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International standards and the ergonomics of the thermal environment
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Ergonomics Vol 26, No. 4, pp. 29SW2, 1995 Copyright @ 1995 Ekvier Science Ltd Printed in Great Britain. All rights reserved ooo3&770!95 $10.00 + 0.w
International standards and the ergonomics of the thermal environment Bjarne W. Olesen D. F. Liedelt ‘Velta’ GmbH,
Hans- Btickler-Ring 41, D 22851 Norderstedt, Germany
The main purpose for heating and air conditioning of workspaces is to provide an environment that is acceptable and does not impair the health and performance of the occupants. Owing to production processes and external climate it may be necessary to work in unacceptable conditions for limited time periods. However, it must be ensured that these conditions do not impair the health of the employees. To do that, standard methods are needed so that different solutions and evaluations of the thermal environment can be done in a comparable way. The standards presented in the present paper include evaluation methods for moderate, hot, and cold environments, supporting standards for measuring and determination of the relevant parameters, and standards for measurement and evaluation of individual physiological conditions of humans. Keywords:
thermal
environment,
thermal
stress,
comfort,
standards,
measurements
annexes. These or other values may then be adapted in national rules for the thermal environment.
The main purpose for heating and air conditioning of workspaces is to provide an environment that is acceptable and does not impair the health and performance of the occupants. Owing to production processes and external climate it may be necess.ary to work in unacceptable conditions for a limited time period. However, it must be ensured that these conditions do not impair the health of the employees. Light, noise, air quality and the thermal environment are all factors that will influence the acceptability and performance of the occupants. The present paper will deal only with the thermal environment. Several standards dealing with methods for the evaluation of the thermal environment have been published by international organizations such as IS0 and CEN, together with national standards in Germany, France, Netherlands, Denmark, Italy, the USA etc. The present paper deals with the IS0 standards, which have been or are being prepared by ISO/TC159/SCYWGl, ‘Ergonomics of the thermal environment’. An overview of the standards issued and documents under preparation is given in Table 2. A review of international standards concerned with the physical environment is presented by Parsons (1995) in this special issue. Several of these standards may be used as a basis for the design and evaluation of buildings, HVAC (heating, ventilation and air conditioning) systems, protective equipment (clothing) and optimization of work-rest schedules. The basic philosophy has been to standardize evaluation methods, while recommended limit values for the different parameters or indices are listed in informative
The thermal
environment
Existing methods for evaluation of the general thermal state of the body, both in comfort and in heat or cold stress, are based on an analysis of the heat balance for the human body: S=M-W-C-R-Esk-C,,,-E,,-K
(1)
where S = heat storage in body; M = metabolic heat production; W = external work; C = heat loss by convection; R = heat loss by radiation; Esk = evaporative heat loss from skin; C,,, = convective heat loss from respiration; E,,, = evaporative heat loss from respiration; and K = heat loss by conduction. The factors influencing this heat balance are: activity level (metabolic rate, met or W mw2);thermal resistance of clothing I,, (clo or m2”C W-l); evaporative resistance of clothing R, (m2 Pa W-l); air temperature ta (“~2); mean radiant temperature tr (“C); air speed v,, (m s-l); partial water vapour pressure pa (Pa). These parameters must be combined so that the thermal storage is 0, or else the working time has to be limited to avoid too much strain on the body. To provide comfort, the mean skin temperature also has to be inside certain limits, and the evaporative heat loss must be low. In existing standards, guidelines or handbooks, different methods are used to evaluate the general thermal state of the body in moderate environ-
293
294
International standards and the ergonomics of the thermal environment: B. W. Olesen
Table 1 Ergonomics
of the thermal environment:
development
of international
standards
Aims of the standard
Title of the document
Status
General presentation of the set of standards in terms of principles and application
Ergonomics of the thermal environment: principles and apphcatlon of international standards
IS0 DIS 11399
Standardization the standards
Ergonomics of the thermal environment: symbols and units
CD 13731
of quantities, symbols and units used in
Thermal stress evaluation in hot environments Analytical method
definitions,
Hot environments: analytical determination and interpretation of thermal stress using calculation of required sweat
IS0 7933
Hot environments: estimation of the heat stress on working man, based on the WBGT index (wet bulb globe temperature)
IS0 7243
Comfort evaluation in moderate environments
Moderate thermal environments: determination of the PMV and PPD indices and specification of the conditions for thermal comfort
IS0 7730
Thermal stress evaluation in cold environments
Evaluation of cold environments: determination required clothing insulation, I,_,
IS0 TR 11079 Technical report
Data collection standards
Metabolic rate
Ergonomics: determination production
Requirements for measuring instruments
Thermal environments: instruments and methods for measuring physical quantities
IS0 7726
Clothing insulation
Estimation of the thermal insulation and evaporative resistance of a clothing ensemble
IS0 9920
Evaluation of thermal strain using physiological measures
Evaluation of thermal strain by physiological measurements
IS0 9886
Subjective assessment of the thermal environment
Assessment of the influence of the thermal environment using subjective judgement scales
IS0 DIS 10551
Selection of an appropriate system of medical supervision for different types of thermal exposure
Ergonomics of the thermal environment: medical supervision of individuals exposed to hot or cold environments
IS0 CD 12894
Contact with hot, moderate and cold surfaces
Documents in draft form
NP 12893
Comfort of the disabled
Documents in draft form
New work item
Documents in draft form
New work item
Documents in preparation
NP 14505
Diagnostic method
Long-term assessment of environmental
quality
Vehicle environments
ments, cold environments and hot environments; but all are based on the above heat balance and the listed factors. Besides the general thermal state of the body, a person may find the thermal environment unacceptable or intolerable if local influences on the body from asymmetric radiation, air velocities, vertical air temperature differences or contact with hot or cold surfaces (floors, machinery, tools, etc.) are experienced. Moderate thermal environments Both ASHRAE (the American Society of Heating, Refrigerating and Ventilation Engineers) and IS0 (the International Organization for Standardization) have recently revised their standards for a comfortable thermal environment (ASHRAE 55-92, 1992 and IS0 7730, 1993). The research that forms the basis for these two standards is mainly performed under environmental conditions similar to commercial and residential buildings, with relatively low activity levels (mainly sedentary, 1.2 met), normal indoor clothing (0.5-1.0 clo) and a limited range of environmental parameters. IS0 7730 (1993) standardizes the PMV-PPD index
of
of metabolic heat
IS0 8996
as the method for evaluation of moderate thermal environments. To quantify the degree of comfort the PMV index gives a value on the seven-point thermal sensation scale: +3 hot, +2 warm, +l slightly warm, 0 neutral, -1 slightly cool, -2 cool, -3 cold. An equation in the standard calculates the PMV index based on the six factors clothing, activity, air and mean radiant temperature, air velocity and humidity. Even if a PMV value of 0 is obtained, there will still be at least 5% of the occupants who will be dissatisfied with the thermal environment. The predicted percentage of dissatisfied (PPD) index can be determined from the equation. PPD = I00 _ 95
e-(0.O3353
PMV4+0.217Y
PMV*)
The standard describes the method, and in an informative annex recommendations for an acceptable environment are given as -0.5 < PMV < 0.5, PPD < 10%. The use of the method is illustrated in Figure I, where the optimal operative temperature (average of air and mean radiant temperature) and the recommended temperature range are shown as a function of clothing and activity.
295
International standards and the ergonomics of the thermal environment: B. W. Olesen m* WW 175 150 125 “E
where v, = mean air velocity (3 min), m s-l; SDw, = standard deviation of air velocity (3 min), m s-‘; ta = air temperature, “C. For v, < 0.05 m s-l insert v, = 0.05 m s-i. For DR > 100% use DR = 100%. In the new, revised standards IS0 7730 and ASHRAE 55-92 the requirements are based upon a 15% dissatisfaction criterion. The recommended limits are shown in Figure 2.
100 6
Hot environments
75 50 0.0 _..
