Effects of Heating Appliances with Different Energy Efficiencies on Associations among Work Environments, Physiological Responses, and Subjective Evaluation of Workload

Industrial Health 2008, 46, 360–368
Original Article
Effects of Heating Appliances with Different
Energy Efficiencies on Associations among Work
Environments, Physiological Responses, and
Subjective Evaluation of Workload
Hiroe MATSUZUKI1, 2*, Makoto AYABE3, 4, Yasuo HARUYAMA2, Akihiko SEO5,
Shizuo KATAMOTO3, Akiyoshi ITO6 and Takashi MUTO2
1The University of Tokyo Kasei Gakuin, 2600 Aihara-cho, Machida-city, Tokyo 194-0292, Japan
2Dokkyo Medical University School of Medicine, 880 Kitakobayashi, Mibu-machi, Tochigi 321-0293, Japan
3Juntendo University, 1–1 Hiragagakuendai, Inba-mura, Chiba 270-1695, Japan
4Fukuoka University, 8–19–1 Nanakuma, Minami-ku, Fukuoka-city, Fukuoka 814-0180, Japan
5Tokyo Metropolitan University, 6–6 Asahigaoka, Hino-city, Tokyo 191-0065, Japan
6University of Occupational and Environmental Health, 1–1 Iseigaoka, Yahata-ku, Kitakyushu-city, Fukuoka
807-8555, Japan
Received November 2, 2007 and accepted April 21, 2008
Abstract: To clarify the association between heat stress, physiological responses and subjective
workload evaluations in kitchens using an induction heating stove (IH stove) or gas stove. The
study design was an experimental trial involving 12 young men. The trial measured ambient
dry-bulb temperature, globe temperature, wet-bulb globe temperature (WBGT) and relative
humidity; the subjects’ weight, heart rate, blood pressure, oxygen uptake, amount of activity,
body temperature, subjective awareness of heat and workload before and after mock cooking for
30 min. The IH stove insignificantly increased heat indicators in the work environment and
workers showed lower oxygen uptake, skin temperature, subjective awareness of heat and work-
load after heat exposure. Both physiological load and subjective awareness of heat and work-
load were slight in kitchens using the IH stove, which provided a better work environment.
Key words: Globe temperature, IH stove, Thermal stress, Physiological response, Feeling of load
Introduction
does generate heat by electromagnetic induction, heat effi-
ciency is high at 90%, and the caloric force is strong. On
In the food service industry, the working environment
the other hand, the heat efficiency of the gas stove is
is considered to be hard due to standing at work in a hot
20–40%. There is therefore little exhaust heat with the
environment, in addition to irregular working hours1–4),
IH stove, and the rise in kitchen temperature is slight.
and the risks of musculoskeletal disease and dermatitis
Concerning workload, there have been many studies on
are also high5).
the heart rate when working in a kitchen8, 10–13), but only
Studies on kitchen labour have often shown a high
a few have studied physiological responses to changes in
ambient temperature in the kitchen working environ-
the working environment by methods including subjective
ment6–8). In recent years, environmental improvements
evaluation of workload by workers themselves. The pur-
by the introduction of electric kitchens with high energy
pose of this study was to measure heat stress on subjects
efficiency have also been reported in Japan9). Because
and their physiological responses, and to evaluate their
the IH stove has a heating characteristic that the pot itself
association; moreover, to clarify what constitutes a com-
fortable kitchen environment based on the results of these
*To whom correspondence should be addressed.
measurements and subjects’ feelings of heat and load.

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EFFECTS OF HEATING APPLIANCES ON WORKERS’ HEALTH
361
Methods
The subjects were 12 healthy men (22.4 ± 1.0 yr,
172.5 ± 4.8 cm) not acclimated to heat stress. The study
design was an experimental trial. The subjects performed
mock cooking once using an induction heating stove (IH
stove) and once using a gas stove (total, 24 times). This
study was approved by The Ethics Committee of Dokkyo
Medical University and complied with the Helsinki
Declaration. All subjects were fully informed of the pur-
pose, procedures and possible risks of the study, and then
gave written informed consent.
