The wet bulb temperature helps calculate humidity.
India is currently experiencing a severe heatwave, with temperatures rising in parts of Uttar Pradesh, Punjab, Rajasthan, Chandigarh and Delhi, among others. In some regions, rising mercury, combined with humidity, is making it even more difficult for people to leave the house for any work.
But how is humidity recorded? The dry bulb, wet bulb and dew point temperatures help in understanding or calculating the condition of moist air. With just two of these values one can derive critical information, such as the water vapor content, but also the sensible and latent energy (enthalpy).
What is the wet bulb temperature?
Wet bulb temperature is a meteorological term used to describe the lowest temperature that can be achieved by evaporating water into the air at constant pressure. It is measured by covering a thermometer bulb with a wet cloth and allowing the water to evaporate. As the water evaporates, it cools the thermometer, displaying the wet bulb temperature.
This temperature helps measure humidity and understand how much water in the air can evaporate, which affects things like comfort, agriculture and weather patterns.
The difference between dry-bulb and wet-bulb temperatures depends on the humidity. Higher humidity means less evaporation and a smaller difference. When the air is fully saturated (100% humidity), the wet-bulb and dry-bulb temperatures are the same.
What is a safe heat/humidity limit?
According to a 2010 study, a wet bulb temperature of 35 degrees Celsius is suggested as the maximum safe limit. Past this point, the human body can no longer cool itself through sweating, which is necessary to maintain a stable core temperature.
However, this recently proved inaccurate when researchers at Penn State University placed young, healthy men and women in a controlled heat environment. Each participant took a pill that recorded their core temperature. They then performed minimal activities, such as showering, cooking and eating, while the researchers gradually increased the temperature or humidity.
The researchers discovered the 'critical environmental limit' – the point at which a person's core temperature begins to rise uncontrollably. Below this limit, the body can maintain a stable core temperature for a long time. Above this limit, core temperature continues to rise, increasing the risk of heat-related illness.
When the body overheats, the heart works harder to pump blood to the skin to release heat. Sweating also depletes body fluids. Prolonged exposure to high heat and humidity can lead to heat stroke, a serious condition that requires immediate medical attention.
The studies showed that the safe limit is lower than 35 degrees Celsius (as the previous study showed). The ideal wet bulb temperature is approximately 31 degrees Celsius with humidity above 50%. This means 31 degrees Celsius at 100% humidity or 38 degrees Celsius at 60% humidity, demonstrating the significant risk that high heat and humidity pose even to healthy people.