0.5
1.0
1.5
Clothing (c/o) Figure 1 The optimal temperature (corresponding to PMV = 0) as a function of activity and clothing. The shaded areas indicate the comfort range f Af around the optimal temperature inside which -0.5 < PMV < +OS. The relative air velocity caused by body movement is estimated to be zero for M < 1 met and v,, = 0.3 (M - 1) for M > 1 met. Relative humidity = 50%
The IS0 philosophy for the assessment of hot environments is to use a simple ‘fast’ method for monitoring the environment, based on the wet bulb globe temperature (WBGT) index (IS0 7243, 1989). If the WBGT values exceed the provided ‘reference’ values, or a more detailed analysis is required, then IS0 7933 (1989) provides an analytical method of assessment. The wet bulb globe temperature heat stress index is calculated inside buildings and outside buildings without solar load as WBGT = 0.7&, + 0.3ta
(4)
and outside buildings with solar load as Because the PMV index assumes that all evaporation from the skin is transported through the clothing to the environment, this method is not applicable for hot environments. It can be used within a range of PMV index of -2 to +2, i.e. thermal environments where sweating is minimal. The recommended range for the use of this standard is:
Metabolic rate: Clothing: Air temperature: Mean radiant temperature: Air velocity: Water vapour pressure:
0.8-4 met (46 232 W m”) O-2 cl0 (O-0.310 m2 “C W-l) lO--30°C 1wO”C O-l m s-’ 90-2700 Pa
Besides the general thermal state of the body, a person may find the thermal environment unacceptable if local influences on the body from asymmetric radiation, draught, vertical air temperature differences or contact with hot or cold surfaces (floors, machinery, tools, etc.,) are experienced. The annex of IS0 7730 also lists a series of recommendations for these local discomfort parameters (Table 2). One of the most critical factors is draught. Many people are very sensitive to air velocities, and therefore draught is a very common cause for occupant complaints in ventilated and air-conditioned spaces. Fluctuations of the air velocity have a significant influence on a person’s sensation of draught. The fluctuations may either be expressed by the standard deviation of the air velocity or by the turbulence intensity Tu, which is equal to standard deviation divided by the mean air velocity v, (SDv,lv,). The percentage of people feeling draught (draught rating, DR) may be estimated from the equation DR = (34 - t,) (v, - 0.05) 0.6223(3.143 + 0.3696SDv.J
(3)
WBGT = 0.7r,, + 0.2& + O.lt,
(5)
where tnw is the natural wet bulb temperature; tg is the temperature at the centre of a 150 mm diameter black globe thermometer; and ta is the air temperature. The WBGT value of the hot environment may be compared with a WGBT reference value, which is included in an informative annex (Table 3). The reference values have been established allowing for a maximum rectal temperature of 38°C for the persons concerned. This corresponds to levels of exposure to which almost all individuals can be ordinarily exposed without any harmful effect, provided there are no preexisting pathological conditions. If the WBGT of the hot environment exceeds the WBGT reference value then the heat stress at the workplace needs to be reduced or a more detailed analysis made (i.e. using IS0 7933). The standard also includes a method to plan a work-rest schedule that will provide tolerable environments. Table 2 Recommended criteria for an acceptable moderate thermal environment
as proposed in IS0 7730 Appendix
General thermal comfort Predicted mean vote Predicted percentage dissatisfied
A
-0.5 < PMV < + 0.5 PPD < 10% (see Figure
I)
Local thermal discomfort DR < 15% (see Figure2)
Draught Vertical air temperature between head and feet
difference
At, < 3 K
Radiant temperature asymmetry from cold vertical surfaces (window, wall)
A& < 10 K
Radiant temperature asymmetry from warm horizontal surfaces (heated ceiling)
At,, < 5 K
Floor surface temperature
19°C < or < 29°C
296
International standards and the ergonomics of the thermal environment: B. W. Olesen aI.5 Wr,q =-
Turbulence intensity 0%
E ‘=?
03)
E max
-4 -
Sweating efficiency:
/
&
.3 -
.2 -
Required SW,,,
760%
>
.I -
r = 1 - 0 5 ed.h (l-wreq)
10%
DR = 15% I 20
.O_ 18
I 22
Local air
I 24
I 26
temperature ("C)
Figure 2 Combination
and turbulence
of mean air velocity, air temperature intensity that will result in less than 15%
dissatisfaction
The method used in IS0 7933 (1989) Required sweat rate, SW,,, is based on the heat balance Equation (1).
Assuming that the heat storage is equal to 0, the necessary evaporation from the skin, Ereq, ensuring a heat balance, is calculated as follows: E req = M - W - C - R - E,.,, - C,,,
maximum evaporation, absorbed by the environment, equation
The
E max =
where
(6)
which can be is estimated from the
E,,,,,,
sweat rate: E r=i = r
(10)
These parameters are used to evaluate how stressful a given hot working environment is. Depending on the physiological limitations for factors such as sweat rate, total sweat loss, heat sto:age and skin wetness, which are listed in Table 4, it is possible to evaluate whether a given environment is acceptable for continuous work. The method also allows calculation of an acceptable working time. Detailed equations for the calculations can be found in the standard (IS0 7933, 1989). The relation between the operative temperature and SW,,, for different combinations of activity and clothing is shown in Table 5. A computer program is provided to allow ease of calculation and efficient use of the standard. This rational method of assessing hot environments allows identification of the relative importance of different components of the thermal environment, and hence can be used in environmental design. The WBGT index is an empirical index, which cannot be used to analyse the influence of the individual parameters. The required sweat rate (SW,,,) has this capability, but lack of data may make it difficult to estimate the benefits of protective clothing.
Psk,s - Pa (7)
R t?T
psk,s =
Cold environments
saturated water vapour pressure at skin;
Pa = water vapour pressure in the environment;
ReT =
total evaporative resistance of clothing and boundary layer. Based on the required evaporation and the maximum evaporation it is then possible to estimate the following factors: Required
skin wetness:
Table 3 Reference
Many industrial workplaces are located in cold environments, such as cold storage, meat packing, workplaces located outdoors, etc. In cold environments, the clothing is the most important factor for obtaining an acceptable thermal environment. Based on the heat balance Equation (1), an analytical method has been proposed by ISO, Required clothing insulation, Zreq (ISO/TR 11079, 1993). The method calculates the insulation of the clothing necessary to keep a heat
values of WBGT (IS0 7243) Metabolic
Reference
rate, M
Metabolic rate class
Related to a unit skin surface area (W m-*)
Total (for a mean skin surface area of 1.8 m2) (W)
Person acclimatized (“0
0 I 2 3
M < 65 6.5 < M < 130 130 < M < 200 200 < M < 260
117 117 < M < 234 234 < M < 360 360 < M < 468
M>260
M > 468
33 30 28 No sensible air movement 25 23
4
(resting)
(9)
Note: The values given have been established
M<
allowing for a maximum
rectal temperature
to heat
Sensible air movement 26 25
value of WBGT Person not acclimatized to heat eo 32 29 26 No sensible air movement 22 18
of 38°C for the persons concerned
Sensible air movement 23 20
International
Table 4 Reference
standards and the ergonomics of the thermal environment:
value for the different criteria of thermal stress and strain in bot environments
Maximum skin wettedness, Maximum sweat rate Rest: M W m- 2 SW,,, %:;k! <,6S M > 65 W mz SW,,, (g h-‘)
Warning
Danger
0.85
0.85
w,,,
(ISO 7933)
Acclimatized
Non-acclimatized subjects
Criterion
(W mm’)
100 260
1.50 390
(W mm2)
200 520
250
50 1000 2600
297
B. W. Oiesen
subjects Danger
Warning
1.0
1.0
200 520
300 780
780
300
400 1040
60
50
60
1250 3250
1500 3900
2000 5200
650
Maximum heat storage
Q,,.W h 6
Maximum water loss L,, (W h mm’) (g) Table 5 Required sweat rate index SW, activity level M equal to 70 W mm2 Relative humidity (%)
Clothing I,, @lo)
0.5
(W m-‘1 and wettedness (W-J as a function of clothing, temperature,