Mock cooking work
The experiment was performed in a large-scale food
Fig. 1. A laboratory floor plan (Large scale food practical
practical training kitchen at The University of Tokyo
training kitchen).
Kasei Gakuin (Fig. 1, 70.15 m2 in area, studding 2.6 m).
1) Unit: mm.
2) Heating appliance: A; IH stove, B; gas stove.
An exhaust hood (1,050 × 600, evacuation air-capacity
3) Subjects standing position: subjects stood at a distance of 45 cm
1,730 m3/h) for the upper part of the cooking stove was
from the center of the cooking plate.
used in the experiment. The subjects were fasted for 8 h
before the experiment. The total weight of clothes (under-
wear, trousers, socks, T-shirt, chef’s coat and work
gloves) was 3.1 kg.
As shown in Figs. 2 and 3, the subjects stood with the
abdomen 45 cm from the center of the cooking plate. The
subjects stood for 10 min and stirred boiling water using
their right hand for 20 min. The subjects were directed
not to change their position. As shown in Fig. 4, they
gripped the end of a rice paddle (length, 20 cm) and
stirred at an angle of 180? at a rate of 10 stirs/min. The
left upper limb was extended along the left side of the
body.
As heat stress, a pan containing 1 kg konjak (alimen-
tary yam paste, 2.0 × 2.0 × 2.0 cm) and 10 kg water was
heated, and the state 6 min after the water temperature
Fig. 2. An experiment elevation view.
1) Unit: mm.
reached 99?C was considered to be stable. In the kitchen
2) Heating appliance: A; IH stove, B; gas stove, C; Japanese pan that
environment, before exposure to heat stress, the ambient
can be used for both electromagnetic appliances and gas stoves.
dry-bulb temperature in front of the stove (height from
3) WBGT meters were set at a distance of 45 cm from the center of
the floor, 120 cm) was adjusted to 25.0 ± 0.5?C using an
the cooking plate at height of 90 (?), 120 (?) and 150 cm (?)
air conditioner in each experiment. The full output of the
from the floor.
2-ring gas stove (10,000 kcal/h) was used. To equalize
4) Body temperature: ?; Rectal temperature, ?; Abdominal tem-
output between the different heat sources, a rising ambi-
perature, ?; Antebrachial skin temperature, ? ; External acoustic
ent temperature test was performed, and 80% of the max-
meatus temperature.
imum output of the IH stove was used.
Royal Choriki Co., Ltd.) that can be used for both elec-
Measurement
tromagnetic appliances and gas stoves were used. The
As heating appliances, IH stoves (rated output, 5 kW;
water temperature was measured at 30-s intervals by fix-
MIR5T-N, Nichiwa Electric Corporation) and gas stoves
ing the tip of a needle-type thermometer to measure inter-
(output, 10,000 kcal/h; 1 burner with 2 rings; Nihon
nal temperature (Anritsu Thermo Printer AP-210 Type E,
Choriki Co., Ltd.) were used. The height of each stove
Anritsu-meter Co., Ltd.) 6 cm from the center of the pan
(from the floor to the bottom of the pan) was 87 cm, and
bottom. The ambient dry-bulb temperature in front of the
to the top of the pan on the cooking stove was 107 cm.
stove near the subjects was measured before and after
Japanese pans (bottom diameter, 36 cm; depth, 20 cm;
exposure to heat stress. The ambient dry-bulb tempera-

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362
H MATSUZUKI et al.
globe temperature, and WBGT were measured after
2 min. We defined the difference the ambient dry-bulb
temperature and globe temperature as radiant heat index.
To confirm the output of the stove at the time of the
experiment, the time required for heating and the amount
of evaporation were compared between the two heat
sources.
As physiological responses, body weight, oxygen
uptake, heart rate, blood pressure, and body temperature
(temperature of the antebrachial skin, abdominal skin,
external acoustic meatus, and rectum) were measured.
