SIST EN ISO 11079:2008
Ergonomics of the thermal environment - Determination and interpretation of cold stress when using required clothing insulation (IREQ) and local cooling effects (ISO 11079:2007)
Ergonomics of the thermal environment - Determination and interpretation of cold stress when using required clothing insulation (IREQ) and local cooling effects (ISO 11079:2007)
This International Standard specifies methods and strategies f or assessing the thermal stress associated with exposure to co ld environments. These methods apply to continuous, intermitte nt as well as occasional exposure and type of work, indoors an d outdoors. They are not applicable to specific effects associ ated with certain meteorological phenomena (e.g. precipitation ), which are assessed by other methods.
Ergonomie der thermischen Umgebung - Bestimmung und Interpretation der Kältebelastung bei Verwendung der erforderlichen Isolation der Bekleidung (IREQ) und lokalen Kühlwirkungen (ISO 11079:2007)
Diese Internationale Norm legt Verfahren und Strategien zur Bewertung der thermischen Belastung fest, die mit dem Aufenthalt in Kälteumgebungen verbunden sind. Diese Verfahren gelten für eine ununterbrochene, unterbrochene und gelegentliche Exposition sowohl für Arbeiten in Innenräumen als auch im Freien. Die vorliegende Internationale Norm ist nicht auf spezifische Effekte, die mit bestimmten meteorologischen Erscheinungen (z. B. Niederschlag) verbunden sind, anwendbar. Diese Effekte sollten nach anderen Verfahren beurteilt werden.
Ergonomie des ambiances thermiques - Détermination et interprétation de la contrainte liée au froid en utilisant l'isolement thermique requis du vetement et les effets du refroidissement local (ISO 11079:2007)
L'ISO 11079:2007 expose des méthodes et des stratégies ayant pour but d'évaluer la contrainte thermique associée à l'exposition aux environnements froids. Ces méthodes s'appliquent aux expositions et aux types de travaux continus, intermittents et occasionnels, aussi bien en intérieur qu'à l'extérieur. Elles ne sont pas applicables aux effets spécifiques liés à certains phénomènes météorologiques (des précipitations, par exemple), qui sont évalués par d'autres méthodes.
Ergonomija toplotnega okolja - Ugotavljanje in razlaga obremenitev zaradi mraza ob uporabi zahtevanih zaščitnih oblačil (IREQ) in zaradi učinkov lokalnega ohlajevanja (ISO 11079:2007)
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
SIST EN ISO 11079:2008
01-april-2008
(UJRQRPLMDWRSORWQHJDRNROMD8JRWDYOMDQMHLQUD]ODJDREUHPHQLWHY]DUDGLPUD]D
REXSRUDEL]DKWHYDQLK]DãþLWQLKREODþLO ,5(4 LQ]DUDGLXþLQNRYORNDOQHJD
RKODMHYDQMD ,62
Ergonomics of the thermal environment - Determination and interpretation of cold stress
when using required clothing insulation (IREQ) and local cooling effects (ISO
11079:2007)
Ergonomie der thermischen Umgebung - Bestimmung und Interpretation der
Kältebelastung bei Verwendung der erforderlichen Isolation der Bekleidung (IREQ) und
lokalen Kühlwirkungen (ISO 11079:2007)
Ergonomie des ambiances thermiques - Détermination et interprétation de la contrainte
liée au froid en utilisant l'isolement thermique requis du vetement et les effets du
refroidissement local (ISO 11079:2007)
Ta slovenski standard je istoveten z: EN ISO 11079:2007
ICS:
13.180 Ergonomija Ergonomics
SIST EN ISO 11079:2008 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
---------------------- Page: 1 ----------------------
EUROPEAN STANDARD
EN ISO 11079
NORME EUROPÉENNE
EUROPÄISCHE NORM
December 2007
ICS 13.180 Supersedes ENV ISO 11079:1998
English Version
Ergonomics of the thermal environment - Determination and
interpretation of cold stress when using required clothing
insulation (IREQ) and local cooling effects (ISO 11079:2007)
Ergonomie des ambiances thermiques - Détermination et Ergonomie der thermischen Umgebung - Bestimmung und
interprétation de la contrainte liée au froid en utilisant Interpretation der Kältebelastung bei Verwendung der
l'isolement thermique requis du vêtement (IREQ) et les erforderlichen Isolation der Bekleidung (IREQ) und lokalen
effets du refroidissement local (ISO 11079:2007) Kühlwirkungen (ISO 11079:2007)
This European Standard was approved by CEN on 14 December 2007.
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 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 Management Centre has the same status as the
official versions.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal,
Romania, 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
© 2007 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 11079:2007: E
worldwide for CEN national Members.
---------------------- Page: 2 ----------------------
EN ISO 11079:2007 (E)
Contents Page
Foreword.3
2
---------------------- Page: 3 ----------------------
EN ISO 11079:2007 (E)
Foreword
This document (EN ISO 11079:2007) 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 June 2008, and conflicting national standards shall be withdrawn at
the latest by June 2008.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.
This document supersedes ENV ISO 11079:1998.
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, Cyprus, Czech
Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain,
Sweden, Switzerland and the United Kingdom.
Endorsement notice
The text of ISO 11079:2007 has been approved by CEN as a EN ISO 11079:2007 without any modification.
3
---------------------- Page: 4 ----------------------
INTERNATIONAL ISO
STANDARD 11079
First edition
2007-12-15
Ergonomics of the thermal
environment — Determination and
interpretation of cold stress when using
required clothing insulation (IREQ) and
local cooling effects
Ergonomie des ambiances thermiques — Détermination et
interprétation de la contrainte liée au froid en utilisant l'isolement
thermique requis du vêtement (IREQ) et les effets du refroidissement
local
Reference number
ISO 11079:2007(E)
©
ISO 2007
---------------------- Page: 5 ----------------------
ISO 11079:2007(E)
PDF disclaimer
This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but
shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In
downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat
accepts no liability in this area.
