2007, Piran, Slovenia

Occupational Thermal Problems
some indoor furnace workplaces which have extremely high heat stress conditions, the
WBGT of which is 40 50°C, where the workers were repeatedly performing their jobs for
short time. Again, although the reference value of the ISO is based on the premise of light
summer clothing, the workers were required to wear heavy clothing such as long-sleeved
clothes, long trousers, safety gloves and boots, helmet for ensuring their safety, without
regard to the prevention of heat stress. Moreover, the outdoor construction workers were also
carrying tools weighing around 5kg, while the indoor furnace workers were wearing
additional radiant heat protective clothing during their work. In reality therefore, their
clothing conditions differ greatly from the kind of light-duty summer garments specified by
the ISO, which suggests that the current reference values of the ISO seriously underestimate
the propensity for heat stress to which workers are actually exposed. Thus, most of the
workers investigated were exposed to severe heat stress due to both the physical environment
and the clothing they were required to wear. Nevertheless, the body core temperature (oral
temperature) of almost all the workers was below 38°C, which suggests that their
thermoregulatory function is well adapted to hot work. On the other hand, many workers
experienced body weight loss (some exceeding 3 %) during work, which suggests that they do
not rehydrate sufficiently as a compensation for excessive body water loss due to heavy
sweating. Furthermore, there were also some workers whose heart rate during work exceeded
the permissible level proposed by the ACGIH (2006): (180-age) bpm for all workplaces.
Regarding subjective heat strain, most of the workers felt uncomfortably hot during work,
which suggests that these hot workplaces are never physically comfortable. In outdoor
construction work, relatively higher number of workers experienced subjective symptoms for
heat-related disorders.
Future needs: Since the present study was carried out between mid-summer and late summer,
the workers investigated are considered to be a predominately heat-acclimated population.
That may be one of the main reasons why almost all workers were well adapted in terms of
body temperature regulation, despite the facts that (i) the environmental heat stress in every
workplace exceeded the ISO heat exposure limit reference values and that (ii) the workers had
an additional heat load due to the requirement to wear heavy protective clothing and
equipment for safety reasons. If the field survey were to have been carried out during early
summer in July, different findings might have been obtained. Many cases of occupational heat
disorders generally occur between early summer and mid-summer in recent years. In order to
know more about heat strain among workers and the true risks of heat disorders for a given
heat stress, we will need to carry out similar field surveys in early summer, when sudden hot
climate change threatens Japan, and workers are less well-adapted to heat stress.
In addition, we also need to revise the current ISO reference values for heat exposure limits,
which presumes the wearing of light summer clothing. As reported in the present study,
workers were required to wear heavy clothing such as long-sleeved shirts, long trousers,
safety gloves, boots, helmets, and to carry tools weighing around 5kg. Some workers are
additionally required to wear additional radiant heat protective clothing. The current reference
value of the ISO, therefore, appears to underestimate the heat stress to which workers are
actually exposed. Furthermore, it is essential to develop a quicker and more reliable method
for monitoring body core temperature during work. This would enable us to assess a net heat
strain and risk of heat disorders resulting from internal and external heat loads regardless of
environmental heat stress and clothing conditions.
CONCLUSION
585