Notre Dame Series Pt. 2 - The Environment

22 April 2021

Notre Dame Series Pt. 2 - The Environment

Notre-Dame de Paris is no stranger to grit and grime.

In 1963, workers began cleaning the cathedral’s façade of centuries of soot. Then between 1991 and 2000, they repeated the effort. Nothing, however, could have prepared those involved in post-fire restoration for the environmental havoc they found.

Notre-Dame’s walls and vaulted ceiling are stone, but its roof and spire are ancient 13th century oak sheathed in lead to protect against water damage. The elegant spire—also called a flèche, or arrow—has been rebuilt several times over the centuries.

Construction techniques, building materials, age, and fire all came together in a perfect storm. Stonework was eroded by weather and pollution; water leaks breached the spire’s lead sheathing. Roof timbers were porous and powdery. Fragility ruled the day.

The commanding role of lead

Essentially, the story of the Notre-Dame fire and the environment is the story of lead.
Lead melts at 300° and vaporizes at 1700° C. Experts studying the fire believed that it never reached vaporization temperature, though it did exceed 600° in places. At 600°, lead oxidizes into microscopic particles, forming an ugly yellow cloud that poured out of the cathedral. A metallurgist at LRMH—the laboratory in charge of preserving French national monuments—commented, “It’s like hairspray.” At 300°, the lead just melted, flowing into gutters and forming stalactites that hung from the ceiling vault. A surreal sight and horrifying indeed.

Air and water quality

Airparif, which monitors air quality in the Paris agglomeration, noted that the winds quickly carried smoke from the fire along the Seine River corridor. The organization didn’t find elevated levels of particulates at close-by monitoring stations. And the Paris police said that breathing the air around the fire site posed no danger.

And yet … average Paris lead levels are typically 5X the indoor limit of 1,000 micrograms per square meter—caused by runoff from the roofs of old buildings. Health authorities recommended blood tests for children and pregnant women living in the area. In July, the Ministry of Health raised the outdoor legal limit for lead to 5000 micrograms/m2. Authorities expressed concern over pollution of the Seine, and plans were made to monitor water quality near the fire site and downstream.

Worker safety

At first, scientists tasked with remediation and restoration showed little concern over own their safety. However, stringent safety requirements were quickly enacted—including the wearing of paper underclothing, hazmat suits, protective masks and limiting exposure to 2.5 hours at a time, followed by showers. One of the scientists commented that he and his colleagues were taking as many as five showers a day and that getting through them was “like getting through the Métro at rush hour.”

We’ll continue this story next week, with an installment that discusses what was lost and what was saved.
Photo by Nivenn Lanos on Unsplash