What is thermal stress and how can it affect us?

Thermal stress is defined as a discomfort we experience when we remain in an excessively hot environment that requires great effort from our body to maintain an internal temperature of 37°C. It is therefore caused by the heat load we receive in our body, which results from our interaction with the environmental space we are in. The clothing we wear and the physical activity we perform also influence it. These three factors condition our comfort inside a building. Workplaces are where thermal stress can occur most easily, especially when it comes to poorly ventilated spaces, unconditioned areas, and high humidity levels. When working under these conditions, the likelihood of a workplace accident increases, and pre-existing ailments such as diabetes, cardiovascular diseases, or hypertension can worsen. Other disorders directly related to excessive heat may also appear, such as cramps, dehydration, heat syncope, or skin rashes.

Factors that influence thermal comfort

The way to dissipate heat to the outside of our body occurs in a sensible manner through conduction, convection, and body radiation. We also use evaporation as a cooling system, through breathing, perspiration through the skin, and sweating. The speed at which a person exchanges this heat with the external environment fundamentally depends on the temperature and humidity of that environment and the degree of insulation of the clothing they are wearing. When the thermal balance between our body and the external environment is balanced, we will feel comfortable having achieved thermal wellbeing.

The energy we give off is measured in "met", a unit whose standard corresponds to the metabolism of a healthy, sitting, and non-working person. Thus, when a person is sleeping, they give off 0.76 met; when lying down, 0.86 met; sitting without working, 1.0 met; standing, 1.3 met; walking, 1.5 met; and so on.

The thermal insulation of our clothing is another factor that influences thermal comfort. We are warm bodies, at an approximate temperature of 37 °C, which varies according to age, the activity we are developing, or the time of day. To maintain it, we wear more or less clothing depending on the activity we perform and the environmental temperature. In this case, the reference measure is "clo", a unit that defines the level of thermal insulation of clothing. Thus, a naked person has an insulation of 0.0 clo; with light summer clothing, 0.10 clo; with work clothing, 0.70 clo; and with winter clothing, 1.50 clo.

Therefore, the clothing factor is very important when determining the thermal wellbeing of an environment shared by several people, in which although everyone could perform the same activity, the difference in the level of thermal insulation of their clothing could cause discomfort for some relative to others at the same ambient temperature.