Heat stress

Hot weather in the UK is becoming more common, and while it may not always reach extreme global temperatures, it can still pose serious risks for workers.

Thankfully, the very hot temperatures of last week have been replaced with more comfortable conditions, but the heat is forecast to return to the high 20s next week.

Many workplaces are not designed for sustained heat so it’s essential that we understand how key factors - humidity, worker clothing, and level of activity can affect safety.

In the UK, high temperatures are often accompanied by moderate to high humidity, which can make conditions feel far hotter than the actual air temperature. Even a day in the high 20s°C can place significant strain on workers, particularly those in physically demanding roles or enclosed environments.

Humidity plays a major role in how the body copes with heat. The body cools itself by sweating, but when the air is humid, sweat evaporates more slowly therefore cooling becomes less effective.  Workers feel hotter and become fatigued tire more quickly.

This means that a warm, humid day in the UK can be more uncomfortable, and potentially more dangerous, than a hotter but drier climate.

Balancing Protection and Heat

Clothing has a direct impact on how well the body can regulate temperature. In many industries, protective clothing is essential, but it can increase heat stress.

Heavy clothing or PPE can trap heat and restrict airflow.

Multiple layers increase heat buildup and discomfort.

Lightweight, breathable fabrics help sweat evaporate and improve cooling.

Employers should consider alternatives where possible and ensure workers are given extra breaks where use of PPE is required.

The harder someone works, the more heat their body produces!

High activity e.g. lifting, manual labour, creates significant internal heat.

Low activity e.g. desk-based work generates much less heat.

During hot weather, physically demanding work can quickly lead to overheating, especially when combined with humidity and restrictive clothing.

Staying Safe in Hot Conditions

To reduce risk during hot spells, workers may need to take regular breaks in cooler or shaded areas and drink water more frequently.  Workloads may require adjustment to the pace of work e.g. heavy work undertaken during the morning when it's cooler.  Workers should wear suitable clothing where possible (including PPE). 

A toolbox talk  can alert workers to signs of heat exhaustion e.g. heavy sweating, pale and clammy skin, intense thirst, dizziness, and a rapid pulse and what to do if they or a colleague are suffering.

Working in hot weather in the UK requires more than just checking the temperature. Humidity, clothing, and activity levels all combine to influence how the body handles heat.

By recognising these factors and adapting working practices, both employers and workers can stay safe and productive during warmer periods.