SIST ENV ISO 11079:2001
(Main)Evaluation of cold environments - Determination of required clothing insulation (REQ) (ISO/TR 11079:1993)
Evaluation of cold environments - Determination of required clothing insulation (REQ) (ISO/TR 11079:1993)
Migrated from Progress Sheet (TC Comment) (2000-07-10): This WI will be an ENV (BTS4 C 3/1996)
Bewertung von Kälteumgebungen - Bestimmung der erforderlichen Isolation der Bekleidung (IREQ) (ISO/TR 11079:1993)
In diesem Technischen Bericht werden Verfahren und Strategien zur Bewertung der thermischen Belastung vorgeschlagen, die mit einem Aufenthalt in Kälteumgebungen verbunden sind. Sie sind anwendbar auf eine ununterbrochene, unterbrochene und gelegentliche Exposition und sie gelten sowohl für Arbeiten in Innenramen als auch im Freien. Spezifische Effekte, die mit bestimmten meteorologischen Erscheinungen verbunden sind (z.B. Niederschlag), werden nicht behandelt, sie sollten mit anderen Verfahren beurteilt werden.
Evaluation des ambiances froides - Détermination de l'isolement requis des vetements (ISO/TR 11079:1993)
Vrednotenje hladnih okolij - Ugotavljanje zahtevane izolacije oblačil (REQ) (ISO/TR 11079:1993)
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
SIST ENV ISO 11079:2001
01-marec-2001
9UHGQRWHQMHKODGQLKRNROLM8JRWDYOMDQMH]DKWHYDQHL]RODFLMHREODþLO 5(4 ,6275
Evaluation of cold environments - Determination of required clothing insulation (REQ)
(ISO/TR 11079:1993)
Bewertung von Kälteumgebungen - Bestimmung der erforderlichen Isolation der
Bekleidung (IREQ) (ISO/TR 11079:1993)
Evaluation des ambiances froides - Détermination de l'isolement requis des vetements
(ISO/TR 11079:1993)
Ta slovenski standard je istoveten z: ENV ISO 11079:1998
ICS:
13.180 Ergonomija Ergonomics
61.020 2EODþLOD Clothes
SIST ENV ISO 11079:2001 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
---------------------- Page: 1 ----------------------
ISO
TECHNICAL
TR 11079
REPORT
First edition
1993-12-15
Evaluation of cold environments -
Determination of required clothing
insulation (IREQ)
- D6 termina tion de I’isolemen t requis
haha tion des ambiances froides
des v&emen ts
Reference number
ISO/TR 11079:1993(E)
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ISOITR 11079:1993(E)
Contents
Page
1 Scope . . . . . . . . . . . . . . .*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .~. . . . . . . . . . 1
2 Normative references . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*.-. 1
3 Symbols and abbreviations
. . . . . . . . . . . . . . . . . . . . . . . . . .*. 1
4 Principles of methods for evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2
5 General cooling . . 3
5.1 Definition of required insulations, IREQ . 3
5.2 Calculating of factors affecting IREQ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*
3
5.3 Calculation of IREQ . . 5
5.4 Interpretation of IREQ . . 5
5.5 Definition and calculation of duration limited exposure, DLE 5
6 Local cooling . .
6
6.1 Indoor conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .-.
6
6.2 Outdoor conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . 6
7 Practical assessment of cold environments . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
7.1 Procedure for the determination of IREQ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Annexes
A Heat exchange equations . . 13
A.1 Determination of respiratory heat exchange . . . . . . . . . . . . . . . . . . . . . . 13
A.2 Determination of evaporative heat exchange . . . . . . . . . . . . . . . . . . . . . 13
A.3 Determination of evaporative resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
A.4 Determination of the clothing area factor
. . . . . . . . . . . . . . . . . . . . . . . . . . . 13
A.5 Determination of the convective heat transfer coefficient . 13
A.6 Determination of relative air velocity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
A.7 Determination of radiation heat transfer coefficient
. . . . . . . . . . 14
0 ISO 1993
All rights reserved. No part of this publication may be reproduced or utilized in any form
or by any means, electronie or mechanical, including photocopying and microfilm, without
permission in writing from the publisher.
International Organization for Standardization
Case Postale 56 l CH-1211 Geneve 20 l Switzerland
Printed in Switzerland
ii
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ISO/TR 11079:1993(E)
.................................. 15
B Physiological criteria in cold exposure
15
B.l Local cooling .
16
....................................................
B.2 Duration limited exposure
17
C Thermal insulation of clothing .