air speed and humidity
at the
Operative temperature, Air velocity V, (m 8’)
G ec,
20
25 30 35 40 50 60 25 30 35 40 30 35
50
80
CO.1
0.2
10 37 65 93 169
(0.03) (0.13) (0.24) (0.37) (0.78)
‘IO 37 65 102 37 76
;;*z; (0:17) (0.37) (0.74) (0.26) (0.82)
8 36 64 94 165 = 8 35 65 99 36 71
0.5 (0.02) (0.12) (0.22) (0.34) (0.72)
2 33 64 95 165 a 2 33 64 98 33 66
;k:;
(0:ls) (0.34) (0.69) (0.23) (0.75)
1.0 (0.01) (0.09) (0.18) (0.29) (0.62)
2.0
29 63 98 171 =
(0.06) (0.14) (0.24) (0.523) (1.00)
24 62 101 182 a
(0.04) (0.11) (0.20) (0.45) (1.00)
29 63 99 29 64
(0.08) (0.22) (0.47) (0.12) (0.48)
24 62 102 24 63
(0.05) (0.17) (0.39) (0.08) (0.38)
;lz; (0.12) (0.28) (0.57) (0.18) (0.61)
No&: “wettedness ?= 1 in a given cold environment by knowing the activity level, air- and mean radiant temperature, air speed and a relative humidity according to the following equation: balance
t sk I req
-
tc1
=
(11) ~4
-
W
-
Esk
-
M-VV-Esk--Cres-Eres=C+R
Ges
-
&es
(12)
The relationship between activity level, operative temperature and Ireq is shown in Figure 4. This is a new method, which has not been widely used, and little experience is available. Therefore the method has been proposed in the form of a technical report, which in the future may be published as an IS0 standard. The index value may be used to select a clothing ensemble, which will provide the required insulation. The clothing insulation can according to Table 6 be predicted either as a minimum, where some strain may be expected on the people, or as a neutral insulation, where people are expected to feel neutral. It is important when selecting the actual clothing (IS0 9920) to allow for individual adjustment of the clothing insulation. Also, the clothing insulation values listed in IS0 9920 are valid for people with standing and sedentary work. For people at higher activities, the clothing values from the tables in IS0 9920 should be
reduced by approximately 20%, owing to body movements (pumping effect). If it is not possible to use or select a clothing ensemble with enough insulation, the method includes a procedure for calculation of a recommended exposure time. The basis for the calculations is the physiological requirements listed in Table 6. For outdoor work there may be a risk for frostbite in wintertime. The report uses the wind chill temperature WCI, calculated as 33 - WC1 tch
=
25.5”C WC1 = 1.16 (10.45 + 10 d/v,, - v,,)(33 - ta) W/m2 where ta = outside air temperature, “C; WC1 = wind chill index, w me2; v,, = relative air velocity, m s-l. Table 7 shows the values depending on outside temperature and wind velocity and Table 8 shows the expected effect. Supporting
standards
The application
of the above standards requires measurement or estimation of a number of parameters. The ‘supporting’ and complementary standards
298
International standards and the ergonomics of the thermal environment: B. W. Olesen
Air velocity = 0.2 m/s Relative humidity = 50%
-
1.24
- 0.93
F y
0.62
v
-_
f
Operative temperature, t (“C) Figure 3 &,,, as function of ambient operative at eight levels of metabolic heat production
temperature
Clothing
Note: The operative temperature is the integrated value of the air temperature and mean radiant temperature weighted according to values of the convective and radiation heat transfer coefficients respectively
described below provide information that is required for the application of standards for assessing thermal environments. They can also be used independently in ergonomics investigations. Metabolic
rate
All assessments of thermal environments require an estimate of the metabolic heat production of the occupants (activity level). IS0 8996 (1989) presents
Table 6 Suggested physiological
criteria for determination
Type of cooling
Parameter
General
IREQ tSk w
three types of method. The first is the use of tables, where estimates are provided based on a description of the activity. These range from a general description (e.g. light, heavy etc.) to methods of summation components of tasks (e.g. basal metabolic rate + posture component + movement component etc.). An example of activity levels is given in Table 9. The second method is by the use of heart rate. The total heart rate is regarded as a sum of several components, and in general is linearly related to the metabolic heat production for heart rates above 120 beats per minute. The third method is to calculate the metabolic heat production from measures of oxygen consumption and carbon dioxide production during activity and recovery.
IS0 9920 (1993) p rovides a large database of thermal insulation values, which have been measured on a standing thermal manikin. One set of tables give the insulation values for a large number of ensembles (Table IO). Another set of tables give insulation values for individual garments (Table II) based upon which the insulation for a whole ensemble can be estimated. The insulation of an ensemble, ICI,may be estimated as the sum of the individual garment insulation values, Zclu:Zcl= X ICI,,.The data on evaporative resistance are not so extensive. A few data are given in the standard, and a method to calculate the evaporative resistance based on the thermal insulation is also given. In the present standard no values are listed for the insulation of chairs, which may add 0.1-0.4 clo. Especially for the assessment of the level of heat stress, data for the
of IREQ, DLE and local cooling (IS0 7R 11079) Minimal IREQ (high strain)
Neutral IREQ (low strain)
35.7-0.0285 h? 0.0001 M
30 0.06
(“C) (n.d.)
DLE (W h mm*)
Qhm Hand temperature WC1 Respiratory tract and eye temperature
Local
(“C) (W mm*) (“C)
Table 7 Cooling power of wind on exposed flesh expressed as a chilling temperature, frostbite Actual thermometer Wind speed (m s?)
1.8 2 3 5 8 11 15 20 Notes: Temperatures
-40
-40
24 -
1.5 1600 t,<-40
teh, under almost calm conditions. Bold types indicate risk of
reading
0
-5
-10
-15
-20
-25
-30
-35
-40
45
0 -1 -4 -9 -13
-5 -6 -10 -1.5 -20
-10 -11 -15 -21 -27
-15 -16 -21 -28 -34
-20 -21 -27 -34
-25 -27 -32 +I
-30 -32 -38 47
-16 -18 -20
-23 -26 -28
-31 -34 -36
-38 -42 -44
41 -46 -49 -52
48 -53 -57 40
-55 40 -65 -68
-35 -37 -44 -53 -62 -68 -73 -76
-44l 42 -49 -59 -69 -75 -80 -84
45 47 -55 -66 -76 -fS3 -M -92
given in “C Almost calm conditions refers to a wind speed of 1.8 m SF’ Values given in bold type correspond to WC1 2 1600 (Table 8)
-50
-50 -52 -60 -72 -I33 -90 -96 -100
International standards and the ergonomics of the thermal environment: B. W. Olesen Table 8 Wind chill index, WCI, chilling temperature, on exposed flesh
fch, and effect
Table 11 Thermal Garment
WC1 (W m-*)
Effect -14
Very cold
1400
-22
Bitterly
1600 1800
-30 -38
Exposed
flesh freezes
2ooo 2200
-I5 -53
Exposed
flesh freezes within 1 min
2400 2600
-61 -69
Exposed
flesh freezes
cold within
1h
within 30 s
Table 9 Metabolic rates Metabolic rates Activity
(W m”)
Reclining Seated,
relaxed
Sedentary activity school, laboratory)
(office,
dwelling,
Standing light activity (shopping, laboratory, light industry) Standing, assistant, work) Walking 2 km 3 km 4 km 5 km
medium domestic
activity (shop work, machine
on the level: h-’ h-’ h-’ h-’
Table 10 Thermal
insulation
46
0.8
58
1.0
70
1.2
93
1.6
116
2.0
110 140 165 200
1.9 2.4 2.8 3.4
for typical clothing ensembles
Shirts/blouses Short sleeves Normal, long sleeves
0.15 0.25
Trousers Shorts Normal
0.06 0.25
Dresses/skirts Light skirts (summer) Heavy skirt (winter) Winter dress, long sleeves
0.15 0.25 0.40
Sweaters Thin sweater Thick sweater
0.20 0.35
Outdoor Coat Parka
Underpants,
boiler
suit, socks,
shoes
Underpants, shirt, boiler suit, socks, shoes Underpants, shirt, trousers, smock, socks shoes Underwear with short sleeves and legs, shirt, trousers, jacket, socks, shoes Underwear with long legs and sleeves, thermo-jacket, socks, shoes Underwear with short sleeves and legs, shirt, trousers, jacket, heavy quilted outer jacket and overalls, socks, shoes cap, gloves Underwear with short sleeves and legs, shirt, trousers, jacket, heavy quilted outer jacket and overalls, socks shoes Underwear with long sleeves and legs, thermo-jacket and trousers, Parka with heavy quilting, overalls with heavy quilting, socks, shoes, cap, gloves
insulation
(clo)
0.25 0.35 0.90 0.35 0.40
clothing 0.60 0.70
