Heat Stress & Outdoor Work

When people work or exert themselves in the heat, their bodies can gain heat faster than they can shed it, leading to heat exhaustion, heat stroke, and, in the worst cases, death. The risk depends not on air temperature alone but on the combination of heat, humidity, radiant load from the sun, and air movement, together with the intensity of the work and what the person is wearing. Employers, sports bodies, the military, and event organizers all have a duty to manage that risk, and doing so means measuring the actual thermal environment rather than guessing from a thermometer. Heat-stress monitoring provides the objective basis for work-rest cycles, hydration schedules, activity limits, and the decision to stop.

As hot spells become more frequent and severe, this shift from ad hoc judgment to measured heat-stress assessment is increasingly built into occupational and sports safety practice.

The central metric is wet-bulb globe temperature (WBGT), the index that combines air temperature, humidity, radiant heat, and air movement into a single figure and is assessed against the ACGIH heat-stress TLV and similar occupational guidance to set safe work-rest limits. Behind it sit the parameters WBGT is built from: air (dry-bulb) temperature, humidity, wet-bulb temperature (reflecting evaporative cooling), and the radiant load from a black-globe measurement. Heat index offers a familiar shade-based figure combining temperature and humidity for general awareness. Measuring these together captures why a moderate air temperature can still be dangerous in strong sun, high humidity, or still air.

Heat-stress monitoring uses a Thiamis gateway connected to a WBGT sensor set (the dry-bulb, natural wet-bulb, and black-globe measurements that combine into the index), sited where the work or activity actually happens, in the sun and conditions the people experience. The logger records continuously and computes WBGT and heat index, driving alerts as the index approaches the threshold for the current workload so that work-rest cycles or a stoppage can be applied in time. Because radiant load is part of the index, a shaded reading is not enough: the black globe must sit in the same exposure as the workers. One station represents a work area with a consistent environment. The recommended configuration below builds a WBGT heat-stress station. Use the configurator to add parameters or extra locations for your site.