SIST EN ISO 7243:2018
(Main)Ergonomics of the thermal environment - Assessment of heat stress using the WBGT (wet bulb globe temperature) index (ISO 7243:2017)
Ergonomics of the thermal environment - Assessment of heat stress using the WBGT (wet bulb globe temperature) index (ISO 7243:2017)
This document presents a screening method for evaluating the heat stress to which a person is exposed
and for establishing the presence or absence of heat stress.
It applies to the evaluation of the effect of heat on a person during his or her total exposure over the
working day (up to 8 h).
It does not apply for very short exposures to heat.
It applies to the assessment of indoor and outdoor occupational environments as well as to other types
of environment, and to male and female adults who are fit for work.
Ergonomie der thermischen Umgebung - Ermittlung der Wärmebelastung durch den WBGT-Index (wet bulb globe temperature) (ISO 7243:2017)
Ambiances chaudes - Estimation de la contrainte thermique de l’homme au travail, basée sur l’indice WBGT (température humide et de globe noir) (ISO 7243:2017)
ISO 7243:2017 décrit une méthode d'examen préalable permettant d'évaluer la contrainte thermique à laquelle est exposée une personne et d'établir la présence ou l'absence de contrainte thermique.
ISO 7243:2017 s'applique à l'évaluation de l'effet de la chaleur sur une personne pendant son exposition totale au cours d'une journée de travail (jusqu'à 8 heures).
ISO 7243:2017 ne s'applique pas à de très courtes expositions à la chaleur.
ISO 7243:2017 s'applique à l'évaluation des environnements de travail intérieur et extérieur ainsi qu'à d'autres types d'environnement, et aux hommes et femmes adultes et aptes au travail.
Ergonomija toplotnega okolja - Ocenitev toplotnega stresa na podlagi kazalnika WBGT (ISO 7243:2017)
Ta dokument predstavlja presejalno metodo za ocenitev toplotnega stresa, ki mu je izpostavljena oseba, ter za ugotavljanje prisotnosti ali odsotnosti toplotnega stresa.
Uporablja se za ovrednotenje vpliva toplote na osebo med njeno skupno izpostavljenostjo v delovnem dnevu (do 8 ur).
Ne uporablja se za zelo kratke izpostavljenosti toploti.
Uporablja se za ocenitev poklicnega okolja v zaprtih prostorih in na prostem ter druge vrste
okolij in za odrasle moške ter ženske, ki so sposobni za delo.
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
SIST EN ISO 7243:2018
01-februar-2018
1DGRPHãþD
SIST EN 27243:2001
Ergonomija toplotnega okolja - Ocenitev toplotnega stresa na podlagi kazalnika
WBGT (ISO 7243:2017)
Ergonomics of the thermal environment - Assessment of heat stress using the WBGT
(wet bulb globe temperature) index (ISO 7243:2017)
Ergonomie der thermischen Umgebung - Ermittlung der Wärmebelastung durch den
WBGT-Index (wet bulb globe temperature) (ISO 7243:2017)
Ambiances chaudes - Estimation de la contrainte thermique de l’homme au travail,
basée sur l’indice WBGT (température humide et de globe noir) (ISO 7243:2017)
Ta slovenski standard je istoveten z: EN ISO 7243:2017
ICS:
13.180 Ergonomija Ergonomics
SIST EN ISO 7243:2018 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST EN ISO 7243:2018
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SIST EN ISO 7243:2018
EN ISO 7243
EUROPEAN STANDARD
NORME EUROPÉENNE
September 2017
EUROPÄISCHE NORM
ICS 13.180 Supersedes EN 27243:1993
English Version
Ergonomics of the thermal environment - Assessment of
heat stress using the WBGT (wet bulb globe temperature)
index (ISO 7243:2017)
Ambiances chaudes - Estimation de la contrainte Ergonomie der thermischen Umgebung - Ermittlung
thermique de l'homme au travail, basée sur l'indice der Wärmebelastung durch den WBGT-Index (wet bulb
WBGT (température humide et de globe noir) (ISO globe temperature) (ISO 7243:2017)
7243:2017)
This European Standard was approved by CEN on 1 July 2017.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2017 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 7243:2017 E
worldwide for CEN national Members.
