Performance
loss among workers due to heat stress in high-temperature workplaces
Beheshti MH, MSc1, Boroumand Nejad E, BSc2,
Bahalgerdy B, BSc2, Mehrafshan F, BSc2, Zamani Arimy A, BSc2
1- Faculty Member, Dept.
of Occupational Health, Faculty of Health, Gonabad University of Medical
Sciences, Gonabad, Iran. 2- BSc in Occupational Health, Dept. of Occupational
Health, Faculty of Health, Gonabad University of Medical Sciences,
Gonabad, Iran.
Abstract
Received:
March 2016, Accepted: June 2016
Background: Heat stress is one of the harmful factors present in
many workplaces. It can lead to performance loss and low functionality of the
labor force. Therefore, the aim of this study was to evaluate exposure to
heat stress and its consequent performance loss among workers functioning in
indoor high-temperature workplaces. Materials and Methods: This descriptive, analytical study was conducted on
indoor high-temperature occupations in spring 2014. This study was conducted
on 15 bakeries, 11 restaurants and kitchens, and 2 industries with heating
processes in Gonabad city, Iran. In total, 1450 individuals worked on the investigated sites and
were exposed to thermal stress. The inclusion criterion for this study was
working in an environment that included a heating process and the exclusion
criterion was unwillingness to participate in the study. Heat stress was
measured based on wet-bulb globe temperature(WBGT) and the ISO 7243standard.
The graph of performance loss versus thermal stress proposed by Kjellstrom et
al. was used to determine the performance loss caused by thermal stress.All
individuals and managers were informed of the aims of the project and were
assured of the confidentiality of the data. Statistical analyses were
performed using SPSS software. Results: The mean exposure to heat stress in Barbari, Sangak,
and Lavash (three types of bread) bakeries were 29.73, 27.89, and 29.43 °C,
with a mean performance loss of 65%, 23%, and 64%, respectively. In some
cases, the performance loss in Lavash bakeries was as high as 98%. The mean
exposure to heat stress in refractory brick and porcelain manufacturing
industries were 32.04 ºC and 32.35 °C, leading to a concomitant
performance loss of 89% and 92%, respectively. The mean WBGT in the kitchens
was 31.88, which could lead to a performance loss of 80%. Conclusions: In addition to a host of diseases and complications
caused by heat stress, extreme heat in the workplace can significantly reduce
the performance of the labor force, and consequently,their production.
Through appropriate planning and control of heat stress in the workplace, not
only are many diseases prevented, but also the performance and efficiency of
workers are greatly improved. |
Keywords: Heat
Stress, Temperature, Workplaces,
Performance
Introduction
Heat is recognized
as a harmful physical factor in many workplaces. Thermal stress due to heat is
caused by a number of internal and external thermal factors which lead to
fatigue and development of disease in the human body (1). Environmental heat
influences the performance and productivity of humans through changing
physiological parameters, such as blood flow and hormone release rate.
Moreover, the global warming phenomenon can also reduce productivity; increase
the prevalence of diseases and its related health costs, immigration,
natural disasters, and etcetera. When people perform physical
activities in hot environments, they are at risk of increase in deep* body temperature (more than 38°C),
decrease the physical work capacity and mental capacity, increase in accident
frequency, and ultimately, heat exhaustion and heat stroke (2). In the same
vein, the results of epidemiological studies and work reports in Taiwan showed
the notable impact of warm weather onsome infectious diseases, such as dengue
fever. However, hot climate can also influence the health of workers and labor
productivity, especially in older people who are more prone to such impacts.
In addition to the
aforementioned complications, extreme heat stress in workers can in some cases
lead to death. Currently, the number of deaths caused by workplace heat stress
in the United States and Canada has amounted to 22 individuals per year. The Toronto
Health Department estimates that this number will increase from 20 in 2001 to
300 cases in 2020 (3). The study by Kjellstrom et al. showed that in countries
with extremely hot seasons, labor forces are required to work in environments
where temperature conditions are warmer than standard conditions for the
suitable functioning of the physiological mechanism of the human body (2). The
excessive increase in workplace temperature will aggravate mental stress,
reduce work capacity, and decrease productivity (4, 5). In addition to its
health related consequences, exposure to heat can deteriorate human performance
under various conditions (6). It has been reported in the National Institute of
Occupational Safety and Health (NIOSH) standard that high wet-bulb globe
temperature (WBGT) level will hamper workers’ performancein their assigned
tasks(7, 8). A natural human reaction to heat stress is lowering physical
activity, which is intended asa strategy to reducecore body heat (2). This
preventive reaction reduces the work capacity of individuals. Thus, the effect
of excessive heat exposure on work capacity is a natural protective reaction
that aims to reduce the risk of heat stroke by reducing the pace of work (2).
