The temperatures perceived by the human body do not always coincide with those recorded by environmental or meteorological thermometers. Factors such as air humidity, wind, the presence of water or sweat on the skin have the effect of altering our thermal perception, sending to the brain the so-called “perceived temperature” from the body, generally different from the absolute recorded temperature from thermometers.
Generally, humans have the ability to maintain a constant body temperature (around 36.5 degrees centigrade) producing sweat when the external environment becomes warmer and burning more calories when the air becomes colder. But what happens when the body heat is subtracted from the skin by the wind? In these cases we speak of windchill effect, which is a phenomenon that occurs when our body is subjected to a constant flow of air. In these conditions the temperature perceived by the body drops directly proportional to the wind speed and to the surface of the body in contact with the air.
More precisely, the windchill effect consists in the rate of heat loss by the body, and is dependent on the velocity of the air current that invests it. Try to blow on your hands: the skin, until then in a state of quiet, is suddenly hit by the jet of air which cools the skin by subtracting heat and producing that typical feeling of cool (or real cold) that we find in these cases. The windchill effect should not be underestimated if there is no suitable shelter or clothing available because, in extreme situations, prolonged exposure to air flow can lower the body temperature to such an extent that hypothermia, even when temperatures are not too low. The following table shows the effects of the windichill effect on the “perceived temperature” through the relationship between the air temperature and the wind speed. Choosing a temperature on the upper part of the table and choosing the wind speed on the left side, it is possible to cross the row and the chosen column to see the temperature perceived by the body:
As you can see from the table, if the air temperature was 0 ° and we were in the middle of an air flow of 20 km / h our body would perceive a temperature of -5 degrees. There are several tables that measure the windchill effect, each based on different considerations and values, but the true purpose of these measurements is not to accurately indicate the centigrade degrees perceived by the skin but to illustrate the incisive wind effect on the resistance of the body in nature.
The windchill effect should not be underestimated at all: a well-made and well-sheltered shelter is of no use if the opening were to be hit by a draft of air during the night! When looking for a good place for your camp, try to keep in mind the windchill effect by orientating its entry point towards a rock wall or some other natural barrier. In these cases it may be useful to keep one thing in mind: at night the air tends to cool, causing the warm air to rise upwards and the cold one to go downhill, thus causing a possible breeze coming from the mountain. and go down to the valley. To avoid being in the middle of a sudden nighttime air flow, try, as far as possible, to direct the entrance of your shelter towards the valley or at least to build an effective “entrance door” able to shelter you!
The windchill effect must also be kept in mind when choosing hiking gear. Garments such as sweatshirts and heavy coats may not be sufficient if they do not have good resistance to the penetration of the air stream between the fibers. To block the wind and prevent the loss of body heat in this way it is not necessary to increase the layers of clothes on the skin, but it is sufficient to choose the right fabric. A good windbreaker, however light and thin, can be much more efficient than a wool coat in keeping the body warm! The ideal rule would be to use insulating fabrics for the maintenance of body heat (wool or fleece) covered externally by a windbreaker able to avoid drafts in the inner layers, with the sleeves and the neck laced by tear or elastic closures .
In this regard, in the best hiking or mountaineering shops there are some machines able to produce wind at about 20km / h to be used to verify the effective capacity of the fabrics to block the advance of the air. Just drive them and place the fabric under examination between the air stream and their hands, verifying the true quality of the garment.
Very similar to the windchill effect, but much more dangerous, is the waterchill effect that causes the loss of body heat when the skin is in contact with water. The ability of water to remove heat from the skin is much more intense than that of the wind and can incur whenever we find ourselves with wet skin due to a sudden storm, a fall in water, a high humidity night or, more simply, because of sweaty clothes. Precisely for this reason it is absolutely necessary to try not to ever wet your clothes or choose little or no breathable fabrics as, in a few minutes of physical effort, we could find ourselves with clothes soaked in sweat.
Let’s try, now, to imagine the combined effect of windchill effect plus waterchill …. the effects on body temperature would be dangerous and disastrous, causing a loss of heat so fast to put us at risk of hypothermia.
If we ever find ourselves in emergency situations under heavy rain and strong winds, the priority would be to protect ourselves from the elements as quickly as possible and keep our clothes dry, at the cost of undressing and staying naked. As contrary to the common logic and instinct this move could make the difference between life and death by hypothermia!