A police investigation is under way into how the fire could have started, including looking into whether there could be any connection with the spire restoration works. The Paris public prosector has said there is no indication any deliberate act was involved in the fire.

However asked about any precautions against fire, Marc Eskenazi, in charge of communications at Le Bras Frères, based in Grand Est, told Connexion there were smoke detectors on the scaffolding, which was on the outside of the spire.

“There were detectors with alarms on the scaffolding, and they did not go off; only alarms inside the cathedral itself went off,” he said.

He said they cannot comment on how the fire could have started, and do not know. They also do not know exactly where the fire broke out.

“Our workers are responding to the police’s questions,” he said.

He added: “There’s no hot point on scaffolding, there was no soldering or anything like that happening. No welding torches, nothing like that. There’s no risk of fire.”

Mr Eskenazi added that no workers were present when the fire started. “Everyone had gone home.”

At present the fire remains a mystery, he said. Asked if the company is shocked by what has happened, he said: “Obviously”.

According to Julien Le Bras, who recently took over as managing director of the company, 12 people were working on the restoration of the spire, which was only in the preliminary stage of setting up the scaffolding.

The firm, a small family business, was founded by his grandfather. It won the Notre-Dame job in 2017 and is experienced in doing similar restoration jobs on historic monuments including other cathedrals and the dome of the Panthéon.

At the time, regional paper le Républicain Lorrain reported on how Mr Le Bras spoke to his employees about his pride in being awarded the job in the face of competition from large international groups.

A report on the complexity of the scaffolding arrangements can be viewed here.