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Wet Bulb Temperature Explained: Know how much hot is too much hot

Wet bulb temperature is a crucial factor in determining how hot it is outside and how our bodies respond to the heat. It is essential to pay attention to this measure and take necessary precautions during hot weather to avoid heat-related illnesses.

Written By: Kristina Das @ New Delhi Updated on: May 28, 2024 16:00 IST
wet bulb temperature
Image Source : FREEPIK Know what is wet bulb temperature.

India is currently experiencing severe heat waves, especially in the parts of Punjab, Uttar Pradesh, Rajasthan and more. So, have you ever walked outside on a summer day and immediately felt like you were being suffocated by the heat? Or perhaps you've heard the term "wet bulb temperature" being thrown around during a heatwave. In either case, understanding wet bulb temperature and its implications is crucial for staying safe and healthy in hot weather.

So, what exactly is wet bulb temperature? 

In simple terms, it is the lowest temperature that can be reached by evaporating water into the air at a constant pressure. This is different from the more commonly known dry bulb temperature, which measures the actual air temperature without taking into account the moisture present in the air.

The wet bulb temperature is affected by factors such as humidity, wind speed, and air pressure. It is usually measured using a special thermometer called a "wet bulb thermometer," which has a thin cloth wick attached to its bulb. The wick is soaked in water, and as the water evaporates, it cools the thermometer's bulb, giving us the wet bulb temperature.

Now that we know what wet bulb temperature is, let's dive into why it matters. The wet bulb temperature is closely linked to our body's ability to cool down through sweating. When the wet bulb temperature is low, our sweat can easily evaporate into the air, taking heat away from our bodies and keeping us cool. However, as the wet bulb temperature increases, the moisture in the air also increases, making it difficult for our sweat to evaporate effectively.

This process can have serious consequences for our health when we are exposed to high wet bulb temperatures for an extended period. Our body's inability to cool down through sweating can lead to heat exhaustion or even heatstroke. These conditions can be life-threatening if left untreated.

According to an NDTV report, a 2010 study recommends a wet-bulb temperature of 35 degrees Celsius as the upper acceptable limit. The human body can no longer cool itself through sweating, which is required to keep the core temperature constant, above this degree.

This was recently shown to be untrue, though, when Penn State University researchers exposed young, healthy men and women to a regulated heat environment. A tablet that measured each participant's core temperature was swallowed. After that, they engaged in minimum tasks including cooking, eating, and taking showers while the researchers progressively raised the humidity or temperature.

The "critical environmental limit"—the point at which a person's body temperature begins to increase uncontrollably—was identified by the researchers. The body can sustain a steady core temperature below this threshold for extended periods. The risk of heat-related illnesses rises as the core temperature rises above this threshold. 

The heart has to work harder to pump blood to the skin to discharge heat when the body overheats. Moreover, sweating reduces bodily fluids. Heat stroke is a dangerous disorder that requires rapid medical attention and can be brought on by prolonged exposure to high temperatures and humidity.

As the previous study had shown, the investigations found that the safe limit is less than 35 degrees Celsius. At humidity levels over 50%, the optimal wet bulb temperature is roughly 31 degrees Celsius. This indicates that even for healthy individuals, extreme heat and humidity pose a serious risk at 31 degrees Celsius at 100% humidity or 38 degrees Celsius at 60% humidity.

So, how much hot is too much hot in terms of wet bulb temperatures? 

According to experts, a wet bulb temperature of 35°C (95°F) is considered extremely dangerous and can lead to heatstroke within a few hours of exposure. A wet bulb temperature of 32°C (90°F) is also considered dangerous and can cause heat exhaustion in vulnerable populations such as the elderly, young children, and those with pre-existing health conditions.

But what about dry bulb temperatures? 

Is there a specific temperature that is considered too hot? The answer is not as straightforward as it may seem. While dry bulb temperatures can give us an idea of how hot it is outside, they do not take into account the moisture in the air, which plays a significant role in our body's ability to cool down. This means that even a relatively low dry bulb temperature can feel much hotter if the wet bulb temperature is high.

For example, let's say the dry bulb temperature is 38°C (100°F), but the wet bulb temperature is 32°C (90°F). This may not seem too extreme based on dry bulb temperature alone, but the high wet bulb temperature indicates that the air is saturated with moisture, making it difficult for our bodies to cool down through sweating. In this scenario, it would be essential to take precautionary measures to avoid heat-related illnesses.

So, how can we protect ourselves from the dangers of high wet bulb temperatures? The most important step is to stay hydrated by drinking plenty of water. Our bodies need water to produce sweat, and without enough fluids, we cannot effectively cool down. It is recommended to drink at least eight glasses of water a day and even more during hot weather.

Another crucial step is to limit your time outdoors during peak heat hours. When the wet bulb temperature is high, it's best to stay indoors in an air-conditioned or well-ventilated space. If you must go outside, try to schedule any outdoor activities for early morning or late afternoon when the temperature is relatively lower.

Wearing light-coloured, loose-fitting clothing can also help in staying cool in high wet bulb temperatures. Dark colours absorb more heat, and tight-fitting clothes can trap heat close to our bodies, making us feel even hotter.

It's also crucial to keep an eye out for any signs of heat-related illness, such as dizziness, nausea, and rapid heartbeat. If you or someone around you experience these symptoms, it's essential to seek immediate medical attention.

ALSO READ: Longer, intense heatwaves linked with rise in premature births: Study


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