This website uses non-intrusive cookies to improve your user experience. You can visit our cookie privacy page for more information.

Social media

Javascript is required to use HSE website social media functionality.

Heat Stress


This page tells you about the risks of overheating when working in hot conditions and gives practical guidance on how to avoid it. The information is also applicable during the hot summer months where there may be an increased risk of heat stress for some people, but in many jobs heat stress is an issue all year round. It explains the risks of overheating when working in hot conditions such as bakeries, compressed air tunnels, foundries and smelting operations. It does not address issues of thermal comfort in the workplace.

Heat stress occurs when the body’s means of controlling its internal temperature starts to fail. As well as air temperature, factors such as work rate, humidity and clothing worn while working may lead to heat stress. Therefore, it may not be obvious to a person passing through the workplace that there is a risk of heat stress.

You and your employees must be aware of how to work safely in heat, the factors that can lead to heat stress, and how to reduce the risk of it occurring.

How does the body react to heat?

The body reacts to heat by increasing the blood flow to the skin’s surface, and by sweating. This results in cooling as sweat evaporates from the body’s surface and heat is carried to the surface of the body from within by the increased blood flow. Heat can also be lost by radiation and convection from the body’s surface.

Typical example of a heat stress situation

Someone wearing protective clothing and performing heavy work in hot and humid conditions could be at risk of heat stress because:

The symptoms will worsen the longer they remain working in the same conditions.

What are the effects of heat stress?

Heat stress can affect individuals in different ways, and some people are more susceptible to it than others.

Typical symptoms are:

Where does heat stress occur?

Examples of workplaces where people might suffer from heat stress because of the hot environment created by the process, or restricted spaces are:

In these industries working in the heat may be the norm. For others it will be encountered more irregularly depending on the type of work being done and changes in the working environment, eg seasonal changes in outside air temperature can be a significant contributor to heat stress.

What do I need to do about heat stress?

Over time people adapt to hot conditions by sweating more, and by changing their behaviour to try and cool down, eg removing clothing, taking cool drinks, fanning themselves, sitting in the shade or a cool area, and/or reducing their work rate. However, in many work situations such behavioural changes may not be possible, eg during asbestos removal. Where there is a possibility of heat stress occurring you will need to carry out a risk assessment.

What do I need to look at in a risk assessment?

Firstly, you will need to talk to the workers involved (and their safety representatives), to see whether they are suffering early signs of heat stress. If it seems likely that there is a problem, you may need to consult with people who are more experienced in determining the risk from hot environments, eg occupational hygienists, nurses or doctors.

How can I reduce the risks?

Remove or reduce the sources of heat where possible:

Free Information Sheet