prEN ISO 7933

Ergonomics of the thermal environment - Analytical determination and interpretation of heat stress using the predicted heat strain model (ISO/DIS 7933:2018)

Ergonomie der thermischen Umgebung - Analytische Bestimmung und Interpretation der Wärmebelastung mit dem Modell der vorhergesagten Wärmebeanspruchung (ISO/DIS 7933:2018)

Ergonomie des ambiances thermiques - Détermination analytique et interprétation de la contrainte thermique fondées sur le calcul de l'astreinte thermique prévisible (ISO/DIS 7933:2018)

Ergonomija toplotnega okolja - Analitično ugotavljanje in razlaga toplotnega stresa s predvideno toplotno obremenitvijo (ISO/DIS 7933:2018)

General Information

• Status: Not Published
• Publication Date: 11-May-2020
• Withdrawal Date: 11-May-2020
• ICS: 13.180 - Ergonomics
• Technical Committee: CEN/TC 122 - Ergonomics
• Drafting Committee: CEN/TC 122/WG 11 - Ergonomics of the Physical Environment
• Current Stage: 4098 - Decision to abandon - Enquiry
• Due Date: 20-Sep-2016
• Completion Date: 05-Feb-2019
• Ref Project: oSIST prEN ISO 7933:2018 - Ergonomics of the thermal environment - Analytical determination and interpretation of heat stress using the predicted heat strain model (ISO/DIS 7933:2018)

Standards Content (Sample)

SLOVENSKI STANDARD
oSIST prEN ISO 7933:2018
01-junij-2018
(UJRQRPLMDWRSORWQHJDRNROMD$QDOLWLþQRXJRWDYOMDQMHLQUD]ODJDWRSORWQHJDVWUHVD
VSUHGYLGHQRWRSORWQRREUHPHQLWYLMR,62',6
Ergonomics of the thermal environment - Analytical determination and interpretation of
heat stress using the predicted heat strain model (ISO/DIS 7933:2018)
Ergonomie der thermischen Umgebung - Analytische Bestimmung und Interpretation der
Wärmebelastung mit dem Modell der vorhergesagten Wärmebeanspruchung (ISO/DIS
7933:2018)
Ergonomie des ambiances thermiques - Détermination analytique et interprétation de la
contrainte thermique fondées sur le calcul de l'astreinte thermique prévisible (ISO/DIS
7933:2018)
Ta slovenski standard je istoveten z: prEN ISO 7933
ICS:
13.180 Ergonomija Ergonomics
oSIST prEN ISO 7933:2018 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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oSIST prEN ISO 7933:2018

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oSIST prEN ISO 7933:2018
DRAFT INTERNATIONAL STANDARD
ISO/DIS 7933
ISO/TC 159/SC 5 Secretariat: BSI
Voting begins on: Voting terminates on:
2018-04-13 2018-07-06
Ergonomics of the thermal environment — Analytical
determination and interpretation of heat stress using the
predicted heat strain model
Ergonomie des ambiances thermiques — Détermination analytique et interprétation de la contrainte
thermique fondées sur le calcul de l'astreinte thermique prévisible
ICS: 13.180
THIS DOCUMENT IS A DRAFT CIRCULATED
This document is circulated as received from the committee secretariat.
FOR COMMENT AND APPROVAL. IT IS
THEREFORE SUBJECT TO CHANGE AND MAY
NOT BE REFERRED TO AS AN INTERNATIONAL
STANDARD UNTIL PUBLISHED AS SUCH.
IN ADDITION TO THEIR EVALUATION AS
ISO/CEN PARALLEL PROCESSING
BEING ACCEPTABLE FOR INDUSTRIAL,
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
STANDARDS MAY ON OCCASION HAVE TO
BE CONSIDERED IN THE LIGHT OF THEIR
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
Reference number
NATIONAL REGULATIONS.
ISO/DIS 7933:2018(E)
RECIPIENTS OF THIS DRAFT ARE INVITED
TO SUBMIT, WITH THEIR COMMENTS,
NOTIFICATION OF ANY RELEVANT PATENT
RIGHTS OF WHICH THEY ARE AWARE AND TO
©
PROVIDE SUPPORTING DOCUMENTATION. ISO 2018

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oSIST prEN ISO 7933:2018
ISO/DIS 7933:2018(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2018
All rights reserved. Unless otherwise specified, or required in the context of its implementation, 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 the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Fax: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii © ISO 2018 – All rights reserved

