Temperatures reached by the roof structure of Notre-Dame de Paris in the fire of April 15th 2019 determined by Raman paleothermometry

When the Notre-Dame de Paris Cathedral burnt, the oak frame was almost completely destroyed. The temperatures reached were determined by an original method of Raman paleothermometry applied to charcoals collected after the fire. The Raman spectra of the charcoals evolve monotonically and irreversibly with the carbonization temperature and can therefore be used as "fossil thermocouples". A calibration curve was constructed from the carbonization between 500 and 1300 degrees C of unburnt oak pieces from the cathedral. Thus, the maximum charcoal formation temperature during the cathedral fire can be determined. The Raman analysis of charcoals sampled in situ serves to construct the first cartography of the carbonization temperatures. The temperatures reach values above 1200 degrees C in the crossing. These experimental data are the basis for a discussion of the consequences of the fire regarding possible lead dissemination and thermal alterations of limestone.