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)
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 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
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
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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.
Contents Page
Foreword.3
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.
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
ISO 11079:2007(E)
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ii © ISO 2007 – All rights reserved
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 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
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.
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 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
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
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
−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 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
ISO 11079:2007(E)
Figure 1 — Procedure for evaluation of cold environments
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
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 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
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 insulation is known.
D shall be calculated from IREQ (default) (see 5.5.2). Other values for thermal sensation can be
lim neutral
selected [see 5.5.2., b)]. If the worker at the onset of exposure has adopted a certain heat debt, the exposure
time shall be reduced accordingly.
After an exposure with body cooling, a recovery period shall be allowed to restore normal body heat balance.
Recovery time (D ) is calculated in the same way as D , substituting the “cold conditions” with the exposure
rec lim
conditions during the recovery period. In other words:
D = Q /S (13)
rec lim
where S is the rate of body heat storage (positive) calculated from Equation (11) for the exposure conditions
during the recovery period.
ISO 11079:2007(E)
Since recovery is supposed to start when the body has achieved a certain heat debt, the value of Q shall be
lim
the same when calculating D /D . The calculation of D requires a new determination if clothing is
rec lim rec
changed during the recovery period, as S will change with different clothing.
The physiological criteria to be used are presented in Annex B and examples of the application of D and
lim
D in Annex E.
rec
6 Local cooling
6.1 General
Local cooling of any part of the body with emphasis on hands, feet and head may produce discomfort,
deterioration of manual and physical performance and cold injury. The amount of knowledge on responses to
local cooling is insufficient for the development of a single evaluation method. Several approaches are
proposed and more research work is encouraged on the subject.
The indoor cold environment is relatively easy to modify by engineering techniques. Light, stationary work
makes a person more prone to unpleasant effects of local cooling, caused by for example draught or radiation
heat loss to cold surfaces. Particular attention should be paid to the evaluation of discomfort.
The outdoor cold environment is determined by weather and climate, and protective measures mostly
comprise adjustment of clothing or control of exposure. All types of local cold stress may occur,
simultaneously or independently.
6.2 Convective cooling
The combination of low temperature and wind accelerates heat loss from warm surfaces. Accordingly,
unprotected parts of the body, such as face and sometimes hands, may cool very quickly and reach low
temperatures with considerable risk of injury. Local convective cold stress is evaluated with a general equation
[Equation (14)] for convective and radiative heat loss of a bare skin surface:
R+=Ch⋅()t −t+h⋅(t −t) (14)
rsk r c sk a
The wind chill temperature, t , is a temperature that describes a cooling effect on the skin. It is derived from
WC
Equation (14), which is solved for t for combinations of wind and heat losses.
a
The expression to be used for the evaluation of t is presented in Annex D.
WC
6.3 Conductive cooling
The contact of cold surfaces produces an immediate heat exchange between warm skin and cold surface. The
risk of incurring unpleasant tissue cooling or at worst a local cold injury shall be assessed in accordance with
ISO 13732-3.
6.4 Extremity cooling
Even at thermoneutral conditions the extremities, the hands in particular may suffer unwanted cooling. This
depends to a large extent on the local climatic conditions, local protection and heat input by blood circulation.
The latter factor is much dependent on the overall thermal balance. If the heat balance is negative, as for
example when protective clothing does not match IREQ, extremity blood flow is reduced due to
vasoconstriction. This may reduce heat input to very low levels. Extremities, in particular fingers and toes, will
gradually cool down and reach unacceptably low temperatures.
Extremity cooling is prevented or reduced by putting on adequate protection, e.g. insulative hand and footgear.
Test methods for determination of thermal insulation of hand-wear shall be in accordance with EN 511.
Required insulation for various wear conditions are also given in EN 511.
10 © ISO 2007 – All rights reserved
ISO 11079:2007(E)
Hand cooling shall be evaluated by the methods and procedures specified in EN 511.
Extremity cooling can also be evaluated by direct skin temperature measurements. Recommended criteria
and temperature levels are given in Annex B.
6.5 Airway cooling
Inhalation of air at low temperatures cools the membranes of the airway walls and can be harmful to the
tissues. Cooling is more pronounced when the ventilated air volume is high (e.g. at high physical activity).
Recommendations for lowest temperatures of inspired air is given in Annex B.
7 Practical assessment of cold environments and interpretation
7.1 General
Procedures for the practical determination of IREQ, D and local cooling effects are described in the
lim
following subclauses.
7.2 Procedure for determination of IREQ and D
lim
The procedure for the assessment of cold environments is specified in steps a) to g), below, and described
schematically in Figure 1.
NOTE A link to a computer program is provided in Annex F for a complete evaluation of the steps from c) to f).
a) Measure or estimate the following climate parameters in accordance with ISO 7726:
⎯ air temperature;
⎯ mean radiant temperature;
⎯ air velocity;
⎯ humidity.
