Two days after the fire that ravaged part of the Notre-Dame cathedral in Paris, the investigators are already at work trying to identify the exact causes.

ON DECRYPT

If the fire is now limited to the Notre-Dame cathedral, the investigation is just beginning to know what caused the loss of the frame, the spire and the roof, among other elements of this iconic building. from the capital.

List the sources of energy

About 50 police officers have been seized, while the accidental trail is preferred. One of the five specialized laboratories of the scientific police was also asked, with a very precise method: one must first freeze the scene and possibly model it in 3D, in order to keep a trace of all the elements of the cathedral. Then you have to collect photos and videos of witnesses.

Once the place is secure, it is necessary to crisscross the area to identify what could have caused a fire start: "We will take inventory of all sources of energy.This may be a cause linked to a human activity, like work, or a butt ... There are also electrical causes, "says Véronique Vidotto, the head of the fire and explosion department of the National Institute of Police Science Haute-Garonne, Toulouse. The goal, in fine, is to determine "all that is likely to give this activation energy"

Reassemble the logic of fire

To verify each hypothesis, we must go back in time. For if a layman sees the fire as a form of chaos, the specialist perceives a logic in the course of this event. "We have a living behavior, or human: fire needs to eat, it is the fuel, so we will be able to follow its path", describes Dominique Deharo, deputy director of the laboratory. "The fire was able to start a few tens of meters away and find a way of development.Our colleagues from the central laboratory of the prefecture of Paris will go back this logic."

The monitoring of the triggering of the alarms could also make it possible to restrict the zone of investigations. But what is certain is that this is a meticulous job that could take long weeks on a site of this magnitude, while Emmanuel Macron has promised to "complete the restoration" of Notre-Dame de Paris within five years, a delay a priori complicated to hold according to specialists.