Hubler et al. in their study on the effects of climate change in Germany found
that, based on empirical studies on its health effects, it can increase the
mortality rate and health costs of heat stress by 3 and 6 times, respectively
(9).
The main factor
underlying these effects is increased deep body temperature along with
dehydration resulting from inadequate water consumption. Excessive dehydration
may result in marked fatigue and clinical diseases, especially renal failures
(2). There is a wide range of health effects caused by climate change, including
direct impacts, such as changing temperature and comfort of individuals,and
indirect effects,such as greater frequency of storms, floods, infectious
disease, food poisoning, and insect-induced and plant-induced allergies (9).
Heat stress can be associated with psychological and physical effects such as
irritability, nervousness, moodiness, depression (mental effects),
cardiovascular complications, perspiration, water and electrolyte imbalance,
and changes in blood flow rate (physical effects). A combination of mental and
physical reactions is embodied in the form of low work efficiency, reduced
labor skills, muscular fatigue, poor concentration, and thus, increased
frequency of mistakes.
Environmental heat
may lead to increased thermal load inside and outside the workplace, thereby
decreasing the productivity of millions of workers (6). In general,
productivity refers to the extent of efficiency in achieving the objectives of
the system and is generally defined as the ratio of input to output (5). Workers
in the construction industry, farmers, and fishermen may suffer from the
thermal effects of climate change on productivity (10). To compensate for the
loss of productivity due to heat stress, workers may be required to work longer
hours or employers may be obliged to hire extra labor forces (6). In middle and
low income countries, given the undesirable workplace conditions for both
outdoor and indoor environments, productivity is often low (6). Currently,
there is a paucity of research about the effects of heat stress on the
performance and productivity of humans.Moreover, the existing data on the real
exposure of workers to high-temperature environments and reduced productivity
and efficiency are rather ambiguous (10). If the necessary control measures are
not taken, high workplace temperature may have considerable effects on
productivity, occupational efficiency, and their related costs. The aim of this
study was to evaluate thermal stress and performance loss caused by
high-temperature indoor work environments in Gonabad, Iran.
It should be noted
that this study is the first of its type in Iran.Thus, its results can be
incorporated in future studies to help prepare systematic plans for the
protection of workers against this problem.
Material and Methods
This
descriptive-analytical study was conducted on indoor high-temperature
workplaces in the city of Gonabad. Consistent with the available literature,
the stratified sampling method was used in the present in which each business
unit or profession was considered as a stratum. Then, in proportion to the size
of each stratum, a number of units were selected randomly. In this study, 15
bakeries, including 3 Barbari, 4 Sangak, and 8 Lavash bread baking bakeries, 11restaurants
and kitchens, and 2 high-temperature industries including refractory brick
manufacturing and porcelain industries all of which are enclosed or indoor
high-temperature jobs, were examined. In total, 1450 individuals worked on the
investigated sites and were exposed to thermal stress. Since in this study
measurement of heat stress was conductedthrough public and environmental
method, personnel demographic characteristics, such as age and sex,were not
considered as intervening factors. The inclusion criterion for this study was
workingin an environment that included a heating process and the exclusion
criterion was unwillingness to participate in the study.All individuals and
managers were informed of the aims of the project and were assured of the
confidentialityof data. The WBGT index was used to measure heat stress.
WBGT-meter device
(Model MK427JY,Casella Company in Australia) was used to measure environmental
parameters such as dry temperature, wet temperature, and radiant temperature in
the 3 positions of the workers’ head (1.7 m), body (1.1 m), and ankle (0.1m),
respectively.Measurements were performed at 3 heights because the level of heat
stress varied at different heights, on average, more than 3 °C, especially in
bakeries.
Considering that
in indoor work environments, usually heat exchange takes place entirely during
45minutes, in all measurements, the thermometers were placed in the desired
site for 45 minutes and the final temperature was recorded. Using the NIOSH
equation (Equation 2), the mean value of this index was determined at
workplaces for each worker. The values of WBGT heat stress index and standard
threshold limit value (TLV) of heat stress were compared with respect to the
type of work, working time, and rest periods.