Adobe is a trademark of Adobe Systems Incorporated.
Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation
parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In
the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below.
COPYRIGHT PROTECTED DOCUMENT
© ISO 2007
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,
electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or
ISO's member body in the country of the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland
ii © ISO 2007 – All rights reserved
---------------------- Page: 6 ----------------------
ISO 11079:2007(E)
Contents Page
Foreword. iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and symbols. 2
4 Principles of methods for evaluation. 4
5 General cooling. 4
6 Local cooling. 10
7 Practical assessment of cold environments and interpretation. 11
Annex A (normative) Computation of thermal balance. 13
Annex B (informative) Physiological criteria in cold exposure . 16
Annex C (informative) Metabolic rate and thermal properties of clothing . 18
Annex D (informative) Determination of wind cooling . 21
Annex E (informative) Examples of evaluation of IREQ . 23
Annex F (informative) Computer program for calculating IREQ . 33
Bibliography . 34
© ISO 2007 – All rights reserved iii
---------------------- Page: 7 ----------------------
ISO 11079:2007(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 11079 was prepared by Technical Committee ISO/TC 159, Ergonomics, Subcommittee SC 5,
Ergonomics of the physical environment.
This first edition of ISO 11079 cancels and replaces the ISO/TR 11079:1993, of which it constitutes a
technical revision.
iv © ISO 2007 – All rights reserved
---------------------- Page: 8 ----------------------
ISO 11079:2007(E)
Introduction
Wind chill is commonly encountered in cold climates, but it is low temperatures that first of all endanger body
heat balance. By proper adjustment of clothing, human beings can often control and regulate body heat loss,
to balance a change in the ambient climate. The method presented here is based therefore on the evaluation
of the clothing insulation required to maintain the thermal balance of the body in equilibrium. The heat balance
equation used takes into account the most recent scientific findings concerning heat exchanges at the surface
of the skin as well as the clothing.
© ISO 2007 – All rights reserved v
---------------------- Page: 9 ----------------------
INTERNATIONAL STANDARD ISO 11079:2007(E)
Ergonomics of the thermal environment — Determination and
interpretation of cold stress when using required clothing
insulation (IREQ) and local cooling effects
1 Scope
This International Standard specifies methods and strategies for assessing the thermal stress associated with
exposure to cold environments. These methods apply to continuous, intermittent as well as occasional
exposure and type of work, indoors and outdoors. They are not applicable to specific effects associated with
certain meteorological phenomena (e.g. precipitation), which are assessed by other methods.
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 7726, Ergonomics of the thermal environment — Instruments for measuring physical quantities
ISO 8996, Ergonomics of the thermal environment — Determination of metabolic rate
ISO 9237, Textiles — Determination of permeability of fabrics to air
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 13732-3, Ergonomics of the thermal environment — Methods for the assessment of human responses to
contact with surfaces — Part 3: Cold surfaces
ISO 15831, Clothing — Physiological effects — Measurement of thermal insulation by means of a thermal
manikin
EN 511, Protective gloves against cold
© ISO 2007 – All rights reserved 1
---------------------- Page: 10 ----------------------
ISO 11079:2007(E)
3 Terms, definitions and symbols
For the purposes of this document, the terms and definitions given in ISO 13731 and the following terms,
definitions and symbols apply.
3.1 Terms and definitions
3.1.1
cold stress
climatic conditions under which the body heat exchange is just equal to or too large for heat balance at the
expense of significant and sometimes uncompensable physiological strain (heat debt)
3.1.2
heat stress
climatic conditions under which the body heat exchange is just equal to or too small for heat balance at the
expense of significant and sometimes uncompensable physiological strain (heat storage)
3.1.3
IREQ
required clothing insulation for the preservation of body heat balance at defined levels of physiological strain
3.1.4
thermoneutral zone
temperature interval within which the body maintains heat balance exclusively by vasomotor reactions
3.1.5
wind chill temperature
temperature related to the cooling effect on a local skin segment
3.2 Symbols
2
A Dubois body surface area, m
Du
-2 −1
ap air permeability, l ⋅ m ⋅ s
−2
C convective heat flow (exchange), W ⋅ m
−1
c water latent heat of vaporization, J ⋅ kg
e
−1 −1
c specific heat of dry air at constant pressure, J ⋅ kg ⋅ K
p
−2
C respiratory convective heat flow (loss), W ⋅ m
res
D duration limited exposure, h
lim
D recovery time, h
rec
−2
E evaporative heat flow (exchange) at the skin, W ⋅ m
−2
E respiratory evaporative heat flow (loss), W ⋅ m
res
f clothing area factor, dimensionless
cl
−2 −1
h convective heat transfer coefficient, W ⋅ m ⋅ K
c
−2 −1
h radiative heat transfer coefficient, W ⋅ m ⋅ K
r
2 −1
I boundary layer thermal insulation, m ⋅ K ⋅ W
a
2 −1
I resultant boundary layer thermal insulation, m ⋅ K ⋅ W
a,r
2 © ISO 2007 – All rights reserved
---------------------- Page: 11 ----------------------
ISO 11079:2007(E)
2 −1
I basic clothing insulation, m ⋅ K ⋅ W
cl
2 −1
I resultant clothing insulation, m ⋅ K ⋅ W
cl,r
2 −1
I basic total insulation, m ⋅ K ⋅ W
T
2 −1
I resultant total insulation, m ⋅ K ⋅ W
T,r
i moisture permeability index, dimensionless
m
2 −1
IREQ required clothing insulation, m ⋅ K ⋅ W
2 −1
IREQ minimal required clothing insulation, m ⋅ K ⋅ W
min
2 −1
IREQ neutral required clothing insulation, m ⋅ K ⋅ W
neutral
−2
