WESTERLY, R.I. — A planned explosion at a quarry in a Rhode Island town sent granite flying into a nearby truck, injuring two town employees.

Authorities say one of the employees of Westerly's Public Works Department suffered head trauma and was kept at the hospital overnight after the blast Wednesday. The other employee was treated and released that day.

Interim Town Manager Mark Rooney says the workers had stopped alongside a road near the blast site to make a phone call when they were hit by flying debris. He says there was some kind of safety failure, but investigators have yet to determine exactly what happened.

A state police bomb squad is assisting in the investigation.