Before and after the experiments, the subjects were
weighed using a digital scale (FG-150KBM, A&D Co.,
Ltd.), wearing underwear alone. Oxygen uptake was mea-
sured using a portable oxygen monitor (K4b2, COSMED
Co., Ltd.), and values during the last 1-min period were
averaged at 5-min intervals. The heart rate and blood
pressure were measured using a portable heart rate/blood
pressure monitor (TNGO Co., Ltd.) at 5-min intervals,
and double product was calculated based on the mea-
Fig. 3. Mock cooking work.
surement values. Body temperature was measured using
The experiment was carried out in a large-scale
surface-type probes (Nikkiso YSI Co., Ltd.). To measure
food practical training kitchen. The subjects
stood with the abdomen 45 cm from the center
temperatures in the antebrachial and abdominal skin, tem-
of the cooking plate. The subjects rested for 10
perature probes were fixed 10 cm above the right wrist
min in the standing position and performed
and above the navel, respectively. In addition, a sensor
mock cooking for 20 min.
for external acoustic meatus temperature measurement
Photo shows the experiment using the gas stove.
(Nikkiso YSI Co., Ltd.) was inserted into the external
acoustic meatus, and a body lumen insertion-type tem-
perature probe (Nikkiso YSI Co., Ltd.) was inserted
10–15 cm from the anus and fixed for the measurement
of rectal temperature. Body temperature values during
the last 1-min period were averaged at 5-min intervals.
The amount of activity using the IH and gas stoves was
estimated using a wrist accelerometer (Actical ITC Co.,
Ltd.). Concerning the working posture, changes in the
trunk inclination angle were evaluated using a 3-axis
acceleration sensor (Asakusagiken).
For subjective evaluation of heat and workload by the
subjects, a questionnaire was performed at the end of the
work. Feelings of heat in the hands, arms, chest, face
and abdomen were classified into 5 categories (1: not hot,
Fig. 4. Mock cooking performance.
2: slightly hot, 3: hot, 4: considerably hot, 5: intolerably
The subjects gripped the upper end of a rice
hot). The feeling of work load was also classified into 5
paddle and stirred at an angle of 180? at a
categories (1: not hard, 2: slightly hard, 3: hard, 4: con-
rate of 10 stirs/min.
siderably hard, 5: intolerably hard), and the mean value
was compared between the two heat sources. To analyze
ture, relative humidity, globe temperature, and WBGT
the association between the work environment based on
were measured using the same WBGT meters (WBGT-
subjective evaluation and physiological responses, the
103, Kyoto Electronics Manufacturing Co., Ltd.). After
above classifications were re-categorized into two cate-
adjusting the dry-bulb temperature at a height of 120 cm,
gories (1–3: slightly hot, slightly hard; 4–5: considerably
three WBGT meters were set 45 cm from the center of
hot, considerably hard), and the two groups were com-
the cooking plate 90, 120, and 150 cm from the floor,
pared. Changes in posture were evaluated using multiple
and the ambient dry-bulb temperature, relative humidity,
choices (raise an arm, lower an arm, turn the body away,
Industrial Health 2008, 46, 360–368

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EFFECTS OF HEATING APPLIANCES ON WORKERS’ HEALTH
363
turn the face away and bend forward).
after exposure.
Physical activity intensity estimated using an
Statistical analysis
accelerometer did not differ between the two heat sources.
The levels of significance of the difference of the envi-
Work posture analysis showed no significant differences
ronmental and physiological parameters were analyzed
between the two heat sources, although the angle of trunk
using two kinds of examination. To compare the IH and
inclination showed a slightly anterior inclination using the
gas stoves, Student’s non-paired t-test was used. To com-
IH stove and slight flexion using the gas stove.
pare between before and after exposure, Student’s paired
t-test was used.