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oSIST prEN ISO 7933:2018
ISO/DIS 7933:2018(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Symbols . 1
4 Principles of the predicted heat strain (PHS) model . 4
5 Main steps of the calculation . 5
5.1 Heat balance equation . 5
5.1.1 Metabolic rate, M .5
5.1.2 Effective mechanical power, W .5
5.1.3 Heat flow by respiratory convection, C .
res 5
5.1.4 Heat flow by respiratory evaporation, E .
res 5
5.1.5 Heat flow by conduction, K .5
5.1.6 Heat flow by convection, C .6
5.1.7 Heat flow by radiation, R .6
5.1.8 Heat flow by evaporation, E.6
5.1.9 Heat storage for increase of core temperature associated with the
metabolic rate, dS .
eq 6
5.1.10 Heat storage, S .6
5.2 Calculation of the required evaporative heat flow, the required skin wettedness
and the required sweat rate . . 7
6 Interpretation of required sweat rate . 7
6.1 Basis of the method of interpretation . 7
6.1.1 Stress criteria . 7
6.1.2 Strain criteria . 8
6.1.3 Reference values . 8
6.2 Analysis of the work situation . 8
6.3 Determination of allowable exposure time, D .
lim 8
Annex A (normative) Data necessary for the computation of thermal balance .10
Annex B (informative) Criteria for estimating acceptable exposure time in a hot
work environment .17
Annex C (informative) Metabolic rate .19
Annex D (informative) Clothing thermal characteristics .21
Annex E (informative) Computer programme for the computation of the predicted heat
strain model .23
Annex F (normative) Examples of the predicted heat strain model computations .31
Bibliography .32
© ISO 2018 – All rights reserved iii

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oSIST prEN ISO 7933:2018
ISO/DIS 7933:2018(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 7933 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 7933:2004).
iv © ISO 2018 – All rights reserved

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oSIST prEN ISO 7933:2018
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Introduction
This series of International Standards describe a coordinated set of methods for the evaluation of
[1]
working conditions as a function of the thermal environment. ISO 15265 describes the assessment
strategy for the prevention of discomfort or health in any thermal working condition, while
[2]
ISO 16595/WP recommends specific practices concerning hot working environments. For these hot
environments, these standards propose to rely on the wet bulb globe temperature (WBGT) heat stress
index described in ISO 7243 [3] as a screening method - for establishing the presence or absence of heat
stress and on the more elaborate method presented in this International standard, to make a more
accurate estimation of stress, to determine the allowable durations of work in these conditions and to
optimize the methods of protection. This method, based on an analysis of the heat exchange between a
person and the environment, is intended to be used directly when it is desired to carry out an intensive
analysis of working conditions in heat.
This International Standard standardizes the method that occupational health specialists are expected
to use to approach a given problem and progressively collect the information needed to control or
prevent the problem.
This third edition of the standard is based on the latest scientific information. Future improvements
concerning the calculation of the different terms of the heat balance equation, or its interpretation, will
still be taken into account in the future when they become available.
In its present form, this method of assessment is not applicable to cases where special protective clothing
(reflective clothing, active cooling and ventilation, impermeable, with personal protective equipment)
is worn. It does not either account for transients in environmental conditions, metabolic rate and/or
clothing and therefore makes possible to predict the evolution of the core temperature and the water
loss in conditions where these parameters remain steady. In addition, occupational health specialists
are responsible for evaluating the risk encountered by a given individual, taking into consideration
[4]
their specific characteristics that might differ from those of a standard subject. ISO 9886 describes
how physiological parameters are used to monitor the physiological behaviour of a particular subject
[5]
and ISO 12894 describes how medical supervision is organized.
© ISO 2018 – All rights reserved v