K conductive heat flow (exchange), W ⋅ m
−2
M metabolic rate, W ⋅ m
p water vapour partial pressure, kPa
a
p saturated water vapour pressure at expired air temperature, kPa
ex
p water vapour pressure at skin temperature, kPa
sk
p saturated water vapour pressure at the skin surface, kPa
sk,s
−2
Q body heat gain or loss, kJ ⋅ m
−2
Q limit value for Q, kJ ⋅ m
lim
−2
R radiative heat flow (exchange), W ⋅ m
2 −1
R total evaporative resistance of clothing and boundary air layer, m ⋅ kPa ⋅ W
e,T
−2
S body heat storage rate, W ⋅ m
t air temperature, °C
a
t clothing surface temperature, °C
cl
t expired air temperature, °C
ex
t operative temperature, °C
o
t radiant temperature
r
t local skin temperature, °C
sk
t mean skin temperature, °C
sk
t wind chill temperature, °C
WC
−1
V respiratory ventilation rate, kg air ⋅ s
−1
v wind speed measured 10 m above ground level, m ⋅ s
10
−1
v air velocity, m ⋅ s
a
−1
v walking speed, m ⋅ s
w
−2
W effective mechanical power, W ⋅ m
w skin wettedness, dimensionless
© ISO 2007 – All rights reserved 3
---------------------- Page: 12 ----------------------
ISO 11079:2007(E)
W humidity ratio of inhaled air, kg water/kg dry air
a
W humidity ratio of exhaled air, kg water/kg dry air
ex
σ Stefan-Boltzmann constant
ε emissivity of clothing surface, dimensionless
cl
4 Principles of methods for evaluation
Cold stress is evaluated in terms of both general cooling of the body and local cooling of particular parts of the
body (e.g. extremities and face). The following types of cold stress are identified.
a) General cooling
For general cooling, an analytical method is presented in Clause 5 for the evaluation and interpretation of
the thermal stress. It is based on a calculation of the body heat exchange, the required clothing insulation
(IREQ) for the maintenance of thermal equilibrium and the insulation provided by clothing ensemble in
use or anticipated to be used.
b) Local cooling
1) convective cooling (wind chill)
2) conductive cooling
3) extremity cooling
4) airway cooling
For local cooling, methods are proposed in Clause 6. Criteria and limit values are also given in Clause 6
and Annex B.
In the following sections, the main steps of evaluation are described.
5 General cooling
5.1 Overview
A general equation for body heat balance is defined. In this equation clothing thermal properties, body heat
production and physical characteristics of the environment are the determinant factors. The equation is solved
for the required clothing insulation (IREQ) for maintained heat balance under specified criteria of physiological
strain. IREQ is subsequently compared with the protection (insulation) offered by the worker's clothing. If worn
insulation is less than required, a duration limited exposure (D ) is calculated on the basis of acceptable
lim
levels of body cooling. Detailed formulas, coefficients and criteria are proposed in Annexes A and B.
The method involves the following steps, outlined schematically in Figure 1:
⎯ measurements of the thermal parameters of the environment;
⎯ determination of activity level (metabolic rate);
⎯ calculation of IREQ;
⎯ comparison of IREQ with resultant insulation provided by clothing in use;
⎯ evaluation of the conditions for thermal balance and calculation of the recommended maximal exposure
time (D ).
lim
4 © ISO 2007 – All rights reserved
---------------------- Page: 13 ----------------------
ISO 11079:2007(E)
Figure 1 — Procedure for evaluation of cold environments
© ISO 2007 – All rights reserved 5
---------------------- Page: 14 ----------------------
ISO 11079:2007(E)
5.2 Definition of required clothing insulation, IREQ
IREQ is the resultant clothing insulation required in the actual environmental conditions to maintain the body in
a state of thermal equilibrium at acceptable levels of body and skin temperatures.
IREQ is
a) a measure of cold stress integrating the effects of air temperature, mean radiant temperature, relative
humidity and air velocity for defined levels of metabolic rate,
b) a method for the analysis of effects of the thermal environment and metabolic rate on the human body,
c) a method for specification of clothing insulation requirements and the subsequent selection of clothing to
be used under the actual conditions, and
d) a method for evaluation of changes in heat balance parameters as measures for improvement of design
and planning of work time and work regimes under cold conditions.
5.3 Derivation of IREQ
5.3.1 General heat balance equation
Calculation of IREQ is based on a rational analysis of a human being's heat exchange with the environment.
The following subclauses review the general principles for calculation of the various factors affecting IREQ.
The general heat balance equation [Equation (1)] is as follows:
M−=WE +C +E+K+R+C+S (1)
res res
where the left-hand side of the equation represents the internal heat production, which is balanced by the
right-hand side which represents the sum of heat exchanges in the respiratory tract, heat exchanges on the
skin and the heat storage accumulating in the body. Variables of Equation (1) are defined in the following. For
the meaning of symbols, see also 3.2.
5.3.2 Metabolic rate
M is the metabolic rate and is evaluated in accordance with ISO 8996.
5.3.3 Effective mechanical power
W is the effective mechanical power. In most industrial situations this is small and can be neglected. See also
information in ISO 8996.
5.3.4 Respiratory heat exchange
Heat is lost from the respiratory tract by warming and saturating inspired air, and is the sum of convective heat
loss (C ) and evaporative heat loss (E ), determined, respectively, by
res res
Cc=⋅V()t −t/A (2)
res p ex a Du
E =⋅cV()W−W/A (3)
res e ex a Du
6 © ISO 2007 – All rights reserved
---------------------- Page: 15 ----------------------
ISO 11079:2007(E)
5.3.5 Evaporative heat exchange
The evaporative heat exchange, E, is defined by
Ep=−()p/R (4)
sk a e,T
5.3.6 Conductive heat exchange
Conductive heat exchange, K, is related to the area of body parts in direct contact with external surfaces.