Sundries Socks Thick, long socks Shoes (thick soled) Boots
0.02 0.10 0.04 0.10
(IS0 9920)
2CI Work clothing
fclU (IS0 9920)
0.03 0.10 0.09
with long legs
Jackets Light, summer jacket Jacket High-insulative, fibre-pelt Boiler suit Trousers Jacket
(met)
garments,
Thermal
description
Underwear Panties Underpants T-shirt
1200
insulation for individual
299
Iel
@lo)
(m* K W-‘)
Daily wear clothing
(clo)
(m* K W-‘)
0.70
0.110
0.30
0.050
0.80
0.125
0.50
0.080
0.90
0.140
Panties, T-shirt, shorts, light socks, sandals Underpants, shirt with short sleeves, light trousers, light socks, shoes Panties, petticoat, stockings, dress, shoes
0.70
0.105
1.00
0.155
Underwear,
0.70
0.110
1.20
1.85
1.00
0.155
1.40
0.220
Panties, shirt, trousers, jacket, socks, shoes Panties, stockings, blouse, long shirt, jacket, shoes
1.10
0.170
2.00
0.310
Underwear with long sleeves and legs, shirt, trousers, V-neck sweater, jacket, socks, shoes
1.30
0.200
2.55
0.395
Underwear with short sleeves and legs, shirt, trousers. vest, jacket, coat, socks. shoes
1.50
0.230
shirt,
trousers,
socks,
shoes
300
International standards and the ergonomics of the thermal environment: B. W. Olesen
rs
Surface
0-50°C
0.5-3.0
0.05-l
kPa
m s-’
Required: Desirable:
+ 1°C +0.5”C
+0.15 kPa This level shall be guaranteed for a difference 1t, - r, of at least 10°C
1
Required: + (0.05 + 0.05 v,) m ss’ Desirable: * (0.02 + 0.07 va) m so’ These levels shall be guaranteed whatever the direction of flow within a solid angle w=3xsr 0.5 s 0.2 s
The shortest possible. Value to be specified as characteristic of the measuring instrument
The shortest possible. Value to be specified as characteristic of the measuring instrument
Required: Desirable:
kPa
m ss’
(t, - 50)
1
Required: <-10°C: f [l + 0.05 (-c - 10) 1 -10°C to 50°C: ?l”C >SO”C: +[l + 0.05
f0.15 kPa These levels shall be guaranteed for a difference 1t, - r, 1of at least 20°C
Required: f (0.1 + 0.05 v,) m SK’ Desirable: f (0.05 + 0.05 v.) m ss’ These levels shallbe guaranteed whatever the direction of flow within a solid angle o=3xsr
and surface
2
temperatures
Desirable: required accuracy
plant radiant
-40 to +120°c
0.5-6.0
0.2-20
Note: At some workplaces in hot environments (steel, coal, glass industries) there may be a need to measure manufacturers of instruments are required to state the accuracy for an extended range.
temperature
pa
“a
Absolute humidity expressed as partial pressure of water vapour
Air velocity
2 These levels shall be guaranteed at least for a deviation 1t,, - r, 1 <2O”C
Desirable: required accuracy
at higher
in this table.
The
Except in the case of a unidirectional air current, the air velocity sensor shall measure the velocity whatever the direction of the air. An indication of the mean value and standard deviation for a period of 3 min is also desirable.
levels than the range
The shortest possible. Value to be specified as characteristic of the measuring instrument
The shortest possible. Value to be specified as characteristic of the measuring instrument
The shortest possible. Value to be specified as characteristic of the measuring instrument
Internationalstandards and the ergonomics of the thermal environment: B. W. Olesen
302 evaporative missing.
resistance
of
clothing
ensembles
are
Instruments and measurements
IS0 7726 (1994 rev.) provides a description of the parameters that should be measured (air temperature, mean radiant temperature, plane radiant temperature, air velocity, humidity), together with methods of measurements and specifications for the instruments (accuracy, respond time, measuring range). Table 12 lists the accuracy required in the standard.
exposures. This guidance is applicable to both occupational and laboratory exposures to extreme environments. In either case an assessment should be made of the expected thermal stress on the individual, but the detailed arrangements for medical supervision may differ in the two situations. Control of occupational exposures must also satisfy national health and safety legislation. The laboratory or climatic chamber studies for which this standard will be relevant include those in which people may be exposed to high or low ambient temperature conditions or local heating or cooling. Other and future standards
Measurements
on individuals
The methods listed above to evaluate the thermal environment assume an average person. As individuals often react very differently, both regarding acceptance of a given environment and regarding the strain that a given environment imposes, it may under certain circumstances be beneficial to take individual physiological and subjective measurements. Also, there may be a need for evaluation of an individual capability for performing a certain job under severe conditions in the field or in an ergonomics laboratory investigation. Physiological measurements
IS0 9886 (1989) p resents the principles, methods and interpretation of measurement of relevant human physiological responses to hot, moderate and cold environments. The standard can be used independently or to complement the use of other standards. Four physiological measures are considered: body core temperature, skin temperature, heart rates and body mass loss. Comments are also provided on the technical requirements, relevance, convenience, annoyance to the subject and cost of each of the physiological measurements. The use of IS0 9886 is mainly in extreme cases, where individuals are exposed to severe environments, or in laboratory investigations into the influence of the thermal environment on humans. Subjective measurements
Subject scales are useful in the measurement of subjective responses of persons exposed to thermal environments. They are particularly useful in moderate environments and can be used independently or to complement the use of objective methods (e.g. thermal indices), which were described previously. IS0 10551 (1995) presents the principles and methodology behind the construction and use of subjective scales, and provides examples of scales that can be used to assess thermal environments. The medical screening standard (ISO/DIS 12894, 1994) provides advice to those concerned with the safety of human exposures to hot or cold thermal environments, about health screening and surveillance that may be appropriate prior to and during such
To help the user, an overview standard (IS0 11399) is being issued. This presents the different standards, and guides the user to which method and standard are applicable for the given situation. In addition, a standard is being prepared which lists all definitions, symbols and units. Ongoing work is dealing with standards for contact with hot, cold and comfortable surfaces, application of the standards in vehicles, and precautions to take when assessing thermal environments for disabled, aged or other groups with special needs. Conclusion The series of standards presented in this paper provides a useful package for assessment and design of HVAC systems and protective equipment to be used in moderate, cold and hot environments. The standards may be used to estimate the optimal combination of the environmental thermal factors that will provide comfortable or tolerable and healthy working conditions. The standards may also be used to establish optimal workrest schedules for environments where the working time must be limited owing to the strain on the human body. Several of these standards are being adopted also as European standards by CEN and as national standards in several countries. Some of the methods used in the standards are based on many years of research and validation, while others are relatively new and not validated to the same degree. It is therefore important to realize that a standard is not an everlasting document, but must be revised on a regular basis. These revisions take place at least each fifth year, where the experience with use and new knowledge are incorporated in the review process. References ASHRAE 1992 ASHRAE standard SS Thermal environmental conditions for human occupancy ASHRAE, Atlanta, GA Parsons, K.C. 1995 ‘Ergonomics of the physical environment: international ergonomics standards concerning speech communication, danger signals, lighting, vibration and surface temperatures’ Appl Ergonomics 26 (4), 281-292 IS0 standards arc listed in Table 1.