(Equation 1)
WhereTnw
is the natural wet-bulb temperature
andTg is the globe
thermometer temperature,
and temperatures may be in either Celsius or Fahrenheit.
Finally,
thermal stress was compared with the standard level (Table 1).
Table1: Occupational permissible exposure limit for heat
stress exposure based on wet-bulb globe temperature (WBGT) index (
Level of care (action) |
PEL |
Level of care (action) |
PEL |
Action limit |
PEL |
Action limit |
PEL |
Percentage (%) |
28 |
31 |
25 |
28 |
- |
- |
- |
- |
75-100 |
28.5 |
31 |
26 |
29 |
24 |
27.5 |
- |
- |
50-75 |
29.5 |
32 |
27 |
30 |
25.5 |
29 |
24.5 |
28 |
25-50 |
30 |
32.5 |
29 |
31.5 |
28 |
30.5 |
27 |
30 |
0-25 |
PEL: Permissible exposure limit
In the table 1,the
percentage column represents the percentage of working time that the individual
is exposed to thermal stress.
To estimate the
decline in production (performance loss) caused by heat stress, we drew on the
findings of Kjellstrom et al. in connection with the relationship between human
work capacity and increased WBGT. Kjellstrom et al., based on ISO standard and
NIOSH, designed a graph to demonstrate work efficiency decline in terms of
increased WBGT value(6). Using ISO standard and NIOSH, they drew a graph of
work capacity for non-adapted individuals as a function of WBGT index, which
represented work capacity in 4 different intensity levels (2).The relationship
between work capacity and WBGT with respect to 4 intensities was first proposed
by Kjellstrom et al. in 2009 (2) in accordance with international standards (8)
recommended by NIOSH, USA (10) (Figure1).
Figure1: The relationship between work capacity and wet-bulb globe
temperature(WBGT) with respect to four intensities
In the above
graph, the vertical axis represents the percentage of maximum physical
capacity. All the studied working groups in this research were working using
their arms and torso and carrying heavy objects.Thus, according to the standard
job categorization of ISO 7243 in terms of the average energy metabolism, the
metabolism production was estimated at about 414 watt, which is categorized as
a heavy job (4). For data analysis, descriptive statistics were used in SPSS
software (version 16; SPSS Inc., Chicago, IL, USA). In addition,
Kolmogorov-Smirnov test was adopted to test the normality of data and the one
sample t-test was used to compare the results with the standards.
Results
The results of
thermal stress measurement and performance loss in different types of bakeries
are shown in table 2 and figure 2.
Figure2.
Thermal stress and its consequent performance loss in bakeries
According to the
results of table 1, mean WBGT index in Barbari, Sangak and Lavash bakeries were
29.73, 27.89, and 29.43 °C, respectively. The results of thermal
stress measurement at the ankle, abdomen, and head showed that, in all 3 types
of bakeries under study, the maximum exposure to thermal stress was in the head
area. The thermal stress in Sangak bakery was found to be lower than Barabri
and Lavash bakeries.
Table
2: Results of heat stress evaluation in bakeries around the city of Gonabad,
Iran, in spring 2014 (℃)
Non-adapted individuals |
Performance loss (%) |
WBGTWhole body |
WBGT Head |
WBGT Waist |
WBGTFoot |
Dispersion index |
Sampling site |
|
Test statistics |
Significance level |
|||||||
11.41 |
< 0.001 |
65 |
29.73 ± 80 |
31.74 ± 1.70 |
29.73 ± 0.81 |
27.73 ± 0.97 |
Mean± SD |
Barbari bakery |
42 |
28.62 |
29.8 |
27.90 |
26.6 |
Minimum |
|||
73 |
30.67 |
34.1 |
30.90 |
28.9 |
Maximum |
|||
1.92 |
0.96 |
23 |
27.89 ± 2.78 |
27.78 ± 3.4 |
27.58 ± 2.66 |
26.8 ± 4.08 |
Mean ±SD |
Sangak bakery |
0 |
23.75 |
24.3 |
23.30 |
22 |
Minimum |
|||
88 |
31.18 |
32.9 |
30.90 |
34.9 |
Maximum |
|||
4.94 |
< 0.001 |
64 |
29.43 ± 2.77 |
32.27 ± 3.18 |
29.50 ± 3.40 |
26.45 ± 2.31 |
Mean |
Lavash bakery |
0 |
25.07 |
29.60 |
22.60 |
22.4 |
Minimum |
|||
98 |
33.55 |
38.50 |
35.50 |
31 |
Maximum |
WBGT: Wet-bulb globe temperature
Table3:Results
of thermal stress in kitchens, and refractory brick and
porcelain manufacturing
industries
Performance loss (%) |
WBGT whole
body |
WBGT head |
WBGT waist |
WBGT foot |
Central or
dispersion index |
Sampling
site |
89 |
32.04 ± 0.62 |
31.53 ±
1.09 |
32.23 ±
0.30 |
