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Technology Factsheet

Heat Stress Monitoring System

Category: Worker Health & Safety > Personal Protective Equipment > Heat & Cold Protection
Reference # : OST No 1953 , DOE/EM-0391 Model No : HSMS

The heat stress monitoring system (HSMS) is a series of probes, a monitor, and a PC that measures vital signs of D&D workers while they are performing work activities. From the supervisory station, as many as ten workers can be monitored simultaneously. The real-time data can be used to instantaneously detect potential problems and adjust work activities accordingly to protect worker safety and ensure optimal productivity.The HSMS consists of a small plastic case to enclose the electronics and wireless radio components; a laptop computer and software; a rechargeable battery supply; and a series of temperature, heart rate, and body activity probes, which are worn by the worker (Figure 1). Body temperature is sensed in the ear. Skin temperature is sensed with a taped-on probe. Heart rate is monitored with a chest band. Motion is sensed with a mercury switch in the transceiver. The wearable monitor weighs less than 0.5 kg (1 lb.) and is 15.5 cm by 9 cm, with a thickness of 3.5 to 4.5 cm. Dimensions of Tech Model In this demonstration, the unit was able to directly monitor up to four channels (heart rate, body activity, and skin and ear canal temperature data). Each monitoring channel on this system can be preset to trigger an alarm set point. The unit has been designed so that, in the future, it can accommodate additional channels for either more physiological signals or for monitoring external sensors such as radiation, toxic chemicals, or noise. As many as ten workers can be monitored in series by a single supervisory station. The data from an individual worker are transmitted in 3 seconds. With ten workers, every 30 seconds the information from one individual is automatically updated and recorded by the computer in a sequential fashion. If incipient heat stress or high heart rate is detected, the system will automatically activate the light-emitting diode warning device mounted near the worker’s eyes per the set parameters. Alternatively, the worker manning the supervisory station can manually alarm a person. After receiving the warning, the worker can withdraw from the work area and consult with the supervisor. If communication is lost, is out of range, or if there is transmission interference, the diode alerts the worker. Another key innovation of this monitoring system is its wireless capability. Utilizing spread spectrum technology, signals can be transmitted over 300 m (1,000 ft). The power is 1 watt, with a frequency range from 902 to 928 megahertz (MHz). The system automatically selects the frequency that provides the clearest transmission of signals. Unauthorized persons cannot readily decode the data being transmitted. The system meets the requirements of FCC Part 15 and requires no licensing.


The VitalSense provides real-time physiological monitoring and logs the data automatically in the computer database for future use, thus preventing a potential heat stress situation. The ability to set a preset alarm levels for each of the four real time monitoring channels is another important feature. As a data base is established for an individual employee, alarm setpoints may be set either lower or higher depending on one’s physical condition and abilities. Accurate alarm setpoints are crucial in utilizing the VitalSense to its greatest capacity for protection of human health.


The transmission signal has some limitations, and the base station location should be tested when being used in areas with thick concrete or steel obstructions. (The range can be readily improved by using either a taller antenna or moving the antenna closer to the monitors with a coaxial cable connection to the base station.) Except for the carrying pouch, the demonstration at the C Reactor indicated no need to modify features of the system.




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