SIST EN ISO 8996:2005

SLOVENSKI STANDARD
SIST EN ISO 8996:2005
01-januar-2005
1DGRPHãþD
SIST EN 28996:2001
Ergonomija toplotnega okolja – Ugotavljanje presnovne toplote (ISO 8996:2004)
Ergonomics of the thermal environment - Determination of metabolic rate (ISO
8996:2004)
Ergonomie der thermischen Umgebung - Bestimmung des körpereigenen
Energieumsatzes (ISO 8996:2004)
Ergonomie de l'environnement thermique - Détermination du métabolisme énergétique
(ISO 8996:2004)
Ta slovenski standard je istoveten z: EN ISO 8996:2004
ICS:
13.180 Ergonomija Ergonomics
SIST EN ISO 8996:2005 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO 8996:2005

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SIST EN ISO 8996:2005



EUROPEAN STANDARD
EN ISO 8996

NORME EUROPÉENNE

EUROPÄISCHE NORM
October 2004
ICS 13.180 Supersedes EN 28996:1993
English version
Ergonomics of the thermal environment - Determination of
metabolic rate (ISO 8996:2004)
Ergonomie de l'environnement thermique - Détermination Ergonomie der thermischen Umgebung - Bestimmung des
du métabolisme énergétique (ISO 8996:2004) körpereigenen Energieumsatzes (ISO 8996:2004)
This European Standard was approved by CEN on 26 August 2004.

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 Central Secretariat 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 Central Secretariat has the same status as the official
versions.

CEN members are the national standards bodies of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France,
Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia,
Slovenia, Spain, Sweden, Switzerland and United Kingdom.




EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

Management Centre: rue de Stassart, 36  B-1050 Brussels
© 2004 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 8996:2004: E
worldwide for CEN national Members.

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SIST EN ISO 8996:2005

EN ISO 8996:2004 (E)





Foreword


This document (EN ISO 8996:2004) 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 April 2005, and conflicting national
standards shall be withdrawn at the latest by April 2005.

This document supersedes EN 28996:1993.

According to the CEN/CENELEC Internal Regulations, the national standards organizations of
the following countries are bound to implement this European Standard: Austria, Belgium,
Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary,
Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland,
Portugal, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.


Endorsement notice

The text of ISO 8996:2004 has been approved by CEN as EN ISO 8996:2004 without any
modifications.

2

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SIST EN ISO 8996:2005


INTERNATIONAL ISO
STANDARD 8996
Second edition
2004-10-01

Ergonomics of the thermal
environment — Determination of
metabolic rate
Ergonomie de l'environnement thermique — Détermination du
métabolisme énergétique




Reference number
ISO 8996:2004(E)
©
ISO 2004

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SIST EN ISO 8996:2005
ISO 8996:2004(E)
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ii © ISO 2004 – All rights reserved

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SIST EN ISO 8996:2005
ISO 8996:2004(E)
Contents Page
Foreword. iv
1 Scope. 1
2 Normative references . 1
3 Principle and accuracy. 1
4 Level 1, screening . 3
4.1 Table for the estimation of metabolic rate by occupation. 3
4.2 Classification of metabolic rate by categories .3
5 Level 2, observation. 3
5.1 Estimation of metabolic rate by task requirements . 3
5.2 Metabolic rate for typical activities . 4
5.3 Metabolic rate for a work cycle. 4
5.4 Influence of the length of rest periods and work periods. 5
5.5 Obtaining values by interpolation . 6
5.6 Requirements for the application of metabolic-rate tables . 6
6 Level 3, analysis. 6
6.1 Estimation of metabolic rate using heart rate. 6
6.2 Relationship between heart rate and metabolic rate. 7
7 Level 4, expertise . 8
7.1 Determination of metabolic rate by measurement of oxygen consumption rate. 8
7.2 The doubly labelled water method for long-term measurements. 14
7.3 Direct calorimetry — Principle. 14
Annex A (informative) Evaluation of the metabolic rate at level 1, screening . 15
Annex B (informative) Evaluation of the metabolic rate at level 2, observation. 17
Annex C (informative) Evaluation of the metabolic rate at level 3, analysis . 20
Annex D (informative) Evaluation of the metabolic rate at level 4, expertise — Examples of the
calculation of metabolic rate based on measured data . 21

