At the time the fire was being fought, its cause was not known, but it was being treated as an accident. The investigation most strongly suspected a case of "accidental destruction by fire", but had not ruled anything out, saying it was too early to know the cause of the fire. It is not yet known if renovation work contributed to the fire. There have been other cases where renovation-related fires smoulder for hours unseen before breaking out. The firm Le Bras Frères that was carrying out the renovations stated they had followed procedure, and would co-operate fully with the investigation. They also stated that none of their personnel were on site at the time the fire broke out.