Each year, more than 450,000 lightning strikes on the ground are detected in mainland France by Météo-France, which has recorded an average of 260 thunderstorm days per year since 2000. On Tuesday July 11, Météo France placed 17 departments on orange alert for violent thunderstorms.
While about ten people die of lightning every year in France, we have gone through the rules to follow in the event of a storm, but also some received ideas.
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Thunderstorms are not sudden and unpredictable. "Nine out of ten storms are perfectly predictable, especially in terms of their evolution over the hour," says Stéphane Schmitt, expert with Météorage. In February 2022, with the meteorologist Michaël Kreitz, he published in the journal La Météorologie an analysis of human accidents caused by lightning in ten years in Europe: in total, 215 lightning strikes having caused 83 deaths and 971 injuries in twenty countries.
“Based on the state of vigilance of the fifty-six cases in France, thanks to access to the archives, no case of absence of vigilance (level “green”) was noted which could have misled the victims on the complete absence of weather hazard," the authors write. They further note that the majority of accidents occur during moderate thunderstorms, and not during “remarkable episodes or severe situations. Which reminds us that "any storm is inherently dangerous".
Of the 215 accidents studied, nearly three out of five victims were engaged in a leisure activity at the time of the storm and had easy access to buildings providing shelter.
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It is not recommended to use any electronic device directly connected to an outlet, because lightning can pass through the electrical or receiving connections. Do not use a computer connected to the mains, a game console, an oven or even a washing machine, as specified in a prevention campaign by the authorities. If the ideal is to have disconnected the sensitive installations before, it is better not to approach the sockets or electrical panels when the stormy episode is in progress.
You should also avoid using a landline phone during the storm. Cell phones, on the other hand, do not increase the risk of being struck by lightning.
Lightning can also be conducted through plumbing: do not bathe, shower, or even wash dishes when there is lightning, and generally avoid contact with water.
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Provided that it is not convertible, a car is a good protection against lightning. Indeed, if a lightning strikes the metal structure of the automobile, the current flows along the bodywork and escapes towards the ground, thus protecting the passengers from electrocution. This is the scientific principle of the Faraday cage, a metal enclosure impervious to electromagnetic fields. Beware, however, of vehicles built with composite materials, such as motorhomes, which do not offer this protection in the event of a storm.
It is still advisable to stop in a safe place and take shelter in a building. The danger in a car is not related to lightning, but to the effects of wind or heavy rain.
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Contrary to an urban legend, tires do not protect against lightning. By bicycle, scooter, motorbike or even Segway, it is therefore advisable to take shelter inside a building, as far as possible. And all contact with metal should be avoided.
“Above all, we must not consider that we are fleeing from lightning because we are moving. There are still many cases of cyclists struck down by lightning,” says Stéphane Schmitt.
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This is the basics of risk reduction during a stormy episode, and yet... According to the study by the journal La Météorologie, in a quarter of the 215 accidents analyzed, the victims of lightning had been affected when they were "under or near trees" or in "a makeshift shelter (wooden shack, shed, etc.)".
The principle is simple: lightning always seeks the shortest path between the cloud and the ground. Even if it rains very hard, you should not take shelter under an isolated tree.
In a forest, the risk of lightning hitting the tree under which you are sheltering is lower, but it is still advisable to move as far away as possible from the trunks and branches, while anticipating their fall. Again, it is better to take shelter in a "hard" building or a car.
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Contrary to this popular saying, lightning can strike the same place twice, since lightning always seeks the shortest point between the cloud and the ground. Thus, very tall and pointed buildings amplify the local electric field and create a "peak effect". This is the principle of the lightning rod. According to Météorage, in ten years (2008-2018), the Eiffel Tower received 37 lightning strikes and the Pic du Midi de Bigorre (Hautes-Pyrénées), located at 2,876 meters above sea level, was struck 1,874 times.
However, this received idea is not completely silly if we exclude large buildings, explains the Météorage expert: "In France, we have approximately one flash per square kilometer per year, the probability that it will fall exactly the same place the following year is extremely low. »
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Of the eighty-three deaths analyzed over the past decade in Europe, two-thirds involved males, according to the aforementioned study. This can be explained by an underestimation of the risk in men, who tend to consider that the storm episode is not dangerous.
Another track, according to the co-author of the study: "Many external activities, such as maintenance or construction trades, are carried out by men". Indeed, the in-depth survey of European accidents shows that 19% of victims were at their workplace outdoors.
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According to Stéphane Schmitt, between 5,000 and 20,000 animals die each year from lightning strikes in France, most often cows, due to the large cattle herd (more than 18 million).
Like humans, cows are rarely hit directly by lightning, but rather fall victim to the phenomenon of "stepping voltage": the impact falls nearby and the electric current spreads to the ground before rising through the legs. If, for humans, the current passes from one leg to the other avoiding the thorax, it is often fatal for quadrupeds since it crosses the whole body and touches the heart. In Norway, three hundred reindeer were struck down simultaneously in August 2016.
True, but...
In principle, running during a thunderstorm increases the risk of "stride strain", i.e. the current passes between the legs with greater strain since the feet are spread apart.
If it is impossible to take shelter, it is therefore often advisable to squat on the ground, feet together, knees against the chest, head tucked in and hands on the ears, so as to reduce the maximum contact with the ground that will conduct electricity. Above all, do not lie down. If there are several of you, you must also avoid grouping together, to prevent the current from spreading from one person to another.
In practice, however, it is better to try to reach a building if it is nearby. "Despite all the physical and electrical considerations, run for cover if you can," advises Stéphane Schmitt of Météorage. If you're on a football pitch, for example, your upper body is the highest point on that flat surface. Better to rush to the locker room than to remain crouched for tens of minutes, in a very uncomfortable position. »
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There is no risk of being electrocuted by touching a person who has just been struck by lightning: the current has only passed through the victim, who does not retain any electrical charge.
On the contrary, it is necessary to come to his aid quickly after having informed the emergency services. If the victim is conscious and breathing normally, they should be covered. If she is unconscious, she should be laid on her side, in the lateral safety position (PLS). Finally, if she is no longer breathing, it is necessary to give her a cardiac massage while waiting for the arrival of help.
If the risk of lightning is persistent, try to take shelter and space yourself at least three meters between each person to avoid a collective lightning strike.
False but...
This is a subject on which not all experts agree. Some consider that an air current could generate a charge of electrons attracting lightning in the home. Others consider it unlikely that this could constitute an additional risk of lightning.
In any case, it is still advisable to close your windows during a storm, at least as a precaution against gusts of wind and rain.
