What is thermal comfort?

Definition

Thermal comfort is defined in British Standard BS EN ISO 7730 as:

‘that condition of mind which expresses satisfaction with the thermal environment.’

So the term ‘thermal comfort’ describes a person’s psychological state of mind and is usually referred to in terms of whether someone is feeling too hot or too cold.

Thermal comfort is very difficult to define because you need to take into account a range of environmental and personal factors when deciding what will make people feel comfortable. These factors make up what is known as the ‘human thermal environment’.

The best that you can realistically hope to achieve is a thermal environment that satisfies the majority of people in the workplace, or put more simply, ‘reasonable comfort’. HSE considers 80% of occupants as a reasonable limit for the minimum number of people who should be thermally comfortable in an environment.

So thermal comfort is not measured by air temperature, but by the number of employees complaining of thermal discomfort. To better understand why air temperature alone is not a valid indicator of thermal comfort, see the six basic factors.

Why is thermal comfort important?

People working in uncomfortably hot and cold environments are more likely to behave unsafely because their ability to make decisions and/or perform manual tasks deteriorates. For example;

• people may take short cuts to get out of cold environments, or
• workers might not wear personal protective equipment properly in hot environments increasing the risks, or
• the workers' ability to concentrate on a given task may start to drop off and increases the risk of errors occurring.

As an employer you should be aware of these risks and make sure the underlying reasons for these behaviours are understood and taken into account. Addressing the underlying reasons for these behaviours is also likely to improve morale and productivity as well as improving health and safety.

Adapting to the thermal environment

People employ adaptive strategies to cope with their thermal environment, eg donning or removing clothing, unconscious changes in posture, choice of heating, moving to cooler locations away from heat sources, etc.

The problems arise when this choice (to remove jacket, or move away from heat source) is removed, and people are no longer able to adapt. In many instances the environment within which people work is a product of the processes of the job they are doing, so they are unable to adapt to their environment.

Next: The six basic factors