Ergonomics Vol 26, No. 4, pp. 29SW2, 1995 Copyright @ 1995 Ekvier Science Ltd Printed in Great Britain. All rights reserved ooo3&770!95 $10.00 + 0.w
International standards and the ergonomics of the thermal environment Bjarne W. Olesen D. F. Liedelt ‘Velta’ GmbH,
Hans- Btickler-Ring 41, D 22851 Norderstedt, Germany
The main purpose for heating and air conditioning of workspaces is to provide an environment that is acceptable and does not impair the health and performance of the occupants. Owing to production processes and external climate it may be necessary to work in unacceptable conditions for limited time periods. However, it must be ensured that these conditions do not impair the health of the employees. To do that, standard methods are needed so that different solutions and evaluations of the thermal environment can be done in a comparable way. The standards presented in the present paper include evaluation methods for moderate, hot, and cold environments, supporting standards for measuring and determination of the relevant parameters, and standards for measurement and evaluation of individual physiological conditions of humans. Keywords:
thermal
environment,
thermal
stress,
comfort,
standards,
measurements
annexes. These or other values may then be adapted in national rules for the thermal environment.
The main purpose for heating and air conditioning of workspaces is to provide an environment that is acceptable and does not impair the health and performance of the occupants. Owing to production processes and external climate it may be necess.ary to work in unacceptable conditions for a limited time period. However, it must be ensured that these conditions do not impair the health of the employees. Light, noise, air quality and the thermal environment are all factors that will influence the acceptability and performance of the occupants. The present paper will deal only with the thermal environment. Several standards dealing with methods for the evaluation of the thermal environment have been published by international organizations such as IS0 and CEN, together with national standards in Germany, France, Netherlands, Denmark, Italy, the USA etc. The present paper deals with the IS0 standards, which have been or are being prepared by ISO/TC159/SCYWGl, ‘Ergonomics of the thermal environment’. An overview of the standards issued and documents under preparation is given in Table 2. A review of international standards concerned with the physical environment is presented by Parsons (1995) in this special issue. Several of these standards may be used as a basis for the design and evaluation of buildings, HVAC (heating, ventilation and air conditioning) systems, protective equipment (clothing) and optimization of work-rest schedules. The basic philosophy has been to standardize evaluation methods, while recommended limit values for the different parameters or indices are listed in informative
The thermal
environment
Existing methods for evaluation of the general thermal state of the body, both in comfort and in heat or cold stress, are based on an analysis of the heat balance for the human body: S=M-W-C-R-Esk-C,,,-E,,-K
(1)
where S = heat storage in body; M = metabolic heat production; W = external work; C = heat loss by convection; R = heat loss by radiation; Esk = evaporative heat loss from skin; C,,, = convective heat loss from respiration; E,,, = evaporative heat loss from respiration; and K = heat loss by conduction. The factors influencing this heat balance are: activity level (metabolic rate, met or W mw2);thermal resistance of clothing I,, (clo or m2”C W-l); evaporative resistance of clothing R, (m2 Pa W-l); air temperature ta (“~2); mean radiant temperature tr (“C); air speed v,, (m s-l); partial water vapour pressure pa (Pa). These parameters must be combined so that the thermal storage is 0, or else the working time has to be limited to avoid too much strain on the body. To provide comfort, the mean skin temperature also has to be inside certain limits, and the evaporative heat loss must be low. In existing standards, guidelines or handbooks, different methods are used to evaluate the general thermal state of the body in moderate environ-
293
294
International standards and the ergonomics of the thermal environment: B. W. Olesen
Table 1 Ergonomics
of the thermal environment:
development
of international
standards
Aims of the standard
Title of the document
Status
General presentation of the set of standards in terms of principles and application
Ergonomics of the thermal environment: principles and apphcatlon of international standards
IS0 DIS 11399
Standardization the standards
Ergonomics of the thermal environment: symbols and units
CD 13731
of quantities, symbols and units used in
Thermal stress evaluation in hot environments Analytical method
definitions,
Hot environments: analytical determination and interpretation of thermal stress using calculation of required sweat
IS0 7933
Hot environments: estimation of the heat stress on working man, based on the WBGT index (wet bulb globe temperature)
IS0 7243
Comfort evaluation in moderate environments
Moderate thermal environments: determination of the PMV and PPD indices and specification of the conditions for thermal comfort
IS0 7730
Thermal stress evaluation in cold environments
Evaluation of cold environments: determination required clothing insulation, I,_,
IS0 TR 11079 Technical report
Data collection standards
Metabolic rate
Ergonomics: determination production
Requirements for measuring instruments
Thermal environments: instruments and methods for measuring physical quantities
IS0 7726
Clothing insulation
Estimation of the thermal insulation and evaporative resistance of a clothing ensemble
IS0 9920
Evaluation of thermal strain using physiological measures
Evaluation of thermal strain by physiological measurements
IS0 9886
Subjective assessment of the thermal environment
Assessment of the influence of the thermal environment using subjective judgement scales
IS0 DIS 10551
Selection of an appropriate system of medical supervision for different types of thermal exposure
Ergonomics of the thermal environment: medical supervision of individuals exposed to hot or cold environments
IS0 CD 12894
Contact with hot, moderate and cold surfaces
Documents in draft form
NP 12893
Comfort of the disabled
Documents in draft form
New work item
Documents in draft form
New work item
Documents in preparation
NP 14505
Diagnostic method
Long-term assessment of environmental
quality
Vehicle environments
ments, cold environments and hot environments; but all are based on the above heat balance and the listed factors. Besides the general thermal state of the body, a person may find the thermal environment unacceptable or intolerable if local influences on the body from asymmetric radiation, air velocities, vertical air temperature differences or contact with hot or cold surfaces (floors, machinery, tools, etc.) are experienced. Moderate thermal environments Both ASHRAE (the American Society of Heating, Refrigerating and Ventilation Engineers) and IS0 (the International Organization for Standardization) have recently revised their standards for a comfortable thermal environment (ASHRAE 55-92, 1992 and IS0 7730, 1993). The research that forms the basis for these two standards is mainly performed under environmental conditions similar to commercial and residential buildings, with relatively low activity levels (mainly sedentary, 1.2 met), normal indoor clothing (0.5-1.0 clo) and a limited range of environmental parameters. IS0 7730 (1993) standardizes the PMV-PPD index
of
of metabolic heat
IS0 8996
as the method for evaluation of moderate thermal environments. To quantify the degree of comfort the PMV index gives a value on the seven-point thermal sensation scale: +3 hot, +2 warm, +l slightly warm, 0 neutral, -1 slightly cool, -2 cool, -3 cold. An equation in the standard calculates the PMV index based on the six factors clothing, activity, air and mean radiant temperature, air velocity and humidity. Even if a PMV value of 0 is obtained, there will still be at least 5% of the occupants who will be dissatisfied with the thermal environment. The predicted percentage of dissatisfied (PPD) index can be determined from the equation. PPD = I00 _ 95
e-(0.O3353
PMV4+0.217Y
PMV*)
The standard describes the method, and in an informative annex recommendations for an acceptable environment are given as -0.5 < PMV < 0.5, PPD < 10%. The use of the method is illustrated in Figure I, where the optimal operative temperature (average of air and mean radiant temperature) and the recommended temperature range are shown as a function of clothing and activity.
295
International standards and the ergonomics of the thermal environment: B. W. Olesen m* WW 175 150 125 “E
where v, = mean air velocity (3 min), m s-l; SDw, = standard deviation of air velocity (3 min), m s-‘; ta = air temperature, “C. For v, < 0.05 m s-l insert v, = 0.05 m s-i. For DR > 100% use DR = 100%. In the new, revised standards IS0 7730 and ASHRAE 55-92 the requirements are based upon a 15% dissatisfaction criterion. The recommended limits are shown in Figure 2.
100 6
Hot environments
75 50 0.0 _..
