27

Thermal Problems in Hyperbaric Environments
Naoshi KAKITSUBA
Department of Environmental Science and Technology, Meijo University
1-501 Shiogamaguchi, Tenpaku-cho, Nagoya-shi 468-8501, Japanemail: naoshi@ccmfs.meijo-u.ac.jp

Abstract
This paper reviews thermal problems in hyperbaric environments and provides information how toestimate thermal comfort zones in hyperbaric environments.
Divers are exposed to hyperbaric helium-oxygen atmospheres when engaged in saturation diving
operations. However, some difficulties to control thermal environments arise from the extremely high thermal conductivity of helium used as a breathing gas and from increased pressure. In order to obtain data
available for control of thermal environments, many theoretical and empirical studies have been carried out
to estimate heat exchange between man and his environments. For example, male divers wearing different
clothing ensembles were exposed to six different pressures for evaluating change in clothing insulation. In
addition, a lightly clothed male diver exercised on a bicycle ergometer while exposed to five different pressures to evaluate changes in clothing permeability. The results demonstrated that clothing insulation decreased with change in ambient gases and clothing permeability decreased slightly despite changes in ambient gas and barometric pressure.
As represented by this example, in hyperbaric helium-oxygen atmospheres, the manner of heat exchange between man and his environments becomes apparently different from that in normobaric air. The
last part of this paper demonstrates the comfort range of ambient temperatures at increased barometricpressures.
Key words: clothing insulation, clothing permeability, hyperbaric environment, thermal comfort,
temperature

1. Introduction
Since a saturation diving system was established in
1970, helium has been used as the major inert breathinggas to prevent decompression sickness because of its
low solubility and high diffusivity in the human bodytissues. However, a hyperbaric helium-oxygen atmosphere has two unique thermophysical characteristics;
high thermal conductivity and low diffusivity of water
vapor, relative to normobaric air.
High thermal conductivity of helium increases theamount of convective heat exchange between the humanbody and its environment for a given temperature difference between the skin and ambient temperature. In addition, convective heat loss or gain by respiration becomessignificant. Low diffusivity of water vapor reduces theevaporative capacity of ambient gases. Therefore, aninappropriately controlled exposure causes a diver toundergo serious thermal stresses, e.g., hypothermia,
hyperthermia, diuresis and heat stroke.
From the mid-1960s to the end of 1980s, many
clinical and scientific studies (for example, Epperson,
1966; Raymond et al., 1968; Timbal et al., 1974;
Global Environmental Research
13/2009: 27-33
printed in Japan

Nakayama, 1979; Kakitsuba et al., 1981) were carriedout primarily to evaluate the effects of theromophysicalproperties on physiological responses that are directly
related to the heat exchange between the human bodyand its environment. At the same time, theoretical studies (for example, Nevins et al., 1965; Nishi & Gagge,1977) attempted to predict optimal thermal conditions
when a man is exposed to hyperbaric helium-oxygen
atmospheres.
Although the basic knowledge of controlling thermal
environments was provided, more extensive studies
have been required for better protection of the divers
from heat stress. Regarding thermoregulation, for example, many studies (Cook, 1950; Young & Cook, 1953;
Matsuda et al., 1975; Shiraki et al., 1984; Mekjavic
et al., 1995) have contributed to understanding of effects
of increased pressure or breathing helium-rich gas onthermoregulation when a man is exposed to pressurizedatmospheres. This paper reviews these pioneer studies
briefly and provides information relevant for controlling
thermal environments in hyperbaric helium-oxygen
atmospheres.
©2009 AIRIES

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N. KAKITSUBA

2. Parameters Relevant for Thermal Control
and Comfort in Hyperbaric Conditions
2.1 Convective heat transfer coefficient of thehuman body in hyperbaric helium-oxygen
atmospheres
As indicated in Fig.1, metabolic heat is mainly dispersed from the skin by convection, radiation, evaporation and conduction to maintain body temperature(Hardy & DuBois, 1937). Convective heat transfer
coefficient of the human body (hc) is an essential factor
to estimate the amount of convective heat exchange
between the human body and its environment. In
normobaric air, many prediction equations have been
proposed for various activities and postures. For example, the hc values of 2.0 to 4.0 (W/m2·°C) are used forthe sedentary subjects in still air.
Definition of convective heat transfer coefficient isdepended on physical properties of ambient gases. For
comparison, theromophysical properties of air andhelium are listed in Table 1. Helium (He) is characterized by high thermal conductivity. Figure 2 illustrates

change in partial pressure of breathing gas components
as a function of depth. According to breathing gas
components at depths, Nishi and Gagge (1977)
attempted to estimate the convective heat transfer coefficient of the human body from the following equation;
Cp ⎞
⎛ρ⎞ ⎛
⎟
hc ∝ κ × ⎜⎜ ⎟⎟ × ⎜⎜ µ ×
κ ⎟⎠
⎝µ⎠ ⎝