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SIST EN ISO 7243:2018
EN ISO 7243:2017 (E)
Contents Page
European foreword . 3
2
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SIST EN ISO 7243:2018
EN ISO 7243:2017 (E)
European foreword
This document (EN ISO 7243:2017) has been prepared by Technical Committee ISO/TC 159
“Ergonomics” in collaboration with Technical Committee CEN/TC 122 “Ergonomics” the secretariat of
which is held by DIN.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by March 2018, and conflicting national standards shall
be withdrawn at the latest by March 2018.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN 27243:1993.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,
Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.
Endorsement notice
The text of ISO 7243:2017 has been approved by CEN as EN ISO 7243:2017 without any modification.
3
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SIST EN ISO 7243:2018
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SIST EN ISO 7243:2018
INTERNATIONAL ISO
STANDARD 7243
Third edition
2017-08
Ergonomics of the thermal
environment — Assessment of heat
stress using the WBGT (wet bulb globe
temperature) index
Ambiances chaudes — Estimation de la contrainte thermique de
l'homme au travail, basée sur l'indice WBGT (température humide et
de globe noir)
Reference number
ISO 7243:2017(E)
©
ISO 2017
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SIST EN ISO 7243:2018
ISO 7243:2017(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2017, Published in Switzerland
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior
written permission. Permission can be requested from either ISO at the address below or ISO’s member body in the country of
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Tel. +41 22 749 01 11
Fax +41 22 749 09 47
copyright@iso.org
www.iso.org
ii © ISO 2017 – All rights reserved
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SIST EN ISO 7243:2018
ISO 7243:2017(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Method . 2
5 Determination of WBGT . 3
6 Determination of metabolic rate . 3
7 Determination of effects of clothing . 3
8 Timing and duration of measurements . 4
8.1 Timing of measurements . 4
8.2 Duration of measurements . 4
9 Spatial and temporal variations . 5
9.1 Measurement specifications relating to heterogeneity of environment
(spatial variations) . 5
9.2 Measurement specifications relating to time variations of WBGT index . 5
9.3 Measurement specifications relating to time variations of metabolic rate . 5
9.4 Measurement specifications relating to time variations of clothing . 5
10 Interpretation . 6
Annex A (informative) Reference values of the WBGT heat stress index . 7
Annex B (normative) Measurement of parameters used in the WBGT index and
specification of instruments. 9
Annex C (informative) Alternative globe thermometers .11
Annex D (informative) Prediction of natural wet bulb temperature .13
Annex E (informative) Estimation of metabolic rate .15
Annex F (informative) Clothing adjustment values (CAVs) .16
Bibliography .17
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SIST EN ISO 7243:2018
ISO 7243:2017(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following
URL: www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 159, Ergonomics, Subcommittee SC 5,
Ergonomics of the physical environment.
This third edition cancels and replaces the second edition (ISO 7243:1989), which has been technically
revised and contains the following changes:
— in Annex A, for information, additional exposure limits are represented in Figure A.1, together with
reference equations;
— the assessment of heat stress now includes the effects of clothing;
— the potential errors and adjustments for non-standard globe temperature sensors are described;
— a method for predicting the natural wet bulb temperature is provided.
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SIST EN ISO 7243:2018
ISO 7243:2017(E)
Introduction
This International Standard provides a method for the assessment of heat stress. It is one of a series of
standards intended for use in the assessment of thermal environments. These include standards for the
assessment of hot, moderate and cold environments involving both the principles of assessment and
their practical application.
The wet bulb globe temperature (WBGT) is a heat stress index and its value represents the thermal
environment to which an individual is exposed. This index is easy to determine in most environments.
