Maintaining thermal comfort in indoor work environments

The term ‘thermal comfort’ describes a person’s state of mind in terms of whether they feel too hot or too cold. Essentially, thermal comfort can be identified by the number of workers complaining of thermal discomfort.

There is a significant difference between thermal discomfort and being exposed to extreme heat or cold:

  • There is little likelihood of a diagnosable medical condition developing as a result of thermal discomfort.
  • The risk to workers’ health increases as the thermal conditions move further away from those considered as comfortable.

Essentially, the more extreme the environment, the higher the risk is to workers of being exposed to serious illnesses and injuries – even death.

Thermal discomfort can seriously impact a worker’s overall morale and work performance. Prolonged exposure can lead to fatigue, lowered concentration and productivity. In addition, worker complaints and absenteeism can increase.

While the work health and safety legislation does not mention thermal comfort specifically, persons conducting a business or undertaking (PCBU) are required to ensure, as far as is reasonably practicable, they provide a work environment (including layout and ventilation) that is without risk to a worker’s health and safety. This means the work environment must be comfortable for workers and not place them at risk, it must suit the work they are doing and enable them to function efficiently both physically and mentally.

Causes of thermal discomfort

Problems with air-conditioning and heating in workplaces are very common. Older buildings can have out-dated heating and cooling systems that can lead to different temperatures within the one building and even in areas that are adjacent to each other. Also, temperatures can vary between different areas of a building depending on time of day, the season; the number of windows/doors; etc.

Air-temperature readings in air-conditioned workplaces may vary according to outside conditions so PCBUs must have systems in place to ensure thermostats are always be set within accepted levels to maintain thermal comfort. For example, thermostats may be set a little higher in summer and lower in winter.

Non air-conditioned environments can pose their own challenges because they can be more exposed to outdoor environmental conditions but have limited options for natural airflow and ventilation.

PCBUs should also consider seasonal variances within their workplaces – whether they are air-conditioned or not.

Factors affecting thermal comfort

The most commonly used indicator of thermal comfort is measuring air temperature but it isn’t only air temperature that affects whether people feel comfortable – there are a range of environmental and personal factors that are involved.

Whether the personal and environmental factors that impact thermal comfort occur independently of each other – or in a combination – they all can affect a worker’s thermal comfort.

Therefore, thermal comfort must be determined by considering each of the following factors.

Environmental factors

Air temperature– the temperature of the air surrounding the body.

  • Optimum comfort for sedentary work is usually between 200C – 260C.
  • Workers doing physical work usually prefer a lower temperature range.
  • Always consider the outdoor temperature when setting the indoor temperature. The perceived “comfortable” temperature inside a workplace depends on the outside temperature, eg: If it is 350C outside, an indoor temperature set at 220C may seem excessively cold when a person enters the work area – whereas, in winter, an indoor temperature of 220C may seem quite warm.

Radiant temperature– the heat that radiates from a warm object.

  • Equipment can produce heat and raise the temperature in a particular area. Heat-producing sources can include heat lamps; spot lighting; skylights etc.
  • Even a small room with a number of workers in it can see a rise in temperature.

Air velocity– the speed of air moving across the worker.

  • Air velocity is a key factor in perceptions of thermal comfort because people are sensitive to air movement.
  • An air flow rate of between 0.1 and 0.2 metres per second is desirable.
  • Little air movement or air that is still or stagnant in indoor environments may cause feelings of fatigue.
  • If the air is cooler than the environment, then it may help to cool workers in a warm environment however, it could cause further discomfort to workers in a cool environment. For example, if someone sits directly under an air conditioning vent, then they may be in a draught and therefore much cooler than is ideal.

Humidity – the amount of evaporated water in the air

  • Humidity in indoor environments can vary greatly and can be dependent on plant being used, eg: those that produce steam.
  • Optimum relative humidity levels between 40% and 70% are easy to achieve via air-conditioning. However, in non-air-conditioned workplaces, or where the outdoor climatic conditions influence the indoor thermal environment, relative humidity can be higher than 70% on warm or hot humid days.
  • If the humidity is too high, it will cause discomfort (excessive perspiration, feelings of tiredness and 'airlessness', etc). Humidity levels over 80% can prevent workers’ sweat from evaporating and expose them to the risk of heat-related illness and injuries.
  • Humidity levels below 40% can cause problems for workers with respiratory conditions, such as sinusitis and dry eyes.

Personal factors that must be considered even if all environmental factors are identified as appropriate

Physical activity required and Duration of exposure

The impact of metabolic rate on thermal comfort is critical:

  • the more physical the work is, the more heat is produced by the body. Care must be taken so workers don’t overheat
  • sedentary work in cool or cold environments can make it difficult for workers to generate heat.

