how the cathedral is protected from another fire like that of 2019

FRANCE – On April 15, 2019, black smoke rose above Paris. First images are flooding social networks and news channels: fiery red flames are devouring the framework of one of the most beautiful monuments in the capital. Notre-Dame is on fire. Five years later, the cathedral reopens its doors this Saturday, December 7, with an absolute priority: to prevent such a disaster from happening again.

To ensure this, the architects modernized the fire-fighting system of the Gothic jewel. An essential step, since this system had shown its limits during the 2019 fire. Indeed, if the start of the fire, the origin of which remains undetermined to date, had been quickly detected, around thirty precious minutes had been lost due to protocol. We had to wait two “removal of doubt” by security agents to attest to the presence of flames and finally notify the firefighters.

Now the cathedral is “army against fire”ensures the public establishment Rebâtir Notre-Dame de Paris, which managed the work for five years. Everything has been redesigned so that Notre Dame can defend itself. A precaution all the more necessary as the monument was rebuilt identically, with its wooden frame and its lead roof, despite the risks generated. “We cannot build wooden frames of this size today without very careful consideration of fire safety”concedes Rémi Fromont, chief architect of historic monuments, responsible for monitoring the site.

If zero risk does not exist, Notre Dame now has an important defense system against fires, which should both detect the fire more quickly and limit its spread.

A sophisticated fire detection system

The air in the cathedral is now monitored 24 hours a day. Tubes constantly suck it in and redirect it to a fire detection center, responsible for analyzing it. In the event of a fire, smoke enters these pipes and the fire alarm is triggered automatically.

Fire can also be detected by thermal cameras, capable of reporting temperature anomalies using infrared energy. Around fifty of these cameras were placed in the cathedral, particularly at the points most at risk such as the spire, the large attic or the electrical panels.

“If you have a circuit breaker burning in an electrical cabinet, the thermal camera will detect that there is a fire in the cabinet and automatically activate the water mist. So nothing can happen without us knowing.”described to AFP Eric Lazzari, manager at French Electronic Detection (DEF), responsible for the new fire-fighting mechanism. If we also count smoke detectors, Notre-Dame now has more than 300 detection points.

A giant mister in the cathedral

This is a great first for a French cathedral. Notre-Dame is now equipped with a misting mechanism, which is triggered automatically when smoke is detected in the monument.

In the event of a fire, millions of microdroplets escape from the pipes, creating a fine mist of water. This cloud reduces the temperature almost instantly: it is capable of dropping it by 500 degrees in one minute. The flames are then smothered, without directly watering the vaults of the building, which would weaken them.

This new device was installed in the form of discreet pipes along the medieval framework and up to the spire, as you can see in the photo below.

Architecture redesigned to limit risks

Every minute counts. It is with this idea in mind that the architects rethought the security of Notre-Dame. Several solutions were put in place during the assembly of the new framework. The battens, for example, were thickened by 15 millimeters. A detail at first glance, however “ every time we add a millimeter to the roof, we gain a minute before the fire pierces the roof”explains Rémi Fromont in the specialized journal The Factory of Notre-Dame. This adjustment should therefore save a precious quarter of an hour.

In the same way, two fire trusses were installed. As you can see in the diagram belowthey separate the upper part of the cathedral into three parts: the nave, the choir and the transept with the spire. In the event of a fire breaking out in one of these three volumes, these farms will help delay “dramatically spread” of the fire, specifies Rebâtir Notre-Dame de Paris.

Finally, access to firefighters has been improved and the dry columns have been redesigned to be easier to use. The flow of water available around the cathedral has also been multiplied by three, to reach 600m3 of water per hour.

If the 2019 fire made the revision of Notre Dame's fire-fighting system inevitable, it also led to a wave of modernization throughout the national territory. The security plans of other French cathedrals were gradually updated by the Drac, with the same challenge as in Paris: knowing how to deal with fire.

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