- What is thermal comfort?
- Six factors that indicate thermal comfort
- Measurement of thermal comfort
- Thermal comfort control
This page explains what "thermal comfort" means in the workplace and how employers and occupational health professionals can measure and maintain it.
We have separate advice for employers and employees on the basic steps they can takecontrol the temperature in the workplace.
What is thermal comfort?
Thermal comfort means taking into account a range of environmental, occupational and personal factors when deciding what constitutes a comfortable temperature in the workplace.
They are theresix basic factorswhich will help you decide if the temperatures are uncomfortable.
Why is thermal comfort important?
People who are uncomfortably hot or cold are more likely to behave insecurely. Their ability to make decisions and/or perform manual tasks is impaired. E.g:
- people may take shortcuts to get out of cold environments
- workers must not wear personal protective equipmentprotective equipment (PPE)properly in hot environments, which increases the risk
- the worker's ability to concentrate may begin to decline, increasing the risk of error
As an employer, you should be aware of these risks and ensure that the underlying causes of these unsafe behaviors are understood and actively discouraged and prevented.
Adaptation to the temperature at the workplace
Humans adapt their behavior to cope with the thermal environment, for example:
- drink more hot or cold drinks
- add or remove clothing
- unconsciously changing your posture
- the choice of heating or moving to or from a cooling/heating source
Where possible, you shouldcontrol temperatures in the workplaceenable workers to adapt.
In some cases the environment people work in or the need to wear uniform or PPE etc means they cannot adapt to their environment.
Therefore, it is important to have:
- adequate ventilationor air conditioning
- windows that can be easily opened or closed
Six factors that indicate thermal comfort
Air temperature alone is not a valid or accurate indicator of comfortable workplace temperature or heat stress. It should always be considered in relation to other environmental and personal factors.
Taking all these factors into consideration will help you decide if your workplace has a comfortable temperature.
- air temperature
- Radiation temperature
- Air movement and speed
- Isolation clothing and PPE
- Work rate and metabolic heat
The temperature of the air surrounding the body is usually given in degrees Celsius (°C). It can be measured with a thermometer, but in itself will not give an indication of thermal comfort.
You should ensure a minimum working temperature in the working rooms – usually at least 16°C or 13°C for hard work.
There is no law for the maximum operating temperature, nor whenit's too hot to work. This is because high temperatures in many indoor workplaces are not seasonal, but due to work activity, for example in bakeries or foundries.
Thermal radiation is heat that radiates from a hot object.
The radiation temperature will have a greater influence than the air temperature on how hot the workplace becomes.
Examples of radiant heat sources include:
- electrical fires
- hot surfaces and machines
- very hot, molten materials such as metal or glass
Air movement and speed
The speed of air moving over the workers can help cool them if the air is cooler than the environment.
This is an important factor in thermal comfort, for example:
- stagnant or stagnant air in artificially heated indoor spaces can cause a feeling of suffocation. It can also lead to odor formation
- moving air under hot or humid conditions can increase heat loss through convection without any change in air temperature
- physical activity also increases air movement, so it can be adjusted according to the person's work
- small air movements in cool or cold environments can be perceived as drafts because people are particularly sensitive to these movements
Indoor humidity can vary greatly. This may depend on whether there are drying processes (in paper mills, laundries, etc.) where steam is released.
An environment with high humidity has a lot of vapor in the air, which prevents sweat from evaporating. In hot environments, humidity is important because less sweat evaporates when the humidity is high (above 80%). Evaporation of sweat is the most important method of heat reduction.
When workers wear certain personal protective equipment (PPE), this can increase the effects of moisture.
Isolation clothing/personal protective equipment
A comfortable working temperature largely depends on the insulating effect of the clothing.
When workers wear vapor impermeable, non-breathable clothingpersonal protective equipment (PPE), for example asbestos or chemical protective suits, the moisture in it increases because sweat cannot evaporate.
Too much clothing or PPE can be the primary causeheat stressalthough the environment is not considered warm or hot.
In cold conditions, if the clothing does not provide sufficient insulation, the wearer may be at riskcold stressand suffering from injuries such as frostbite or hypothermia.
Make sure people can add or remove layers of clothing to more easily control their thermal comfort. Consider situations where workers are required to wear a special uniform or PPE.
It is important to determine how work clothing contributes to thermal comfort or discomfort. By periodically evaluating the level of protection provided by existing PPE and evaluating newer types of equipment, you may be able to improve your thermal comfort level.
Work rate and metabolic heat
The effect of work speed on thermal comfort is critical because physical activity generates more body heat.
