Article by Li Yundi “Ming Pao”
As the weather continues to be hot, portable fans have become a portable magic weapon for many people.
Only experts warn that using a fan in an environment higher than 35°C will not make it cooler, but will make it hotter and hotter, and even cause heat stroke!
(Hong Kong News) If you want to cool down outdoors in hot weather, you cannot rely on a fan alone, and you need to use it in conjunction with different conditions.
Why does blowing fan cause heatstroke? First of all, we must understand the principle of cooling fans. Cai Xiaohua, Academic Coordinator (Life Science) of the International College of Hong Kong Baptist University explained: “This involves two physical principles. One is air convection. The fan makes the air circulate continuously. Through the principle of hot air rising and cold air falling, the temperature will follow The other principle is to evaporate sweat: when the weather is hot, the body temperature rises and sweats, sweat absorbs the ‘latent heat’ of the skin, and the electric fan accelerates the evaporation of sweat to take away the latent heat in the body to achieve the effect of heat dissipation.”
Physiological function difficult to regulate cooling
Family doctor Mo Kunyang also pointed out that the fan itself cannot cool down. Its function is to increase the air flow and take away the sweat on the surface of the skin through continuous air flow.
Whether a portable fan will keep you cool depends on the ambient temperature.
Cai Xiaohua said that the normal body temperature of the human body is about 37°C.
The skin temperature is about 35°C, which is slightly lower than body temperature.
Because the skin has 3 layers (i.e. epidermis, dermis, subcutaneous tissue),
There are hairs, hair follicles, microfilament blood vessels, etc. in the middle,
The oil and sweat produced can help regulate body temperature and have a cooling effect.
The skin temperature was maintained at about 35°C.
If the ambient temperature is lower than the skin temperature, based on the principle of air convection, the fan will help to speed up the air flow, causing the hot air to rise and the cold air to fall, and the body’s functions will automatically adjust to cool down, making you feel cool. Once the ambient temperature is too high and the surrounding is filled with hot air, the fan will only circulate the hot air continuously.
Cai Xiaohua said that if the outdoor temperature is as high as 37°C or 38°C, the fan will only heat up the space. The situation is like being in a back alley full of air-conditioning tanks, and you will only feel the endless heat.
Mo Kunyang said that if the temperature exceeds 35°C, it is not suitable to use a fan. It will only bring heat into the body, and it will be more difficult to adjust the physiological function to cool down. The demarcation point of the electric fan.
Below 35 ℃ fan to help cool down
If the portable fan is used improperly, the body temperature will rise instead of drop, increasing the risk of heat stroke. How to use it to improve the cooling effect? Based on the opinions of the two interviewees, the following suggestions are summarized.
1. Shade intercepts sunlight radiation
If you really need outdoor activities under the scorching sun, you should wear a hat and hold an umbrella to block the sun. Otherwise, you can find a cool place to avoid prolonged exposure to the sun. The shade of trees is a good shade. The huge canopy is like a sun umbrella, which can block sunlight from reaching the ground and help reduce the temperature of the ground. According to the Proceedings of the National Academy of Sciences of the United States (PNAS), when three-quarters of the road surface is shaded by trees, the temperature drop can exceed 2.5°C.
Use a portable fan in the shade, the cooling effect is relatively ideal. Mo Kunyang said: “Assuming the outdoor environment is over 35°C, it is useless to turn on the fan, it will only blow more and more heat, but if the temperature in the shade is lower than 35°C, the fan will drive the air to have a cooling effect.”
2. Ice compress to help heat dissipation
Mo Kunyang pointed out that the neck, armpits, and groin are places close to the passage of major arteries, where blood flow is higher and heat dissipation is faster. Applying an appropriate amount of ice compresses can help heat dissipation. When using a portable fan, if you place frozen objects such as canned drinks, antipyretic stickers, wet towels, ice pads, etc. on these parts that dissipate heat quickly, the wind chill effect will be more pronounced.
The fan makes the air flow continuously, taking away the sweat heat from the skin surface and accelerating the cooling effect. If direct skin contact with the frozen object is uncomfortable, place a thin cloth over the frozen object first. As for how long it lasts, it depends on personal experience.