Amount and type of clothing being worn

  • Clothing can be both a potential cause of thermal discomfort as well as a control for it.
  • Workers can manage thermal comfort if they can add layers of clothing (when feeling too cold), or remove layers of clothing (when feeling too warm).
  • Businesses that provide uniforms must ensure the fabrics are suitable to the work environment and the tasks involved, as well as allow workers to make reasonable variations to their clothing (such as wearing a personal cardigan or jacket if such items are not included as part of a uniform)

Physical fitness and

General health

  • Workers may have physical or medical health conditions that make them more likely to be affected by heat or cold, eg: overweight; underweight; respiratory disease; taking any medication, drugs or alcohol
  • Thermal comfort can be affected by a worker’s age, fitness level and sex. For example:
    • a fit body regulates its temperature more efficiently
    • aging can make it harder for people to keep warm or to stay cool due to hormone changes
    • women tend to feel the cold more than men because they’re less muscular and commonly wear less layers of clothing
  • Tense or stressed workers can feel colder.

Managing thermal comfort

Effective control starts with recognising all potential sources of risk.

Talk with workers about anything that could result in them being exposed to thermal discomfort. Are they positioned in direct sunlight; under an air-conditioning vent or skylight; or near an open door or heat-generating equipment? Is there adequate airflow? Are any objects or fixtures impeding airflow? Do they have any personal factors to consider?

In work environments, where thermal discomfort has been reported as a problem, PCBUs should respond immediately and manage it effectively. Aim to achieve a thermal environment that satisfies the majority (at least 80%) of workers.

Where necessary, consult with building managers and other relevant parties – it’s more likely that suitable, long term solutions to the problem can be found when everyone works together.

PCBUs must then eliminate or reduce the risk.

PCBUs must have systems in place to reduce the risk, focusing on the hierarchy of controls as much as possible and using the higher level controls first. Administrative controls and PPE should only be used to supplement the higher controls that have been implemented. Usually, a combination of controls is needed to get the best results and any control measures must be determined in consultation with workers (or their HSRs).

Eliminate the hazard

  • design buildings that incorporate good ventilation and air flow. Consider this particularly for hot processes, eg via windows, shutters or roof design (to encourage ‘chimney effects’ to help dissipate heat from the structure)
  • where possible, relocate workstations away from hazard areas, such as direct sunlight or air-conditioning vents so workers are not exposed to thermal discomfort
  • redesign the job to remove an affected worker from a hazard area

Isolate the hazard

  • insulate around heat or cold generating plant and pipes
  • isolate heat-producing equipment to limit exposure to radiant heat

Engineering controls

  • provide effective ventilation, extractors or air conditioning to increase air movement and control the temperature and humidity. This can range from small units that lower the air temperature, but don’t control humidity levels or air movement, to large units that can cope with extreme conditions as well as humidity and air movement. Whatever type is used, make sure:
    • there is adequate air flow: Feelings of stuffiness can result when air flow is low, and draughts result when air flow is high
    • that the direction of air flow is satisfactory so that the air doesn’t blow directly onto any workers and the air flow reaches all areas in the workplace, otherwise some workers may complain of feeling cold while others are feeling hot
    • the air-conditioning unit is regularly serviced and maintained
    • the thermostat is not situated directly in front of a vent
    • outside climate conditions, how workers are dressed and the type of work being done are all considered
  • provide evaporative coolers for warmer work environments. They operate by passing hot air over water-saturated pads with the water evaporation effect reducing the air temperature and increasing humidity
  • provide fans (e.g. desk, pedestal or ceiling-mounted fans)
  • provide portable heating appliances for cooler work environments
  • control draughts and thermal differences between the head and the feet (thermal gradients) by installing barriers or similar structures to shield workers against thermal discomfort in particular work areas
  • install blinds, louvres, reflective film and the like to windows or skylights etc to control direct/indirect sunlight (radiant heat)
  • ensure windows can be opened, where practicable
  • provide mechanical aids to assist with physically demanding jobs

Administrative controls

  • If uniforms are worn, evaluate:
    • alternative designs, new materials and/or items etc to improve suitability of clothing
    • the formality of the dress code to allow workers to adapt their clothing where possible. Multiple layers of clothing enable workers to make reasonable adjustments to their clothing based on their own subjective feelings.
  • develop safe work systems to manage thermal comfort, eg: include thermal comfort as part of regular workplace risk assessments
  • allow workers to adjust thermostats or open windows or doors as appropriate
  • consider the impact of thermal discomfort on workers who are pregnant, have an illness or disability, are older or are on medication. Obtain medical advice where necessary
  • provide training to all workers on how to report hazards. Also ensure they are aware of how the air-conditioning is managed in your building, explain any roadblocks in the way of ensuring an even temperature and advise about the control measures in place.

Personal protective equipment (PPE)

Wearing PPE in warmer environments with high work rates can increase the risk of exposure to thermal discomfort and heat-related illness. If PPE is to be worn, make sure that workers are wearing it correctly and that they are not wearing more PPE than is required.

Measuring thermal comfort

In complex situations, such as where concerns about thermal comfort are reported by a number of workers or are longstanding, PCBUs should establish a clearer picture of the issue by obtaining the services of an appropriately qualified person (such as an occupational hygienist with skills in indoor air quality and thermal comfort assessment) and then appropriate control measures can be developed in consultation with the affected workers. In these situations, the thermal conditions may need to be monitored and where possible recorded as part of the workplace risk management program.

Further information

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