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SIST EN ISO 8996:2005
ISO 8996:2004(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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
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.
ISO 8996 was prepared by Technical Committee ISO/TC 159, Ergonomics, Subcommittee SC 5, Ergonomics
of the physical environment.
This second edition cancels and replaces the first edition (ISO 8996:1990), which has been technically revised.
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SIST EN ISO 8996:2005
INTERNATIONAL STANDARD ISO 8996:2004(E)

Ergonomics of the thermal environment — Determination of
metabolic rate
1 Scope
The metabolic rate, as a conversion of chemical into mechanical and thermal energy, measures the energetic
cost of muscular load and gives a numerical index of activity. Metabolic rate is an important determinant of the
comfort or the strain resulting from exposure to a thermal environment. In particular, in hot climates, the high
levels of metabolic heat production associated with muscular work aggravate heat stress, as large amounts of
heat need to be dissipated, mostly by sweat evaporation.
This International Standard specifies different methods for the determination of metabolic rate in the context of
ergonomics of the climatic working environment. It can also be used for other applications — for example, the
assessment of working practices, the energetic cost of specific jobs or sport activities, the total cost of an
activity, etc.
The estimations, tables and other data included in this International Standard concern an “average” individual:
2
 a man 30 years old weighing 70 kg and 1,75 m tall (body surface area 1,8 m );
2
 a woman 30 years old weighing 60 kg and 1,70 m tall (body surface area 1,6 m ).
Users should make appropriate corrections when they are dealing with special populations including children,
aged persons, people with physical disabilities, etc.
2 Normative references
The following referenced documents are indispensable for the application 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 9886, Ergonomics — Evaluation of thermal strain by physiological measurements
ISO 15265, Ergonomics of the thermal environment — Risk assessment strategy for the prevention of stress
or discomfort in thermal working conditions
3 Principle and accuracy
The mechanical efficiency of muscular work — called the “useful work”, W — is low. In most types of industrial
work, it is so small (a few percent) that it is assumed to be nil. This means that the total energy consumption
while working is assumed equal to the heat production. For the purposes of this International Standard, the
metabolic rate is assumed to be equal to the rate of heat production.
Table 1 lists the different approaches presented in this International Standard for determining the metabolic
rate.
These approaches are structured following the philosophy exposed in ISO 15265 regarding the assessment of
exposure. Four levels are considered here:
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SIST EN ISO 8996:2005
ISO 8996:2004(E)
Level 1, screening: Two methods simple and easy to use are presented to quickly characterize the mean
workload for a given occupation or for a given activity:
 method 1A is a classification according to occupation;
 method 1B is a classification according to the kind of activity.
Both methods provide only a rough estimate and there is considerable scope for error. This limits their
accuracy considerably. At this level, an inspection of the work place is not necessary.
Level 2, observation: Two methods are presented for people with full knowledge of the working conditions
but without necessarily a training in ergonomics, to characterize, on average, a working situation at a specific
time:
 in method 2A, the metabolic rate is determined by adding to the baseline metabolic rate the metabolic
rate for body posture, the metabolic rate for the type of work and the metabolic rate for body motion
related to work speed (using group assessment tables);
 in method 2B, the metabolic rate is determined by means of the tabulated values for various activities.
A procedure is described to record the activities with time and compute the time-weighted average metabolic
rate, using the data from the two methods above.
The possibility for errors is high. A time and motion study is necessary to determine the metabolic rate in work
situations that involve a cycle of different activities.
Level 3, analysis: One method is addressed to people trained in occupational health and ergonomics of the
thermal environment. The metabolic rate is determined from heart rate recordings over a representative period.
This method for the indirect determination of metabolic rate is based on the relationship between oxygen
uptake and heart rate under defined conditions.
Level 4, expertise: Three methods are presented. They require very specific measurements made by
experts:
 in Method 4A, the oxygen consumption is measured over short periods (10 min to 20 min) (a detailed time
and motion study is necessary to show the representativity of the measurement period);
 method 4B is the so-called doubly labelled water method aiming at characterizing the average metabolic
rate over much longer periods (1 to 2 weeks);
 method 4C is a direct calorimetry method.
The main factors affecting the accuracy of the estimations are the following:
 individual variability;
 differences in the work equipment;
 differences in work speed;
 differences in work technique and skill;
 gender differences and anthropometric characteristics;
 cultural differences;
 when using the tables, differences between observers and their level of training;
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SIST EN ISO 8996:2005
ISO 8996:2004(E)
 when using level 3, the accuracy of the relationship between heart rate and oxygen uptake, as other
stress factors also influence the heart rate;
 at level 4, the measurement accuracy (determination of gas volume and oxygen fraction).
The accuracy of the results, but also the costs of the study, increase from level 1 to level 4. Measurement at
level 4 gives the most accurate values. As far as possible, the most accurate method should be used.
Table 1 — Levels for the determination of the metabolic rate
Level Method Accuracy Inspection of the work place
Not necessary, but information
1A: Classification according to
needed on technical equipment,
occupation Rough information
1
work organization
Screening
Very great risk of error
1B: Classification according to

