Notre Dame Cathedral was 'vulnerable' to fire, expert says

"If there is a most vulnerable time for a church, it is when it is under construction," one fire expert said.

Firefighters continue to extinguish flames at the Notre Dame Cathedral in Paris on April 15, 2019.Philippe Wojazer / Reuters

The cause of the massive blaze that engulfed the iconic Notre Dame Cathedral in Paris is under investigation, authorities said Monday as firefighters continued to work to save the world-famous landmark.

But some experts said the extensive renovations going on at the historic building could have contributed to the fire.

There is a history of churches, synagogues and temples going up in flames while under repair, said Glenn Corbett, an associate professor of fire science at John Jay College in New York.

Notre Dame, which was built in the 12th and 13th centuries, has a wooden roof.

"If there is a most vulnerable time for a church, it is when it is under construction because we get people who are using torches or welding or cutting, that are of course sources of ignition, to set the wood roof structure on fire," Corbett said, noting that the interior of the Paris cathedral was covered in scaffolding when the fire began at about 6:50 p.m. local time Monday, near the start of Holy Week.

In 1998, Central Synagogue, a national and New York City landmark, was heavily damaged in a fire that resulted from a construction worker's blowtorch during renovations. The roof and its supports were destroyed in the fire.

Sparks from welders are often so far off the ground that they are out of reach of firefighters with standard fire-suppression methods, such as water from hoses, which makes it harder to fight the fire, Corbett said.

On the other hand, the collapse of Notre Dame's roof in the blaze could help firefighters by "putting the fire closer to them rather than up in the sky," he said.

"Once the roof is consumed, all that burning debris is going to fall at the floor level and of course, everything that’s down there will be on fire," Corbett said.

With the fire at ground level, officials could then work with structural engineers to save the remaining walls, adding that it could take up to a week for firefighters to completely extinguish the fire.

Michel Picaud of the Friends of Notre Dame, a U.S.-based foundation dedicated to fundraising for the cathedral's reconstruction efforts, said the entire roof was destroyed.

"The fire started up near the roof top, while another fire started in the north bell tower," Picaud told NBC News. "All damage seems to be up high and did not go into the lower part of church or touch the organ or stained-glass windows."

Notre Dame draws 13 million visitors a year.

And Corbett said its popularity and rich history could ultimately aid in ensuring it is restored.

"Fortunately, for Notre Dame, I’m sure they’ve got deeper pockets to rebuild this church," Corbett said. "But there are a lot of churches that, if they lose their building, that’s it."