Although it may be of significant importance for local heat balance, conductive heat exchange is mostly small
and can be accounted for by the expressions for convective and radiation heat exchange.
5.3.7 Radiative heat exchange
The radiative heat exchange, R, between the clothing surface including uncovered skin and the environment is
defined by
R=⋅fh⋅−()t t (5)
cl r cl r
5.3.8 Convective heat exchange
The convective heat exchange, C, between the clothing surface including uncovered skin and the environment
is defined by
Cf=⋅h⋅−()t t (6)
cl c cl a
5.3.9 Heat exchange through clothing
Heat exchange through clothing takes place by conduction, convection and radiation and by the transfer of
evaporated sweat. The effect of clothing on latent heat exchange is accounted for by Equation (4). The effect
of clothing on dry heat exchange is determined by the thermal insulation of the clothing ensemble and the
skin-to-clothing surface temperature gradient. Dry heat flow to the clothing surface is equivalent to the heat
transfer between the clothing surface and the environment. Heat exchange through clothing, therefore, is
expressed by the resultant, thermal insulation of clothing:
tt−
sk cl
= R+CM=−W−−−E C E−S (7)
res res
I
cl,r
5.4 Calculation of IREQ
On the basis of Equations (1) to (7), in steady state and using the hypothesis made concerning heat flow by
conduction, the required clothing insulation, IREQ, is calculated on the basis Equation (8):
tt−
sk cl
IREQ= (8)
R+ C
Equations (7) and (8) express the dry heat exchange at the clothing surface when the body is in thermal
equilibrium and state the relationship between I and IREQ. I is the value of clothing insulation corrected
cl,r cl,r
for the effects of wind penetration and activity, taking into account the air permeability of the outer garment
layer. IREQ is the thermal insulation required for the maintenance of thermal equilibrium.
Equation (8) contains two unknown variables (IREQ and t ). Therefore, Equation (8) is solved for t as follows
cl cl
tt= −IREQ⋅(M−W−−−E C E) (9)
cl sk res res
© ISO 2007 – All rights reserved 7
---------------------- Page: 16 ----------------------
ISO 11079:2007(E)
This expression replaces t in the computation formulas for the variables in Equation (8), where the formulas
cl
for R and C contain t [see Equations (5) and (6)]. The value of IREQ that satisfies Equation (8) is then
cl
calculated by iteration. A computer program is referenced in Annex F for this purpose. IREQ is expressed in
2 −1 1)
square metre degrees Kelvin per watt (m ⋅ K ⋅ W ). It may also be expressed in clo .
5.5 Interpretation of IREQ
5.5.1 IREQ as a cold index
IREQ is a measure of the thermal stress presented by the combined effects of internal heat production and
heat exchange with the environment. The greater the cooling power of the environment, the higher the value
of IREQ at any given activity level. At any given set of climatic conditions, cold stress and thereby IREQ is
reduced with increasing activity due to the extra demand for dissipation of metabolic heat.
5.5.2 IREQ and physiological strain
Thermal equilibrium can be achieved at different levels of thermoregulatory strain, defined in terms of values
for mean skin temperature, sweating (skin wettedness) and change in body temperature.
IREQ is defined at the following two levels of physiological strain.
a) IREQ defines a minimal thermal insulation required to maintain body thermal equilibrium at a
min
subnormal level of mean body temperature. The minimal IREQ represents some body cooling, in
particular of peripheral parts of the body. With prolonged exposures extremity cooling may become a
limiting factor for duration of exposure.
b) IREQ is defined as the thermal insulation required to provide conditions of thermal neutrality, i.e.
neutral
thermal equilibrium maintained at a normal level of mean body temperature. This level represents none or
minimal cooling of the human body.
The relevant physiological criteria are presented in Annex B.
5.5.3 IREQ and clothing insulation
IREQ is a resultant clothing insulation value that is required for the actual conditions. It may, therefore, serve
as a basis for the evaluation of the protection provided by clothing in use or as a guideline for the selection of
appropriate clothing. The IREQ value is compared with the resultant insulation value of the selected clothing
ensembles. This evaluation is described in 5.6.
5.5.4 IREQ and design of work
Any of the parameters of the heat balance equation can be changed and the calculated value of IREQ will
indicate the relative importance of this particular factor.
5.6 Comparison of IREQ and selected clothing insulation
The primary purpose of the IREQ method is to analyse whether or not the selected clothing provides
insulation that is sufficient to establish a defined level of heat balance. The most commonly reported insulation
value of a clothing ensemble is its basic insulation value, I (see ISO 9920). In order to use this information
cl
for a comparison with IREQ, the value must be corrected for several factors. The corrected value, I , is not
cl,r
readily available, as it depends on the user conditions. Therefore it needs to be determined on the basis of
available information for the actual clothing (basic insulation, air permeability) wind and activity level.
2 −1
1) 1 clo = 0,155 m ⋅ K ⋅ W .
8 © ISO 2007 – All rights reserved
---------------------- Page: 17 ----------------------
ISO 11079:2007(E)
Values for basic insulation of clothing ensembles and air permeability shall be determined in accordance with
ISO 9920. Examples of values are provided in Annex C. The final correction algorithms are given in Annex A.