activity
2A: Group assessment tables Time and motion study necessary
High error risk
2
Observation
Accuracy: ± 20 %
2B: Tables for specific activities
Medium error risk
3 Heart rate measurement under Study required to determine a
Analysis defined conditions representative period
Accuracy: ± 10 %
4A: Measurement of oxygen
Time and motion study necessary
consumption
Errors within the limits of the
accuracy of the measurement
Inspection of work place not
4
or of the time and motion
4B: Doubly labelled water method necessary, but leisure activities
Expertise
study
must be evaluated.
Accuracy: ± 5 %
Inspection of work place not
4C: Direct calorimetry
necessary

4 Level 1, screening
4.1 Table for the estimation of metabolic rate by occupation
Table A.1 in Annex A shows the metabolic rate for different occupations. The values are mean values for the
whole working time, but without considering longer rest pauses, for example lunchtime. Significant variation
may arise due to differences in technology, work elements, work organization, etc.
4.2 Classification of metabolic rate by categories
The metabolic rate can be estimated approximately using the classification given in Annex A. Table A.2
defines five classes of metabolic rate: resting, low, moderate, high, very high. For each class, an average and
a range of metabolic rate values are given as well as a number of examples. These activities are supposed to
include short rest pauses. The examples given in Table A.2 illustrate the classification.
5 Level 2, observation
5.1 Estimation of metabolic rate by task requirements
Here, the metabolic rate is estimated from the following observations:
 the body segment involved in the work: both hands, one arm, two arms, the entire body;
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SIST EN ISO 8996:2005
ISO 8996:2004(E)
 the workload for that body segment: light, medium, heavy, as judged subjectively by the observer;
 the body posture: sitting, kneeling, crouching, standing, standing stooped;
 the work speed.
Table B.1 in Annex B gives the mean value and the range of metabolic rates for a standard person, seated, as
a function of the body segment involved and the workload. Table B.2 gives the corrections to be added when
the posture is different from seated.
5.2 Metabolic rate for typical activities
Table B.3 in Annex B provides values of metabolic rate for typical activities. These values are based on
measurements performed in the past in many different laboratories.
5.3 Metabolic rate for a work cycle
To determine the overall metabolic rate for a work cycle, it is necessary to carry out a time and motion study
that includes a detailed description of the work. This involves classifying each activity and taking account of
factors such as the duration of each activity, the distances walked, the heights climbed, the weights
manipulated, the number of actions carried out, etc.
The time-weighted average metabolic rate for a work cycle can be determined from the metabolic rate of the
respective activity and the respective duration using the equation:
n
1
M = Mt (1)
ii
∑
T
i=1
where
M is the average metabolic rate for the work cycle, in watts per square metre;
M is the metabolic rate for activity i, in watts per square metre;
i
t is the duration of activity i, in minutes;
i
T is the duration, in minutes, of the work cycle considered, and is equal to the sum of the partial
durations t .
i
The recording of occupational activities and the duration of the activities for a working day or for a particular
period may be simplified by using the diary described in Table B.4 and Table B.5. Activities are recorded when
they are changed, using a classification code derived from the tables for the estimation of metabolic rate by
task components. The number of components to be considered will vary depending upon the complexity of the
activity.
The procedure is as follows:
a) Fill in the name and other details of the person under study.
b) Observe the work of the person under study (at least 2 h to 3 h).
c) Determine each individual task component and the corresponding metabolic rate estimated from
Table B.1, B.2 or B.3.
d) Always fill in the diary when the task component is changed.
e) Calculate the total length of time spent on each task component.
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SIST EN ISO 8996:2005
ISO 8996:2004(E)
f) Multiply the length of time spent on each task component by the corresponding metabolic rate.
g) Add the values.
h) Divide the sum by the total length of the observation period.
Forms for the evaluation are given in Tables B.4 and B.5.
5.4 Influence of the length of rest periods and work periods
The tables in Annex B cannot be used for the evaluation of the average metabolic rate for working conditions
with an intermittent sequence of short periods of activity and long rest periods. In this case, the technique
described in 5.3. would lead to an underestimation of the metabolic rate, known as the Simonson effect. The
limit of validity of combinations of work and rest periods is shown by the curve in Figure 1. Example 1
concerns a cycle of 8 min of rest and 1 min of work. In this case, the technique described in 5.3 would lead to
an underestimation of the metabolic rate and the tables in Annex B cannot be used. For work-rest cycles such
as in Example 2, the tables can be used with the indicated accuracy.
Figure 1 only applies if there is no physical workload during the rest periods.
An increase in the metabolic rate due to this effect depends on the type of work and the muscle groups used.
Further information on this problem is not given here, because of its complexity and because of its low
relevancy at this level of evaluation.