(W/m2·°C)(eq.1)

where κ = thermal conductivity (W/m·°C); ρ = density(kg/m3); µ = viscosity (kg/m·h); Cp = specific heat
(J/kg·°C).
Equation 1 defines the ratio of hc in normobaric air
to that in hyperbaric helium-oxygen atmospheres in therange of the forced convection, i.e., the range wherewind velocity is greater than 0.5 m/s. The results
demonstrated that the hc value at 3,000 kPa was twelve
times higher than in normobaric air. Therefore, thehuman body will lose so much more heat from the skin,even if ambient temperature is controlled within the
comfortable range in normobaric air.
Raymond et al. (1968) first measured heat exchange
between the divers’ body and its environments when thedivers were exposed to six different pressures up to
1,460 kPa. The amounts of sensible and insensible heatloss from the skin and metabolic heat production were
measured while the unclad divers were seated quietly.
Table 1 Theromophysical properties of various gases.
(Nishi, Y., 1981)

_
tsk

Gases

Specificheat(J/kg·°C)

Thermalconductivity(W/m·°C)

Air

1004

0.023

1.2

0.088

O2

911

0.026

1.33

0.088

N2

1027

0.026

1.17

0.088

He

5200

0.148

0.166

0.271

Legends in the figure stand for
M: Metabolic heat production (W/m2)
C: Convective heat exchange (W/m2)
R: radiative heat exchange (W/m2)
Esk: Evaporative heat loss (W/m2)
Rres: Respiratory heat exchange (W/m2)
Cd: Conductive heat exchange (W/m2).
C，R and Esk can be_ defined as follows;
C = hc×（ _ｔsk – ta）
R = hr×（ ｔsk – MRT)
Esk = he×w×(Psk* – Pa)
where hc， hr， he=convective, radiative and_ evaporative heattransfer coefficients (W/m2·°C) in order; ｔsk，ta, MRT=mean skintemperature, ambient temperature and mean radiant temperature(°C) in order; w=skin wettedness; Psk*=saturated vapor pressure at
the skin; Pa=vapor pressure of ambient gas.
The rate of body heat storage_ can then be defined as follows;
S = (Cp×m/As)×dTb/d t = M – (±R ±C+Esk ±Cd)
where
Cp=specific body heat (J/kg·°C)，As=body surface area (m2),_
Tb=mean body temperature_ (°C) derived from weighed average ofbody temperature and ｔsk.

Partialpressure (kPa)(kPa)
Partial pressure

10000

Fig. 1 Heat exchange between the human body andits environments.

Density Diffusivity(kg·m3)(m2/h)

HeliumNitrogen
Oxygen

1000

100

10

1
0

20

40

60

80 100 120 140 160 180 200
Depth(m)Depth(m)

Fig. 2 Change in breathing gas components at depths.
Total pressure is equal to pressure at depths. Oxygen
partial pressure is controlled at 30 kPa more than
40 m depths. Nitrogen partial pressure is constantly
controlled at 83 kPa.

Thermal Problems in Hyperbaric Environments

Kakitsubaetetal.
al.(1978)(1978)
kakitsuba
Raymond etetal.
al.(1968)(1968)
Raymond○

Convective
heattransfer
transfercoefficient
coefficient (W/m
(W/m22・·°C)
C)
Convectiveheat

