Red vigilance for heat waves, the highest level of the “national heat wave plan”, which will be in force on Tuesday August 22 in four departments, corresponds to both an exceptional weather event and a health alert justifying “maximum mobilization”.
The four departments placed in heat wave red vigilance by Météo-France from Tuesday, August 22 noon are Drôme, Ardèche, Rhône and Haute-Loire. Forty-nine other departments will be on orange alert.
When is Red Vigilance triggered?
“The level of red vigilance corresponds to an extreme heat wave, exceptional in terms of its duration, intensity, geographical extension and presents a strong health impact for the entire population and societal impacts (drought, supply of drinking water, development or cessation of certain activities, etc.), “says Météo-France.
This system was created in 2004 by Météo-France and the health authorities after the heat wave of 2003. Last year, red vigilance for a heat wave was declared in June in fourteen departments of the South-West and in July in fifteen departments of the Atlantic seaboard.
“A system of criteria has been defined for each department with health actors (Public Health France in particular) based on the observed health impacts of high temperatures (maximum and minimum)”, details Météo-France. These criteria can be “modulated” according to certain aggravating factors, such as the duration or precocity of the heat wave, pollution, humidity, or mitigating factors (shortness of the episode, etc.).
“Météo-France forecasters thus compare the weather forecasts with the benchmarks established by Public Health France, based on epidemiological studies of past events, to estimate the level of heatwave vigilance”, adds the public body.
The prefects of the departments placed in red vigilance can thus prohibit or limit the extent of certain events such as sporting events or festivals.
Who is threatened?
“Each of us is threatened, even subjects in good health”, specifies Météo-France.
The increase in temperature can particularly endanger people at risk, i.e. the elderly, disabled, with chronic illnesses or mental disorders, pregnant women, people who regularly take medication , isolated people, details the meteorological agency. It also warns people who work outdoors, athletes, precarious or homeless people, prisoners and invites them to watch over young children as well.
What are we risking?
With high temperatures, one of the most serious health risks is “heatstroke”, a process of overheating of the body which can be fatal.
Faced with heat, which affects its functioning as soon as the temperature exceeds 25°C, the human body triggers several cooling mechanisms to maintain itself at 37°C (perspiration, increased blood flow in the most surface vessels). But sometimes that’s not enough, and the internal thermostat turns bright red. It’s heatstroke.
Under the effect of this hyperthermia, the heart rate is disturbed and accelerates sharply, breathing and pulmonary ventilation too. Despite the rise in internal temperature, the body comes to conserve water as much as possible, sweating stops and urine darkens or even disappears for several hours.
In the multiple warning signs to watch out for: fever over 40°C, extremely rapid pulse, hot, red and dry skin, headache, nausea and vomiting, impaired consciousness (drowsiness or, on the contrary, confusion, irritability, even aggressiveness).
Heat stroke is much more serious than other accidents also caused by heat, but without fever (heat cramps), or with moderate fever (sunstroke…). It can lead to blood clotting disorders causing brain damage, coma, and even death without timely medical treatment.
Young children, under the age of 5, and the elderly, with less efficient defense mechanisms, are most at risk. But healthy adults are not immune to such thermal failure. Especially if they work or play sports outdoors in scorching temperatures.
Intense or prolonged muscular effort under the sun exposes, in fact, to the risk of “exertional heat stroke” or “malignant hyperthermia of effort”, by aggravating the risk that the body temperature exceeds the bearable limits.
Behavioral abnormalities appear: the person has a drunken gait, appears increasingly irritable. Loss of consciousness or agitation with incoherent talk may appear afterwards. Faced with a heat stroke with the associated signs of severity, you must call the emergency services.
What behavior to adopt?
Behavioral advice is the same as for departments in orange alert, but also applies to healthy subjects:
Instructions can also be sent to crèches, leisure centers and holiday organizations to cancel outings, sports activities and festive events. Some establishments may even have to close if the temperature in their premises is too high.
