The state fire marshal’s office has suspended the licenses of a pyrotechnician and a fireworks company after unexploded shells were found left behind at several of their recent shows, including the July 3 fireworks display on the Stoughton High School football field. A Stoughton High maintenance worker set off a large shell Tuesday morning while mowing a field behind the school. The explosion lifted the mower off the ground, but the worker was not injured, officials said. State Fire Marshal Stephen Coan ordered the suspension of the pyrotechnician at the Stoughton show, and lifted the operating certificate for Pyrotecnico Inc., of New Castle, Pa. Unexploded fireworks were also found after Pyrotecnico shows in Waltham, Ware and Worcester, authorities said. Fireworks companies are required to conduct “first light” inspections the morning after a show to collect any unexploded shells. Coan also ordered a review of all shows Pyrotecnico has performed in the past 45 days. The company must undergo an administrative hearing before Coan in order to regain its user’s certificate.