Not just high temperatures: the combination with humidity prevents sweat from evaporating and therefore cooling the body. Here are the worrying parameters measured on healthy adults in the laboratory
Every year a few records are broken regarding heat and extreme temperatures and it looks like this won’t be the last scorching summer. For this reason, scientists are examining various aspects related to heat waves, trying to dissect possible all-round consequences on the human body and climate adaptability.
Not just high temperatures
With regard to extreme climates, the question that researchers at Pennsylvania State University asked themselves when the heat becomes really unbearable for carrying out normal daily activities even for young and healthy adults?
The answer goes beyond the degrees that thermometers report, because it concerns a specific combination of temperature and humidity. The wrong combination of high temperature and high humidity becomes dangerous at levels lower than previously believed by scientists. In particular, the human body suffers when the air is so saturated with water vapor that it prevents the evaporation of water from a sweaty body. If sweat cannot evaporate, the body cannot cool itself to maintain a stable body temperature.
The US study
American scientists experimented with heat stress in a controlled environmental chamber in Penn State University’s Noll laboratory. To do this, each participant swallowed a small telemetry pill that monitored their deep body temperature. Participants sat in a climate chamber, moving around just enough to simulate the minimal activities of daily living, such as showering, cooking, and eating. The researchers slowly increased the chamber temperature or humidity in hundreds of separate experiments and monitored when the subject’s core temperature began to rise. The combination of temperature and humidity at which a person’s core temperature begins to rise steadily is called the critical environmental limit. Below these limits, the body is able to maintain a relatively stable core temperature for long periods of time. Above these limits, the core temperature rises continuously and the risk of heat-related illnesses increases. For example, when the body gets hot, the heart has to work harder to pump blood to the skin to dissipate heat: body fluids are reduced and, in the most extreme case, heat stroke (a life-threatening problem that requires immediate cooling).
The results
The result of the experiments showed that the environmental limit is lower than previously believed: it occurs at a temperature of about 31 C in a range of environments all above 50% relative humidity, which is equivalent to 31 at 100% relative humidity. or 38 at 60% humidity.
Current heat waves around the world are exceeding these critical environmental limits. However, these are laboratory experiments (published in the Journal of Applied Physiology), serve to point the finger at the physical suffering to which some workers and the weakest categories are exposed: the heart rate begins to increase long before it reaches the limit of heatstroke and prolonged exposure to these climates can become disastrous for vulnerable populations such as the elderly and people with chronic diseases. In fact, people over the age of 65 account for 80% to 90% of the victims of heatwaves.
July 29, 2023 (change July 29, 2023 | 12:51)
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