32.16
± 1.04 |
Mean ± SD |
Refractory
brick manufacturing industry |
33 |
30.67 |
30.5 |
30.5 |
31.2 |
Minimum |
|
90 |
32.92 |
32.4 |
33.1 |
33.1 |
Maximum |
|
92 |
32.35 ± 3.79 |
36.56 ± 4.83 |
32.66 ±
4.27 |
27.53 ±
1.80 |
Mean ± SD |
Porcelain
manufacturing industry |
58 |
28.63 |
31 |
29 |
25.52 |
Minimum |
|
100 |
35.69 |
39.7 |
37.1 |
28.88 |
Maximum |
|
80 |
31.88 ± 3.12 |
33.96 ±
3.55 |
31.90 ±
3.03 |
29.76 ±
2.89 |
Mean ± SD |
Kitchens |
0 |
25.30 |
26.3 |
25.30 |
24.30 |
Minimum |
|
100 |
37.47 |
40.1 |
37.70 |
34.40 |
Maximum |
According to the
results of table 2 and figure 2, performance loss caused by heat stress,whichwas
estimated using figure1, was 65%, 23%,
and 64% in Barbari, Sangak, and Lavash bakeries, respectively. The highest
performance loss was observed in Lavash bakery in which human performance could
reduce up to 98%. The results of thermal stress measurement and its consequent
performance loss in kitchens, and refractory brick and porcelain manufacturing
industries are shown in table 3.
According to the
results of table 2, the mean exposure to heat stress in porcelain and
refractory brick manufacturing industries was 32.04 and 32.35 °C, which may
lead to the loss of human performance as much as 89% and 92% , respectively.
Figure
3: Results of test statistics
measurement and level of significance with respect to wet-bulb globe
temperature (WBGT) in the studied professions
The mean WBGT
value in kitchens was 31.88, which can cause a performance loss of up to 80% in
humans. The results of the present study indicated high variation in WBGT in
kitchens, with a related performance loss of 0 to 100 in humans. The results of
test statistics measurement and level of significance with regard to WBGT are
shown in the figure 3. In the following figure, the vertical axis represents
test statistics and significant levels.
Discussion
In the present
study, mean exposure to heat stress in Barbari, Sangak, and Lavash bakeries was
compared with the standard values (11) (Table 1).The results showed that, with
the assumption that all tasks in bakeries are classified as heavy work with a
50% to 75% working capacity, all bakeries are exposed to excessive thermal
stress (27.5 ºC) and its related health effects. The study byHannani on
175 workers in 100 bakeries revealed that 61% of them were subject to thermal
stress (8). Their findings are consistent with the results of the present study.
In another study
by Mohammad Ali Qajar Kohestani in 2004, the heat stress index was investigated
in 70 randomly selected bakeries in the city of Sari, Iran (12). Their results
suggested that WBGT values significantly differed in various bakeries, which
were consistent with the results of the present study (12). In addition to the
health effects, bakery workers experience performance loss due to heat stress.
According to the results of table 1 and figure 2, 65%, 23%, and 64% performance
loss was observed in Barbari, Sangak, and Lavash bakeries, respectively, which
in some cases, can reduce human performance by around 98%.
The workers in the
refractory brick manufacturing industry are also exposed to excessive heat
stress and its consequent performance loss because the measured WBGT value in
this industry (32.04°C) can result in a performance loss of 82% in humans. The
work schedule of workers in the furnace unit of this industry is comprised of
75% working hours and 25% rest hours, and their job is classified as heavy in
terms of energy consumption.
In general, in the
two industries examined in this study, WBGT values were higher than the
permissible exposure limit (PEL), with their workers experiencing performance
loss as well as other complications associated with excessive thermal stress.
According to the results presented in table 3, the mean WBGT value in kitchens
was 31.88, which could lead to 80% loss of human performance. The results of
this study showed high variation range of WBGT in kitchens with a subsequent
performance loss of 0 to 10% in humans. Moreover, the results of this study
suggested that workers engaged in indoor high-temperature professions such as
bakeries, kitchens, and furnace units of various industries in the city of
Gonabad were exposed to heat stress.