It should be regarded as a screening method to establish the presence or absence of heat stress.
A method of estimating the thermal stress, based on an analysis of the heat exchange between a person
and the environment, allows a more accurate estimation of stress and an analysis of the methods of
protection (see ISO 7933). Such a method should be used either directly when it is desired to carry
out an intensive analysis of working conditions in heat, or in addition to the method presented in this
standard, which is based upon the WBGT index, when the WBGT values obtained exceed the reference
values shown.
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SIST EN ISO 7243:2018
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SIST EN ISO 7243:2018
INTERNATIONAL STANDARD ISO 7243:2017(E)
Ergonomics of the thermal environment — Assessment
of heat stress using the WBGT (wet bulb globe
temperature) index
1 Scope
This document presents a screening method for evaluating the heat stress to which a person is exposed
and for establishing the presence or absence of heat stress.
It applies to the evaluation of the effect of heat on a person during his or her total exposure over the
working day (up to 8 h).
It does not apply for very short exposures to heat.
It applies to the assessment of indoor and outdoor occupational environments as well as to other types
of environment, and to male and female adults who are fit for work.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 7933, Ergonomics of the thermal environment — Analytical determination and interpretation of heat
stress using calculation of the predicted heat strain
ISO 13731, Ergonomics of the thermal environment — Vocabulary and symbols
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 13731 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at http://www.iso.org/obp
— IEC Electropedia: available at http://www.electropedia.org/
3.1
wet bulb globe temperature
WBGT
simple index of the environment that is considered along with metabolic rate to assess the potential for
heat stress among those exposed to hot conditions
Note 1 to entry: The WBGT combines the measurement of two derived parameters: natural wet-bulb temperature
(t ) and black globe temperature (t ). Where the sensors are influenced by direct incident radiation from the
nw g
sun (solar load), either outdoors or indoors, the weighting of the globe temperature is reduced by including air
temperature (t ).
a
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SIST EN ISO 7243:2018
ISO 7243:2017(E)
3.2
effective wet bulb globe temperature
effective WBGT
WBGT
eff
WBGT value adjusted for the effects of clothing
Note 1 to entry: It gives the WBGT environment when the actual clothing worn is equivalent to that when
standard work clothing is worn (thermal insulation index I = 0,6 clo, i = 0,38). See ISO 9920.
cl m
3.3
clothing adjustment value
CAV
adjustment to the WBGT value to account for the effects of clothing that has different thermal properties
from that of standard work clothing
4 Method
The degree of heat stress to which a person is exposed depends on
a) the characteristics of the environment governing heat transfer between the ambient environment
and the body,
b) the production of heat inside the body as a result of physical activity, and
c) the clothing worn, which modifies the exchange of heat with the environment.
A detailed analysis of the influence of the environment on heat stress requires knowledge of the
following four basic parameters: air temperature, mean radiant temperature, air velocity, and absolute
humidity (ISO 7726). However, an estimation of this influence can be made by measuring parameters
derived from these basic parameters and which are a function of the physical parameters of the
environment investigated. The WBGT index is used to give a first approximation of the heat stress on a
person (see Clause 5).
The internal thermal load is the result of metabolic energy caused by activity. The rate of metabolic
heat production is usually estimated (see Clause 6).
The heat stress threshold assumes a long sleeve cotton shirt and cotton trousers/pants. An adjustment
shall be made for other clothing (see Clause 7).
This method for estimating heat stress is based on the assessment of these different parameters and
the calculation of mean values taking into account changes in location, duration and activity, as well as
variations in time (see Clause 8).
The WBGT reference values (exposure limits) presented correspond to levels of sustained exposure for
up to 8 h.
The WBGT values obtained using the method are compared with WBGT reference values (exposure
limits). If the values are greater than the reference values, then the risk of heat-related disorders
increases and it will be necessary to either
— reduce directly the heat stress or strain at the workplace by appropriate methods, or
— carry out a detailed analysis of the heat stress using ISO 7933.
