Handling the heatwave: thermal comfort in the workplace

UK temperatures recently hit the high 20s, with some parts of the country cooking in heat of 30 degrees and over. Although the weather has seemingly cooled for the time being, what should employers be aware of regarding their working environments when hot conditions are forecast? 

What is 'reasonable'?

In working spaces, the temperature must be reasonable. At present, there is no law for a maximum working temperature, or when it could be considered too hot to work. According to the Workplace (Health, Safety and Welfare) Regulations 1992, indoor workplaces should provide 'thermal comfort', with temperatures at a comfortable level and air that's clean and fresh.

The most common indicator of thermal comfort is air temperature - it is easy to use and most can relate to it. But alone, it is not a valid or accurate indicator of thermal comfort or thermal stress. According to the Health and Safety Executive's (HSE) guidance for employers, it should be considered in relation to other environmental and personal factors in the workplace.

What about…

  • …radiant temperature? This may be present if there are additional heat sources in an environment, for example fire, ovens, dryers, hot surfaces and machinery, molten metals etc. It has a greater influence than air temperature on how we lose or gain heat.
  • …air velocity? This describes the speed of air moving across the employee and may help cool them if the air is cooler than the environment.
  • …humidity? If water is heated and it evaporates to the surrounding environment, the resulting amount of water in the air will provide humidity. In workplaces with no air conditioning, or where weather conditions may influence the indoor thermal environment, relative humidity may be higher than 70%. Higher humidity stops sweat evaporating from the skin, thwarting our main method of heat reduction.
  • …clothing? Clothing is a potential cause of thermal discomfort, but can also let us adapt to the climate in which we work. Many employees, however, are limited in their ability to adapt their clothing to the weather as they have to wear a uniform or personal protective equipment (PPE).
  • …work rate? Of course, the more physical our work is, the more heat we produce, and the more we will need to lose to avoid overheating.
  • …metabolic heat? An individual's metabolic rate is critical to thermal comfort. Physical characteristics such as size, age, fitness level and gender should always be borne in mind when considering thermal comfort.

Employer considerations

The Trades Union Congress (TUC) has called for the introduction of an upper limit on workplace temperature so that employers would be forced to act when the temperature inside reaches 24°C. It could mean staff being sent home or employers being prosecuted if temperatures hit 30°C (or 27°C for those engaged in physically demanding work).

To minimise or mitigate any potential issues, employers can look to improve conditions by ensuring:

  • windows are open
  • fans are provided and radiators can be switched off or air conditioning units are maintained
  • work systems limit exposure, such as flexible hours or early/late starts to help avoid the highest temperatures
  • formal dress codes are relaxed
  • hot plant or pipes are insulated
  • workstations are moved away from hot plant or out of direct sunlight
  • thermal risk is assessed as part of workplace risk assessments

Mentor provides advice on health and safety and employment law.

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