Always consider a person's physical characteristics when considering their thermal comfort.
Factors such as their size and weight, age and fitness level can affect how they feel, even if other factors such as air temperature, humidity and air movement speed are held constant.
Measurement of thermal comfort
An easy way to assess the level of thermal comfort in your workplace is to ask your workers or their safety representatives (such as unions or employee associations) if they are satisfied with the thermal environment.
You can use a workplace temperature checklist to determine whether there is a risk of thermal discomfort for your employees.
Please note that this basic checklist is not a substitute for an appropriate and adequate risk assessment taking thermal comfort into account.
Assessment of thermal comfort
Once you have identified the problem using the checklist, the guidelines on this website will in most cases be sufficient to allow you to improve the thermal comfort in your workplace.
If you need to take additional steps to measure thermal comfort, please refer to the appropriateBritish standards.
If thermal comfort is an issue in your workplace, you may need to consider this as part of your risk assessment process.
They are theresix basic factorswhich affects the thermal comfort. Think about how they can affect your employees and how you can get rid of those who have the most influence.
If the environment is affected by seasonal factors, it may be necessary to reassess the risk at different times of the year. For example, consider scheduling maintenance work for cooler times of the day.
Is heat stress a problem at your workplace?
Unless someone collapses from heat exhaustion, the potential health effects may not be apparent. This means that you must determine whether the workers who may be at risk of heat stress are suffering from heat-related illnesses.
You can use information you already have to identify people who may be at risk, for example:
- look for patterns in absenteeism, types of illnesses and their frequency, worker complaints, etc. Pay particular attention to where people work, their jobs, how experienced they are, whether any illnesses recur, etc.
- read possiblyRIDDOR reportsand any internal accident or injury reports. Are there patterns in the nature of reported accidents or injuries? Can the repeated accidents be attributed to the effects of the heat, e.g. fatigue, loss of concentration, etc.?
- talk to other companies in the same industry as your organisation, contact industry associations or associations etc.
- make an observation of your workplace and record any findings. Ourlist of heat stresscan help you assess the risk
Measurement of thermal stress
Measuring heat stress can be complex – you may need the help of an occupational health and safety professional to measure it in your workplace. This may include:
- measuring the heat stress to which an individual is exposed (eg using a technique such as the moisture globe temperature index, see BS EN 27243)
- estimation of metabolic rate (see BS 8966)
- heart rate measurement
- assessment of the clothing's insulation value (see BS ISO 9920)
- if other alternatives cannot be used, consider physiological monitoring (see ISO 9886)
British Standards are available atBSI Group.
Control measures to make the workplace temperature more comfortable
There are several ways in which you can make the temperature in the workplace more comfortable.
Control the environment
- Replace warm air with cold air, or replace cold air with warm air as needed
- Humidify or dehumidify the air as needed
- Increase air movement with ventilation or air conditioning
- Reduce drafts by directing ventilation or air movement so that it does not blow directly on workers, for example by using baffles
Separate the source of heat or cold from the worker
- Use barriers that protect or isolate the work area or limit access
- Redesign jobs to remove workers from the area
Control the task
- Reduce the time workers are exposed to hot or cold conditions
- Check the amount of work and the expected work rate of people
- Introduce mechanical aids (e.g. lifting aids or power tools) for physically demanding jobs in warm and hot environments or when workers wear a lot of clothing
Control your clothes
- Make sure workers don't carry more than necessary
- If uniforms are worn, choose designs or materials that improve the thermal comfort of the clothing
- Relax the dress code so workers can customize their clothing where possible
- Layered clothing allows workers to make reasonable adjustments to their clothing based on their individual needs
Allow workers to adjust their behavior
- Where possible, remove any restrictions that may prevent workers from making minor adjustments to their clothing or work pace
- Provide heating or cooling
- Provide personal heaters or fans
- Allow workers to adjust thermostats or open windows as needed
Follow the employee
- Provide appropriate supervision and training
- Ask for medical help from aexpert in occupational medicinefor workers who are pregnant, have an illness or disability or are on certain medications, e.g.in very hot weather
- Your risk assessment should already cover thishazards to pregnant workers, but once your employee has informed you in writing that she is pregnant, you must complete an individual risk assessment and make the necessary changes to support them
The use of control measures on these pages must ensure the well-being of people with hormonal imbalance due to menopause or thyroid imbalance.