The operative temperature may replace the air temperature and mean radiant temperature when it is
calculated as a weighted average of the two using the convective and radiative heat transfer coefficients,
respectively. Water content of air at low temperature is very small, so a standard value of 50 % relative
humidity may be used below −5 °C.
b) Determine the metabolic rate in accordance with ISO 8996. Values for selected examples of physical
activity are given in Annex C.
c) Determine external work rate. For most types of manual work and movements on the ground, the work
rate can be set to 0.
d) Determine the basic clothing insulation of the cold protective clothing in use in accordance with
ISO 15831 or from the corresponding tables given in ISO 9920 and Annex C. The program provided in
Annex F can be used to calculate the resultant clothing insulation value, I (see Annex C).
cl,r
e) Calculate IREQ from Equation (8). With intermittent exposure or activity (e.g. fixed work–rest regimens),
IREQ is calculated for each different work and rest period, and the time-weighted average for a minimum
of 1 h then calculated. The individual period may depend on the organization and nature of the work but
should be at least 15 min.
ISO 11079:2007(E)
f) Evaluate the conditions for heat balance by comparison of IREQ with the corrected clothing insulation
value, I .
cl,r
Three cases apply:
1) I > IREQ
cl,r neutral
The selected clothing ensemble provides more than sufficient insulation. Too much insulation can
increase the risk of overheating, excessive sweating and moisture absorption by clothing and a
prospective risk of progressive hypothermia. Clothing insulation shall be reduced.
2) IREQ u I u IREQ
min cl,r neutral
Selected clothing ensemble provides adequate insulation. The level of physiological strain may vary
from high to low and the thermal conditions are perceived as “slightly cold” to “neutral”. No action is
required, except for further evaluation of local cooling effects.
3) I < IREQ
cl,r min
The selected clothing ensemble does not provide adequate insulation to prevent body cooling. There
is an increasing risk of hypothermia with progressive exposure:
i) clothing insulation shall be increased;
ii) a time limited exposure shall be selected and D calculated [see g) below].
lim
g) Determine the duration limited exposure time (D ) and the required recovery time (D ) if I is less
lim rec cl,r
than IREQ . If the clothing is changed during recovery, a new calculation shall be made. D and
neutral lim
D are by default calculated for neutral conditions.
rec
The IREQ index applies to cool and cold environments. It is recommended that the index be used within the
following limits of the main parameters:
t u 10 °C;
a
−1 −1
0,4 m ⋅ s u v u 18 m ⋅ s ;
a
2 −1
I > 0,078 m ⋅ K ⋅ W (0,5 clo).
cl
7.3 Local cooling
In cold environments there is always a risk of local cold stress. This problem is dealt with according to the
following:
⎯ convective cooling (see Annex D);
⎯ conductive cooling (see ISO 13732-3);
⎯ extremity cooling (see EN 511);
⎯ airway cooling (see Annex B).
12 © ISO 2007 – All rights reserved
ISO 11079:2007(E)
Annex A
(normative)
Computation of thermal balance
A.1 General
The formulas, coefficients and values for the calculation of the various forms of heat exchange presented in
this annex should only be applied within the limit values of the main parameters. They are based on the most
recent and accepted experimental investigations available in the literature (see the Bibliography). The symbols
and units given in 3.2 apply.
A.2 Determination of respiratory heat exchange
Respiratory heat loss is related to M and is calculated from the formulas for convective and evaporative
respiratory heat loss presented below.
E=⋅0,017 3Mp⋅ −p (A.1)
( )
res ex a
CM=⋅0,0014⋅t−t (A.2)
( )
res ex a
tt=+29 0,2⋅ (A.3)
ex a
It is assumed that expired air is saturated and has a temperature (t ), that is related to inspired (ambient)
ex
temperature (t ) using Equation (A.3).
a
A.3 Determination of evaporative heat exchange
Skin evaporative heat exchange (E) is determined by
Ew=⋅()p −p/R (A.4)
sk,s a E,T
The skin wettedness factor may be regarded as the wetted fraction of the skin, participating in evaporative
heat exchange. The factor, w, can vary approximately from 0,06, when skin diffusion is the only form of
evaporation, to 1,0, when evaporation is maximal and the skin is fully wet. The saturated water vapour
pressure at the skin surface, p , is calculated from the mean skin temperature by
sk,s
(17,27⋅t )
sk
(2t +3,3)
sk
p=⋅610,78 e (A.5)
sk,s
The mean skin temperature is determined automatically as a function of the metabolic rate (see Annex C).