................... 17
Basic and resultant insulation .
Cl
17
..............................................................
C.2 Moisture absorption
................ 17
C.3 Individual behaviour and clothing requirements
............................ 19
Values for calculating the wind chill index
D
21
.........................................................
E Examples of evaluation .
21
.............................................................
E.l Continuous exposure
21
............................................................
E.2 Intermittent exposure
21
.....................................................
E.3 Duration limited exposure
. 22
F Computer program for calculating IREQ, DLE, RT and WCI
30
...................................... .......................................
G Bibliography
. . .
Ill
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lSO/TR 11079:1993(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. Esch member body interested in a subject for
which a technical committee has been established has the right to be re-
presented on that committee. International organizations, governmental
and non-governmental, in liaison with ISO, also take patt in the work. ISO
collaborates closely with the International Electrotechnical Commission
(IEC) on all matters of electrotechnical standardization.
The main task of technical committees is to prepare International Stan-
dards, but in exceptional circumstances a technical committee may pro-
pose the publication of a Technical Report of one of the following types:
- type 1, when the required support cannot be obtained for the publica-
tion of an International Standard, despite repeated efforts;
- type 2, when the subject is still under technical development or where
for any other reason there is the future but not immediate possibility
of an agreement on an International Standard;
- type 3, when a technical committee has collected data of a different
kind from that which is normally published as an International Standard
(“state of the art”, for example).
Technical Reports of types 1 and 2 are subject to review within three years
of publication, to decide whether they tan be transformed into lnterna-
tional Standards. Technical Reports of type 3 do not necessarily have to
be reviewed until the data they provide are considered to be no longer
valid or useful.
ISOnR 11079, which is a Technical Report of type 2, was prepared by
Technical Committee lSO/TC 159, Ergonomics, Sub-Committee SC 5,
Ergonomics of the physical environments.
A series of international Standards related to the assessment of thermal
environments are being produced within the framework of
ISOnC 159/SC5. For cold environments there are few methods available,
insufficient experimental support and limited practical experience. More
experimental work is needed to validate and further elaborate the methods
contained in this Technical Report before there is a basis for the develop-
ment of an International Standard.
?his document is being issued in the type 2 Technical Report series of
publications (according to subclause G.4.2.2 of part 1 of the lSO/IEC Di-
rectives, 1992) as a “prospective Standard for provisional application” in
the field of assessment of thermal environments because there is an ur-
gent need for guidance on how Standards in this field should be used to
meet an identified need.
iV
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ISO/TR 11079:1993(E)
“International Standard”. lt is
This document is no% to be regarded as an
proposed for provisional application so that Information and experience of
its use in practice may be gathered. Comments on the content of this
document should be sent to the ISO Central Secretariat.
A review of this type 2 Technical Report will be carried out not later than
two years after its publication with the Options of: extension for another
two years; conversion into an International Standard; or withdrawal.
Annexes A and B form an integral part of this Technical Report. Annexes
C, D, E, F and G are for information only.
V
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ISO/TR 11079:1993(E)
Introduction
Wind-chill is commonly encountered in cold climates, but low tempera-
tures first of all endanger body heat balance. By proper adjustment of
clothing, man tan often control and regulate body heat loss to balance
a Change in the ambient climate. The method presented here is there-
fore based on the evaluation of the clothing insulation required to
maintain in equilibrium the thermal balance of the body. The heat bal-
ante equation used takes into account the most recent scientific findings
concerning heat exchanges at the surface of the skin as well as the
clothing.
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ISO/TR 11079:1993(E)
TECHNICAL REPORT
Evaluation of cold environments - Determination of required
clothing insulation (IREQ)
3 Symbols and abbreviations
1 Scope
This Technical Report proposes methods and strat-
egies to assess the thermal stress associated with
exposure to cold environments. They apply to con-
n body surface area, in Square metres
tinuous, intermittent and occasional exposure and in
du
m*
both indoor and outdoor work. Specific effects as-
( >
sociated with certain meteorological phenomena
n body surface area partaking in radiation
r
(e.g. precipitation) are not covered and should be
heat exchange, in Square metres (m’>
assessed by other methods.
c convective heat exchange, in Watts per
Square metre (W/m*)
c latent heat of evaporation, in joules per
‘e
2 Normative references
kilogram
The following Standards contain provisions which, specific heat of dry air at constant press-
cP
through reference in this text, constitute provisions Ure, in joules per kilogram of dry air
of this Technical Report. At the time of publication,
c respiratory convective heat exchange, in
the editions indicated were valid. All Standards are res
Watts per Square metre (W/m*)
subject to revision, and Parties to agreements based
on this Technical Report are encouraged to investi-
DLE duration limited exposure, in hours (h)
gate the possibility of applying the most recent edi-
tions of the Standards indicated below. Members of
E evaporative heat exchange by sweating,
IEC and ISO maintain registers of currently valid
in Watts per Square metre (W/m*)
International Standards.