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oSIST prEN ISO 7933:2018

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oSIST prEN ISO 7933:2018
DRAFT INTERNATIONAL STANDARD ISO/DIS 7933:2018(E)
Ergonomics of the thermal environment — Analytical
determination and interpretation of heat stress using the
predicted heat strain model
1 Scope
The main objective of this International Standard is to describe a mathematical model (the predicted
heat strain model) for the analytical determination and interpretation of the thermal stress (in terms
of water loss and core temperature) experienced by a subject in a hot environment and to determine
the “maximum allowable exposure times”, with which the physiological strain is acceptable for 95% of
the exposed population. (the maximum tolerable core temperature and the maximum tolerable water
loss are not exceeded by 95% of the exposed people).
The various terms used in this prediction model, and in particular in the heat balance, show the
influence of the different physical parameters of the environment on the thermal stress experienced
by the subject. In this way, this International Standard makes it possible to determine which parameter
or group of parameters can be changed, and to what extent, in order to reduce the risk of physiological
strains.
This International Standard does not predict the physiological response of individual subjects, but only
considers standard subjects in good health and fit for the work they perform. It is therefore intended to
be used by ergonomists, industrial hygienists, etc. Recommendations about how and when to use this
model are given in ISO 15265, Ergonomics of the thermal environment -- Risk assessment strategy for
the prevention of stress or discomfort in thermal working conditions
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 undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 7726, Ergonomics of the thermal environment — Instruments for measuring physical quantities
ISO 8996, Ergonomics of the thermal environment — Determination of metabolic rate
ISO 9886, Ergonomics — Evaluation of thermal strain by physiological measurements
ISO 9920, Ergonomics of the thermal environment — Estimation of thermal insulation and water vapour
resistance of a clothing ensemble
ISO 13731, Ergonomics of the thermal environment — Vocabulary and symbols
ISO 13732-1, Ergonomics of the thermal environment — Methods for the assessment of human responses to
contact with surfaces — Part 1: Hot surfaces
ISO 15265, Ergonomics of the thermal environment — Risk assessment strategy for the prevention of stress
or discomfort in thermal working conditions
ISO 16595/WP, Ergonomics of the thermal environment: Working practices in hot environments
3 Symbols
For the purposes of this document, the symbols and abbreviated terms, designated in Table 1 as
“symbols” with their units, are in accordance with ISO 13731.
© ISO 2018 – All rights reserved 1

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However, additional symbols are used for the presentation of the predicted heat strain index. A complete
list of symbols used in this International standard is presented in Table 2.
Table 1 — Symbols and units conforming to ISO 13731
Symbol Term Unit
α fraction of the body mass at the skin temperature ‒
α skin-core weighting at time t ‒
i i
α
skin-core weighting at time t ‒
i–1 i–1
ε skin emissivity ‒
ε emissivity of clothing ‒
cl
θ angle between walking direction and wind direction °
2
A DuBois body area surface m
Du
A
fraction of the body surface covered by the reflective clothing ‒
p
A 2
effective radiating area of a body m
r
-2
C convective heat flow W⋅m
-1
c water latent heat of vaporization J⋅kg
e
C correction factor for the static moisture permeability index ‒
orr,im
C correction factor for the static boundary layer thermal insulation ‒
orr,Ia,st
C correction factor for the static clothing thermal insulation ‒
orr,Icl,st
C correction factor for the static total clothing thermal insulation ‒
orr,Itot,st
-1 -1
c specific heat of dry air at constant pressure J⋅kg ⋅K
p
-1 -1
c specific heat of the body J⋅kg ⋅K
p,b
-2
C respiratory convective heat flow W⋅m
res
D allowable exposure time min
lim
D allowable exposure time for heat storage min
lim,tcr
D allowable exposure time for water loss, 95 % of the working population min
lim,loss
D maximum water loss g
max
D maximum water loss to protect 95 % of the working population g
max,95
-2
dS body heat storage at the time i W⋅m
i
body heat storage rate due to increase of core temperature associated with the
-2
dS W⋅m
eq
metabolic rate
-2
E evaporative heat flow at the skin surface W⋅m
-2
E maximum evaporative heat flow at the skin surface W⋅m
max
-2
E predicted evaporative heat flow at the skin surface W⋅m
p
-2
E required evaporative heat flow at the skin surface W⋅m
req
-2
E respiratory evaporative heat flow W⋅m
res
f
clothing area factor ‒
cl
F reduction factor for radiation heat exchange due to wearing reflective clothes ‒
cl,R
F Reflection coefficients for different special materials ‒
r
H body height m
b
-2 -1
h dynamic convective heat transfer coefficient W⋅m ⋅K
c,dyn
-2 -1
h radiative heat transfer coefficient W⋅m ⋅K
r
2 -1
I dynamic boundary layer thermal insulation m ⋅K⋅W
a,dyn
2 -1
I static boundary layer thermal insulation m ⋅K⋅W
a,st
2 -1
I dynamic clothing thermal insulation m ⋅K⋅W
cl,dyn
2 -1
I static clothing thermal insulation m ⋅K⋅W
cl,st
2 © ISO 2018 – All rights reserved

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ISO/DIS 7933:2018(E)

