Heat Stress Monitoring
A warmer climate puts workers, particularly those performing manual work outdoors, at an increased risk of heat stress. Based on Singapore Workplace Safety and Health (WSH) Act and the latest framework to assess and protect workforce against the risks of heat stress, all workplaces are to assess if the work can be carried out safely, including implementing an effective heat stress management programme.
Wet Bulb Globe Temperature (WBGT) index is a simple and actionable heat stress index. Comprising of 3 measurements of dry bulb temperature, wet bulb temperature and globe temperature, WBGT accounts for the effects of air temperature, relative humidity, radiation and wind on human exposure to heat.
The design for WBGT monitoring instruments was established by ISO 7243:2017 Ergonomics of the thermal environment — Assessment of heat stress using the WBGT (wet bulb globe temperature) index. ISO7243 required that wet bulb temperature to be directly measured whenever possible, as indirect calculation of wet bulb temperature in outdoor environment is neither simple nor reliable.
Outdoor Heat
Stress System
APAQ Group offers turnkey solution for outdoor heat stress monitoring with reference WBGT sensors designed as per ISO7243 requirements, for most reliable, continuous unattended monitoring in outdoor environment. The system can be deployed at a fixed location with a pole mast, or with a tripod and tie-ropes. It can also be fully solar-powered to run off-grid.
The system is equipped with a data logger to measure real-time WBGT readings, and compute WBGT index on a rolling hourly basis to assess continuous workplace exposure to heat. Alarm function can be integrated with a strobe/siren unit, or with remote communication and Telegram/SMS messages. APAQ Group has also designed an Outdoor Heat Stress Viewer dashboard with data hosting services, to offer more flexibility in data viewing, downloading and to provide more tailored health advisory information such as WBGT-effective with clothing adjustment factor, and work-rest ratio for different work activities.
At request, this system can be extended with optional sensors to also measure wind speed/direction, solar irradiance, and to compute other indices such as Universal Thermal Climate Index (UTCI) for heat research.
ISO7243 reference
WBGT sensors
APAQ Group offers reference WBGT sensors with direct output signals, or integrated with industrial protocols such as MODBUS for convenient interfacing with industrial PLCs or IOT data acquisition systems.
- Wet bulb temperature sensor is a cotton wick-covered sensor immersed in distilled water, and shaded from direct sunlight. The sensor design comes with a large water holder that is able to last a few months in the field without drying up, thus maximising reliability of unattended operation.
- Globe temperature sensor is designed with a 150cm diameter copper sphere with black paint of 0.95 emissivity coefficient, to be most responsive to change in radiation.
- Air temperature sensor is shaded with a radiant screen and naturally ventilated to be sensitive to air temperature change. The sensor performance conforms to World Meteorological Organisation (WMO) standards.
Users of the reference WBGT sensors include Meteorological Service Singapore (MSS), Ministry of Defence (MINDEF) and leading chemical industry companies.
Portable WBGT system - Heat Shield
Heat Shield is a potable, cost-effective monitoring system for WBGT index for industrial hygienists and workplace safety auditors. It is designed with below sensors:
- Air temperature and relative humidity sensor
- Real wet bulb temperature measurement using a small water holder to last several hours to a day
- Choice of small 50cm globe temperature sensor and large 150cm globe temperature sensor
- Optionally, hot wire anemometer or wind cup sensor for measurement of indoor thermal comfort and PMV/PPD indices
Heat Shield can be configured with a master unit and 2 satellite units with radio transmission for simultaneous monitoring at different heights, or different locations in the controlled environment.