Subjective evaluation of heat stress
To compare proportions, the ? 2 test or Fisher’s exact
The feeling of heat in the hands, arms, chest, face and
test was used. Analysis was performed using SPSS.Ver.
abdomen was significantly more marked for the gas stove
15.0 (Japan SPSS, Tokyo). In the two-sided test, p<0.05
than for the IH stove at 2.8 vs 4.1, 1.9 vs 3.1, 1.8 vs 2.7,
was considered significant.
1.8 vs 3.7, and 1.4 vs 2.8, respectively; however, the feel-
ing of work load did not significantly differ between the
Results
two heat sources. In response to heat stress due to the
gas stove, the subjects used avoidance postures and
Environment in front of the stove when using IH and gas
actions such as raising their arm (58.3%), turning their
stoves
body away (41.7%), and turning their face away (33.3%).
As shown in Table 1, after heating to stabilize heat
Free descriptions also showed a feeling of heat in the fin-
stress before exposure, the ambient dry-bulb temperature,
gers, arms, and face for the gas stove but no such feel-
globe temperature, radiant heat index, and WBGT were
ing for the IH stove.
significantly higher using the gas stove than using the IH
stove. At a height of 90 cm, the radiant heat index using
Association between work environment and physiological
the gas stove was about 10 times higher than using the
responses according to the feeling of heat
IH stove. After exposure to heat stress for 30 min, the
As shown in Table 3, the percentage of subjects who
environmental values in front of the IH stove did not
felt “considerably hot” in their abdomen and hands was
change, while ambient dry-bulb temperature, globe tem-
slightly higher for the gas stove than for the IH stove, but
perature, radiant heat index, and WBGT significantly
for the face, it was significantly higher. In the groups
increased in front of the gas stove at each height. Relative
who felt “considerably hot” in the abdomen, hands and
humidity 120 cm and 150 cm above the gas stove showed
face, there were significant differences in ambient dry-
significantly decreased heat stress at 30 min, but there
bulb temperature, globe temperature and body tempera-
was no similar change with the IH cooking stove.
ture (abdomen and antebrachial skin temperature) between
The time required for heating did not significantly dif-
the IH and gas stoves; however, there were no significant
fer between the IH stove (63.5 ± 10.1 min) and the gas
differences in ambient dry-bulb temperature at 150 cm or
stove (59.0 ± 7.0 min), and water evaporation also did not
external acoustic meatus temperature between the IH and
differ between the IH stove (59.8 ± 9.5%) and the gas
gas stoves.
stove (57.1 ± 5.7%), showing the same output state
between the two types of stove.
Association between environment in front of the stove and
physiological responses according to the feeling of work-
Physiological responses to heat stress
load
As shown in Table 2, physiological responses did not
As Table 4 shows, the percentage of subjects who felt
differ between the two heat sources before exposure to
that the workload was “considerably hard” was slightly
heat stress, but significantly increased for both the IH and
higher for gas stoves than for IH stoves. In the groups
gas stoves after mock cooking work except for oxygen
who felt that the workload was “considerably hard”, there
uptake and external acoustic meatus temperature of the
were significant differences in ambient dry-bulb temper-
IH stove. After mock cooking work, heart rate, temper-
ature except for 150 cm, globe temperature and body tem-
ature of the antebrachial skin, abdominal and external
perature (abdomen, antebrachial skin and external
acoustic meatus, and oxygen uptake significantly differed
acoustic meatus temperature) between the IH and gas
between the two heat sources. Although oxygen uptake
stoves.
and external acoustic meatus temperature did not differ
between the two heat sources before heat stress, because
Discussion
those of the gas stove significantly increased by heat
stress, there was a difference between the two heat sources
In this study, we found that using the IH stove with

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364
H MATSUZUKI et al.
Table 1. Environment in front of stove before and after exposure to heat stress
Before exposure1)
After exposure2)
n
mean
SD
p-value3)
n
mean
SD
p-value3)
p-value4)
Ambient dry-bulb temperature, ?C
IH stove
12
25.4
0.4
12
25.6
0.6
n.s.