Key
X length of work period, min
Y length of rest pause, min
1 Example 1
2 Example 2
Figure 1 — Curve showing limit of validity of combinations of work and rest periods
when estimating metabolic rate
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SIST EN ISO 8996:2005
ISO 8996:2004(E)
5.5 Obtaining values by interpolation
It is possible to obtain metabolic-rate values by interpolation. When working speeds differ from those given in
the tables in Annex B, conversion is only possible within a range of ± 25 % of the indicated speed, however.
5.6 Requirements for the application of metabolic-rate tables
To allow comparison of values from different sources, values reported in the tables in Annexes A and B have
been standardized with respect to the standard person working in a comfortable thermal environment.
The metabolic rate for a given person performing a given task may vary within certain limits around the mean
values given in the tables, due to the influence of the factors mentioned in Clause 3.
However, it can be estimated that:
 for the same work and under the same working conditions, the metabolic rate can vary from person to
person by about ± 5 %;
 for a person trained in the activity, the variation is about 5 % under Iaboratory conditions;
 under field conditions, i.e. when the activity to be measured is not exactly the same from test to test, a
variation of up to 20 % can be expected.
Considering this risk of error, it is normally not justified, at this level of evaluation, to take into consideration
differences in height or gender.
The consideration of the weight of the subject might be warranted only for activities involving movements of
the whole body, such as walking, climbing, lifting weights.
−2 −2
In hot conditions, a maximum increase of 5 W⋅m to 10 W⋅m may be expected due to increased heart rate
and sweating. Such a correction is not justified.
−2
On the other hand, in cold conditions, an increase of up to 200 W⋅m may be observed when shivering
occurs. The wearing of heavy clothing will also increase metabolic rate, by increasing the weight of the subject
and decreasing the subject's ease of movement.
6 Level 3, analysis
6.1 Estimation of metabolic rate using heart rate
The heart rate at a given time may be regarded as the sum of several components:
HR = HR + ∆HR + ∆HR + ∆HR + ∆HR + ∆HR (2)
0 M S T N E
where
HR is the heart rate, in beats per minute, at rest in a prone position under neutral thermal conditions;
0
∆HR is the increase in heart rate, in beats per minute, due to dynamic muscular load, under neutral
M
thermal conditions;
∆HR is the increase in heart rate, in beats per minute, due to static muscular work (this component
S
depends on the relationship between the force used and the maximum voluntary force of the
working muscle group);
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SIST EN ISO 8996:2005
ISO 8996:2004(E)
∆HR is the increase in heart rate, in beats per minute, due to heat stress (the thermal component is
T
discussed in ISO 9886);
∆HR is the increase in heart rate, in beats per minute, due to mental load;
N