The hc value was then defined as a function of barometric pressure. However, since overestimation of the hc
value due to disregard of respiratory heat loss waspointed out, they repeated the human experiment during
the simulation diving at the dry chamber in 1974. The
divers were exposed to seven different pressures up to
4,950 kPa. The amounts of sensible and insensible
respiratory heat losses were measured while the divers
were seated quietly. They then proposed another prediction equation (Raymond et al., 1974). In the same year,
Timbal et al. (1974) also measured heat exchange
between the divers’ body and its environment with apartitional calorimetry when the divers were exposed tosix different pressures up to 3,080 kPa. The partitional
calorimetry developed by Burton (1935), Stolwijk andHardy (1966) and Winslow et al. (1936) has been widelyused to estimate body heat balance. In their experiments,
divers were nude and in a supine position. The hc value
was then defined as a function of pressure and theconvective constants, i.e., β × Cp × κ/µ, which was introduced by Webb and Annis (1966). The results demonstrated that the hc value was correlated more closelywith the convective character than with barometric pressure. According to the definition by Webb (1970), theconvective character is “a ratio that normalizes the fluid
to air by dividing the convective constants of the fluid bythat of normobaric air.”Kakitsuba et al. (1981) measured heat exchange
between the divers’ body and its environments with thepartitional calorimetry when the divers were exposed tonine different pressures up to 3,100 kPa. They were
nude and in a sedentary position during experiments.
The hc value was then defined as a function of barometric pressure. Figure 3 relates empirical data and corresponding equations for the convective heat transfer
coefficients (hc) to barometric pressure. Although the hc
values in normobaric air are markedly different due tothe difference in posture, all the equations may predict

Epperson (1966)

30
25

0.71
= 0.00614×P(Timbal,1974)
hc = hc
0.00614×P(Timbal,1974)
0.53（Kakitsuba et al.)
0.53
hc
=
0.223×P
hc = 0.223×P(Kakitsuba et al.1980)
0.71

20
15
10

0.63（Raymond，1975)
0.0971×P0.63
hhc(Raymond, 1975)
c == 0.0971×P

5
0
0

1000

2000

3000
4000
Barometricpressure (kPa)(kPa)
Barometric pressure

Fig. 3 Change in convective heat transfer coefficients withbarometric pressure.
Empirical data was described with corresponding equations
for hc to barometric pressure. Although the hc values innormobaric air are markedly different due to the difference inposture, all the equations may predict adequate hc values inhyperbaric helium-oxygen atmospheres.

29

adequate hc values in hyperbaric helium-oxygen atmospheres. However, those prediction equations are only
applicable to sedentary divers in still air. The hc values
become much greater when a diver moves around or is
exposed to high wind velocity. For example, the hc value
was estimated to be 23 (W/m2·°C) when wind velocity
increased to 1.0 m/s at 3,100 kPa (Kakitsuba et al.,1980).
2.2 Clothing insulation in hyperbaric heliumoxygen atmospheres
The main functions of clothing are its insulation andpermeability. In general, clothing insulation is mainly
dependent on the insulative value of still air trapped
within the clothing fabrics because still air is the mostinsulative material. Therefore, clothing with high porosity in the range of 70% to 80% is commonplace if highinsulation is required in everyday life. However, when
the air trapped with fabrics is displaced with a different
gas such as helium, clothing insulation is changed by thethermal characteristics of ambient gas.
Kakitsuba et al. (1981) took advantage of Mochida’s
model (1975) and proposed the following prediction
equation;
I cle =

0.03 × I 0
0.75 × κ He − O 2 + 0.015(clo)(eq.2)

where κHe–O2 = thermal conductivity (W/m·°C); I0 =clothing insulation in normobaric air (clo). In addition,
κHe–O2 was defined by the following equation;

κ He − O = 0.21 − 0.157 × ⎛⎜ p − 1 ⎞⎟2

⎝ 101 ⎠

− 0.24(W/m·°C)(eq.3)

where p = pressure (kPa).
In order to verify reliability of the equation, threedifferent ensembles of training wears were tested while
they were worn by the divers in hyperbaric heliumoxygen atmospheres. Training wears tested were woven
by cotton and polyester. As indicated in Fig. 4, clothinginsulation decreased significantly in the range of
1,000 kPa to 1,500 kPa where the major displacementfrom air to helium rich gas took place. Once displacement is completed, however, clothing insulation may notdecrease markedly. So, the results demonstrated that
there was a good agreement between experimental dataand predictions by eq.2 and eq.3.
2.3 Insensible heat loss and sweat evaporation in
hyperbaric helium-oxygen atmospheres
Heat loss by sweat evaporation prevails when thehuman body is exposed to temperature higher than bodytemperature. Although the entire skin is covered withsweat, evaporation is limited by the maximum evaporation (Emax) that is a product of evaporative heat transfer
coefficient (he; W/m2·kPa) and vapor pressure difference
between the skin and ambient gas. Since vapor pressure
is independent from barometric pressure, vapor pressure
difference between the skin and ambient gas may be in