It should be noted that the exposure thresholds described in this document are designed to reduce the
risk of heat-related illness and that this does not preclude the possibility of other outcomes associated
with heat stress exposures (e.g. risk of burns and accidents, loss of productivity, or lack of comfort).
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SIST EN ISO 7243:2018
ISO 7243:2017(E)
5 Determination of WBGT
Formulae (1) and (2) provide equations for the calculation of WBGT and show the relationship between
the different parameters:
— without solar load
WBGT = 0,7t + 0,3t (1)
nw g
— with solar load
WBGT = 0,7t + 0,2t + 0,1t (2)
nw g a
Globe temperature assesses the total radiant heat load from the sun and other sources. Formula 2
accounts for an overestimation of direct radiant heat from the sun (solar load). That is, the provisions
of this document are applicable where there is radiant heat load with or without direct solar radiation
[Formulae (1) and (2)].
The reference values were selected so that the level of heat stress could be sustained during the total
exposure over the working day (up to 8 h). The time interval for analysis is about 1 h, representative
of the exposure. If there are spatial and/or temporal variations in the environment, it is necessary to
adjust for those variations, as described in 9.1 (spatial variation) and 9.2 (temporal variation).
Annex B presents the requirements for sensors associated with the measurement of the WBGT.
NOTE 1 There are variations in the design of actual sensors in instrumentation that are used to assess WBGT.
The common variations in design are described in Annex C, along with a discussion of the design implications
when compared with the design adopted in this document and specified in Annex B.
NOTE 2 The preferred method for determining WBGT values is direct measurement using the sensors
specified in Annex B. However, it is sometimes of interest to predict WBGT values from the four parameters, air
temperature, mean radiant temperature, relative humidity and air velocity. (See Annex C and D)
6 Determination of metabolic rate
The quantity of heat produced inside the body is an important contributor to heat stress and a valid
estimate of this is essential for the assessment. Metabolic rate, which represents the total quantity of
energy consumed inside the body over time, is a good estimation for most situations (i.e. the energy
consumed can be assumed to be the heat produced, as the energy used for other functions such as
external work is usually negligible by comparison).
Metabolic rate may be classified as resting, low metabolic rate, moderate metabolic rate, high metabolic
rate or very high metabolic rate according to Annex E. The values provided in Table E.1 are based on
continuous work at the described levels of effort. In the case of intermittent work, a time-weighted
averaging shall be performed in accordance with 9.3.
If a more detailed estimation is required, then the methods presented in ISO 8996 should be used.
7 Determination of effects of clothing
The reference values (exposure limits) provided in Annex A were developed with cotton work
clothes (0,6 clo and i = 0,38) as the reference clothing. Different clothing, especially with a different
m
evaporative resistance, is likely to have a different effect on the heat stress level. For clothing materials
and configurations different from standard work clothing, clothing adjustment values (CAVs) in WBGT
temperature units are provided. The CAV is added to the measured WBGT to produce an effective
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SIST EN ISO 7243:2018
ISO 7243:2017(E)
WBGT (WBGT ) that represents an estimate of the heat stress provided by the actual clothing worn as
eff
an equivalent environment, i.e.
WBGT = WBGT + CAV (3)
eff
Annex F provides a list of CAVs. It should be remembered that the effects of clothing can be complex and
that the CAV is a simple adjustment and a first approximation to taking account of the heat stress on a
person as determined from laboratory results.
There may be a clothing ensemble for which a CAV is not directly known. In this case, the CAV may be
estimated from clothing with similar thermal properties. The thermal properties of a wide range of
clothing are provided in ISO 9920.
For clothing ensembles for which the CAV cannot be determined, this document shall not be used and a
detailed analysis of the heat stress, using ISO 7933, shall be carried out.
CAV is an approximation of the effect of wearing clothing that differs from “ordinary work clothes” for
which the reference values given in Annex A apply without any adjustment for clothing (CAV = 0). In
general, the CAV increases with increasing evaporative resistance (or decreasing permeability index).