Administrative controls may include:
- scheduling 'hot' work for cooler times of the day
- have flexible working hours to avoid the worst effects of working at high temperatures
You can also use more permanent controls, for example:
- emergency procedures for responding to extreme heat
- have competent first aid providers who can recognize and treat heat-related illnesses and ensure you have adequate first aid equipment
Reducing or eliminating the hazard should be the first choice. Although the initial costs of engineering controls may seem high, they are often outweighed by the resulting production improvements.
Any practical solution for thermal comfort control will likely require a combination of the various options developed inconsultationwith workers, with workers and their representatives.
Many types of heating systems are available:
- hot air heating systems
- water-based central heating systems with radiators
- combined heating and ventilation systems using air conditioning
- electric heating systems using electric heaters
- underfloor heating systems that use either electric coils or heated fluids
- air heating system
Most of these systems are useful. However, the beneficial effects may in some situations be limited to the immediate location of the heat source.
Air movement and speed
There are many methods of increasing airflow, such as fans of different sizes, but these can cause problems with drafts or noise.
Large diameter ceiling fans can provide efficient air movement over a wide area. Large exhaust fans, mounted on roofs and walls, are useful for removing heated air and drawing in cooler air from outside.
This can range from small units that reduce air temperature but do not control humidity levels or air movement, to large units that can handle extreme conditions as well as humidity and air movement.
When air conditioning is used, care must be taken to ensure an even distribution of air throughout the workplace, otherwise some workers may complain of being cold and others hot.
Air conditioners must be operated according to the manufacturer's instructions.
Evaporative coolers produce a moderate drop in air temperature and increase air humidity. They work by directing warm air over pads saturated with water, and the effect of water evaporation reduces the air temperature.
There are many different types of thermal insulation materials, e.g. loose fill, stone wool and insulation boards. The material acts as a barrier, which slows down the flow of heat in the summer and heat loss in the winter.
However, it is only effective where there is a temperature difference between the inside and outside of the building or between two areas inside the building.
You should provide a minimum working temperature in workrooms – usually at least 16°C or 13°C for strenuous work.What are the 4 most important factors in thermal comfort? ›
- Air temperature.
- Radiant temperature.
- Air movement and speed.
- Clothing and PPE insulation.
- Work rate and metabolic heat.
Thick or well-insulated walls, proper openings, screening systems, and outdoor spaces (e.g. courtyards) offering shade and natural ventilation are some of the possible solutions to increase thermal comfort and at the same time to save energy.How much temperature is maintained in the AC for thermal comfort? ›
Humans generally feel comfortable between temperatures of 22 °C to 27 °C and a relative humidity of 40% to 60%.What is normal thermal temperature? ›
While typically 98.6°F (37.0°C) is considered a “normal” temperature, some studies have shown that "normal" body temperature can be within a wide range, from 97°F (36.1°C) to 99°F (37.2°C).What are the 6 parameters of thermal comfort? ›
The PMV model relates thermal comfort scale with six different factors: air temperature, mean radiant temperature, relative humidity, air speed, metabolic rate, and clothing insulation (see Figure 1).What is the Ashrae standard for thermal comfort? ›
For thermal comfort—this is the standard.
ASHRAE Standard 55 specifies conditions for acceptable thermal environments and is intended for use in design, operation, and commissioning of buildings and other occupied spaces.
The ASHRAE guidelines recommend 68 F to 74 F in the winter and 72 F to 80 F in the summer. The ASHRAE guidelines recommend a relative humidity (RH) of 30 to 60 percent.What is thermal comfort in HVAC? ›
Thermal comfort can be defined as a subjective response, or state of mind, when a person expresses satisfaction with the surrounding environment (ASHRAE Standard 55). The environment must provide light, air, and thermal comfort. Proper acoustics and hygiene are also important for physical comfort.At what temperature should you stop using AC? ›
In most cases, especially in residential applications, you should not run your air conditioner when outdoor temperatures are below 60 degrees. The air conditioner does function, but you are going to burn out the compressor fairly quickly.