30

N. KAKITSUBA

the same range as compared with that in normobaric air
for a given thermal condition. The he value is thenestimated as hc × LR. The Lewis relation (LR) can be
defined by the following equation;
2

1⎛ D ⎞3−
LR = 133 × ⎜⎜ ⎟⎟ × (β × C p ) 3⎝κ ⎠(°C/Pa)(eq.4)

0.8

0.7clo0.7

0.6clo0.5cloPredicted values

0.6
0.5

2.4 Clothing permeability in hyperbaric heliumoxygen atmospheres
Kakitsuba et al. (1980) proposed the prediction equation for clothing permeability in hyperbaric heliumoxygen atmospheres as follows;µξ=

1 + f cl ×

(N.D.)

hea
hecl

2.5 Respiratory heat exchange in hyperbaric
helium-oxygen atmospheres
Respiratory heat exchange in hyperbaric heliumoxygen atmospheres becomes a major pathway for heatloss or gain. Particularly, attention must be paid when adiver undergoes exercise or are exposed to low ambient
temperatures. In such cases, a significant increase inrespiratory heat loss is expected. The amount of dry

0.7clo0.6clo0.4

0.5clo

0.3
0.2
0.1
0
0

10

20
30
40
Barometricpressurepressure (100kPa)
Barometric(100 kPa)

Fig. 4 Change in effective clothing insulation at depths.
Clothing insulation decreased significantly in the range of 1,000 kPa to
1,500 kPa where the major displacement from air to helium rich gas
took place. The results demonstrate that there is a good agreement
between experimental data and predictions by eq.2 and eq.3.
Clothing ensembles are as follows;●： Training trousers，half sleeve shirts，socks▲： Training trousers，half sleeve shirts, long sleeve shirts and socks■： Training trousers，half sleeve shirts, long sleeve shirts, trainer, andsocks(eq.5)

where µ = porosity (N.D.); hea = evaporative heattransfer coefficient of ambient gas (= LR × hc;
W/m2·kPa); hecl = evaporative heat transfer coefficientof clothing layer (= k × D; W/m2·kPa; k is the constant).
Using the same clothing ensembles for determinationof clothing insulation (= 0.2 clo in normobaric air), a
diver underwent exercise on a bicycle ergometer until
the whole skin was covered with sweat. Under thecondition of fully wetted skin, we could theoreticallyestimate vapor pressure at the skin. Clothing permeability was then calculated from the partitional calorimetry.
The results are indicated in Fig. 5. The important findingis the slight decrease in clothing permeability in hyperbaric helium-oxygen atmospheres as compared with thatin normobaric air and a good agreement between experimental data and predictions by eq.5.

● Experimental data

1.0
Clothingpermeability(N.D.)
permeability (N.D.)
Clothing

Effective(clo)
Effectiveclothing
clothing insulation
insulation (clo)where D = diffusivity of water vapor (m2/h).
Nishi (1981) calculated the LR values for hyperbaric
helium-oxygen atmospheres from equation 4, and founda dramatic decrease to 6.65 (°C/Pa) at 3,000 kPa as
compared with 293 (°C/Pa) in normobaric air. The hc
value, however, increases twelve times more than innormobaric air. Therefore, according to the definition,
the he value decreases to 0.23 (W/m2·kPa) at 3,000 kPa
that is about one forth of 0.96 (W/m2·kPa) in normobaric air. Since Emax is solely estimated from he for agiven vapor pressure difference between the skin andambient gas, a man may not survive for long in the heat
when exposed to hyperbaric atmospheres due to limited
heat loss by evaporation.
The amount of heat loss by insensible perspirationfrom the skin (Ediff) is about one forth of metabolic heatproduction when man is exposed to optimal thermal
conditions in normobaric air. According to the prediction equation applicable for normobaric air, Ediff maychange with Emax, so that the Ediff value in hyperbaric
atmospheres decreases to one forth of that in normobaric
air. Nevertheless, Ediff values of 8 to 20 (w/m2) at
3,000 kPa were recorded from the human experiments
in hyperbaric environments (Raymond et al., 1974;
Timbal, 1974; Kakitsuba et al., 1981). They reported nostatistical difference as compared with those in normobaric air. Although, as opposed to their results, Carlyle
et al. (1979) reported significant decrease in Ediff in

hyperbaric environments, it is plausible that Ediff remains
unchanged under pressurized atmospheres. If so, a fixedvalue of 0.06 for skin wettedness in the thermoneutral
zones may not be applicable in hyperbaric environments.
Instead, skin wettedness may increase with barometricpressure because of unchanged Ediff.