I is compared with the calculated IREQ for the given conditions and criteria. The following interpretation is
cl,r
made:
I > IREQ warm, overheating zone — clothing insulation shall be reduced
cl,r neutral
IREQ u I u IREQ neutral, regulatory zone — no action required
min cl,r neutral
I < IREQ cold, cooling zone — clothing insulation shall be increased
cl,r min
or D calculated (see 5.7).
lim
The interval between IREQ and IREQ may be regarded as a clothing regulatory zone, in which each
min neutral
individual chooses the appropriate protection level. With insulation values lower than IREQ there is a risk of
min
progressive body cooling. With values higher than IREQ conditions will be considered warm and
neutral
overheating can occur. In the final evaluation, the result can also be presented in terms of basic insulation
needed for the given conditions (see Annex E).
5.7 Definition and calculation of duration limited exposure, D
lim
When the corrected value of a selected or used clothing ensemble is less than the calculated required
insulation (IREQ), exposure has to be time limited to prevent progressive body cooling. A certain reduction in
body heat content (Q) is acceptable during an exposure of a few hours and can be used to calculate the
duration of exposure when the rate of heat storage is known.
Duration limited exposure (D ) to cold is defined as the recommended maximum time of exposure with
lim
available or selected clothing. D is calculated using Equation (10):
lim
Q
lim
D = (10)
lim
S
where Q is the limit value of Q (see Annex B) and S is calculated from
lim
SM=−W−E −C −E−R−C (11)
res res
Equation (11) contains unknown t . Therefore, it is solved by mathematical iteration:
cl
tt= −I⋅()M−W−−−E C E−S (12)
cl sk cl,r res res
Equation (12) is similar to Equation (9), the difference being that Equation (9) is used in steady state to
calculate IREQ and Equation (12) in the actual conditions when clothing
...
SLOVENSKI oSIST prEN ISO 11079:2006
PREDSTANDARD
januar 2006
Ergonomija toplotnega okolja - Ugotavljanje in razlaga obremenitev zaradi
mraza ob uporabi zahtevanih zaščitnih oblačil (IREQ) in učinkov lokalnega
ohlajevanja (ISO/DIS 11079:2005)
(istoveten prEN ISO 11079:2005)
Ergonomics of the thermal environment - Determination and interpretation of cold
stress when using required clothing insulation (IREQ) and local cooling effects
(ISO/DIS 11079:2005)
ICS 13.180 Referenčna številka
oSIST prEN ISO 11079:2006(en)
© Standard je založil in izdal Slovenski inštitut za standardizacijo. Razmnoževanje ali kopiranje celote ali delov tega dokumenta ni dovoljeno
---------------------- Page: 1 ----------------------
EUROPEAN STANDARD
DRAFT
prEN ISO 11079
NORME EUROPÉENNE
EUROPÄISCHE NORM
November 2005
ICS Will supersede ENV ISO 11079:1998
English Version
Ergonomics of the thermal environment - Determination and
interpretation of cold stress when using required clothing
insulation (IREQ) and local cooling effects (ISO/DIS
11079:2005)
Ergonomie des ambiances thermiques - Détermination et
interprétation de la contrainte liée au froid en utilisant
l'isolement thermique requis du vêtement et les effets du
refroidissement local (ISO/DIS 11079:2005)
This draft European Standard is submitted to CEN members for parallel enquiry. It has been drawn up by the Technical Committee
CEN/TC 122.
If this draft becomes a European Standard, 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.
This draft European Standard was established by CEN 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 Management Centre 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.
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.
Warning : This document is not a European Standard. It is distributed for review and comments. It is subject to change without notice and
shall not be referred to as a European Standard.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36 B-1050 Brussels
© 2005 CEN All rights of exploitation in any form and by any means reserved Ref. No. prEN ISO 11079:2005: E
worldwide for CEN national Members.
---------------------- Page: 2 ----------------------
prEN ISO 11079:2005 (E)
Foreword
This document (prEN ISO 11079:2005) 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 document is currently submitted to the parallel Enquiry.
This document will supersede ENV ISO 11079:1998.
Endorsement notice
The text of ISO 11079:2005 has been approved by CEN as prEN ISO 11079:2005 without
any modifications.
2
---------------------- Page: 3 ----------------------
DRAFT INTERNATIONAL STANDARD ISO/DIS 11079
ISO/TC 159/SC 5 Secretariat: BSI
Voting begins on: Voting terminates on:
2005-11-17 2006-04-17
INTERNATIONAL ORGANIZATION FOR STANDARDIZATION • МЕЖДУНАРОДНАЯ ОРГАНИЗАЦИЯ ПО СТАНДАРТИЗАЦИИ • ORGANISATION INTERNATIONALE DE NORMALISATION
Ergonomics of the thermal environment — Determination and
interpretation of cold stress when using required clothing
insulation (IREQ) and local cooling effects
Ergonomie des ambiances thermiques — Détermination et interprétation de la contrainte liée au froid en
utilisant l'isolement thermique requis du vêtement et les effets du refroidissement local
(Revision of ISO/TR 11079:1993)
ICS 13.180
ISO/CEN PARALLEL ENQUIRY
The CEN Secretary-General has advised the ISO Secretary-General that this ISO/DIS covers a subject
of interest to European standardization. In accordance with the ISO-lead mode of collaboration as
defined in the Vienna Agreement, consultation on this ISO/DIS has the same effect for CEN
members as would a CEN enquiry on a draft European Standard. Should this draft be accepted, a
final draft, established on the basis of comments received, will be submitted to a parallel two-month FDIS
vote in ISO and formal vote in CEN.
To expedite distribution, this document is circulated as received from the committee secretariat.
ISO Central Secretariat work of editing and text composition will be undertaken at publication
stage.
Pour accélérer la distribution, le présent document est distribué tel qu'il est parvenu du
secrétariat du comité. Le travail de rédaction et de composition de texte sera effectué au
Secrétariat central de l'ISO au stade de publication.
THIS DOCUMENT IS A DRAFT CIRCULATED 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 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 NATIONAL REGULATIONS.
