Working at high temperatures is detrimental to the health of employees. It is possible to cause many discomforts from heat stroke to heart attack. The risk of a heart attack increases as soon as the human body temperature exceeds 40. Humidity, which increases the temperature as well as the temperature, is an important factor for employee health. The general health status, physical condition, age, type of clothing and caloric amount spent on the job increases the risk that employees are exposed to.

Greenhouse gases that protect the earth ensure that the world's temperature is at a certain level. However, carbon dioxide and other greenhouse gases, which are released more into the atmosphere in recent years, cause the earth's temperature to increase. If the earth is too hot or too cold, it is a danger to all living things. In the present situation caused by the industrial revolution, more carbon dioxide is released into the atmosphere and as a result climate changes have started to occur. Air temperatures and the amount of moisture in the air are gradually increasing.

The increase in the temperature felt in such an environment affects the work efficiency and concentration of the employees negatively and decreases the operating efficiency. In spite of the precautions taken, the temperatures felt especially in hot regions will increase and the working environment will become more unfavorable. In order to prevent this, more heating and cooling systems will be used in workplaces and residences.

There are two basic standards for determining thermal comfort conditions:

• TS EN ISO 7730 Medium thermal media - Determination of PMV and PPD indices Determination of conditions for thermal comfort
• TS EN 27243 Hot environments - Estimation of heat pressure on the worker according to WBGT index

Of these, the TS EN ISO 7730 standard is a standard used in temperate environments. The first part of this standard covers the conditions of personal dissatisfaction and the second part covers the conditions of environmental dissatisfaction. Personal variables are related to the metabolism of the employee, that is, the current job and the insulation resistance of the garments. Environmental variables are related to air temperature, radiant heat (effect of surface temperature with radiation), relative humidity and air velocity. There are two indicators in this standard that establish the conditions of personal dissatisfaction:

• PMV (predicted mean vote)
• PPD (predicted percentage dissatisfied) ie average dissatisfied percentage (personal dissatisfaction percentage)

This method is widely used worldwide to determine thermal comfort. The important point here is to bring the PMV value closer to zero (in the calculations a value between -3 and + 3 is obtained).

If the PMV value is high, the TS EN ISO 27243 standard used for hot environments is used in these environments. In this case, the temperature index to be measured is the wet bulb globe temperature (WBGT). This method is also called heat pressure method. With this measurement method, it is determined how long the employees, who are exposed to high ambient temperature, can work in that environment at most.

In fact, although comfort varies from person to person, thermal comfort is an expression of the physical and mental effect of temperature, relative humidity, radiant heat, air velocity, and similar parameters on workers in a working environment. Therefore, for the vast majority of employees, an environment where physical and mental disturbances are minimal is considered to be comfortable. In a comfortable working environment, employees' perception, understanding, attention, efficiency and performance are high. Accordingly, the health and safety of the employees in that workplace has been ensured and occupational accidents have been minimized.

Thermal Comfort Coverage

The effect of temperature is higher in humid weather. The dry air temperature is the temperature measured by the thermometer. For those working indoors without sunlight and those working outside in sunlight, the temperature effect is different. However, in addition to climatic factors, there are metabolic factors that affect the thermal comfort of employees. For example, the amount of energy that employees spend. The heavier the job, the higher the amount of energy used and the thermal comfort is negatively affected. In addition, the air flow in the working environment and whether the person is accustomed to the temperature of the working environment also affects thermal comfort. Different rest and working times have been determined in terms of thermal comfort. In the TS EN ISO 27243 standard, these times are considered as percent 25 work, percent 75 rest, percent 50 work, percent 50 rest, percent 75 work, percent 25 rest and continuous work.

Thermal comfort is not immediately noticed in a closed working environment. After a certain period of time, this is recognized. If there are no thermal comfort conditions, employees feel distress first and then they start to feel uncomfortable. Unfavorable ambient conditions and heat influences in the working environment are important factors in the occurrence of work accidents and decrease in production.

As explained above, the following four factors are effective in exchanging heat with employees: air temperature, air humidity, air flow rate and radiant heat.

A number of measurements, analyzes and evaluations are carried out by the test and inspection bodies to evaluate the work environments in terms of thermal comfort. The areas where workers are most exposed to thermal stress are generally areas where high heat emitting equipment such as melting boilers, rolling furnaces and the like are present. These areas are most common in the steel industry, foundries, glass and ceramics.

The WBGT index is a dimension of the thermal load to which workers are exposed. In general, measurements are taken and averaged over an eight-hour shift. These measurements include the weather conditions of the working environment in terms of thermal load and are determined by three parameters:

• Radiant temperature / sphere
• Wet thermometer temperature
• Dry thermometer (air) temperature