ISO 11079:2007(E)
A.4 Determination of evaporative resistance
The value of R is calculated on the basis of clothing insulation and permeation properties to water vapour.
e,T
Due to the limited contribution from evaporative heat loss in the cold for defined levels of physiological strain,
it is sufficient with the following approximate estimation of R :
e,T
⎛⎞I
0,06
a,r
RI=⋅ + (A.6)
⎜⎟
e,T cl,r
if
mcl
⎝⎠
The expression within brackets is the total insulation value. I is calculated using Equation (A.13). A limited
a,r
number of values for R and i are available in the literature (see ISO 9920). For common (vapour
e,T m
permeable) clothing, an i of 0,38 is assumed and Equation (A.6) becomes
m
⎛⎞I
a,r
RI=⋅0,16 + (A.7)
⎜⎟
e,T cl,r
f
⎝⎠cl
A.5 Determination of the clothing area factor
In all calculations, f is calculated with
cl
f=+1, 0 1, 97⋅ I (A.8)
cl cl
A.6 Determination of the convective heat transfer coefficient
h is calculated with
c
f
cl
hh=− (A.9)
cr
I
a,r
−1 −1 −1 −1
For 0,4 m ⋅ s u v u 18 m ⋅ s and 0 m ⋅ s u v u 1,2 m ⋅ s ; I is determined using Equation (A.13).
a w a,r
A.7 Determination of radiation heat transfer coefficient
In environments with a predominantly low temperature radiation, h is approximated by
r
(tt+−273) (+ 273)
cl r
h≈⋅σε⋅ (A.10)
rcl
tt−
cl r
−8 −2 −4
where σ is the Stefan-Boltzmann constant, equal to (5,67 × 10 ) W ⋅ m ⋅ K , ε is the emissivity of the
cl
clothing.
The emissivity of the clothing depends on the temperature of the radiation source.
With low temperature radiation, emissivity is independent of the colour of clothing and shall be 0,97.
With high temperature radiation (e.g. sunshine), the colour of clothing is important and an appropriate value
−2
shall be chosen. A completely dark outer surface layer may absorb up to 100 W⋅m more than a white
surface.
14 © ISO 2007 – All rights reserved
ISO 11079:2007(E)
A.8 Determination of resultant clothing insulation
The basic insulation value (I ) of a selected clothing ensemble is corrected for the effects of wind penetration
cl
and activity, taking into account the air permeability of the outer garment layer. Air permeability shall be
determined in accordance with ISO 9237. This correction gives a resultant insulation value (I ) that is more
cl,r
realistic for a comparison with IREQ.
I is calculated using Equation (A.11) from corrected values of total insulation [Equation (A.12)] and
cl,r
boundary layer thermal insulation [Equation (A.13)]. This value of I is used for the calculation of D (see
cl,r lim
5.7).
I
a,r
II=− (A.11)
cl,r T,r
f
cl
(0,075⋅−In(ap) 0,15⋅v−0,22⋅v )
⎡⎤aw
II=⋅ 0,54⋅e − 0,06⋅In(ap)+ 0,5 (A.12)
T,r T
⎢⎥
⎣⎦
The relationship for air layer reduction calculations is derived from Equation (A.12) by inserting
−2 −1 2 −1
ap = 10 000 l ⋅ m ⋅ s and replacing I by I = 0,085 m ⋅ K ⋅ W . The formula then becomes:
T a
(0,15⋅−vv0,22⋅ )
aw
I=⋅0,092 e − 0,004 5 (A.13)
a,r
−1 −1 −1 −1
Equations (A.12) and (A.13) apply for 0,4 m ⋅ s u v u 18 m ⋅ s and 0 m ⋅ s u v u 1,2 m ⋅ s , and for the
a m
conditions of Equation (A.14).
If walking speed is unknown or not applicable (stationary work), the movement generated, increased air
velocity around the body, can be calculated by
vM=⋅0,005 2 (− 58) (A.14)
w
−1
The effect of body movement is limited to values lower than 0,7 m ⋅ s .
Equation (A.15) shall be used to determine the required I as a function of the previous equations. This
cl
provides a complementary evaluation of required insulation. The necessary corrections are made by the
program and the result is a required I value that can be compared directly with information from tables (see
cl
Annex C) or static manikin data.
I required is determined by replacing I in Equation (A.15) with the IREQ value:
cl cl,r
()0,15⋅−vv0,22⋅
⎡⎤
aw
If+⋅0,092 e − 0,004 5
cl,r cl
⎢⎥
⎣⎦
I=− 0,085 f (A.15)
cl cl
0,075⋅−ln(ap) 0,15⋅vv−0,22⋅
⎡⎤()
aw
0,54⋅−e 0,06⋅ln(ap)+ 0,5
⎢⎥
⎣⎦
Examples of basic insulation values are given in Annex C.
ISO 11079:2007(E)
Annex B
(informative)
Physiological criteria in cold exposure
B.1 General cooling
Two sets of physiological criteria are defined to identify
a) low physiological strain, characterized by a neutral thermal state of the body, corresponding to a “neutral”
thermal sensation, and
b
...
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