3. Mist fan is better
Different types of portable fans have slightly different cooling effects. Mo Kunyang recommends choosing a portable fan with a spray device. Through the wind-chill effect, the wind will scatter the mist around, and when it touches the skin, it will take away the latent heat to achieve a cooling effect. Just like turning on a fan indoors and placing a glass of water or ice cubes in front of the fan, the wind is cooled and becomes “cold wind”, just like self-cooling air, which can blow away the heat energy on the skin and accelerate the evaporation of sweat. This is also the wind chill effect.
Cai Xiaohua said that the air supply angle of the portable fan will also affect the cooling effect. Based on the principle that hot air rises and cold air descends, the air supply angle of the fan should not be too high, preferably below the neck, so that the cold air accumulated in the lower part can be blown up again, so that the cold air can be continuously circulated to achieve the cooling effect .
As for someone putting a portable electric fan into the clothes, Cai Xiaohua pointed out, “If the space inside the clothes is already very hot, it will only circulate the hot air continuously, and the cooling effect will not be exerted. But if it is not too hot, it may It has a little effect.”
4. Wiping sweat frequently
When sweat has already covered the surface of the skin, using a portable electric fan cannot cool down, and may even increase the risk of heatstroke. At this time, frequent sweating is more effective than simply turning on an electric fan to cool down.
Cai Xiaohua explained that when the environment is too hot, the heat of the body evaporates the sweat on the skin to achieve the effect of regulating body temperature. When sweat evaporates, it will increase the humidity of the space. If the sweat is not wiped, the sweat cannot continue to evaporate and dissipate heat. Therefore, wipe sweat frequently and cooperate with the fan to blow away the air with high relative humidity. The faster the sweat evaporates, the more pronounced the cooling feeling will be.
5. Hydrate more
The two interviewees reminded in unison that we must drink more water in hot weather. Sufficient water can be added to the body to help sweat evaporate and dissipate heat. The effect of cooling the body is more effective than relying on portable electric fans alone.
Mo Kunyang said that a normal person drinks 2 liters of water a day, and loses about 1,800 milliliters of water through urination and breathing. If the water loss exceeds replenishment, there will be water shortage and increase the risk of heat stroke. A rough but close estimate is whether the water supply is sufficient , “The color of urine tends to be transparent, which means sufficient water.”
fandon’t wantBlow in the face waiveddust mite virus nose
Maybe you have also tried it, facing the fan for a long time, making you dizzy and even sick; there is a saying in the market that turning on the fan all night while sleeping and blowing on a certain part of the body fixedly can cause the relevant muscles to become tense. stiffness and even increase the risk of stroke.
Will the fan blow to a stroke?
Mo Kunyang, a family doctor, said that the high temperature on hot days, and the temperature generally exceeds 25°C at night, is not a factor that induces stroke.
On the contrary, winter is the season of stroke and heart attack. Maintaining a low temperature of around 8°C to 10°C for a long time will increase the risk of stroke.
As for the electric fan fixedly blowing a certain part of the body will cause a stroke, there is no scientific basis for the time being. After all, the causes of stroke are complex, and many factors can trigger blockage or burst of blood vessels in the brain. Unhealthy daily living and eating habits are the key to the disease.
There is no scientific basis for causing stroke
So why do some people think that the fan will make you sick? Mo Kunyang believes that it may be related to the air quality where the fan is placed. If the air in the relevant place is poorly circulated, there are many sundries, and there are many dust mites, when the fan is turned on, the air flow will be increased, and the allergens and viruses in the air will be “active”, which is easy to cause diseases, especially increasing the risk of colds, colds, and nasal Sensitivity and other risk of upper respiratory disease.
Waking up with a sore throat the next day may also be caused by opening the mouth during sleep and inhaling allergens or viruses into the mouth.
Swing left and right to help blow away dust mites
If you don’t want the fan to blow you sick, what’s the countermeasure? He suggested that the fan should not blow towards the face, otherwise it will be easier to blow dust mites, allergens, viruses, etc. virus etc.