Height, 90 cm5)
0.001
0.001
gas stove
12
26.4
0.3
12
26.9
0.5
0.001
IH stove
12
25.3
0.4
12
25.4
0.6
n.s.
Height, 120 cm5)
0.001
0.001
gas stove
12
26.0
0.5
12
26.5
0.5
0.001
IH stove
12
25.5
0.2
12
25.6
0.5
n.s.
Height, 150 cm5)
n.s.
0.010
gas stove
12
25.7
0.6
12
26.2
0.6
0.007
Relative humidity, %
IH stove
12
73.5
13.0
12
74.4
10.6
n.s.
Height, 90 cm
n.s.
0.032
gas stove
12
67.0
6.6
12
65.7
7.6
n.s.
IH stove
12
74.2
13.3
12
74.5
12.1
n.s.
Height, 120 cm
n.s.
0.026
gas stove
12
67.2
6.6
12
64.7
7.5
0.008
IH stove
12
74.6
12.4
12
74.5
12.4
n.s.
Height, 150 cm
n.s.
0.034
gas stove
12
67.2
6.7
12
64.9
7.6
0.025
Globe temperature, ?C
IH stove
12
26.7
0.4
12
26.8
0.7
n.s.
Height, 90 cm
0.001
0.001
gas stove
12
37.5
0.7
12
38.7
0.7
0.002
IH stove
12
27.2
0.4
12
27.3
0.6
n.s.
Height, 120 cm
0.001
0.001
gas stove
12
31.3
0.6
12
32.5
0.5
0.001
IH stove
12
27.1
0.3
12
27.2
0.5
n.s.
Height, 150 cm
0.001
0.001
gas stove
12
28.7
0.5
12
29.6
0.4
0.001
Radiant heat index6), ?C
IH stove
12
1.3
0.1
12
1.2
0.2
n.s.
Height, 90 cm
0.001
0.001
gas stove
12
11.2
0.5
12
11.8
0.6
0.020
IH stove
12
1.9
0.1
12
1.9
0.1
n.s.
Height, 120 cm
0.001
0.001
gas stove
12
5.2
0.5
12
6.0
0.4
0.001
IH stove
12
1.7
0.1
12
1.7
0.1
n.s.
Height, 150 cm
0.001
0.001
gas stove
12
3.0
0.3
12
3.5
0.2
0.001
WBGT, ?C
IH stove
12
23.7
1.1
12
23.9
1.3
n.s.
Height, 90 cm
0.001
0.001
gas stove
12
26.9
0.4
12
27.4
0.9
0.017
IH stove
12
23.8
1.2
12
24.1
1.5
n.s.
Height, 120 cm
0.010
0.021
gas stove
12
24.8
0.7
12
25.3
1.0
0.005
IH stove
12
24.0
1.2
12
23.8
1.2
n.s.
Height, 150 cm
n.s.
n.s.
gas stove
12
23.9
0.8
12
24.3
1.1
0.022
1) Before exposure: After 10-min heating for stabilization of heat stress before Subject’s exposure.
2) After exposure: 30 min after the initiation of exposure to heat.
3) Comparison between the heat sources: Student’s non-paired t-test.
4) Comparison between before and after exposure: Student’s paired t-test.
5) Measurement was conducted at distance of 45 cm from the center of the stove each height.
6) Radiant heat index: The difference between ambient dry-bulb temperature and globe temperature.
high energy efficiency, heat stress was slight, and no
showed a close association between these feelings and
changes were observed in the kitchen environment.
ambient black globe temperature rather than ambient dry-
Although physiological responses significantly increased
bulb temperature.
for both the IH and gas stoves after mock cooking work,
This study showed the following characteristics. The
the changes using the IH stove were slight. In addition,
first was the evaluation of heat stress to which subjects
subjective evaluation of the feeling of heat and workload
were exposed from multiple aspects by measuring the
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EFFECTS OF HEATING APPLIANCES ON WORKERS’ HEALTH
365
Table 2. Physiological responses before and after exposure to heat stress
Before exposure1)
After exposure2)
Physiological items
n
mean
SD
p-value3)
n
mean
SD
p-value3)
p-value4)
Weight, kg
IH stove
12
63.1
7.3
12
63.0
7.3
0.001
n.s.
