Introduction In Japan, the prevention of fatal heat strokes at work has become more important along with the global warming.

Methods This research introduces the transition of methods to prevent heat stroke at workplaces in Japan within the latest 20 years.

Results The number of fatal heat stroke at work in Japan had been less than 20 until 1993; however, it exceeded 20 in 1994 and in 1995, consecutively because of the heat wave attack during summer. Therefore, in 1996, the guideline on prevention of heat stroke at work was formulated and publicised by the Labour Standard Bureau, Ministry of Health, Labour and Welfare. It advocated fundamental methods for the prevention of heat stroke such as working environment management, work management, health management and occupational health education at workplaces exposed to heat stress. Besides, the government started to announce the number of compensated cases of heat strokes every year. In 2005, another guideline was issued advocating the measurement of WBGT at the workplaces and the utilisation of the value for appropriate countermeasures. In 2009, the first guideline was totally revised by adding many new contents: the utilisation of WBGT, the promotion of heat acclimation, the method of desirable water and salt intake, the consideration for vulnerable persons with underlying diseases and the management of daily physical conditions. In addition, due to the impact of the Great East Japan Earthquake in 2011, nuclear power generation in Japan was temporarily suspended, and the need for the development of measures against heat stroke that did not use electric power as much as possible had increased, from the viewpoint of energy saving. Therefore, sports drinks and oral rehydration, salt candy, cool best to cool the body, clothing of quick-drying/cool feeling materials, etc. have started to be sold and widely spread.

Discussion Although the motivation for the prevention of heat strokes have spread rapidly during the last 20 years, according to the guidelines formulated by the government, the number of mortality often exceeds 20, including 47 in the historically worst year of 2010. While easy and inexpensive devices to prevent heat stroke such as nutritional supplements and special wears have become widespread, it is important to verify its effectiveness in an objective manner and to standardise the definition of devices able to cool down the body heat.