∆HR is the change in heart rate, in beats per minute, due to other factors, for example respiratory
E
effects, circadian rhythms, dehydration.
In the case of dynamic work using major muscle groups, with only a small amount of static muscular load and
in the absence of thermal strain and mental loads, the metabolic rate may be estimated by measuring the
heart rate while working. Under such conditions, a linear relationship exists between the metabolic rate and
the heart rate. If the above-mentioned restrictions are taken into account, this method can be more accurate
than the level 1 and level 2 methods of estimation (see Table 1) and is less complex than the measurement of
oxygen consumption, which provides the most accurate results.
The heart rate may be recorded continuously, for example by the use of telemetric equipment, or, with a
further reduction in accuracy, measured manually by counting the arterial pulse rate (see ISO 9886).
The mean heart rate HR may be computed over fixed time intervals, for example 1 min, over different working
cycles or over the whole shift time.
In the presence of considerable thermal load, static muscular work, dynamic work with small muscle groups
and/or mental loads, the slope and form of the heart rate to metabolic rate relationship can change drastically.
The procedure used to correct the heart rate measurements for thermal effects is described in ISO 9886.
6.2 Relationship between heart rate and metabolic rate
The relationship between heart rate and metabolic rate can be measured by recording the heart rate at
different stages of defined muscular load during an experiment in a neutral climatic environment. Heart rate
and corresponding oxygen consumption or physical work performed is measured during dynamic muscular
work at different load stages. As the type of work (cycle ergometer, step test, treadmill) and the sequence and
duration of the load stages have an influence on both parameters, it is necessary to use a standardized
procedure.
In general, linearity holds true for the range extending
 from a lower limit of 120 beats per minute (bpm), because the mental component can then be neglected;
 up to 20 beats below the maximum heart rate of the subject, because the heart rate tends to level off
above this value.
Within this range, the relationship between heart rate and metabolic rate can be written as:
HR = HR + RM × (M − M ) (3)
0 0
where
M is the metabolic rate, in watts per square metre;
M is the metabolic rate at rest, in watts per square metre;
0
RM is the increase in heart rate per unit of metabolic rate;
HR is the heart rate at rest, under neutral thermal conditions.
0
This relationship is used to derive the metabolic rate from the measured heart rate.
When this expression is derived from HR and M measurements during an experiment, the precision can be
estimated at about 10 %.
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SIST EN ISO 8996:2005
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With a further loss of accuracy, the expression can be derived from estimations of:
 the heart rate at rest under neutral thermal conditions HR ;
0
 the metaboli
...