0.5
1.0
1.5
Clothing (c/o) Figure 1 The optimal temperature (corresponding to PMV = 0) as a function of activity and clothing. The shaded areas indicate the comfort range f Af around the optimal temperature inside which -0.5 < PMV < +OS. The relative air velocity caused by body movement is estimated to be zero for M < 1 met and v,, = 0.3 (M - 1) for M > 1 met. Relative humidity = 50%
The IS0 philosophy for the assessment of hot environments is to use a simple ‘fast’ method for monitoring the environment, based on the wet bulb globe temperature (WBGT) index (IS0 7243, 1989). If the WBGT values exceed the provided ‘reference’ values, or a more detailed analysis is required, then IS0 7933 (1989) provides an analytical method of assessment. The wet bulb globe temperature heat stress index is calculated inside buildings and outside buildings without solar load as WBGT = 0.7&, + 0.3ta
(4)
and outside buildings with solar load as Because the PMV index assumes that all evaporation from the skin is transported through the clothing to the environment, this method is not applicable for hot environments. It can be used within a range of PMV index of -2 to +2, i.e. thermal environments where sweating is minimal. The recommended range for the use of this standard is:
Metabolic rate: Clothing: Air temperature: Mean radiant temperature: Air velocity: Water vapour pressure:
0.8-4 met (46 232 W m”) O-2 cl0 (O-0.310 m2 “C W-l) lO--30°C 1wO”C O-l m s-’ 90-2700 Pa
Besides the general thermal state of the body, a person may find the thermal environment unacceptable if local influences on the body from asymmetric radiation, draught, vertical air temperature differences or contact with hot or cold surfaces (floors, machinery, tools, etc.,) are experienced. The annex of IS0 7730 also lists a series of recommendations for these local discomfort parameters (Table 2). One of the most critical factors is draught. Many people are very sensitive to air velocities, and therefore draught is a very common cause for occupant complaints in ventilated and air-conditioned spaces. Fluctuations of the air velocity have a significant influence on a person’s sensation of draught. The fluctuations may either be expressed by the standard deviation of the air velocity or by the turbulence intensity Tu, which is equal to standard deviation divided by the mean air velocity v, (SDv,lv,). The percentage of people feeling draught (draught rating, DR) may be estimated from the equation DR = (34 - t,) (v, - 0.05) 0.6223(3.143 + 0.3696SDv.J
(3)
WBGT = 0.7r,, + 0.2& + O.lt,
(5)
where tnw is the natural wet bulb temperature; tg is the temperature at the centre of a 150 mm diameter black globe thermometer; and ta is the air temperature. The WBGT value of the hot environment may be compared with a WGBT reference value, which is included in an informative annex (Table 3). The reference values have been established allowing for a maximum rectal temperature of 38°C for the persons concerned. This corresponds to levels of exposure to which almost all individuals can be ordinarily exposed without any harmful effect, provided there are no preexisting pathological conditions. If the WBGT of the hot environment exceeds the WBGT reference value then the heat stress at the workplace needs to be reduced or a more detailed analysis made (i.e. using IS0 7933). The standard also includes a method to plan a work-rest schedule that will provide tolerable environments. Table 2 Recommended criteria for an acceptable moderate thermal environment
as proposed in IS0 7730 Appendix
General thermal comfort Predicted mean vote Predicted percentage dissatisfied
A
-0.5 < PMV < + 0.5 PPD < 10% (see Figure
I)
Local thermal discomfort DR < 15% (see Figure2)
Draught Vertical air temperature between head and feet
difference
At, < 3 K
Radiant temperature asymmetry from cold vertical surfaces (window, wall)
A& < 10 K
Radiant temperature asymmetry from warm horizontal surfaces (heated ceiling)
At,, < 5 K
Floor surface temperature
19°C < or < 29°C
296
International standards and the ergonomics of the thermal environment: B. W. Olesen aI.5 Wr,q =-
Turbulence intensity 0%
E ‘=?
03)
E max
-4 -
Sweating efficiency:
/
&
.3 -
.2 -
Required SW,,,
760%
>
.I -
r = 1 - 0 5 ed.h (l-wreq)
10%
DR = 15% I 20
.O_ 18
I 22
Local air
I 24
I 26
temperature ("C)
Figure 2 Combination
and turbulence
of mean air velocity, air temperature intensity that will result in less than 15%
dissatisfaction
The method used in IS0 7933 (1989) Required sweat rate, SW,,, is based on the heat balance Equation (1).
Assuming that the heat storage is equal to 0, the necessary evaporation from the skin, Ereq, ensuring a heat balance, is calculated as follows: E req = M - W - C - R - E,.,, - C,,,
maximum evaporation, absorbed by the environment, equation
The
E max =
where
(6)
which can be is estimated from the
E,,,,,,
sweat rate: E r=i = r
(10)
These parameters are used to evaluate how stressful a given hot working environment is. Depending on the physiological limitations for factors such as sweat rate, total sweat loss, heat sto:age and skin wetness, which are listed in Table 4, it is possible to evaluate whether a given environment is acceptable for continuous work. The method also allows calculation of an acceptable working time. Detailed equations for the calculations can be found in the standard (IS0 7933, 1989). The relation between the operative temperature and SW,,, for different combinations of activity and clothing is shown in Table 5. A computer program is provided to allow ease of calculation and efficient use of the standard. This rational method of assessing hot environments allows identification of the relative importance of different components of the thermal environment, and hence can be used in environmental design. The WBGT index is an empirical index, which cannot be used to analyse the influence of the individual parameters. The required sweat rate (SW,,,) has this capability, but lack of data may make it difficult to estimate the benefits of protective clothing.
Psk,s - Pa (7)
R t?T
psk,s =
Cold environments
saturated water vapour pressure at skin;
Pa = water vapour pressure in the environment;
ReT =
total evaporative resistance of clothing and boundary layer. Based on the required evaporation and the maximum evaporation it is then possible to estimate the following factors: Required
skin wetness:
Table 3 Reference
Many industrial workplaces are located in cold environments, such as cold storage, meat packing, workplaces located outdoors, etc. In cold environments, the clothing is the most important factor for obtaining an acceptable thermal environment. Based on the heat balance Equation (1), an analytical method has been proposed by ISO, Required clothing insulation, Zreq (ISO/TR 11079, 1993). The method calculates the insulation of the clothing necessary to keep a heat
values of WBGT (IS0 7243) Metabolic
Reference
rate, M
Metabolic rate class
Related to a unit skin surface area (W m-*)
Total (for a mean skin surface area of 1.8 m2) (W)
Person acclimatized (“0
0 I 2 3
M < 65 6.5 < M < 130 130 < M < 200 200 < M < 260
117 117 < M < 234 234 < M < 360 360 < M < 468
M>260
M > 468
33 30 28 No sensible air movement 25 23
4
(resting)
(9)
Note: The values given have been established
M<
allowing for a maximum
rectal temperature
to heat
Sensible air movement 26 25
value of WBGT Person not acclimatized to heat eo 32 29 26 No sensible air movement 22 18
of 38°C for the persons concerned
Sensible air movement 23 20
International
Table 4 Reference
standards and the ergonomics of the thermal environment:
value for the different criteria of thermal stress and strain in bot environments
Maximum skin wettedness, Maximum sweat rate Rest: M W m- 2 SW,,, %:;k! <,6S M > 65 W mz SW,,, (g h-‘)
Warning
Danger
0.85
0.85
w,,,
(ISO 7933)
Acclimatized
Non-acclimatized subjects
Criterion
(W mm’)
100 260
1.50 390
(W mm2)
200 520
250
50 1000 2600
297
B. W. Oiesen
subjects Danger
Warning
1.0
1.0
200 520
300 780
780
300
400 1040
60
50
60
1250 3250
1500 3900
2000 5200
650
Maximum heat storage
Q,,.W h 6
Maximum water loss L,, (W h mm’) (g) Table 5 Required sweat rate index SW, activity level M equal to 70 W mm2 Relative humidity (%)
Clothing I,, @lo)
0.5
(W m-‘1 and wettedness (W-J as a function of clothing, temperature,