Predicted values

0.8
0.6
0.4
0.2
0.0
0

10

20
30
40
Barometric
Barometricpressure（100pressure (100kPa)
kPa)

Fig. 5 Change in clothing permeability in hyperbaric
atmospheres.
The results indicate a slight decrease in clothing
permeability in hyperbaric helium-oxygen atmospheresas compared with that in normobaric air.

100

Very hot50

Total thermal
thermalsensation
sensationvote
vote

Respiratorydry
dry heatheat loss or
Respiratoryor gaingain(W)(W)

Thermal Problems in Hyperbaric Environments

1,500 kPa

0-50
3,000 kPa

-100
-150

4,500 kPa

Sedentary
Clothing 0.8～1.0clo

Hot
Warm
NeutralCool
ColdVery cold

28

-200
0

10

20

30

40

50

Respiratory
Respiratorygas
gastemperaturetemperature(°C)( C)○

Fig. 6 Change in respiratory dry heat loss in hyperbaric
atmospheres (Webb & Annis, 1966).
The amount of respiratory gas was set at 10 liter/min.
When respiratory gas temperature is constant, theamount of heat loss increases with barometric pressure.

respiratory gas heat exchange can be estimated asfollows;

C res = Ve × ρ × C p × (Tin − Tex )×60
As(W/m2)(eq.6)

where Ve: respiratory gas volume (liter/min. BTPS), As:body surface area (m2), Tin, Tex: respiratory and expiratory gas temperature, respectively.
With the exception of extreme conditions such as
high ventilation rates due to vigorous exercise andinhalation of cold and dry air, inhaled air is generally
heated to body temperature and is saturated with vapor
in normobaric air when being expired. Therefore, heatloss or gain by respiration may be negligible. In hyperbaric helium-oxygen atmospheres, the expired gas may
not be heated to body temperature due to high conductivity of helium. In order to predict expired gas temperature, the following equation was proposed by Webb andAnnis (1966) and Goodman et al. (1971);
Tex = 24 + 0.32 × Tin

(°C)

31

(eq.7)

Thus, assuming respiratory volume of 10 liter/min
for a sedentary subject, the amount of respiratory heatexchange can be estimated from equations 6 and 7. The
results are presented in Fig. 6 for the condition of a constant respiratory gas temperature. The amount of
respiratory heat exchange increases with barometricpressure.

3. Evaluation on Thermal Comfort inHyperbaric Helium-oxygen Atmospheres
3.1 Mean skin temperature and thermal sensation
Breathing compressed air at more than 600 kPa may
induce nitrogen narcosis and breathing hydrogen or
helium with oxygen at more than 3,000 kPa may induce
hyperbaric nervous syndrome (HPNS). These symptoms
are known to directly affect sympathetic or parasympa-

30

32

34

36

Mean
Meanskinskintemperaturetemperature ((°C)C)
〇

Fig. 7 Relation of mean skin temperature and the relative
magnitude of thermal sensation at 1,620 kPa.
Open and closed circles indicate warm sensations andcold sensations, respectively. A thermally neutral Tsk of
33.0°C was predicted from the regression line (dashedline) under warm or hot conditions whereas a thermallyneutral Tsk of 34.0°C was predicted from the regression
line (solid line) under cool or cold conditions.