E respiratory evaporative heat exchange,
res
ISO 7726:1985, Thermal environmenfs - Instruments
in Watts per Square metre (W/m*)
and methods for measuring physical guantities.
ratio of surface area of the clothed body
f Cl
to the surface area of the nude body, di-
ISO 7730: 1984, Moderate thermal environmenfs -
mensionless
Determination of the PMV and PPD indices and
specification of the conditions for thermal comfort.
h convective heat transfer coefficient, in
C
Watts per Square metre degree Celsius
ISO 8996:1990, Ergonomics - Determination of
(W/m*.‘C)
metabolic heat production.
h radiation heat transfer coefficient, in
r
ISO 9920: -‘1, Ergonomics of the thermal environment
Watts per Square metre degree Celsius
- Estimation of the thermal insulation and
(W/m*.“C)
evaporative resistance of a clothing ensemble.
1) Ts be published.
---------------------- Page: 8 ----------------------
ISO/TR 11079:1993(E)
boundary air layer insulation, in Square rate of Change in body heat content, in
metre degrees Celsius Watt Watts per Square metre (W/m*)
Per
m*.O
W)
(
ambient air temperature, in degrees
I basic clothing insulation, in Square metre Celsius (“C)
Cl
degrees Celsius per watt (m*.OC/W)
t
chilling temperature, in degrees Celsius
ch
0
1 resultant clothing insulation, in Square
clr ( c>
mejre degrees Celsius watt
Per
clothing surface temperature, in degrees
m ao
W)
(
Celsius (“C)
z total insulation of clothing and boundary
T
t
expired air temperature, in degrees
in Square metre degrees ex
air layer,
Celsius (“C)
Celsius per watt (m*.OC/W)
operative temperature, in degrees
z resultant total insulation, in Square metre
Tr
Celsius (T)
degrees Celsius per watt (m*.OC/W)
mean radiant temperature of the en-
t,
Woodcock permeability index, dimen-
im
vironment, in degrees Celsius (“C)
sionless
t local skin temperature, in degrees
sk
IREQ required clothing insulation, in Square
Celsius (“C)
metre degrees Celsius watt
Per
m*.O
W)
(
mean skin temperature, in degrees
isk
Celsius (“C)
minimal required clothing insulation, in
Square metre degrees Celsius per watt
V Ventilation rate, in kilograms per second
m*.O
W)
(
(kg 1s)
neutral required clothing insulation, in
air velocity, in metres per second (m/s)
va
sqyare metre degrees Celsius per watt
m eo
CW)
V relative air velocity, in metres per second
(
ar
(mb>
K conductive heat exchange, in Watts per
Square metre (W/m*)
W effective mechanical power, in Watts per
Square metre (W/m*)
h4 metabolic power, in Watts per Square
metre (W/m*)
W skin wettedness, the equivalent fraction
of the skin surface which tan be con-
ambient water vapour pressure, in
Pa
sidered as fully wet, dimensionless
kilopascals (kPa)
W humidity ratio of inhaled air, in kilograms
a
saturated water vapour pressure at ex-
P ex
of water per kilogram of dry air
pired air temperature, in degrees Celsius
0
( C) W
humidity ratio of exhaled air, in kilograms
ex
of water per kilogram of dry air
water vapour pressure at skin tempera-
psk
ture, in kilopascals (kPa)
WCI wind chill index, Watts per Square metre
(wlm2>
saturated water vapour pressure at skin
Psks
temperature, in kilopascals (kPa)
body heat gain or loss, in watt hours per
&
Square metre (W.h/m*) 4 Principles of methods for evaluation
limit value for , in watt hours per Square
Q lim
Cold stress is suggested to be evaluated in terms
P
metre (W=h/m )
of both general cooling of the body and local cooling
of particular Parts of the body (e.g. extremities and
radiation heat exchange, in Watts per
R
face).
