Network Construction × Wearable Heat CountermeasuresNTT Device Technology Laboratories
    Research Planning Department

    Network Construction × Wearable Heat Countermeasures

    • heat countermeasures
    • wearable sensors
    • health management

    One of NTT’s key roles in the 2021 international sporting event held in Japan was the construction of a large-scale network during the hot and humid Tokyo summer to provide a stable and secure communication environment. We built and installed a health-management system that involves wearable biological/environmental sensors to prevent heat-related health issues and enable construction work to be carried out more safely.

    Kazuhiko Takagahara†1/Hiroyoshi Togo†1
    Naomi Nagai†2
    NTT Device Technology Laboratories†1
    Research Planning Department†2

    Background and objectives

    The numbers of deaths and emergency room visits caused by heat stroke have been increasing due to climate change and other factors, and this has become a major issue for society in general. According to a survey by the Fire and Disaster Management Agency of the Ministry of Internal Affairs and Communications of Japan, 46,299 people required emergency hospital treatment for heat stroke between June 1 and October 3, 2021, and according to the Ministry of Health, Labour and Welfare of Japan, there were 829 cases of heat stroke at the workplace in 2020 resulting in an absence of four days or more, of which 22 cases resulted in fatalities. The Ministry of Health, Labour and Welfare and other organizations published guidelines and manuals on how to prevent heat stroke in the workplace.
    At NTT, we developed a method for implementing heat-related health issue prevention measures for individual workers by estimating health risks on the basis of vital-sign data and issuing alerts when necessary. To verify the effectiveness of this method, we conducted a demonstration experiment with the cooperation of NTT EAST. We monitored 49 construction workers in the Tokyo, Kanagawa, and Hokkaido areas for a total of 834 person-days in August and September 2020. We asked the construction workers to fill out questionnaires about how hot or cool they felt while working, and we were able to confirm the relationship between their estimated internal-body-temperature fluctuations and whether they felt hot or cool.

    Method for estimating health risks and issuing alerts

    Our method estimates the risk of heat-related health issues by means of logic for estimating changes in internal body temperature,*1 which was created in a new joint research project with Nagoya Institute of Technology (NIT). This logic is based on an original program developed by NIT that combines electromagnetic field analysis and thermal analysis by taking into account factors such as a person’s internal-body-temperature regulation, clothing, and level of activity. In a joint experiment among NTT, Yokohama National University, Shigakkan University, and NIT, we conducted clinical experiments in the artificial weather room at Shigakkan University that confirmed the applicability of the logic for estimating internal-body-temperature fluctuations.*2 On the basis of the theory of thermal and exercise physiology, we also created criteria for using internal-body-temperature fluctuations and other factors to trigger alerts (Fig. 1). Together, the estimation logic and alert criteria constitute our method for estimating health risks.

    1. *1Since the method described here is not a medical procedure, the expression ”internal body temperature” is used instead of ”core temperature.”
    2. *2Shigakkan University Research Ethics Review Committee: Accession number 124.
    Fig. 1. Flow of our health-risk estimation method.

    Wearable biological/environmental sensors

    Wearable biological/environmental sensors*3 are used to acquire an individual’s heart rate, temperature inside clothing, and humidity. In addition to a TX02 transmitter marketed by NTT TechnoCross based on wearable biological/environmental sensors developed by NTT Device Innovation Center, we use either a piece of C3fit IN-pulse clothing made by GOLDWIN Inc. or a hitoe™ shirt or belt developed by Toray Industries, Inc. [1] (Fig. 2) to monitor various parameters including the wearer’s heart rate, R-R interval, step count, and upper-body tilt.

    1. *3This sensor is not a medical device. hitoe™ is a functional fabric developed by Toray Industries, Inc. and NTT to collect biomedical signals, which are weak electrical signals emitted from the body, with little burden on the wearer. The functional fabric hitoe™ is a trademark of both companies.
    Fig. 2. Wearable biological/environmental sensors.

    Operation support for the 2021 international sporting event

    By applying this method to construction work at venues used for the international sporting event in 2021, we were able to prevent heat-related health issues among construction workers, enabling the event to be held safely and securely. From May 24 to September 30, 2021, the health-management system applying this method was used by a total of twelve construction workers at two sites [2]. In addition to remotely monitoring health risks, the system also issued appropriate alerts to the construction workers and their site managers based on the above-mentioned alert criteria. A total of ten alerts were issued during this period. In each case, the site manager was able to check the physical condition of the affected construction worker and take measures such as encouraging them to take a break if necessary. As a result, we were able to prevent the occurrence of health issues, such as heat stroke, among the construction workers.


    At NTT, we will continue to deepen our knowledge by introducing this method to more sites with the aim of ensuring that large-scale events around the world can be held safely and securely.


    1. [1]K. Takagahara, Y. Hashimoto, K. Matsunaga, Y. Higuchi, N. Matsuura, K. Kuwabara, H. Togo, T. Kawahara, A. Hirata, H. Tanaka, and T. Miyazawa, ”Physical-condition Management Technology for Creating More Comfortable Work Sites,” NTT Technical Review, Vol. 19, No. 6, pp. 48-54, 2021.
    2. [2]Press release issued by NTT TechnoCross, June 15, 2021 (in Japanese).
    Kazuhiko Takagahara, Hiroyoshi Togo, and Naomi Nagai

    Kazuhiko Takagahara, Hiroyoshi Togo, and Naomi Nagai

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