© International Organization for Standardization, 2005
---------------------- Page: 4 ----------------------
ISO/DIS 11079
PDF disclaimer
This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but shall
not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In
downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat
accepts no liability in this area.
Adobe is a trademark of Adobe Systems Incorporated.
Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation
parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In the
unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below.
Copyright notice
This ISO document is a Draft International Standard and is copyright-protected by ISO. Except as permitted
under the applicable laws of the user's country, neither this ISO draft nor any extract from it may be
reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, photocopying,
recording or otherwise, without prior written permission being secured.
Requests for permission to reproduce should be addressed to either ISO at the address below or ISO's
member body in the country of the requester.
ISO copyright office
Case postale 56 CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Reproduction may be subject to royalty payments or a licensing agreement.
Violators may be prosecuted.
©
ii ISO 2005 – All rights reserved
---------------------- Page: 5 ----------------------
ISO 11079:2005
Contents Page
Foreword.iv
Introduction .v
1 Scope.7
2 Normative references .7
3 Terms, definitions and symbols .7
3.1 Definitions.7
3.2 Symbols.9
4 Principles of methods for evaluation.11
5 General cooling.11
5.1 General.11
5.2 Definition of required insulation, IREQ.12
5.3 Derivation of IREQ .12
5.4 Calculation of IREQ.13
5.5 Interpretation of IREQ.14
5.6 Comparison of IREQ and selected clothing insulation.14
5.7 Definition and calculation of duration limited exposure, D .15
lim
6 Local cooling .16
6.1 General.16
6.2 Convective cooling .16
6.3 Conductive cooling.16
6.4 Extremity cooling.17
6.5 Airway cooling.17
7 Practical assessment of cold environments and interpretation .17
7.1 General.17
7.2 Procedure for determination of IREQ and D .17
lim
7.3 Local cooling .19
Annex A (normative) Heat exchange equations.20
Annex B (informative) Physiological criteria in cold exposure .23
Annex C (informative) Metabolice heat production and thermal properties of clothing.25
Annex D (informative) Determination of wind cooling.28
Annex E (informative) Examples of evaluation .30
Annex F (informative) Figures.32
Annex G (informative) Computer program.38
Annex H (informative) Bibliography .39
© ISO 2005 – All rights reserved iii
---------------------- Page: 6 ----------------------
ISO DIS 11079:2005
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 3.
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.
International Standard ISO 11079 was prepared by Technical Committee ISO/TC 159, Ergonomics,
Subcommittee SC 5, Ergonomics of the Physical Environment.
This is the first edition of this ISO standard and replaces the technical report (ISO TR11079:1993).
iv © ISO 2005 – All rights reserved
---------------------- Page: 7 ----------------------
ISO 11079:2005
Introduction
Wind-chill is commonly encountered in cold climates, but low temperatures first of all endanger body
heat balance. By proper adjustment of clothing man can often control and regulate body heat loss, to
balance a change in the ambient climate. The method presented here is therefore based on the
evaluation of the clothing insulation required to maintain in equilibrium the thermal balance of the
body. The heat balance equation used takes into account the most recent scientific findings
concerning heat exchanges at the surface of the skin as well as the clothing.
© ISO 2005 – All rights reserved v
---------------------- Page: 8 ----------------------
ISO 11079:2005
Ergonomics of the thermal environment — Determination and
interpretation of cold stress when using required clothing
insulation (IREQ) and local cooling effects
1 Scope
This International Standard specifies methods and strategies to assess the thermal stress associated
with exposure to cold environments. These methods apply to continuous, intermittent as well as
occasional exposure and type of work, indoors and outdoors. This International Standard is not
applicable to specific effects associated with certain meteorological phenomena (e.g. precipitation).
These effects must be assessed by other methods.
2 Normative references
The following standards contain provisions that, through reference in this text, constitute provisions of
the Technical Report. At the time of publication, the editions indicated were valid. All standards are
subject to revision, and parties to agreements based on this Technical Report are encouraged to
investigate the possibility of applying the most recent editions of the standards indicated below.
Members of IEC and ISO maintain registers with currently valid International Standards.
ISO 7726, Thermal Environments — Specifications relating to appliances and methods for measuring
physical characteristics of the environment
ISO 8996, Ergonomics of the thermal environment — Determination of metabolic rate
ISO 9920, Ergonomics of the thermal environment — Estimation of the thermal insulation and
evaporative resistance of a clothing ensemble
ISO 9237, Textiles — Determination of permeability of fabrics to air
ISO/FDIS 13732-3, Ergonomics of the thermal environment — Methods for assessment of human
responses to contact with surfaces — Part 3: Cold surfaces
ISO 15831 Clothing — Physiological effects — Measurement of thermal insulation by means of a
thermal manikin
3 Terms, definitions and symbols
3.1 Definitions
Terms and definitions used are described in ISO 13731, Ergonomics of the thermal environment –
vocabulary and symbols.
7
---------------------- Page: 9 ----------------------
ISO DIS 11079:2005
Additional definitions used in this document are given below.
3.1.1
cold stress
climatic conditions under which the body heat exchange is just equal or too large for heat balance at
the expense of significant and sometimes uncompensable physiological strain (heat debt)
3.1.2
heat stress
climatic conditions under which the body heat exchange is just equal or too small for heat balance at
the expense of significant and sometimes uncompensable physiological strain (heat storage)
3.1.3
IREQ
required clothing insulation for the preservation of body heat balance at defined levels of physiological
strain
3.1.4
thermoneutral zone
the temperature interval within which the body maintains heat balance exclusively by vasomotor
reactions
3.1.5
wind chill index
defines a temperature that is related to the cooling sensation on a local skin segment
8
---------------------- Page: 10 ----------------------
ISO 11079:2005
3.2 Symbols
Symbols and units used in subsequent equations are described below.