Square metre (W/m*)
For general cooling, an analytical method is pre-
R resultant evaporative resistance of cloth-
T
sented in clause 5 for the evaluation and interpret-
ing and boundary air layer, in Square
ation of the thermal stress. lt is based on a
metre kilopascals per watt (m*-kPa/W)
calculation of the body heat exchange and of the
required clothing insulation (IREQ) for the mainten-
RT recovery time, in hours (h)
ante ofthermal equilibrium.
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ISO/TR 11079:1993(E)
For local cooling, several methods are proposed in - a method for the analysis of effects of specific
clause 6 for the evaluation of local thermal effects, Parameters and evaluation of measures of im-
e.g. cold injury or cold hands. provement;
The scientific basis of each of the proposed methods
-
a method for specification of clothing insulation
in this Technical Report tan be found in the relevant
requirements and the subsequent selection of
publications cited in annex G.
clothing to be used under the prevailing en-
vironmental conditions.
5.2 Calculating of factors affecting IREQ
5 General cooling
Calculation of IREQ is based on a rational analysis
A general equation for body heat balance is defined.
of man’s heat exchange with the environment. The
In this equation, clothing thermal properties, body
following subclauses review the general principles
heat production and physical characteristics of the
for calculation of the various factors affecting IREQ.
environment are the determinant factors. The
equation is solved for the required clothing insu-
52.1 General heat balance equation
lation (IREQ) for maintained heat balance under
specified criteria of physiological strain. As there is
The general heat balance equation is as follows:
an upper limit for the amount of insulation clothing
Ilif - W= Eres + Cres + E + K + R + C + S
tan provide, a duration limited exposure (DLE) is
calculated for the existing clothing insulation on the
. . .
(1)
basis of acceptable levels of body cooling. Detailed
equations, coefficients and criteria are proposed in
where the left hand side of the equation represents
annexes A and B.
the internal heat production, which is balanced by
the right hand side which represents the sum of heat
The method involves the following Steps, outlined
exchanges in the respiratory tract, heat exchanges
schematically in figure 1:
on the skin and the heat storage accumulating in the
body.
- measurem ents of the thermal Parameters of the
environme nt;
52.2 Metabolic power
- determination of activity level (metabolic rate);
M is the metabolic power and is evaluated using
methods specified in ISO 8996.
- calculation of required clothing insulation (IREQ);
52.3 Effective mechanical power
-
comparison with insulation provided by existing
clothing;
W is the effective mechanical power. In most indus-
trial situations this is small and tan be neglected.
-
evaluation of the conditions for thermal balance
and calculation of recommended maximal ex-
52.4 Respiratory heat exchange
posure time (DLE).
Heat is lost from the respiratory tract by warming
and saturating inspired air and is the sum of
5.1 Definition of required insulations, IREQ
convective heat loss (C;-es) and evaporative heat loss
(Eres), determined, respectively, by
IREQ is defined as the resultant clothing insulation
required during the actual environmental conditions
C . . .
res = cp v(t,x - ta)/Adu
(2)
to maintain the body in a state of thermal equilib-
rium at acceptable levels of and skin tem-
peratures.
E . . .
res = Ce Vwex - wa>/ncju (3)
IREQ tan be applied as
52.5 Evaporative heat exchange
- a measure of cold stress integrating the effects
of air temperature, mean radiant temperature,
The evaporative heat exchange, E, is defined by
humidity, air velocity and metabolic heat pro-
. . .
duction; E = w(p,ks -p,)lRT
(4)
3
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ISO/TR 11079:1993(E)
Cold environment
Measure I
Local cooling
Air temperature Operative
Mean radiant temperature temperature
1
Indoors
Ab velocl t y
(Humidity)
Local draught
I
Hand skin temperature
,
General cooling
+
.
. l
Determine IREQ Select clot hlng
tlme-welght If requlred ------- Determlne Icl
Compare IREQ and
Correct /cl for body motlon.
resultant Insulatlon
posture, wlnd, molsture etc.
IREQ min -C 1 c~r -E IREQ neu trat Iclr ’ IREQ neutral
/ rlr ( IREQ min
Clothlng sufflclent.
Posslble risk of over-
heatlng at high
Levels ot actlvlty
1.
~~f.iin~.~.~ves.~~.:,~~~:.~~~.:.~~~~j~~-~~~~~~~~~~
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . .
. . . . . .
t~.prot~ctiun.-Ob-Tods-Und-feeS.-.-.-.-.-.-
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 1 - Procedure for the evaluation of cold environments
5.2.8 Radiation heat exchange
5.2.6 Conductive heat exchange
The radiation heat exchange between the clothing
Conductive heat exchange is related to the area of
surface including uncovered skin and the environ-
body Parts in direct contact with extemal surfaces.
