What precautions might I take?

Some experts recommended staying away from the immediate vicinity of Notre-Dame, particularly if you have children under 6.

“I would be saying to parents, ‘Don’t panic, these are the three or four things you should do,” said Dr. Sean Palfrey, a professor of pediatrics and public health at Boston University and director of the Boston Lead Poisoning Prevention Program, a state public health service.

Dr. Palfrey said that residents should be careful to wash their infants’ hands, so that they don’t pick up dust and put it in their mouths.

He also urged parents to be sure that their children had a diet with a good, nutritional dose of iron and calcium, which can displace lead in the body and make the body less likely to absorb it.

Residents should be sure to clean their apartments with wet mops or cloths, not brooms, which can simply stir up the dust. Vacuum cleaners with special filters, called Hepa filters, can also be used, experts said.

“If I could tell parents one thing, it’s that they should leave shoes at the door, keep the house really clean of dust and make sure everyone washes up before they eat,” said Jessica Wolpaw Reyes, a professor of economics at Amherst, in Massachusetts, who has done extensive studies on lead.

And everyone said that the government needed to clean up the city and its schools as soon as possible.