2
A body surface area, m
Du
-2 -1
ap air permeability, lm s
2
A effective radiating area of the body, m
r
-2
C convective heat flow, W m
-1
c water latent heat of vaporization, Jkg
e
-1 -1
c specific heat of dry air at constant pressure, Jkg K
p
-2
C respiratory convective heat flow, Wm
res
D duration limited exposure, h
lim
D recovery time, h
rec
-2
E evaporative heat flow at the skin, Wm
-2
E respiratory evaporative heat flow, Wm
res
f clothing area factor, n.d.
cl
-2 -1
h convective heat transfer coefficient, W m K
c
-2 -1
h radiative heat transfer coefficient, W m K
r
2 -1
I boundary layer thermal insulation, m K W
a
2 -1
I basic clothing insulation, m K W
cl
2 -1
I resultant clothing insulation, m K W
clr
2 -1
I mathematical symbol for IREQ, m K W
IREQ
2 -1
I total insulation, m K W
T
2 -1
I resultant total insulation, m K W
Tr
i moisture permeability index, n.d.
m
2 -1
IREQ required clothing insulation, m K W
2 -1
IREQ minimal required clothing insulation, m K W
min
2 -1
IREQ neutral required clothing insulation, m K W
neutral
-2
K conductive heat flow, Wm .
-2
M metabolic rate, Wm
p water vapour partial pressure, kPa
a
© ISO 2005 – All rights reserved 9
---------------------- Page: 11 ----------------------
ISO DIS 11079:2005
p saturated water vapour pressure at expired air temperature, kPa
ex
p water vapour pressure at skin temperature, kPa
sk
p saturated water vapour pressure at skin temperature, kPa
sks
-2
Q body heat gain or loss, kJm
-2
Q limit value for Q, kJm
lim
-2
R radiation heat flow, Wm
2 -1
R total evaporative resistance of clothing and boundary air layer, m kPa W
eT
-2
S body heat storage rate, W•m
t air temperature, °C
a
t effective cooling temperature, °C
wc
t clothing surface temperature, °C
cl
t effective temperature resulting from wind chill, °C
eff
t expired air temperature, °C
ex
t operative temperature, °C
o
t mean radiant temperature, °C
r
t local skin temperature, °C
sk
t mean skin temperature, °C
sk
-1
V respiratory ventilation rate, kg air s
-1
v wind speed measured 10 m above ground level, ms
10
-1
v air velocity, ms
a
-1
v relative air velocity, ms
ar
-1
v walking speed, ms
w
-2
W effective mechanical power, Wm
w skin wettedness, n.d.
W humidity ratio of inhaled air, kg water per kg dry air
a
W wind chill index, °C
c
W humidity ratio of exhaled air, kg water per kg dry air
ex
10
---------------------- Page: 12 ----------------------
ISO 11079:2005
4 Principles of methods for evaluation
Cold stress is evaluated in terms of both general cooling of the body and local cooling of particular
parts of the body (e.g. extremities and face). The following types of cold stress are identified:
General cooling
Local cooling
convective cooling (wind chill)
conductive cooling
extremity cooling
airway cooling
For general cooling an analytical method is presented in Clause 5 for the evaluation and
interpretation of the thermal stress. It is based on a calculation of the body heat exchange, the
Required Clothing Insulation (IREQ) for the maintenance of thermal equilibrium and the insulation
provided by clothing ensemble in use or anticipated to be used.
For local cooling methods are proposed in Clause 6. Criteria and limit values are also given in
Clause 6 and Annex B.
In the following sections the main steps of evaluation are described.
5 General cooling
5.1 General
A general equation for body heat balance is defined. In this equation clothing thermal properties, body
heat production and physical characteristics of the environment are the determinant factors. The
equation is solved for the required clothing insulation (IREQ) for maintained heat balance under
specified criteria of physiological strain. IREQ is subsequently compared with the protection
(insulation) offered by the worker's clothing. If worn insulation is less than required, a duration limited
exposure (D ) is calculated on the basis of acceptable levels of body cooling. Detailed formulas,
lim
coefficients and criteria are proposed in Annex A and B.
The method involves the following steps, outlined schematically in Figure F.1:
measurements of the thermal parameters of the environment;
determination of activity level (metabolic rate);
calculation of required clothing insulation – IREQ;
comparison of IREQ with insulation provided by clothing in use;
evaluation of the conditions for thermal balance and calculation of recommended maximal
exposure time (D ).
LIM
© ISO 2005 – All rights reserved 11
---------------------- Page: 13 ----------------------
ISO DIS 11079:2005
5.2 Definition of required insulation, IREQ
IREQ is defined as the resultant clothing insulation required during the actual environmental conditions
to maintain the body in a state of thermal equilibrium at acceptable levels of body and skin
temperatures.
IREQ is
1) a measure of cold stress integrating the effects of air temperature, mean radiant temperature,
humidity and air velocity for defined levels of metabolic heat production;
2) a method for the analysis of effects of specific parameters and evaluation of measures of
improvement;
3) a method for specification of clothing insulation requirements and the subsequent selection
of clothing to be used under the prevailing environmental conditions;
4) a method for designing and planning of work time and work regimes under cold conditions.
5.3 Derivation of IREQ
5.3.1 General heat balance equation
Calculation of IREQ is based on a rational analysis of man's heat exchange with the environment. The
following sub-clauses review the general principles for calculation of the various factors affecting IREQ.
The general heat balance equation is as follows
M−W= E + C + E+ K+ R+ C+ S (1)
res res
where the left hand side of the equation represents the internal heat production, which is balanced by
the right hand side which represents the sum of heat exchanges in the respiratory tract, heat
exchanges on the skin and the heat storage accumulating in the body.
5.3.2 Metabolic power
M is the metabolic power and is evaluated using ISO-8996.