n.s.
gas stove
12
62.9
7.1
12
62.8
7.1
0.001
Heart rate, bpm
IH stove
11
78.6
9.8
12
101.0
13.7
0.001
n.s.
n.s.
gas stove
12
76.6
10.2
12
108.8
16.9
0.001
Systolic blood pressure, mmHg
IH stove
11
113.8
9.3
12
124.3
12.3
0.008
n.s.
n.s.
gas stove
12
115.9
11.3
12
128.0
11.1
0.042
Diastolic blood pressure, mmHg
IH stove
11
71.5
6.3
12
84.3
7.4
0.001
n.s.
n.s.
gas stove
12
72.8
7.9
12
84.8
6.6
0.001
Double product, bpm*mmHg
IH stove
11
8,931
1,535
12
12,505
2,201
0.001
n.s.
n.s.
gas stove
12
8,864
1,643
12
13,758
1,891
0.001
Oxygen uptake, ml*kg–1*min–1/kg
IH stove
11
4.3
0.7
11
5.4
1.0
n.s.
n.s.
0.006
gas stove
12
4.6
1.4
12
6.5
0.8
0.001
Amount of activity, METs
IH stove
12
1.1
0.2
10
1.6
0.2
0.001
n.s.
n.s.
gas stove
12
1.1
0.3
12
1.8
0.3
0.001
Antebrachial skin temperature, ?C
IH stove
12
34.2
1.1
11
36.8
0.5
0.001
n.s.
0.001
gas stove
12
34.1
1.1
12
39.7
1.1
0.001
Abdominal temperature, ?C
IH stove
11
34.2
0.9
11
35.2
0.7
0.001
n.s.
0.001
gas stove
12
34.2
0.8
12
38.4
0.8
0.001
External acoustic meatus temperature, ?C
IH stove
12
36.3
0.3
11
36.4
0.3
n.s.
n.s.
0.001
gas stove
12
36.1
0.3
12
37.2
0.6
0.001
Rectal temperature, ?C
IH stove
12
37.1
0.3
11
37.2
0.3
0.009
n.s.
n.s.
gas stove
12
37.1
0.3
12
37.3
0.3
0.005
1) Before exposure: After 10-min heating for stabilization of heat stress before subjects’ exposure.
2) After exposure: 30 min after the initiation of exposure to heat.
3) Comparison between the heat sources: Student’s non-paired t-test.
4) Comparison between before and after exposure: Student’s paired t-test.
Table 3. Association between work envirinment and physiolosical responses according to the subjectives evaluation of hotness
Feeling of hotness
Ambient1)
Body
considerably hot
Dry-bulb temperature, ?C
Globe temperature, ?C
Body temperature, ?C
n
(%)
p-value3)
mean
SD
p-value4)
mean
SD
p-value
mean
SD
p-value
IH stove
3
22.5
25.6
0.6
26.9
0.6
35.9
0.4
Abdomen2)
n.s.
0.006
0.001
0.003
gas stove
8
66.7
27.0
0.6
38.7
0.8
38.4
1.0
IH stove
6
50.0
25.6
0.7
27.5
0.7
37.1
0.5
Hands
n.s.
0.008
0.001
0.001
gas stove
11
91.7
26.4
0.4
32.5
0.5
39.8
1.0
IH stove
2
16.7
25.7
0.2
27.4
0.2
36.6
0.1
Face
0.001
n.s.
0.001
n.s.
gas stove
12
100.0
26.3
0.6
29.7
0.5
37.0
0.4
1) Measurement was conducted at each height, concerning feeling of hotness at abdmen, hands and face was at a height of 90, 120 and
150 cm, respectively.