air speed and humidity
at the
Operative temperature, Air velocity V, (m 8’)
G ec,
20
25 30 35 40 50 60 25 30 35 40 30 35
50
80
CO.1
0.2
10 37 65 93 169
(0.03) (0.13) (0.24) (0.37) (0.78)
‘IO 37 65 102 37 76
;;*z; (0:17) (0.37) (0.74) (0.26) (0.82)
8 36 64 94 165 = 8 35 65 99 36 71
0.5 (0.02) (0.12) (0.22) (0.34) (0.72)
2 33 64 95 165 a 2 33 64 98 33 66
;k:;
(0:ls) (0.34) (0.69) (0.23) (0.75)
1.0 (0.01) (0.09) (0.18) (0.29) (0.62)
2.0
29 63 98 171 =
(0.06) (0.14) (0.24) (0.523) (1.00)
24 62 101 182 a
(0.04) (0.11) (0.20) (0.45) (1.00)
29 63 99 29 64
(0.08) (0.22) (0.47) (0.12) (0.48)
24 62 102 24 63
(0.05) (0.17) (0.39) (0.08) (0.38)
;lz; (0.12) (0.28) (0.57) (0.18) (0.61)
No&: “wettedness ?= 1 in a given cold environment by knowing the activity level, air- and mean radiant temperature, air speed and a relative humidity according to the following equation: balance
t sk I req
-
tc1
=
(11) ~4
-
W
-
Esk
-
M-VV-Esk--Cres-Eres=C+R
Ges
-
&es
(12)
The relationship between activity level, operative temperature and Ireq is shown in Figure 4. This is a new method, which has not been widely used, and little experience is available. Therefore the method has been proposed in the form of a technical report, which in the future may be published as an IS0 standard. The index value may be used to select a clothing ensemble, which will provide the required insulation. The clothing insulation can according to Table 6 be predicted either as a minimum, where some strain may be expected on the people, or as a neutral insulation, where people are expected to feel neutral. It is important when selecting the actual clothing (IS0 9920) to allow for individual adjustment of the clothing insulation. Also, the clothing insulation values listed in IS0 9920 are valid for people with standing and sedentary work. For people at higher activities, the clothing values from the tables in IS0 9920 should be
reduced by approximately 20%, owing to body movements (pumping effect). If it is not possible to use or select a clothing ensemble with enough insulation, the method includes a procedure for calculation of a recommended exposure time. The basis for the calculations is the physiological requirements listed in Table 6. For outdoor work there may be a risk for frostbite in wintertime. The report uses the wind chill temperature WCI, calculated as 33 - WC1 tch
=
25.5”C WC1 = 1.16 (10.45 + 10 d/v,, - v,,)(33 - ta) W/m2 where ta = outside air temperature, “C; WC1 = wind chill index, w me2; v,, = relative air velocity, m s-l. Table 7 shows the values depending on outside temperature and wind velocity and Table 8 shows the expected effect. Supporting
standards
The application
of the above standards requires measurement or estimation of a number of parameters. The ‘supporting’ and complementary standards
298
International standards and the ergonomics of the thermal environment: B. W. Olesen
Air velocity = 0.2 m/s Relative humidity = 50%
-
1.24
- 0.93
F y
0.62
v
-_
f
Operative temperature, t (“C) Figure 3 &,,, as function of ambient operative at eight levels of metabolic heat production
temperature
Clothing
Note: The operative temperature is the integrated value of the air temperature and mean radiant temperature weighted according to values of the convective and radiation heat transfer coefficients respectively
described below provide information that is required for the application of standards for assessing thermal environments. They can also be used independently in ergonomics investigations. Metabolic
rate
All assessments of thermal environments require an estimate of the metabolic heat production of the occupants (activity level). IS0 8996 (1989) presents
Table 6 Suggested physiological
criteria for determination
Type of cooling
Parameter
General
IREQ tSk w
three types of method. The first is the use of tables, where estimates are provided based on a description of the activity. These range from a general description (e.g. light, heavy etc.) to methods of summation components of tasks (e.g. basal metabolic rate + posture component + movement component etc.). An example of activity levels is given in Table 9. The second method is by the use of heart rate. The total heart rate is regarded as a sum of several components, and in general is linearly related to the metabolic heat production for heart rates above 120 beats per minute. The third method is to calculate the metabolic heat production from measures of oxygen consumption and carbon dioxide production during activity and recovery.
IS0 9920 (1993) p rovides a large database of thermal insulation values, which have been measured on a standing thermal manikin. One set of tables give the insulation values for a large number of ensembles (Table IO). Another set of tables give insulation values for individual garments (Table II) based upon which the insulation for a whole ensemble can be estimated. The insulation of an ensemble, ICI,may be estimated as the sum of the individual garment insulation values, Zclu:Zcl= X ICI,,.The data on evaporative resistance are not so extensive. A few data are given in the standard, and a method to calculate the evaporative resistance based on the thermal insulation is also given. In the present standard no values are listed for the insulation of chairs, which may add 0.1-0.4 clo. Especially for the assessment of the level of heat stress, data for the
of IREQ, DLE and local cooling (IS0 7R 11079) Minimal IREQ (high strain)
Neutral IREQ (low strain)
35.7-0.0285 h? 0.0001 M
30 0.06
(“C) (n.d.)
DLE (W h mm*)
Qhm Hand temperature WC1 Respiratory tract and eye temperature
Local
(“C) (W mm*) (“C)
Table 7 Cooling power of wind on exposed flesh expressed as a chilling temperature, frostbite Actual thermometer Wind speed (m s?)
1.8 2 3 5 8 11 15 20 Notes: Temperatures
-40
-40
24 -
1.5 1600 t,<-40
teh, under almost calm conditions. Bold types indicate risk of
reading
0
-5
-10
-15
-20
-25
-30
-35
-40
45
0 -1 -4 -9 -13
-5 -6 -10 -1.5 -20
-10 -11 -15 -21 -27
-15 -16 -21 -28 -34
-20 -21 -27 -34
-25 -27 -32 +I
-30 -32 -38 47
-16 -18 -20
-23 -26 -28
-31 -34 -36
-38 -42 -44
41 -46 -49 -52
48 -53 -57 40
-55 40 -65 -68
-35 -37 -44 -53 -62 -68 -73 -76
-44l 42 -49 -59 -69 -75 -80 -84
45 47 -55 -66 -76 -fS3 -M -92
given in “C Almost calm conditions refers to a wind speed of 1.8 m SF’ Values given in bold type correspond to WC1 2 1600 (Table 8)
-50
-50 -52 -60 -72 -I33 -90 -96 -100
International standards and the ergonomics of the thermal environment: B. W. Olesen Table 8 Wind chill index, WCI, chilling temperature, on exposed flesh
fch, and effect
Table 11 Thermal Garment
WC1 (W m-*)
Effect -14
Very cold
1400
-22
Bitterly
1600 1800
-30 -38
Exposed
flesh freezes
2ooo 2200
-I5 -53
Exposed
flesh freezes within 1 min
2400 2600
-61 -69
Exposed
flesh freezes
cold within
1h
within 30 s
Table 9 Metabolic rates Metabolic rates Activity
(W m”)
Reclining Seated,
relaxed
Sedentary activity school, laboratory)
(office,
dwelling,
Standing light activity (shopping, laboratory, light industry) Standing, assistant, work) Walking 2 km 3 km 4 km 5 km
medium domestic
activity (shop work, machine
on the level: h-’ h-’ h-’ h-’
Table 10 Thermal
insulation
46
0.8
58
1.0
70
1.2
93
1.6
116
2.0
110 140 165 200
1.9 2.4 2.8 3.4
for typical clothing ensembles
Shirts/blouses Short sleeves Normal, long sleeves
0.15 0.25
Trousers Shorts Normal
0.06 0.25
Dresses/skirts Light skirts (summer) Heavy skirt (winter) Winter dress, long sleeves
0.15 0.25 0.40
Sweaters Thin sweater Thick sweater
0.20 0.35
Outdoor Coat Parka
Underpants,
boiler
suit, socks,
shoes
Underpants, shirt, boiler suit, socks, shoes Underpants, shirt, trousers, smock, socks shoes Underwear with short sleeves and legs, shirt, trousers, jacket, socks, shoes Underwear with long legs and sleeves, thermo-jacket, socks, shoes Underwear with short sleeves and legs, shirt, trousers, jacket, heavy quilted outer jacket and overalls, socks, shoes cap, gloves Underwear with short sleeves and legs, shirt, trousers, jacket, heavy quilted outer jacket and overalls, socks shoes Underwear with long sleeves and legs, thermo-jacket and trousers, Parka with heavy quilting, overalls with heavy quilting, socks, shoes, cap, gloves
insulation
(clo)
0.25 0.35 0.90 0.35 0.40
clothing 0.60 0.70