Although it tan be of significant importante for local ment, R, is defined by
heat balance, conductive heat exchange is mostly
. . .
R =Ll hrC 41 - t;> (6)
small and tan be accounted for by the expressions
for convective and radiation heat exchange.
5.2.9 Heat exchange through clothing
52.7 Convective exchange
Heat exchange through clothing takes place by con-
duction, convection and radiation (dry heat ex-
The heat exchange by convection between the
Change) and by the transfer of evaporated sweat
clothing surface including uncovered skin and the
(latent heat). The effect of clothing on latent heat
environment, C, is defined by
exchange is accounted for in equation (4). The effect
. . .
(5) of clothing on dry heat exchange is determined by
---------------------- Page: 11 ----------------------
ISO/TR 11079:1993(E)
activity due to
the thermal insulation of the clothing ensemble and the extra demand for dissipation of
metabolic heat.
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 5.4.2 IREQ and physiological strain
the environment. Heat exchange through clothing,
therefore, tan be expressed in terms of the factual,
Thermal equilibrium tan be achieved at different
resultant, thermal insulation of the clothing, &, as
levels of thermoregulatory strain, defined in terms
follows:
of values for mean skin temperature, sweating (skin
wettedness) and Change in body heat content. lt is
Ck - 41
suggested that IREQ be defined at two levels of
=R+C=M- W-Er,,-C,,,-E
r
%lr
physiological strain.
. . .
(7)
defines a minimal thermal insulation re-
a) IREQmin
quired to maintain body thermal equilibrium at a
subnormal level of mean body temperature. The
5.3 Calculation of IREQ
minimal IREQ represents the highest admissible
body cooling in occupational work.
On the basis of equations (1) to (7) and using the
hypothesis made concerning heat flow by con-
is defined as the thermal insulation
W IREQneutral
duction, the required clothing insulation, IREQ, tan
required to provide conditions of thermal neu-
now be calculated on the basis of the following two
trality, i.e. thermal equilibrium maintained at a
equations:
normal level of mean body temperature. This
level represents no or minimal cooling of the
Gk - kl
. . .
IREQ =
(8)
human body.
Ad - W - Er,, - (;;es - E
Relevant ysiolog ical criteria are presented and
h4 - W - Ere, - Cres - E = R + C . . . Ph
(9)
discussed in annex B.
Equation (8) expresses the dry heat exchange at the
54.3 IREQ and existing clothing insulation
clothing surface and is rewritten from equation (7).
Equation (9) states that the dry heat exchange must
IREQ is the resultant clothing insulation value that
balance the internal heat production minus
is required for the actual conditions. lt may, there-
evaporative and respiratory heat losses and is re-
fore, serve as a guideline for the selection of ap-
written from equation (7).
propriate clothing by a comparison with measured
Equation (8) contains two unknown variables (IREQ
insulation values of ensembles. Almost all thermal
and t,,). Therefore, equation (8) is solved for &, as
insulation values reported for existing clothing en-
folIows:
sembles are measured with a static, thermal
manikin and defined as basic insulation values, Zc,.
t = isk - IREQ (M - W- Eres - Cres - E) . . . (10)
Cl
Their protective value during wear and to what ex-
tent they compare with IREQ, tan only be judged by
This expression replaces &, in the computation for-
determining their resultant insulation (ICI,-). This
mulas for the variables in equation (9), where the
subject is dealt with in annex C.
formulas for Z< and C contain t,, [see equations (5)
and (S)]. The value of IREQ that satisfies
The interval between IREQmi” and IREQ,-,,“,ra, tan be
equation (9) is then calculated by iteration. A com-
regarded as a clothing regulatory Zone, in which
Puter program is provided in annex F for this pur-
each individual chooses the appropriate protection
pose. IREQ is expressed in Square metre degrees
level. With insulation values lower than IREQ,i”
C/W). lt may also be ex-
Celsius per watt (m2eo
there is a risk of progressive body cooling. With
pressed in clo-units (1 clo = 0,155 m2.0C/W).
values higher than IREQ,,“,,,,, conditions will be
considered warm and overheating tan occur.