Other effects are radiant heat, air velocity, body movements, clothing configurations and humidity. Of
these, the CAV is greatly affected by a combination of high evaporative resistance and humidity. In this
case, and because of the simplistic nature of the adjustment, the CAV should be a high estimate to allow
for a margin of safety. The effects of radiant heat on the CAV are not known.
8 Timing and duration of measurements
8.1 Timing of measurements
The determination of the WBGT index allows only the estimation of the heat stress to which a worker
is subjected at the time the measurements were carried out. Consequently, it is recommended that
measurements are carried out at the time of the year when heat stress is most likely to occur: during
the hot summer period. For the same reason, the representative period of the exposure is best selected
during the middle of the day, or the period of the exposure which is most likely to induce heat stress.
If the work over a day is divided into distinctly different types or categories then it may be necessary to
make separate measurements and separate assessments of the different types of work.
EXAMPLE When there is mainly light work in the morning and heavy work in the afternoon, or when the
WBGT values are significantly different for periods of over an hour.
8.2 Duration of measurements
A measurement of the WBGT is required over a representative period of about 1 h. The duration of
each measurement depends on the response time of the sensor, which on certain occasions can be
considerable (globe temperature especially). A steady-state value for all sensor readings should be
established prior to recording the values assigned for that reading. The total duration of measurement
may therefore be greater than the single hour used as the time base in the analysis (see 9.2).
It is possible to record environmental measurements with high resolution (e.g. every second or minute)
and store large amounts of data in digital form.
Time constants, accuracy and sensitivity of instrumentation need to be taken into consideration when
measuring the value of any parameter.
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SIST EN ISO 7243:2018
ISO 7243:2017(E)
9 Spatial and temporal variations
9.1 Measurement specifications relating to heterogeneity of environment (spatial
variations)
The WBGT values should normally be measured at the position of the abdomen (ISO 7726) of those
exposed to the heat. When parameters in the space surrounding these people are not homogeneous,
measurement should be made at the position where heat stress is highest.
In the case where it is impossible to situate the sensors at the normal place of work, they should be
situated where they will be exposed to the same influence from the environment.
9.2 Measurement specifications relating to time variations of WBGT index
If the analyses of the environment and of the activity have shown that a parameter does not exhibit a
constant value in time, a representative mean value has to be determined.
The most accurate procedure consists in measuring the continuous development of this parameter as
a function of time and deducing from it the mean value by integration. As this method can only be used
with difficulty in many cases, the variations of each parameter are classified into almost constant levels.
The mean value of the parameter considered is then obtained by weighting the levels of the different
categories by the total time during which each of these levels was obtained.
The time base T for the calculation of the mean values is a period of about 1 h, which is representative
of the possible heat stress exposure. The mean value of a parameter, p — for example, air temperature,
natural wet bulb temperature, globe temperature or WBGT in the case of simultaneous measurement of
the three parameters of the environment — for which the development as a function of time has been
broken down into n levels is therefore expressed by Formula (4):
pt× +×pt ++. pt×
() () ()
11 22 nn
p = (4)
tt++.t
12 n
where p , p , . p is the level of the parameter obtained during time t , t , . t ;
1 2 n 1 2 n
t + t + . = T = 1 h (5)
1 2
The number of measurements to be carried out depends on the variation speed of the parameters, the
response characteristics of the sensors used and the desired accuracy of measurement.
9.3 Measurement specifications relating to time variations of metabolic rate
Formula (4) applies to the determination of the time-weighted mean value of the metabolic rate based
on values measured or estimated from reference tables. The metabolic rate is classified under one of the
five main classes presented in Annex E. The mean metabolic rate level is determined from Formula (4),
where the parameter is metabolic rate, by taking, for each elementary activity, the mean value of the
metabolic rate given in Table E.1.
When there is doubt with regard to the metabolic rate value to be adopted, the refere
...
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