What does science say about working in hot weather?

Above a certain amount, high temperatures can lead to heat stress*. Heat stress is caused by overheating of the body and manifests as various physical and mental complaints, such as headaches, cramps, dizziness or aggression. In very severe cases, heat stress can even result in death. Moreover, for people who suffer from heat stress during work, the risk of work accidents is also higher.

Some workers are more susceptible to heat stress due to the nature and conditions of their work. Research points to five factors that increase the risk:

• physical and health characteristics
• performing physical labor
• the work environment
• the work schedule,
• protective clothing that has low ventilation (Horie 2013; Morabito et al. 2021).

Warm temperatures additionally impact the physical and mental capabilities of workers. This affects not only occupational safety, but also productivity. Research shows that 30% of the employees who experience heat stress during a shift, experience productivity loss, and that this loss increases gradually for every degree increase above 24°C WBGT*(Borg et al. 2021; Flouris et al. 2018). Research estimates that the global economic cost of this productivity loss is greater than that of all other disruptions caused by climate change (Morabito et al. 2021).

Good news is that negative effects of hot weather can be prevented with proper heat safety measures. However, the successful implementation of these measures assumes that employees are adequately informed, sensitized and trained (Morrissey et al. 2021).

In Belgium, employees are entitled to protective measures when the maximum temperature is exceeded: the employer must provide protective equipment (e.g., headgear), provide free refreshments, and install a ventilation system within 48 hours. In case of persistent nuisance, employers have to allow rest periods or a decision can be made to introduce temporary unemployment (FPS Employment Labor and Social Dialogue).

Additional, preventive protective measures can also be taken. Some examples:

• a heat plan at the organizational level
• follow up on weather forecasts and heat warnings
• optimize work schedules (shorter working hours, frequent breaks, starting earlier)
• identify vulnerable employees, such as pregnant women or the chronically ill
• inform employees about the risks of heat and how to protect themselves
• Inform employees of the symptoms of heat stress and how to intervene when they or their colleagues become unwell

*WBGT or Wet Bulb Globe Temperature is a measure of heat stress in direct sunlight that takes into account temperature, humidity, wind speed, sun position and cloud cover.

• Borg, Matthew A. et al. 2021. “Occupational Heat Stress and Economic Burden: A Review of Global Evidence.” Environmental Research 195(January): 110781.
• Flouris, Andreas D. et al. 2018. “Workers’ Health and Productivity under Occupational Heat Strain: A Systematic Review and Meta-Analysis.” The Lancet Planetary Health 2(12): e521–31.
• FOD Werkgelegenheid Arbeid en Sociaal overleg. “Rechten van Werknemers Bij Warm Weer.” https://werk.belgie.be/nl/them...
• Horie, Seichi. 2013. “Prevention of Heat Stress Disorders in the Workplace.” Japan Medical Association Journal 56(3): 186–92.
• Morabito, Marco et al. 2021. “Heat-Related Productivity Loss: Benefits Derived by Working in the Shade or Work-Time Shifting.” International Journal of Productivity and Performance Management 70(3): 507–25.
• Morrissey, Margaret C. et al. 2021. “Heat Safety in the Workplace: Modified Delphi Consensus to Establish Strategies and Resources to Protect
  the US Workers.” GeoHealth 5(8): 1–32.
• WHO. 2022. “Climate Change Is Increasing the Risk of Heatwaves: Preparing for a Warm and Dry Summer in the European Region.”