Table 1 (continued)
Symbol Term Unit
i dynamic moisture permeability index ‒
m,dyn
i static moisture permeability index ‒
m,st
incr time increment from time t to time t min
i–1 i
2 -1
i dynamic total clothing thermal insulation m ⋅K⋅W
T,dyn
2 -1
i static total clothing thermal insulation m ⋅K⋅W
T,st
-2
K conductive heat flow W⋅m
k time constant of the increase of the sweat rate min
sw
time constant of the variation of the core temperature as function of the met-
k min
tcreq
abolic rate
k time constant of the variation of the skin temperature min
tsk
-2
M metabolic rate W⋅m
p water vapour partial pressure at air temperature kPa
a
p
saturated water vapour pressure at skin temperature kPa
sk,s
-2
R radiative heat flow W⋅m
2 -1
R dynamic clothing total water vapour resistance m ⋅Pa⋅W
e,T,dyn
r required evaporative efficiency of sweating ‒
req
-2
S body heat storage rate W⋅m
body heat storage for increase of core temperature associated with the meta-
-2
S W⋅m
eq
bolic rate
-2
Sw maximum sweat rate capacity W⋅m
max
-2
Sw predicted sweat rate W⋅m
p
-2
Sw predicted sweat rate at time t W⋅m
p,i i
-2
Sw predicted sweat rate at time t W⋅m
p,i–1 i–1
-2
Sw required sweat rate W⋅m
req
t time min
t air temperature °C
a
t clothing surface temperature °C
cl
t core temperature °C
cr
t steady state core temperature as a function of the metabolic rate °C
cr,eq
t
t core temperature as a function of the metabolic rate at time °C
cr,eq i i
t
t core temperature as a function of the metabolic rate at time °C
cr,eq i–1 i–1
t steady state value of core temperature as a function of the metabolic rate °C
cr,eq,m
t core temperature at time t °C
cr,i i
t core temperature at time t °C
cr,i-1 i–1
t expired air temperature °C
ex
t mean radiant temperature °C
r
t rectal temperature °C
re
t maximum acceptable core temperature °C
cr,max
t rectal temperature at time t °C
re,i i
t rectal temperature at time t °C
re,i–1 i–1
t skin temperature °C
sk
t steady state mean skin temperature °C
sk,eq
t steady state mean skin temperature for clothed subjects °C
sk,eq,cl
t steady state mean skin temperature for nude subjects °C
sk,eq,nu
© ISO 2018 – All rights reserved 3

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oSIST prEN ISO 7933:2018
ISO/DIS 7933:2018(E)

Table 1 (continued)
Symbol Term Unit
t mean skin temperature at time t °C
sk,i i
t mean skin temperature at time t °C
sk,i–1 i–1
-1
V expired volume flow rate L⋅min
ex
-1
v air velocity m⋅s
a
-1
v relative air velocity m⋅s
ar
-1
v walking speed m⋅s
w
w skin wettedness ‒
-2
W effective mechanical power W⋅m
W humidity ratio of inhaled air kg /kg
a water air
W body mass kg
b
W humidity ratio of expired air kg /kg
ex water air
w maximum skin wettedness ‒
max
w predicted skin wettedness ‒
p
w required skin wettedness ‒
req
4 Principles of the predicted heat strain (PHS) model
The PHS model is based on the thermal energy balance of the body which requires the values of the
following parameters, which are estimated or measured according to ISO 7726:
a) the parameters of the thermal environment:
— air temperature, t ;
a
— mean radiant temperature, t ;
r
— partial vapour pressure, p ; and
a
— air velocity, v ;
a
b) the mean characteristics of the subjects exposed to this working situation:
— the metabolic rate, M, estimated on the basis of ISO 8996; and
— the clothing thermal characteristics, estimated on the basis of ISO 9920.
Clause 5 describes the principles of the calculation of the different heat exchanges occurring in the
thermal balance equation, as well as those of the water loss necessary for the maintenance of the
thermal equilibrium of the body. The mathematical expressions for these calculations are given in
Annex A.
Clause 6 describes the method for interpreting the results from Clause 5, which leads to the
determination of the predicted sweat rate, the predicted core temperature and the allowable exposure
times. The determination of the allowable exposure times is based on two strain criteria: maximum
core temperature increase and maximum body water loss, given in Annex B.
The precision with which the predicted sweat rate and the exposure times are estimated is a function
of the model (i.e. of the expressions in Annex A) and the maximum values which are adopted. It is also a
function of the accuracy of estimation and measurement of the physical parameters and of the precision
with which the metabolic rate and the thermal insulation of the clothing are estimated.
4 © ISO 2018 – All rights reserved

