminants (parameters) classified in this document are present
simultaneously. Furthermore, the probability is low that the concentrations of those
contaminants actually present increase simultaneously and homogeneously. Depending on the
local situation, there are often higher values of one contaminant only. The values specified for
class 1C1 will normally be experienced in rural areas and areas with low industrial activity. The
values specified for class 1C2 are experienced in urban areas. Therefore the severity of each
of these two classes shall be considered as the requirements for the combined effect of all
parameters stated. The severities of class 1C3, however, cannot be combined as the
requirement for the combined effect of all parameters stated in order to avoid any
uneconomical overdesign. For that class, it is possible to select only the severities of those
single parameters which might be relevant in the case of application. If single parameters of
class 1C3 are selected for the description of the chemically active substances present at a
location, the severities of class 1C2 are valid for all other parameters which are not specially
named.
Chemically active liquids and chemically active solids other than sea salts or road salts are not
considered in this document.
– 14 – IEC 60721-3-1:2018 © IEC 2018
Bibliography
IEC 60721-2 (all parts), Classification of environmental conditions – Part 2: Environmental
conditions appearing in nature
IEC 60721-2-1, Classification of environmental conditions – Part 2-1: Environmental conditions
appearing in nature – Temperature and humidity
IEC 60721-2-2, Classification of environmental conditions – Part 2-2: Environmental conditions
appearing in nature – Precipitation and wind
IEC 60721-2-3, Classification of environmental conditions – Part 2-3: Environmental conditions
appearing in nature – Air pressure
IEC 60721-2-4, Classification of environmental conditions – Part 2-4: Environmental conditions
appearing in nature – Solar radiation and temperature
IEC 60721-2-5, Classification of environmental conditions – Part 2: Environmental conditions
appearing in nature – Section 5: Dust, sand, salt mist
IEC 60721-3 (all parts), Classification of environmental conditions – Part 3: Classification of
groups of environmental parameters and their severities
IEC 60721-3-0, Classification of environmental conditions – Part 3: Classification of groups of
environmental parameters and their severities – Introduction
IEC 60721-3-2, Classification of environmental conditions – Part 3: Classification of groups of
environmental parameters and their severities – Section 2: Transportation
IEC TR 62130, Climatic field data including validation
IEC TR 62131-5, Environmental conditions – Vibration and shock of electrotechnical equipment
– Part 5: Equipment during storage and handling

___________
– 16 – IEC 60721-3-1:2018 © IEC 2018
SOMMAIRE
AVANT-PROPOS . 17
1 Domaine d’application et objet . 19
2 Références normatives . 19
3 Termes et définitions . 19
4 Généralités . 20
5 Classification des groupements des agents d’environnement et de leurs sévérités . 21
5.1 Généralités . 21
5.2 Conditions climatiques (K) . 21
5.3 Conditions climatiques spéciales (Z) . 24
5.4 Conditions biologiques (B) . 24
5.5 Substances chimiquement actives (C) . 24
5.6 Substances mécaniquement actives (S) . 25
5.7 Conditions mécaniques (M) . 26
Annexe A (informative)  Substances chimiquement actives . 27
Bibliographie . 28

Tableau 1 – Classification des conditions climatiques . 23
Tableau 2 – Classification des conditions climatiques spéciales . 24
Tableau 3 – Classification des conditions biologiques . 24
Tableau 4 – Classification des substances chimiquement actives . 25
Tableau 5 – Classification des substances mécaniquement actives . 26
Tableau 6 − Classification des conditions mécaniques . 26

COMMISSION ÉLECTROTECHNIQUE INTERNATIONALE
____________
CLASSIFICATION DES CONDITIONS D’ENVIRONNEMENT –

Partie 3-1: Classification des groupements des agents
d’environnement et de leurs sévérités – Stockage

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