Under pressure from labor inspectors concerned about lead risks, the Paris region administration suspended cleanup work at the cathedral last week, and ordered new checks of schools and nurseries in the neighborhood.
The administration announced in a statement Friday that workers will be allowed back starting Aug. 12, but in smaller numbers and with tougher new decontamination measures and equipment "to prevent any release of polluting elements to the outside."
Critics say authorities didn't move fast enough to protect workers and residents when the cathedral's massive lead roof and spire melted in the April fire, spewing toxic dust into the Paris air.
A lawsuit has been filed, and a union-led collective is demanding the "total confinement" of the site.
No dangerous levels have been registered, however, in nearby streets, where tourists and residents continue to circulate and souvenir shops and restaurants have reopened.
But environmental groups say authorities weren't aggressive or open enough about warning the public about lead levels at the time of the fire.
Children are especially vulnerable to health problems from lead poisoning and exposure, so authorities ordered a deep clean for neighborhood schools and recommended blood tests for children under 7 and pregnant women who live near Notre Dame.
The new security measures for the cathedral will limit the number of workers allowed inside at any time to 30-40 instead of the 60-70 currently allowed, at least until new decontamination kits are delivered in the autumn when the pace of work is expected to pick up.
The main focus is "to ensure that the work doesn't generate any pollution outside the work zone," the statement said.
This story has been corrected to show that work will resume later this month, not next month.