5.4 Interpretation of IREQ
5.5 Definition and calculation of duration
limited exposure, DLE
54.1 IREQ as a cold index
When the resultant insulation value of the selected
IREQ is a measure of the thermal stress presented clothing ensemble (Zc,r) is less than the calculated
by the combined effects of internal heat production
required insulation (IREQ), exposure has to be
and heat exchange with the environment. The time-limited to prevent progressive body cooling. A
greater the cooling power of the environment, the certain reduction in body heat content (Q) is ac-
higher is the value of IREQ at any given activity ceptable during an exposure of a few hours and tan
level. At any given set of climatic conditions, cold be used to calculate the duration of exposure when
stress, and thereby IREQ, is reduced with increasing the rate of heat storage is known.
---------------------- Page: 12 ----------------------
ISO/TR 11079:1993(E)
Duration limited exposure (DLE) to cold, is defined temperatu res, respiratory and eye protection tan be
required.
as the recommended maximum time of exposure
with available or selected clothing. DLE is calculated
by the following formula
6.1 Indoor conditions
DLE = Q,,,/S . . .
(11)
Light, stationary work makes a person more prone
to unpleasant effects of local cooling, caused by
where Q,,, is the limit value of (2 and S is calculated
draught or radiation heat loss to cold surfaces, for
from equation (12), in which tc, is substituted for the
example. Evaluation of discomfort due to these fac-
expression in equation (13). Available insulation
tors should be based on the Same criteria as for
(lc,r) replaces IREQ and is used to calculate tc, and
moderate thermal environments (ISO 7730). In ad-
S. The equation is then solved by mathematical
dition, a physiological criteria related to hand skin
iteration.
temperature is applied.
. . . (12)
s=iW-- W- Cres- Eres- E- R- C
t = T&- Jc,r(M - W - Cres - Eres - E - S). . . (13)
Cl 6.2 Outdoor conditions
DLE may be calculated for both levels of strain (see
For outdoor conditions, cold stress is determined by
5.4.2). The Same amount of reduction in body heat
calculating the local cooling effect of wind, i.e. the
content is applied. However, the deficit in thermal
wind-chill. As a complement, measurements of hand
insulation between selected clothing and IREQ,,,,, is
skin temperature are used.
always smaller than between selected clothing and
Accordingly, the exposure (DLE) be-
I REQneutral -
6.2.1 Definition and calculation of wind-chill
Comes longer at a higher level of strain for IREQ,,,.
If, at the onset of exposure, the worker has adopted
The wind-chill index (WCI) is defined as the rate of
a certain heat debt, the exposure time should be
heat loss from an unprotected skin surface area. lt
reduced accordingly.
is given by the general equation:
After exposure, a recovery period should be allowed
. . .
WC1 = (h, + hr) (tsk - t,)
(14)
to restore normal body heat balance. Recovery time
(RT) is calculated in the Same way as DLE, substi-
where the values of the coefficients h, and h, are
tuting the “cold conditions” with the exposure con-
those for a local skin Segment. The value of 12, is al-
ditions during the recovery period. In other words,
most constant and independent of the wind and be-
RT = p,,,/S’, where S’ is the rate of heat storage
Comes small in relation to h, at high air velocities.
(positive) calculated from equations (12) and (13) for
The expression to be used for the heat transfer co-
the exposure conditions during the recovery period.
efficients and examples of the evaluation of WCI and
Since recovery is supposed to Start when the body
tch are presented in annex D.
has achieved a certain heat debt, the value of e,i,
should be the Same when calculating RT.
7 Practical assessment of cold
The physiological criteria to be used are presented
environments
in annex B and examples of the application of DLE
and RT in annex D.
7.1 Procedure for the determination of IREQ
The procedure for the assessment of cold environ-
6 Local cooling
ments is shown schematically in figure 1 and is as
follows:
Local cooling of any patt of the body with emphasis
on hands, feet and head, tan produce discomfort,
a) Measure the following climate Parameters ac-
deterioration of manual and physical Performance
cording to ISO 7726:
and cold injury. The amount of knowledge on re-
sponses to local cooling is insufficient for the devel-
1) air temperature;
opment of a Single evaluation method. Several
approaches are proposed and more research work
mean radiant temperature;
2)
is encouraged on the subject.
3) air velocity; and
Effects of local cooling should be evaluated separ-
ately for indoor and outdoor conditions. The indoor
thermal environment is relatively easily modified by 4) humidity.
whereas the outdoor en-
engineering techniques,
The operative temperature may replace air and
vironment is determined by weather and climate,
mean radiant temperatures. The water content
and protective measures mostly comprise adjust-
of air at low temperatures is very small, so a
ment of clothing or control of exposure. At very low
6
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ISO/TR 11079:1993(E)
Selec
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