2007, Piran, Slovenia

Occupational Thermal Problems
HEAT STRESS AND STRAIN AT WORK IN HOT ENVIRONMENTS:
RECENT FINDINGS ON JAPANESE WORKERS
Shin-ichi Sawada 1 , Tatsuo Oka 1 , Hideki Fukuda 1 , Satoru Ueno 1 , Seichi Horie 2 , Ronaldo
Kenzou Fujii 2
1
National Institute of Occupational Safety and Health, Kawasaki, Japan
2
University of Occupational and Environmental Health, Kitakyushu, Japan
Contact person: sawada@h.jniosh.go.jp
INTRODUCTION
In Japan, industrial accidents due to occupational heat disorders have recently occurred in
many outdoor workplaces such as civil engineering and construction work during the summer
seasons. According to official data from the Japanese Ministry of Health, Labour and
Welfare, between the years 2001-03, ~500 workers were absent from work for more than 4
days, with more than 60 documented deaths due to heat disorders. Thus, the prevention of
occupational heat disorders has become an urgent occupational health issue in Japanese
society.
So far, several permissible levels for heat stress exposure have been proposed domestically
(Japan Society for Occupational Health, 2006) and internationally (American Conference of
Governmental Industrial Hygienists (ACGIH, 2006) and International Standard Organization
(ISO7243, 2003)) to help prevent heat disorders at work. All of these heat exposure limits are
based on WBGT (Wet Bulb Globe Temperature) measurements, mainly because WBGT is a
simple, practical and relatively reliable index for comprehensively assessing heat stress
resulting from air temperature, humidity, air movement and heat radiation measurements in
hot environments. Nevertheless, the application of WBGT is not popular in many hot
workplaces in Japan. As a result, little information is available on how much Japanese hot
workers are exposed to heat stress in relation to WBGT. This study reports the current
situation of heat exposure and the resultant heat strain among workers of outdoor and indoor
workplaces in summer. Based on the findings, the future issue to prevent occupational heat
stress will be discussed.
METHODS
Several field surveys were carried out in Japan between August and September, 2005, during
which time five different hot workplaces outdoors and indoors were investigated. The outdoor
workplaces consisted of a high-rise apartment construction site, a school building construction
site, and telephone wire connection work (linesmen); whereas the indoor workplaces a small
metal processing factory and a large steel foundry. A total of 60 presumably heat-acclimatized
workers (aged 21-67 y) from the above workplaces participated. For assessing environmental
heat stress during work, dry-bulb, wet-bulb and globe temperatures, relative humidity and air
velocity were measured every one minute and WBGT index was calculated. WBGT less than
28°C were adopted as a permissible level of heat stress according to the ISO reference values
because the metabolic rate of the workers was estimated moderate and the workers
themselves were presumed to be heat-acclimated (ISO7243, 2003). Oral temperature
immediately after each work shift, heart rate during work and body weight loss between prework
and post-work were measured as indices of physiological strains, together with thermal
discomfort and hot sensation as indices of subjective heat strain. Symptoms of heat disorders
(dizziness, nausea, headache, tinnitus, fatigue, sluggishness, lameness, myalgia, comvulsion,
sensory abnormality of limb etc.) were also checked after work. For assessing the
physiological heat strain, oral temperature below 38.5°C, heart rate below (180-age) bpm and
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