Heat is the greatest climate risk in the workplace, and it is getting worse. 95% of all climate-related deaths in Europe are associated with heat waves — not floods, not storms, but heat. Employees performing physically demanding work in hot conditions are among the most vulnerable groups. Yet heat stress in the workplace remains underestimated in many companies.

60% of Europe experienced in 2024 more days than average with at least strong heat stress.

ESOTC 2024, Copernicus/WMO via meteo.be

The trend is clear: summers are getting hotter, heat waves more frequent and workplace risks greater. As an employer, you are legally required to manage thermal risks.

In this article we explain what heat stress is, how to recognise it, what the legislation requires and which PPE solutions truly work.

Sources: Copernicus/WMO – European State of the Climate 2024 via meteo.be | VMM – Heat victims indicator via vmm.vlaanderen.be | EEA – Heat and Health via climate-adapt.eea.europa.eu

In this article

1. What is heat stress and when does it occur?
2. Consequences and impact in the workplace
3. Legislation: Belgium & the Netherlands
4. Organisational and technical measures
5. PPE solutions

1. What is heat stress and when does it occur?

Heat stress is the physical strain that occurs when the body can no longer adequately dissipate its excess heat. The core temperature rises, sometimes to dangerous levels. From a body temperature of 38°C, the first symptoms appear: fatigue, dizziness and loss of concentration. If the temperature rises above 40°C, we are dealing with a life-threatening medical emergency.

Causes: more than just the sun

The most obvious causes are environmental factors:

• High outdoor temperatures
• Direct sun exposure
• High humidity
• Poor ventilation

But heat stress is rarely the result of a single factor. Personal characteristics such as age, physical condition, medication use and hydration status play an equally important role.

In the workplace, occupational factors are added: physically demanding work, high work pressure and long working hours significantly increase the body's heat production. The choice of PPE is also decisive. Thick or poorly breathable clothing, multiple layers of clothing and airtight protective suits hinder heat dissipation and accelerate overheating.

Important: heat stress is not a seasonal problem. In many sectors, employees work year-round in warm indoor environments, for example near blast furnaces, ovens, melting installations or other industrial heat sources.

2. Consequences of heat stress and impact on the workplace

High temperatures are more than a matter of comfort. Anyone working in hot conditions – on a construction site, in a warehouse, a factory or outdoors in the field – is exposed to risks that systematically undermine the body.

Physiological consequences

The human body is designed to keep the core temperature stable around 37°C. It uses two mechanisms for this:

• Thermogenesis: This is the process by which your body produces heat to maintain its temperature. This happens automatically through your metabolism (your body functions and uses energy) and through muscle activity (e.g. exercise).
• Thermolysis: This is the process by which your body dissipates excess heat to prevent overheating. This occurs through the release of heat into the environment, contact with cooler surfaces and, of course, sweating, whereby evaporation provides cooling.

At ambient temperatures above 35°C, evaporation through sweat is the only effective mechanism for dissipating heat, but in humid environments this works much less well.

When the body sweats heavily to cool itself, it loses significant amounts of fluid and electrolytes – leading to headaches, nausea, muscle cramps and measurable cognitive decline.

The heart works harder (increased heart rate) to dissipate heat and improve blood circulation, which can become directly dangerous for employees with cardiovascular disease.

Skin irritation and heat rash are further signs that the body is reaching its limits.

From discomfort to medical emergency

Heat stress has a clear progression in which each phase requires a different response.

Heat cramps are the first warning signal: painful muscle cramps due to salt and fluid loss.

Heat exhaustion is more serious. The employee shows weakness, dizziness, a rapid heart rate, nausea and cold, clammy skin. This is the moment to intervene immediately: cool down, hydrate, rest.

Heat stroke is an absolute medical emergency. Body temperature rises above 40°C. Without immediate intervention, this can be life-threatening.

Cognitive decline: the hidden risk

What receives too little attention in safety analyses are the cognitive effects of heat. And it is precisely these effects that make heat stress so dangerous in the workplace. At high temperatures, concentration falls, reaction times slow and decision-making deteriorates. Employees make more errors at the very moments they are working with machines, vehicles or hazardous substances. The risk of occupational accidents increases significantly, while the cause remains invisible at first glance.

Chronic exposure: the creeping danger

A single exposure to heat is taxing. Prolonged or repeated exposure is outright harmful. The body gradually loses its ability to efficiently regulate its core temperature: sweat production becomes less effective, blood circulation to the skin is disrupted. The heart and kidneys are systematically placed under greater strain, increasing the risk of cardiovascular disease and kidney problems. Chronic fatigue and a structurally lower work capacity are the result.

The economic impact for employers

Heat stress is a business risk with direct consequences. Reduced alertness leads to more occupational accidents. Physical and mental exhaustion depresses productivity. Absenteeism rises. And the costs of errors, downtime and medical interventions quickly mount up.

3. Legislation on heat and thermal stress