2) Abdomen: Abdomina temperature, Hand: Antebrachial skin temperature, Face: External acoustic meatus temperature.
3) Fisher’s exact test.
4) Comparison between IH and gas stove: Student’s non-paired t-test.
environment in front of the stove where the subjects stood
observation of the physiological responses of the subjects
at multiple measurement heights, and using multiple tem-
to a certain degree of heat stress by an IH or gas stove
perature parameters such as ambient dry-bulb tempera-
without allowing avoidance behavior. The third was the
ture, globe temperature and WBGT. The second was
evaluation of comfortable kitchen conditions in terms of

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366
H MATSUZUKI et al.
Table 4. Association between work envirinment and physiolosical responses according to the subjectives eval-
uation of work load
considerabley hard
Physiological/environmental items
IH stove
Gas stove
n
mean
SD
n
mean
SD
p-value1)
4
(33.4%)
9
(75.0%)
n.s.2)
Ambient
Dry-bulb temperature, ?C 90 cm3)
4
25.6
0.3
9
26.9
0.5
0.001
120 cm3)
4
25.4
0.3
9
26.6
0.5
0.001
150 cm3)
4
25.5
0.3
9
26.2
0.6
n.s.
Globe temperature, ?C 90 cm
4
26.7
0.3
9
38.7
0.7
0.001
120 cm
4
27.3
0.3
9
32.5
0.3
0.001
150 cm
4
27.1
0.4
9
29.7
0.4
0.001
Heart rate, bpm
4
107.5
15.2
9
113.9
13.8
n.s.
Systolic blood pressure, mmHg
4
125.5
6.4
9
129.1
10.7
n.s.
Diastolic blood pressure, mmHg
4
88.5
10.0
9
75.1
7.8
n.s.
Double product, bpm*mmHg
4
13,405
1,909
9
14,539
1,390
n.s.
Oxygen uptake, ml*kg–1*min–1/kg
3
6.0
0.3
9
6.4
0.7
n.s.
Amount of activity, METs
3
1.7
0.2
9
1.7
0.3
n.s.
Antebrachial skin temperature, ?C
4
37.1
0.6
9
39.7
1.2
0.002
Abdominal temperature, ?C
4
34.7
0.7
9
38.4
1.0
0.001
External acoustic meatus temperature, ?C
4
36.3
0.4
9
37.2
0.6
0.026
Rectal temperature, ?C
4
37.2
0.3
9
37.3
0.3
n.s.
1) Comparison between IH and gas stove: Student’s non-paired t-test.
2) Fisher’s exact test.
3) Measurement was conducted at distance of 45 cm from the center of the stove each height.
the relationship between the environmental temperature in
heat sources, and the absence of avoidance behavior due
front of the stove and skin temperature based on subjec-
to heat stress was confirmed by the absence of a differ-
tive evaluation.
ence in the trunk inclination angle. Thus, since the
We consider that this study has high internal validity
amount of physical activity did not differ between the two
based on the following points. First, the ambient tem-
heat sources in this study, and differences in physiologi-
perature for each subject before exposure to heat stress
cal responses are considered to be due to differences in
was controlled at 25.0 ± 0.5?C to control the experimen-
heat stress.
tal environment. In addition, the output level of the stove
Compared with the gas stove, the IH stove with high
was confirmed to be similar in terms of the time required
energy efficiency showed no changes in ambient dry-bulb
for heating and water evaporation rate. Second, in the
temperature, relative humidity, globe temperature, radiant
measurement of physiological responses, there was no age
heat index, and WBGT after 30-min heating, suggesting
bias, and subjects not acclimated to heat stress underwent
good maintenance of the thermal environment in the
both experiments using the IH or gas stove once each.
