That can make fighting fires tough.

Church fires are “one of the most difficult challenges to fire departments around the world,” Mr. Nigro said. “A fire in a house of worship has always been a cause for concern. I didn’t start worrying about them yesterday.”

As Mr. Nigro puts it, the goal is simple: “Put enough cooling power, which is water, on the fuel.”

He said extinguishing flames could be hard in a church like Notre-Dame because “that building is longer than a football field.”

It is “an elevated lumberyard being held up by stone walls.”

In New York, the Cathedral Church of St. John the Divine is bigger and younger than Notre-Dame, but looks a lot like it.

“The renderings I’m looking at in my office are very similar,” said James Patterson, director of facilities and capital projects at St. John, in Manhattan’s Morningside Heights neighborhood.

A small fire in the basement forced Palm Sunday services and soup kitchen operations to move outside. Nobody was injured. In 2001, a major fire damaged the north side of the church.

Mr. Patterson said installing sprinklers at St. John could be ineffective or potentially dangerous. The church has a lot of granite and limestone, which complicates firefighting strategies, he explained.

“When the stone heats up, if there ever was a fire, the last thing you want to do is spray it with water,” he added. “What it does is it just pops all the stones apart.”