Heat stress

[edit] Introduction

Temperatures in the workplace are governed by the Workplace (Health, Safety and Welfare) Regulations 1992, which require employers to maintain a reasonable indoor temperature in the workplace. The regulations do not specify a maximum or minimum temperature, but instead set a general duty to ensure thermal comfort so far as is reasonably practicable.

The associated Approved Code of Practice (ACOP) advises that, in most indoor workplaces, the temperature should normally be at least 16°C, or 13°C where work involves severe physical effort. These figures are guidance rather than legal limits.

There is no statutory maximum workplace temperature in the UK. This reflects the complexity of thermal environments and the fact that acceptable temperature varies depending on activity, environment, and personal factors.

Historically, the Health and Safety Executive (HSE) described thermal comfort in broad terms (often cited as approximately 13°C to 30°C), with lower temperatures suited to more physically demanding work and higher temperatures to sedentary tasks. However, HSE guidance now places less emphasis on fixed temperature ranges and more on risk assessment and environmental heat stress indicators.

In 2006, the Trades Union Congress (TUC) suggested a maximum workplace temperature of 30°C, or 27°C for strenuous work. More recently, similar thresholds have been referenced in political discussions and policy proposals, including Labour Party proposals in 2019 to explore enforceable maximum workplace temperatures through a proposed Royal Commission on Health and Safety at Work. However, these remain policy proposals rather than statutory requirements.

[edit] Thermal comfort

Thermal comfort cannot be determined by air temperature alone.

The HSE recognises the Wet Bulb Globe Temperature (WBGT) index as a useful method for assessing heat stress risk in occupational environments. WBGT incorporates:

• natural wet-bulb temperature
• globe temperature (radiant heat)
• air temperature

However, thermal comfort is influenced by a combination of environmental and personal factors, including:

• air temperature
• air movement (velocity)
• radiant temperature
• relative humidity
• clothing insulation
• metabolic rate (activity level)
• acclimatisation
• health status and individual tolerance
• access to hydration

Because of this complexity, thermal comfort should be assessed using a holistic approach rather than a single temperature value.

[edit] Heat stress

Heat stress occurs when the body’s ability to regulate its internal temperature is overwhelmed. This can lead to a rise in core body temperature and associated physiological strain. It is more likely in environments involving high heat loads, such as industrial processes including smelting, foundries, brick firing, kitchens, or poorly ventilated plant rooms and roof spaces in hot weather. Where humidity is high or where personal protective equipment (PPE) restricts evaporation of sweat, the body’s ability to cool itself is reduced, increasing risk.

Heat stress is a personal physiological response, meaning that individuals exposed to the same conditions may experience different effects depending on clothing, workload, hydration, and health status.

Symptoms may include:

• dehydration
• headache, reduced concentration, and confusion
• muscle cramps
• heat rash
• fatigue
• dizziness or fainting
• nausea
• in severe cases, convulsions

If untreated, severe heat stress can lead to heat exhaustion or heat stroke, which can be fatal.

[edit] Employer duties and risk control

Under the Management of Health and Safety at Work Regulations 1999, employers are required to assess risks to health and safety, including those arising from heat, and implement reasonably practicable control measures.

Typical mitigation measures include:

• reducing heat exposure through engineering or process changes
• improving ventilation or cooling
• limiting duration of exposure and introducing rest breaks
• allowing time for acclimatisation
• providing adequate drinking water
• adjusting workload and work rate where possible
• using suitable PPE that balances protection with heat burden
• training workers to recognise symptoms of heat stress
• monitoring workplace conditions and worker health where appropriate

[edit] Related articles on Designing Buildings

• BREEAM Thermal comfort.
• Cold stress.
• Construction work in hot weather.
• Dry bulb temperature.
• Globe temperature.
• ‎Maximum and minimum workplace temperatures.
• Occupational health.
• Overheating.
• Personal protective equipment.
• Preventing overheating.
• Relative humidity.
• Temperature.
• Tempering heating.
• Thermal comfort.
• Types of heating system.
• Wet bulb globe temperature.
• Wet bulb temperature.