Thermal comfort in the workplace

Thermal comfortIn March 2014, the Met Office published a report exploring the potential causes of the extreme weather events of recent years in the UK and what the future holds for UK seasonal weather. Among the conclusions, the paper states that “climate change has at least doubled the risk of a heatwave exceeding the temperatures experienced in the European heat wave of 2003” and that “by the 2040s, more than half of summers are projected to be warmer than that seen in 2003”.

With potential for more significant summer heat waves and colder winters, thermal comfort within the office environment may become an issue for many employers. The questions to be addressed are what the risks could be and what action should be taken to control any intolerable risks.

Defining thermal comfort

Thermal comfort is not just related to air temperature alone. It takes into account a range of other environmental and personal factors including radiant temperature, air velocity, humidity, clothing insulation and metabolic heat. These factors make up what is known as the “human thermal environment”.

Thermal comfort is actually defined in British Standard BS EN ISO 7730 as “that condition of mind which expresses satisfaction with the thermal environment”. Conversely, thermal discomfort is where people start to feel uncomfortable, i.e. they are too hot or too cold, but are not necessarily made unwell by the conditions.

The Health and Safety Executive (HSE) website notes that an acceptable zone of thermal comfort for most people in the UK lies roughly between 13°C (56°F) and 30°C (86°F), “with acceptable temperatures for more strenuous work activities concentrated towards the bottom end of the range, and more sedentary activities towards the higher end”.

Most individuals will not suffer medical symptoms due to thermal discomfort, beyond irritability and tiredness. However, in some circumstances exposure to excessive cold can result in poor circulation and hypothermia while excessive heat can result in more severe conditions such as heatstroke and dehydration.

As well as affecting the health of employees, extreme temperatures in the indoor workplace can reduce worker morale and productivity, and increase absenteeism and mistakes.

Assessing the risk

The UK Climate Change Risk Assessment (CCRA) highlights that, although climate change does not necessarily create new risks, it can represent a change in existing risk profiles.

The UK Climate Impacts Programme (UKCIP) has developed the Business Areas Climate Impacts Assessment Tool (BACLIAT) for exploring the implications of climate change.

BACLIAT comprises a simple checklist for assessing the potential impacts of climate change under a number of headings: logistics, finance, markets, process, people, premises and management implications.

Guidance for BACLIAT notes that it may prove difficult to adapt existing buildings to sufficiently tolerate new climatic conditions.

Assessing the risks from the impacts can be challenging but guidance from the Chartered Institution of Building Services Engineers (CIBSE) and UKCIP can assist in this. They propose the following approach.

  • Identify the problems and objectives, i.e. how can we manage temperature risks and maintain thermal comfort?
  • Establish decision-making criteria and performance targets for thermal discomfort
  • Assess the risk using qualitative and quantitative criteria
  • Identify and evaluate the adaptation options for keeping premises at a suitable temperature that are reasonable and cost-effective
  • Implement and monitor the effectiveness of the adaptations.

There are no fixed means of determining if thermal comfort is or will be a problem. According to the HSE, an historical indicator could be if 10-15% of employees complain of discomfort.

Adaptation and thermal comfort

Decisions will have to be made as to whether the thermal discomfort is likely to create an unacceptable risk, based on the benchmark criteria. CIBSE suggests that, when making decisions, the following need to be considered.

  • To what extent will passive measures be able to improve thermal comfort?
  • How effective (including cost-effectiveness) will different approaches to comfort cooling continue to be under the changing climate?
  • What are the energy use implications of the various strategies?

Issues that can contribute to the thermal environment and therefore require consideration in terms of adaptation will include building design and materials such as glazing, ventilation, air tightness, thermal mass, plant and equipment, waste heat, etc. Other factors may have to be given consideration including working patterns, activities and workforce profile (e.g. age and vulnerabilities).

As CIBSE observes, it is unlikely that one single adaptation will be sufficient. A “mixed mode approach” will have to be adopted. The action to be taken can be based around a number of areas.

  • Adaptation of building elements: including reflective films on windows, intelligent glazing systems, insulation of hot pipes, ensuring windows can be opened
  • Provision of equipment: including adequate blinds, provision of portable fans/eaters or air-conditioning units, better use of existing machinery
  • Safe systems: including modification of activities, working patterns, dress codes, relocating work (e.g. home working)
  • Management action: including training of staff, provision of hot/cold drinking water, monitoring of vulnerable staff.

CIBSE notes that buildings are designed to last for a significant period and will remain significantly unchanged, which “imposes severe limitations on how the building can be modified to take account of changing climatic conditions”. However, the main principle is to limit heat loss and gains to spaces so as to reduce the need for mechanical heating and cooling.

What is deemed to be reasonable is a matter of debate, but the HSE states that “the best that you can realistically hope to achieve is a thermal comfort environment that satisfies the majority of people in the workplace”, which is between 80% and 90% of the workforce.

Further information

From the UK Climate Impacts Programme (UKCIP):
From the Health and Safety Executive:
From the Chartered Institution of Building Service Engineers:
From the Met Office:

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