thetic nervous systems (Bennett, 1982). In order to mitigate these symptoms, tri-mixed breathing gas, i.e.,helium, oxygen and nitrogen mixtures, was deployed(Shilling et al., 1976). Since human temperature regulation is controlled by sympathetic or parasympathetic
nervous systems, artificial breathing gases may change
their functions. Considering this point of view, Mekjavic
et al. (1995) demonstrated effects of narcosis on
temperature regulation.
Under normobaric air, a linear relation of the relative
magnitude of thermal sensation (RMTS) to mean skintemperature (Tsk ) is confirmed by many scientists (forexample, Winslow et al., 1936). Generally, a man will
vote thermal neutral when Tsk is about 33.5°C. As
shown in Fig. 7, a relation of RMTS to Tsk when divers
were exposed to various temperatures at 1,620 kPa
implies that psychological thermal neutrality may
correspond with Tsk in the range of 33.0°C to 34.0°C
even in hyperbaric helium-oxygen atmospheres. However, it is interesting to note that a thermally neutral
Tsk of 33.0°C was predicted from the regression line
(dashed line) under warm or hot conditions whereas athermally neutral Tsk of 34.0°C was predicted from theregression line (solid line) under cool or cold conditions.
This discrepancy may be resulted from increased
sensibility of temperature sensations in hyperbaric
atmospheres demonstrated by Mekjavic et al. (2003).
3.2 Comfortable and safety thermal conditions in
hyperbaric helium-oxygen atmospheres
As mentioned earlier, data necessary to predict theranges of comfortable and safe thermal conditions in
hyperbaric helium-oxygen atmospheres have been acquired. So, we now have a powerful tool to predict the
comfortable zone in hyperbaric helium-oxygen atmospheres. For example, by incorporating thermophysicalfactors for hyperbaric environments into the heat balance equations, a comfortable range was predicted on a

32

N. KAKITSUBA

Fig. 8 Change in the thermal comfort zone at 3,140 kPa(Raymond, 1971).
Raymond et al. (1971) provided the thermal comfort
zone for unprotected subjects at 3,140 kPa, anddemonstrated that the comfortable temperature range isnarrowed with increasing wind velocity. To ensure
thermal comfort in hyperbaric helium, a careful control
over the target temperature is requisite. In this chart,
the target temperatures may be identified with the line
between warm and cool zones. Therefore, the thermal
comfort zone at 3,140 kPa can be specified with therange of 29°C in still air to 34°C at 0.6 m/s.

psychometric chart for various barometric pressures(Kakitsuba, 1988). More specifically, as shown in Fig. 8,
Raymond (1971) provided comfortable temperature
ranges for unprotected subjects at 3,140 kPa, and demonstrated that the comfortable temperature range isnarrowed with increasing wind velocity.
The chart shows that a wide range of ambient temperature is thermally acceptable same as normobaric air
if warm and cool zones are included into the comfortable zone. For example, ambient temperatures of 22°C
to 35°C may be thermally accepted in still air. However,
the reality is different. To ensure thermal comfort in
hyperbaric helium, a careful control over the target temperature is requisite. In this chart, the target temperatures may be specified with the line between warm andcool zones. Therefore, the thermal comfort zone at
3,140 kPa can be identified with the range of 29°C instill air to 34°C at 0.6 m/s.

4. Conclusions
This paper reviewed thermal problems in hyperbaric
environments and provided information available forcontrolling thermal environments within comfortable
ranges in hyperbaric helium-oxygen atmospheres.
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33
Naoshi KAKITSUBA

In 1979, Naoshi Kakitsuba was granted
Ph.D in Eng. from Graduate School ofEngineering, Nihon University. After
granted Ph.D, he was a research fellow inthe research center, Nihon University forone year. From 1981 to 1983, he was a
postdoctoral fellow of School of
Medicine, Hawaii University. From 1983 to 1984, he was a postdoctoral
fellow of U.S. National Research Council to work at the Submarine Baseat Groton, Connecticut. From 1984 to 1986, he was a research fellow of
School of Kinesiology, Simon Fraser University. After back to Japan in
1986, he run the consultancy company from 1986 to 1993. He was an
associate professor of Department of Architecture, Toyota National
College of Technology in 1993, and then promoted to be a professor in
1996. From 1999 to 2004, he was a professor of Department ofArchitecture Ashikaga Institute of Technology. From 2004, he is currently
a professor of Department of Environmental Science and Technology,
School of Eng., Meijo University. Although his basic training wasArchitecture, his doctor thesis is entitled “A study of evaluation on
thermal environments in hyperbaric helium atmosphere” because he wasinvolved in a series of Diving Simulation Projects in 1976-1979. Since
then, his major interest has been evaluation on indoor and outdoor thermal
environments.

(Received 2 October 2008, Accepted 30 January 2009)