Ergonomics of the Thermal Environment: Evaluation of Heat Stress Using the WBGT Index

Ergonomics of the Thermal Environment-Assessment of Heat Stress Using the WBGT (Wet Bulb Global Temperature) Index

What is the WBGT Index?

The WBGT is a parameter used to assess heat stress and is calculated by combining the following three factors

1. Natural Global Temperature (Globe Temperature): Measures radiant heat from the sun and environmental surfaces.
2. Wet Bulb Temperature: Measures the rate of evaporation of moisture in the air.
3. Dry Bulb Temperature: Represents the general air temperature of the environment.

Formula:

• For enclosed spaces: WBGT = 0.7 × WBT + 0.3 × GT
• For open areas: WBGT = 0.7 × WBT + 0.2 × GT + 0.1 × DBT

These calculations provide basic information to assess the thermal load of the environment.

Wet bulb globe temperature (WBGT) is one of the measurements defined as an index if the experiment shows the heat pressure to which the person is exposed, and is one of the measurements carried out by İSGÜM-approved Environmental Laboratories within the scope of Occupational Hygiene - Thermal Comfort Measurements.

In the construction of Occupational Hygiene Thermal Comfort Measurements, PMW, PPD and WBGT values are determined and evaluated within the scope of the standards determined by İSGÜM. Within the scope of TS EN ISO 7730 standard, after PMV (Predicted Average Vote) and PPD (Personal Dissatisfaction Percentage) are determined, the comfort level is estimated with a 7-point scale.

The desired result after Thermal Comfort Measurements is between -2 and +2. If the value obtained is above +2, the “Wet chamber globe temperature (WBGT)” value is tried to be determined based on the ISO 7243 standard.

With the determination of the wet bulb globe temperature (WBGT) value, it is aimed to evaluate the heat stress in work environments. In general, PMW, PPD and WBGT measurements are performed to determine the degree of exposure of employees to heat and cold.

Why is Heat Stress Important?

Excessive heat exposure can affect workers' physical and mental performance and lead to health problems. Heat stress is associated with the following negative effects:

• Heat exhaustion: Fatigue, dizziness and muscle cramps.
• Heat stroke: Life-threatening temperature rise and loss of consciousness.
• Loss of productivity: Slowdown in the work process and increase in error rate.

Ergonomic assessment of the thermal environment is critical to prevent these problems and ensure occupational safety standards.

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