The average normal body temperature is generally accepted as 98.6°F (37°C). Some studies have shown that the "normal" body temperature can have a wide range, from 97°F (36.1°C) to 99°F (37.2°C). A temperature over 100.4°F (38°C) most often means you have a fever caused by an infection or illness.Does thermal mean hot or cold? ›
The Greek word therme, meaning “heat,” is the origin of the adjective thermal. Something that is thermal is hot, retains heat, or has a warming effect. If your sweatshirt has a thermal lining, its texture might remind you of a waffle-that's what traps your body heat.What is the minimum temperature for thermal energy? ›
Absolute zero is the lowest limit of the thermodynamic temperature scale, a state at which the enthalpy and entropy of a cooled ideal gas reach their minimum value, taken as zero kelvin.What is the ISO for thermal comfort? ›
ISO defines the hard limit as ranging between -2 and +2, while for old buildings the acceptable comfort limits range between -0.7 and +0.7, and new buildings between -0.5 and +0.5.What is optimal temperature and humidity? ›
Monitor and maintain ideal home humidity and temperature: The EPA recommends indoor humidity stays between 30% and 60%. Comfortable room temperatures are generally considered to be around 68° Fahrenheit. At night, some sleep experts recommend keeping a bedroom around 65°F.What is a reasonable temperature and humidity? ›
Air treatment is defined under the engineering recommendations as, "the removal of air contaminants and/or the control of room temperature and humidity." OSHA recommends temperature control in the range of 68-76° F and humidity control in the range of 20%-60%.Is 72 too cold for AC? ›
Since 72 degrees is generally agreed upon to be an ideal indoor temperature, most people would probably still feel comfortable setting their AC units slightly higher than this, perhaps at around 75.How cool should my AC keep my house in 100 degree weather? ›
What Temperature Should You Set Your Thermostat When It's 100 Degrees? A good rule of thumb is during the hottest days when the dial reaches 100 degrees it is best to set your AC to somewhere between 75 and 80 degrees.Is 68 too cold for AC? ›
The Dangers of “Too Cold”
Additionally, lower settings can cause your evaporator coil to freeze. There isn't enough heat exchange, so ice forms on the coil, causing the system to stop working until it defrosts. Any temperature below about 68 degrees puts you in danger of freezing.
- Temperature. Temperatures in homes can fluctuate dramatically between sun shining through windows, drafts throughout your home or even your own body temperature.
- Humidity. ...
- Air quality. ...
1. Mass of object 2. Temperature of the object 3. Phase (solid, liquid, gas) of the object Thermal Energy Page 8 Thermal Expansion An increase in the volume of a material due to a temperature increase.What are 4 factors that affect thermal conductivity? ›
Temperature, moisture content, and density are the most important factors. Other factors include thickness, air velocity, pressing, and aging time. The relationship between main factors with thermal conductivity is presented.What are the 4 main factors that affect temperature? ›
The latitude of the place. The altitude of the place. Distance from the sea. The air- mass circulation.What are the principles of thermal comfort? ›
The main factors that influence thermal comfort are those that determine heat gain and loss, namely metabolic rate, clothing insulation, air temperature, mean radiant temperature, air speed and relative humidity. Psychological parameters, such as individual expectations, also affect thermal comfort.What is a comfort chart? ›
As used by the American Society of Heating and Air Conditioning Engineers, a diagram showing curves of relative humidity and effective temperature superimposed upon rectangular coordinates of wet-bulb temperature and dry-bulb temperature.What is the 5 point comfort scale? ›
Comfortable was defined as a score of 4 (comfortable) or 5 (very comfortable) on the Likert scale. Uncomfortable was defined as a score of 3 (neutral) or less (uncomfortable, very uncomfortable) on the Likert scale.
The major components of thermal properties are: Heat capacity. Thermal Expansion. Thermal conductivity.What 3 things does thermal energy depend on? ›
A substance's total thermal energy depends on its temperature, number of atoms, and physical state. More atoms and higher temperature mean more thermal energy. If all other conditions are the same, substances in gas form have the most thermal energy, followed by liquids, then solids.What are the 3 characteristics of thermal energy? ›
Thermal energy transfers, or moves, between objects in three ways: radiation, conduction, and convection. Let's look at what these words mean and some examples of each.What are the four 4 factors that affect the resistance of a conductor? ›
The factors affecting resistance are Length, Area of cross-section, Temperature, and Nature of material.
Mainly metals have very high thermal conductivity which compares well to what is known about metals. As well, insulating materials such as aerogel and insulation used in homes has a low thermal conductivity, indicating that they do not let heat pass through them easily.What are the factors affecting heat? ›
Thus, Heat energy is dependent on mass, specific heat, and changes in the temperature of the body.What are the two most important factors in temperature? ›
The two most important factors in the climate of an area are temperature and precipitation. The yearly average temperature of the area is obviously important, but the yearly range in temperature is also important. Some areas have a much larger range between highest and lowest temperature than other areas.What are the five main factors that control temperature? ›
- The latitude of the Place.
- The altitude of the Place.
- Distance From The Sea.
- The presence of warm and cold ocean Currents.
- Local Aspects.
Many factors affects temperature. Among them, three factors that affect temperature are altitude, latitude and distance from sea. This note provides an information about the factors affecting climate.