In addition to
external heat, physical activities can also generate heat in the human body,
with a subsequent increase in body temperature, which can affect the health and
productivity of humans (5).
Reduced efficiency
of physical and mental activities resulting from thermal stress has been proven
(13). It is generally observed that with an abnormal increase in dehydration
and a 10% decline in body water, body functions are increasingly reduced (14). The
study by Kjellstrom et al. showed that in countries with warmer seasons,
increase in the workers’ internal body temperature due to heat exposure was
greater than the capacity of their physiological mechanism (15).
According to the
results of the studyby Kjellstrom et al. in 2009, work capacity is reduced
significantly with the increase of WBGT from 26 to 30 °C (15). The findings of
another study suggest that in the absence of any specific compliance strategy, most countries in Southeast Asia, Central America, and
the Caribbean will face a production decline of 10% to 27% (6).Based on the
conceptual distribution graph of human productivity versus WBGT values based on
ISO 7243 standard (16), in WBGT of higher than 25 °C, the human work capacity
begins to drop.Moreover, in WBGT of over 40 °C, the performance of physical
actions will be extremely difficult for all individuals (17).
Performance loss
caused by heat stress can also decrease gross domestic product (GDP) from 0.1%
to 0.5% (9). Studies have shown that at a temperature slightly above
comfortable temperature (slightly higher than 20°C), the human performance
begins to drop from 3% to 50%.Furthermore, in temperatures above comfort level
(35 to 37 °C), this reduction can be as high as 75% (9). For example, office
workers reach their maximum work capacity at a temperature of 23 °C, while
their productivity is reduced up to 70% at a temperature of 30 °C (9). A study
by the Ministry of Labor and Social Affairs of France showed that heat stress
exposure among French workers was 16.6% (18).
In the present study, the results of thermal
stress evaluation among workers of high-temperature industries of Gonabad
indicated that furnace workers in the studied industries were exposed to
thermal stress. Husseini, in his study on a tile manufacturing company based on
WBGT index, concluded that thermal stress in the dryer department was greater
than the PEL, though it was at normal level in other parts of the factory (4).
This finding is consistent with the results of the present study. In addition,
the results of another study by Srivastava on a glass industry in India showed
that heat stress exposure of workers was greater than the recommended levels
specified in the American Conference of Governmental Industrial Hygienists
(ACGIH) standard (19). Additionally, the tight protective clothing used for
pesticides may increase the risk of heat stress. Moreover, heavy physical work
can also be a cause of thermal threat among construction workers as it can lead
to an increase in work-related accidents. Accordingly, further serious problems
should be prevented with the adoption of professional health control measures,
including training and the application of personal protective equipment and air
conditioning systems.The present study had some limitations.One limitation was
that this study was conducted in the spring and due to seasonal temperature
changes, the results of this study cannot be generalized to other seasons.Moreover,some business executives were not willing to cooperate
with the project managers.
Conclusion
Most indoor
high-temperature professions in the city of Gonabad entail exposure to thermal
stress and its related complications and performance loss.Thus, it is necessary
to take appropriate controlling and organizing measures to protect the workers
subject to heat stress. As such, the following controlling measures are
recommended:
1. Developing
specific rules and guidelines for working in high-temperature workplaces and
monitoring the implementation of such regulations
2. Organizing
training programs about prevention and control of heat-related complications
for workers and employers
3. Obligating all
workers to pass heat adaptability courses before starting their work so as to
prevent the effects of heat stress
4. Adopting
engineering control measures as one of the most effective ways to manage heat
stress
It should be
notedthat it was not possible to separate adapted and non-adapted individuals
in this study.Therefore, this study was carried out assuming that workers were
not adapted to thermal conditions.Nevertheless, in the real situations, most
workers are adapted to their workplace conditions, and thus, their performance
loss will be less than the values reported in this study.
As a result,
further studies are required to investigate performance loss among heat-adapted
workers.
Acknowledgments
This study was
approved as research project No. 44/92 at Gonabad University of Medical
Sciences. The authors express their gratitude and appreciation to the Research
Deputy of Gonabad University of Medical Sciences.
Conflict of interest: None
declared.
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* Corresponding author: Fatemeh Mehrafshan, Dept. of Occupational Health, Faculty
of Health, Gonabad University of Medical Sciences, Gonabad, Iran.
Email: fatemehmehrafshan@yahoo.com