5.3.3 Effective mechanical power
W is the effective mechanical power. In most industrial situations this is small and can be neglected.
See also information in ISO-8996
5.3.4 Respiratory heat exchange
Heat is lost from the respiratory tract by warming and saturating inspired air and is the sum of
convective heat loss (C ) and evaporative heat loss (E ), determined, respectively, by
res res
C = c⋅V (t − t )/ A (2)
res p ex a du
H = c⋅V (W −W )/ A (3)
res e ex a du
5.3.5 Evaporative heat exchange
The evaporative heat exchange E is defined by
12
---------------------- Page: 14 ----------------------
ISO 11079:2005
E= ( p − p )/ R (4)
sk a eT
5.3.6 Conductive heat exchange
Conductive heat exchange is related to the area of body parts in direct contact with external surfaces.
Although it may be of significant importance for local heat balance, conductive heat exchange is
mostly small and can be accounted for by the expressions for convective and radiation heat exchange.
5.3.7 Convective heat exchange
The heat exchange by convection between the clothing surface including uncovered skin and the
environment, C is defined by
C= f ⋅ h⋅ (t − t ) (5)
cl c cl a
5.3.8 Radiation heat exchange
The radiation heat exchange between the clothing surface including uncovered skin and the
environment, R, is defined by
R= f ⋅ h⋅ (t − t ) (6)
cl r cl r
5.3.9 Heat exchange through clothing
Heat exchange through clothing takes place by conduction, convection and radiation and by the
transfer of evaporated sweat. The effect of clothing on latent heat exchange is accounted for by
equation 4. The effect of clothing on dry heat exchange is determined by the thermal insulation of the
clothing ensemble and the skin to clothing surface temperature gradient. Dry heat flow to the clothing
surface is equivalent to the heat transfer between the clothing surface and the environment. Heat
exchange through clothing, therefore, is expressed by the factual, resultant, thermal insulation of
clothing:
t − t
sk cl
= R+ C= M−W− E − C − E± S (7)
res res
I
clr
5.4 Calculation of IREQ
On the basis of equations (1) to (7) and using the hypothesis made concerning heat flow by
conduction, the required clothing insulation, IREQ, is calculated on the basis of the following two
equations:
t − t
sk cl
I = (8)
IREQ
M− W− E − C − E
res res
M− W− E − C − E= R+ C (9)
res res
© ISO 2005 – All rights reserved 13
---------------------- Page: 15 ----------------------
ISO DIS 11079:2005
Equation (8) expresses the dry heat exchange at the clothing surface when the body is in thermal
equilibrium and is rewritten from equation (7). Equation (9) states that the dry heat exchange must
balance the internal heat production minus evaporative and respiratory heat losses and is rewritten
from equation (7).
Equation 8 contains two unknown variables (IREQ and t ). Therefore, equation 8 is solved for t as
cl cl
follows
t = t − I ⋅(M− W− E − C − E) (10)
cl sk IREQ res res
This expression replaces t in the computation formulas for the variables in equation (9), where the
cl
formulas for R and C contain t (see equations (5) and (6)). The value of IREQ that satisfies equation
cl
(9) is then calculated by iteration. A computer program is provided in Annex G for this purpose. IREQ
2 -1
is expressed in square metre degree Celsius per watt (m K W ). It may also be expressed in clo–
2 -1
units (1 clo=0,155 m K W ).
5.5 Interpretation of IREQ
5.5.1 IREQ as a cold index
IREQ is a measure of the thermal stress presented by the combined effects of internal heat production
and heat exchange with the environment. The greater the cooling power of the environment, the
higher is the value of IREQ at any given activity level. At any given set of climatic conditions cold
stress, and thereby IREQ, is reduced with increasing activity due to the extra demand for dissipation of
metabolic heat.
5.5.2 IREQ and physiological strain
Thermal equilibrium can be achieved at different levels of thermoregulatory strain, defined in terms of
values for mean skin temperature, sweating (skin wettedness) and change in body temperature.
IREQ is defined at two levels of physiological strain.
1) IREQ defines a minimal thermal insulation required to maintain body thermal equilibrium at
min
a subnormal level of mean body temperature. The minimal IREQ represents some body
cooling, in particular of peripheral parts of the body. With prolonged exposures extremity
cooling may become a limiting factor for duration of exposure.
2) IREQ is defined as the thermal insulation required to provide conditions of thermal
neutral
neutrality, i.e. thermal equilibrium maintained at a normal level of mean body temperature.
This level represents none or minimal cooling of the human body.
Relevant physiological criteria are presented in Annex B.
5.5.3 IREQ and clothing insulation
IREQ is a resultant clothing insulation value that is required for the actual conditions. It may, therefore,
serve as a basis for the evaluation of the protection provided by clothing in use or as a guideline for
the selection of appropriate clothing. The IREQ-value is compared with the resultant insulation value
of the selected clothing ensembles. This evaluation is described in clause 5.6.
5.6 Comparison of IREQ and selected clothing insulation
The primary purpose of the IREQ method is to analyze if the selected clothing provides insulation that
is sufficient enough to establish a defined level of heat balance. The most commonly reported
insulation value of a clothing ensemble is its basic insulation value – I (ISO 9920). In order to use
cl
14
---------------------- Page: 16 ----------------------
ISO 11079:2005
this information for a comparison with IREQ, the value must be corrected for several factors. The
corrected value – I - is not readily available, as it depends on the user conditions. Therefore it needs
clr
to be determined on the basis of available information for the actual clothing; basic insulation, air
permeability, wind and activity level.
Values for basic insulation of clothing ensembles and air permeability shall be determined in
accordance with ISO 9920. Examples of values are provided in Annex C. The final correction
algorithms are given in Annex A.
I is compared with the calculated IREQ for the given conditions and criteria.
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.