Sundries Socks Thick, long socks Shoes (thick soled) Boots
0.02 0.10 0.04 0.10
(IS0 9920)
2CI Work clothing
fclU (IS0 9920)
0.03 0.10 0.09
with long legs
Jackets Light, summer jacket Jacket High-insulative, fibre-pelt Boiler suit Trousers Jacket
(met)
garments,
Thermal
description
Underwear Panties Underpants T-shirt
1200
insulation for individual
299
Iel
@lo)
(m* K W-‘)
Daily wear clothing
(clo)
(m* K W-‘)
0.70
0.110
0.30
0.050
0.80
0.125
0.50
0.080
0.90
0.140
Panties, T-shirt, shorts, light socks, sandals Underpants, shirt with short sleeves, light trousers, light socks, shoes Panties, petticoat, stockings, dress, shoes
0.70
0.105
1.00
0.155
Underwear,
0.70
0.110
1.20
1.85
1.00
0.155
1.40
0.220
Panties, shirt, trousers, jacket, socks, shoes Panties, stockings, blouse, long shirt, jacket, shoes
1.10
0.170
2.00
0.310
Underwear with long sleeves and legs, shirt, trousers, V-neck sweater, jacket, socks, shoes
1.30
0.200
2.55
0.395
Underwear with short sleeves and legs, shirt, trousers. vest, jacket, coat, socks. shoes
1.50
0.230
shirt,
trousers,
socks,
shoes
300
International standards and the ergonomics of the thermal environment: B. W. Olesen
rs
Surface
0-50°C
0.5-3.0
0.05-l
kPa
m s-’
Required: Desirable:
+ 1°C +0.5”C
+0.15 kPa This level shall be guaranteed for a difference 1t, - r, of at least 10°C
1
Required: + (0.05 + 0.05 v,) m ss’ Desirable: * (0.02 + 0.07 va) m so’ These levels shall be guaranteed whatever the direction of flow within a solid angle w=3xsr 0.5 s 0.2 s
The shortest possible. Value to be specified as characteristic of the measuring instrument
The shortest possible. Value to be specified as characteristic of the measuring instrument
Required: Desirable:
kPa
m ss’
(t, - 50)
1
Required: <-10°C: f [l + 0.05 (-c - 10) 1 -10°C to 50°C: ?l”C >SO”C: +[l + 0.05
f0.15 kPa These levels shall be guaranteed for a difference 1t, - r, 1of at least 20°C
Required: f (0.1 + 0.05 v,) m SK’ Desirable: f (0.05 + 0.05 v.) m ss’ These levels shallbe guaranteed whatever the direction of flow within a solid angle o=3xsr
and surface
2
temperatures
Desirable: required accuracy
plant radiant
-40 to +120°c
0.5-6.0
0.2-20
Note: At some workplaces in hot environments (steel, coal, glass industries) there may be a need to measure manufacturers of instruments are required to state the accuracy for an extended range.
temperature
pa
“a
Absolute humidity expressed as partial pressure of water vapour
Air velocity
2 These levels shall be guaranteed at least for a deviation 1t,, - r, 1 <2O”C
Desirable: required accuracy
at higher
in this table.
The
Except in the case of a unidirectional air current, the air velocity sensor shall measure the velocity whatever the direction of the air. An indication of the mean value and standard deviation for a period of 3 min is also desirable.
levels than the range
The shortest possible. Value to be specified as characteristic of the measuring instrument
The shortest possible. Value to be specified as characteristic of the measuring instrument
The shortest possible. Value to be specified as characteristic of the measuring instrument
Internationalstandards and the ergonomics of the thermal environment: B. W. Olesen
302 evaporative missing.
resistance
of
clothing
ensembles
are
Instruments and measurements
IS0 7726 (1994 rev.) provides a description of the parameters that should be measured (air temperature, mean radiant temperature, plane radiant temperature, air velocity, humidity), together with methods of measurements and specifications for the instruments (accuracy, respond time, measuring range). Table 12 lists the accuracy required in the standard.
exposures. This guidance is applicable to both occupational and laboratory exposures to extreme environments. In either case an assessment should be made of the expected thermal stress on the individual, but the detailed arrangements for medical supervision may differ in the two situations. Control of occupational exposures must also satisfy national health and safety legislation. The laboratory or climatic chamber studies for which this standard will be relevant include those in which people may be exposed to high or low ambient temperature conditions or local heating or cooling. Other and future standards
Measurements
on individuals
The methods listed above to evaluate the thermal environment assume an average person. As individuals often react very differently, both regarding acceptance of a given environment and regarding the strain that a given environment imposes, it may under certain circumstances be beneficial to take individual physiological and subjective measurements. Also, there may be a need for evaluation of an individual capability for performing a certain job under severe conditions in the field or in an ergonomics laboratory investigation. Physiological measurements
IS0 9886 (1989) p resents the principles, methods and interpretation of measurement of relevant human physiological responses to hot, moderate and cold environments. The standard can be used independently or to complement the use of other standards. Four physiological measures are considered: body core temperature, skin temperature, heart rates and body mass loss. Comments are also provided on the technical requirements, relevance, convenience, annoyance to the subject and cost of each of the physiological measurements. The use of IS0 9886 is mainly in extreme cases, where individuals are exposed to severe environments, or in laboratory investigations into the influence of the thermal environment on humans. Subjective measurements
Subject scales are useful in the measurement of subjective responses of persons exposed to thermal environments. They are particularly useful in moderate environments and can be used independently or to complement the use of objective methods (e.g. thermal indices), which were described previously. IS0 10551 (1995) presents the principles and methodology behind the construction and use of subjective scales, and provides examples of scales that can be used to assess thermal environments. The medical screening standard (ISO/DIS 12894, 1994) provides advice to those concerned with the safety of human exposures to hot or cold thermal environments, about health screening and surveillance that may be appropriate prior to and during such
To help the user, an overview standard (IS0 11399) is being issued. This presents the different standards, and guides the user to which method and standard are applicable for the given situation. In addition, a standard is being prepared which lists all definitions, symbols and units. Ongoing work is dealing with standards for contact with hot, cold and comfortable surfaces, application of the standards in vehicles, and precautions to take when assessing thermal environments for disabled, aged or other groups with special needs. Conclusion The series of standards presented in this paper provides a useful package for assessment and design of HVAC systems and protective equipment to be used in moderate, cold and hot environments. The standards may be used to estimate the optimal combination of the environmental thermal factors that will provide comfortable or tolerable and healthy working conditions. The standards may also be used to establish optimal workrest schedules for environments where the working time must be limited owing to the strain on the human body. Several of these standards are being adopted also as European standards by CEN and as national standards in several countries. Some of the methods used in the standards are based on many years of research and validation, while others are relatively new and not validated to the same degree. It is therefore important to realize that a standard is not an everlasting document, but must be revised on a regular basis. These revisions take place at least each fifth year, where the experience with use and new knowledge are incorporated in the review process. References ASHRAE 1992 ASHRAE standard SS Thermal environmental conditions for human occupancy ASHRAE, Atlanta, GA Parsons, K.C. 1995 ‘Ergonomics of the physical environment: international ergonomics standards concerning speech communication, danger signals, lighting, vibration and surface temperatures’ Appl Ergonomics 26 (4), 281-292 IS0 standards arc listed in Table 1.