Fire investigators say a carbon monoxide leak at a Kittery daycare was caused by a concrete saw.

The Maine Fire Marshal’s Office says seven people at the Building Blocks Learning Center on Route 236 were hospitalized Wednesday with non-life-threatening injuries.

An investigation found that the leak came from a propane-powered concrete saw that was being used indoors at an adjacent suite that’s not affiliated with the daycare.

Investigators also found that fire alarm detectors in the area where the saw was being used had been covered and the necessary permits for construction had not been sought through the fire marshal or local code enforcement.