Basic factors for thermal comfort
How hot or cold employees are while they go about their work can affect their health and safety. Being too warm can increase the risk of heat stroke, collapse, or worse. If the body’s temperature drops too low, there’s a risk of employees developing headaches, throat irritation, fatigue, eye irritation and lack of concentration. Being tired and not feeling their best could cause employees to put themselves or others at risk.
Unfortunately, thermal comfort is not easy to define as it is not as simple as an ideal temperature range. The Health and Safety Executive states that thermal comfort is “a person’s state of mind in terms of whether they feel too hot or too cold”. The HSE recommends that 80% of employees should be thermally comfortable in the workplace.
To be able to ensure that the majority of people in a workplace are satisfied with how warm or cold they feel you need to understand what affects thermal comfort.
Not every factor is in your control, such as how warm it is outside, but giving employees a degree of control over their environment, such as the option to don or remove layers of clothing, to move closer to or away from heat sources, or to change activities, can help to reduce the risks associated with thermal discomfort.
The six basic factors of thermal comfort
Environmental factors
Humidity
If a work environment has high humidity it means there is a lot of water in the air. This prevents the evaporation of sweat from the skin, which is the main way we cool down.
Relative humidity (the ratio between how much water vapour is in the air and how much water vapour the air can hold at that air temperature) between 40% and 70% does not majorly impact thermal comfort. However, in non-air conditioned offices or where weather conditions outdoors influence the thermal environment indoors, relative humidity can reach above 70%, which makes it hard for employees to cool down.
Air temperature
Air temperature is the temperature, usually measured in degrees Celsius, of the air surrounding the body. This is what is measured using a thermometer.
Radiant temperature
Radiant temperature, or thermal radiation, is warmth that radiates from a warm object such as the sun, radiators, hot surfaces and machinery, cookers, etc. Ever noticed how much warmer it is in the kitchen when the oven’s on? Even if the air temperature in the home is similar in each room, the thermal radiation from the cooker increases the temperature in the kitchen.
Air velocity
How quickly air is moving across an employee is an important factor in thermal comfort. Still air in an artificially heated indoor environment can make people feel stuffy. If someone is hot, feeling a cool breeze can help to cool them down. Even if the air temperature is not reduced, moving air in a warm or humid office can increase heat loss by convection, which explains why a fan can help us to feel cooler.
On the other hand, if it’s cold or cool in the office, small air movements can be felt as a draught.
Personal factors
Clothing insulation
Wearing too many or too few clothes for the environment is a major potential cause for thermal discomfort. Even if the environment itself is not consider too warm, wearing too much clothing can cause heat stress.
Unfortunately, through the wearing of uniforms and PPE, many employees are not able to adapt their clothing to suit how hot or cold they are. Employers need to identify how the clothing their employees are wearing contributes to thermal comfort or discomfort.
Metabolic heat
The more physically active you are at work, the more heat you produce. Employees who do physical work, and produce more heat, need to lose more heat to prevent themselves from overheating.
Individual employees’ metabolic rate will affect their thermal comfort. You’ll also need to consider their physical characteristics, including size, weight, age, gender and fitness level, as these can impact how warm or cold they feel.
If you’re responsible for ensuring thermal comfort in your workplace, this Thermal comfort checklist from HSE may be useful.
To manage the thermal comfort of your employees it will be necessary to undertake risk assessments. The NEBOSH Level 3 General Certificate in Occupational Health and Safety covers management of health and safety and controlling workplace hazards. Contact us today to find out more about this recognised qualification.