Ergonomics of the thermal environment - Determination and interpretation of cold stress when using required clothing insulation (IREQ) and local cooling effects (ISO 11079:2007)

ISO 11079:2007specifies 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.

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 Beurteilung der thermischen Belastung fest, die mit dem Aufenthalt in Kälteumgebungen verbunden ist. Diese Verfahren gelten für eine ununterbrochene, eine unterbrochene sowie eine gelegentliche Exposition sowohl für Arbeiten in Innenräumen als auch im Freien. Sie sind nicht auf spezifische Wirkungen im Zusammenhang mit bestimmten meteorologischen Erscheinungen (z. B. Niederschlag) anwendbar, die 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 vêtement (IREQ) 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

Status
Published
Publication Date
14-Dec-2007
Current Stage
6060 - Definitive text made available (DAV) - Publishing
Due Date
15-Dec-2007
Completion Date
15-Dec-2007

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SLOVENSKI STANDARD
SIST EN ISO 11079:2008
01-april-2008
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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

---------------------- 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.

---------------------- 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)
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© 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.
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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
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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
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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
A Dubois body surface area, m
-2 −1
ap air permeability, l ⋅ m ⋅ s
C convective heat flow (exchange), W ⋅ m
c water latent heat of vaporization, J ⋅ kg
−1 −1
c specific heat of dry air at constant pressure, J ⋅ kg ⋅ K
C respiratory convective heat flow (loss), W ⋅ m
res
D duration limited exposure, h
lim
D recovery time, h
rec
E evaporative heat flow (exchange) at the skin, W ⋅ m
E respiratory evaporative heat flow (loss), W ⋅ m
res
f clothing area factor, dimensionless
−2 −1
h convective heat transfer coefficient, W ⋅ m ⋅ K
−2 −1
h radiative heat transfer coefficient, W ⋅ m ⋅ K
2 −1
I boundary layer thermal insulation, m ⋅ K ⋅ W
2 −1
I resultant boundary layer thermal insulation, m ⋅ K ⋅ W
a,r
2 © ISO 2007 – All rights reserved
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ISO 11079:2007(E)
2 −1
I basic clothing insulation, m ⋅ K ⋅ W
2 −1
I resultant clothing insulation, m ⋅ K ⋅ W
cl,r
2 −1
I basic total insulation, m ⋅ K ⋅ W
2 −1
I resultant total insulation, m ⋅ K ⋅ W
T,r
i moisture permeability index, dimensionless
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
K conductive heat flow (exchange), W ⋅ m
M metabolic rate, W ⋅ m
p water vapour partial pressure, kPa
p saturated water vapour pressure at expired air temperature, kPa
p water vapour pressure at skin temperature, kPa
p saturated water vapour pressure at the skin surface, kPa
sk,s
Q body heat gain or loss, kJ ⋅ m
Q limit value for Q, kJ ⋅ m
lim
R radiative heat flow (exchange), W ⋅ m
2 −1
R total evaporative resistance of clothing and boundary air layer, m ⋅ kPa ⋅ W
e,T
S body heat storage rate, W ⋅ m
t air temperature, °C
t clothing surface temperature, °C
t expired air temperature, °C
t operative temperature, °C
t radiant temperature
t local skin temperature, °C
t mean skin temperature, °C
t wind chill temperature, °C
V respiratory ventilation rate, kg air ⋅ s
v wind speed measured 10 m above ground level, m ⋅ s
v air velocity, m ⋅ s
v walking speed, m ⋅ s
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
W humidity ratio of exhaled air, kg water/kg dry air
σ Stefan-Boltzmann constant
ε emissivity of clothing surface, dimensionless
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
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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
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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
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

for R and C contain t [see Equations (5) and (6)]. The value of IREQ that satisfies Equation (8) is then

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

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
lim
D = (10)
lim
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:

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
...

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