kitchen. These findings were consistent with those in pre-
To exclude the influence of familiarity with the work,
vious studies12, 13). In this study, 3 types of temperature
training was performed before experiments. The number
(ambient dry-bulb temperature, glove temperature and
of subjects in the group performing the experiment using
WBGT) were simultaneously measured, and each showed
the IH stove first was the same as that in the group per-
the highest value using the gas stove at a height of 90 cm
forming the experiment using the gas stove first. In addi-
after exposure to thermal stress; however, the highest
tion, to exclude the influence of the experimental initia-
WBGT value was below the permissible high temperature
tion time on physiological responses, the two experiments
range14), and the ambient dry-bulb temperature also did
for each subject were initiated at a fixed time of day, and
not exceed 27?C, indicating a lower temperature than that
the subjects fasted for 8 h before experiments. Third, the
in kitchens during actual cooking7, 8). This may be
amount of activity evaluated using an accelerometer and
because the temperature in front of the stove was con-
a portable oxygen monitor did not differ between the two
trolled using an air conditioner, and there was only one
Industrial Health 2008, 46, 360–368

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EFFECTS OF HEATING APPLIANCES ON WORKERS’ HEALTH
367
stove as a source of heat stress. Based on only ambient
The results of this study suggest the following 3 impor-
dry-bulb temperature and WBGT, the experimental envi-
tant points to improve the kitchen environment: the use
ronment using either the IH or gas stove was more com-
of heating appliances with high energy efficiency pro-
fortable than the actual working environment.
ducing low heat radiation, because of the association
The IH stove induced no changes in the work envi-
between an increase in globe temperature and an increase
ronment due to heat stress. Rectal temperature after heat
in body temperature; the control of globe temperature
stress exposure did not differ between the two groups that
using an air conditioner because of the marked feeling of
differed in ambient temperature in front of the stove.
total body load at a high black globe temperature; and
Previous studies using a higher dry-bulb temperature,
evaluation of the improvement of the kitchen working
black globe temperature and a longer exposure time than
environment in terms of not only heat stress but also
our study have shown rectal temperature similar to in this
humidity. This is because of frequent exposure to high
study15, 16). Another study of glass craftsmen showed a
humidity in the kitchen due to many types of work using
heart rate of 90–100 beats/min when working in the sit-
water, and the rectal temperature is high with high humid-
ting position despite a radiant heat of about 20?C, sug-
ity19) at the same air temperature, causing marked feel-
gesting a low load on circulation17). Therefore, consid-
ings of workload17), although work leading to increasing
ering the intensity of heat stress, mock cooking using only
humidity was excluded from this study.
the upper limbs when standing upright, and the exposure
The limitations of this study were a small sample size,
time of 30 min in this study, the workload may not have
lack of evaluation of the reliability and validity of the
been so great as to change the heart rate and rectal tem-
questionnaire used for subjective assessment, and the
perature.
inclusion of only young men as subjects. Even under the
Because this study does not measure detailed physio-
same conditions, the increase in body temperature differs
logical endpoints such as blood data, establishing the
between the aged and young15), and the working temper-
direct effect is difficult, and is a theme of future research,
ature range considered to be comfortable differs between
but a previous study showed that oxygen uptake rises by
males and females20); therefore, it is difficult to general-
the activation of peripheral tissues such as skin tempera-
ize the results of studies in young men, ignoring sex and
ture18). The measurement accuracy of the breathing gas
age. In societies with a decrease in the productive pop-
analyzer was not affected in this study.
ulation, hopes are placed on the work of women and the
Concerning the feeling of heat and workload, it is
elderly. In the future, studies with a greater sample size,
thought that significant difference was not observed
including comparisons among age groups and between
because of the small sample size. Concerning the asso-
genders, are necessary. Because both physiological load
ciation between the feeling of heat and skin temperature
and subjective awareness of heat and workload were slight
or ambient temperature, the number of subjects who felt
in kitchens using the IH stove, which provided a better
that their hands were “considerably hot” was higher than
work environment, the electrified kitchen is thought to be
that of subjects who felt that their abdomen or face was
preferable as a comfortable work environment for work-
“considerably hot”. This may be due to the influence of
ers.
the ascending air current of boiled water on the hands
above the pan. Since ambient temperature was measured
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