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5 Main steps of the calculation
5.1 Heat balance equation
The thermal energy balance of the human body may be written as:
M − W = C + E + K + C + R + E + S (1)
res res
This equation expresses that the internal heat production of the body, which corresponds to the
metabolic rate, M, minus the effective mechanical power, W, are balanced by the heat exchanges in the
respiratory tract by convection, C , and evaporation, E , as well as by the heat exchanges on the skin
res res
by conduction, K, convection, C, radiation, R, and evaporation, E.
If the balance is not satisfied, some energy is stored in the body, S.
The different terms of Equation (1) are successively reviewed in 5.1.1 to 5.1.10 in terms of the principles
of calculation (detailed expressions are shown in Annex A).
5.1.1 Metabolic rate, M
The estimation or measurement of the metabolic rate is described in ISO 8996. Indications for the
evaluation of the metabolic rate are given in Annex C.
5.1.2 Effective mechanical power, W
In most industrial situations, the effective mechanical power is small and can be neglected.
5.1.3 Heat flow by respiratory convection, C
res
The heat flow by respiratory convection may be expressed, in principle, by the following equation:
tt− 
ex a
Cc=×0,00002 V × (2)
 
resp ex
A
 Du 
5.1.4 Heat flow by respiratory evaporation, E
res
The heat flow by respiratory evaporation can be expressed, in principle, by the following equation:
 
WW−
ex a
Ec=×0,00002 V × (3)
 
resee x
A
 Du 
5.1.5 Heat flow by conduction, K
Heat flow by thermal conduction occurs on the body surfaces in contact with solid objects. It is usually
quite small, not directly taken into account and quantitatively assimilated to the heat losses by convection
and radiation which would occur on these surfaces if they were not in contact with any solid body.
[6]
ISO 13732-1 deals specifically with the risks of pain and burns when parts of the body contact hot
surfaces.
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5.1.6 Heat flow by convection, C
The heat flow by convection on the bare skin may be expressed by the following equation:
C = h × (t – t) (4)
c,dyn sk a
For clothed person, the heat flow by convection occurs at the surface of the clothing and is expressed by
the following equation:
C = h × f × (t – t) (5)
c,dyn cl cl a
Annex D provides some indications for the evaluation of the clothing thermal characteristics.
5.1.7 Heat flow by radiation, R
The heat flow by radiation may be expressed by the following equation:
R = h × f × (t – t) (6)
r cl cl a
where the radiative heat transfer coefficient, h , takes into account the clothing characteristics, (e.g.
r
emissivity and the presence of reflective clothing) and the effective radiating area of the subject related
to the position (e.g. standing, seated, crouching subject)”.
5.1.8 Heat flow by evaporation, E
The maximum evaporative heat flow, E , is that which can be achieved in the hypothetical case of the
max
skin being completely wetted. In these conditions:
pp−
sk,s a
E = (7)
max
R
e,T,dyn
where the dynamic clothing total water vapour resistance, R , takes into account the clothing
e,T,dyn
characteristics as well as the movements of the subject and the air.
The actual evaporation heat flow, E, depends upon the fraction, w, of the skin surface wetted by sweat
and is given by:
E = w × E (8)
max
5.1.9 Heat storage for increase of core temperature associated with the metabolic rate, dS
eq
Even in a neutral environment, the core temperature rises towards a steady state value, t , as a
cr,eq
function of the metabolic rate.
The core temperature reaches this steady state temperature exponentially with time. The heat storage
t t
associated with the increase from time to time , dS does not contribute to the onset of sweating
i–1 i eq,
and should therefore be deducted from the heat balance equation.
5.1.10 Heat storage, S
The heat storage of the body is given by the algebraic sum of the heat flows defined previously.
6 © ISO 2018 – All rights reserved

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5.2 Calculation of the required evaporative heat flow, the required skin wettedness and
the required sweat rate
Taking into account the hypotheses made concerning the heat flow by conduction, the general heat
balance equation (1) can be written as:
E + S = M – W – C – E – C – R (9)
res res
The required evaporative heat flow, E , is the evaporation heat flow required for the maintenance of
req
the thermal equilibrium of the body and, therefore, for the body heat storage rate to be equal to zero. It
is given by:
E = M – W – C – E – C – R – dS (10)
req res res eq
The required skin wettedness, w , is the ratio between the required evaporative heat flow and the
req
maximum evaporative heat flow at the skin surface.
The calculation of the required sweat rate is made as follows on the basis of the required evaporative
heat flow, but taking account of the evaporative efficiency of the sweating, r
req:
E
req
w = (11)
req
E
max
The required sweat rate is then given by:
E
req
S = (12)
wreq
r
req
-2 -2 -1
NOTE The sweat rate in W⋅m represents the equivalent in heat of the sweat rate expressed in g⋅m h
-2 -2 -1 -1 ²
1 W⋅m corresponds to a flow of sweat of 1,47 g⋅m h or 2,67 g⋅h for a standard subject (1,8 m of body
surface).
6 Inter
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