A 34-year-old man was hospitalized following a Saturday evening unofficial fireworks display at a Somerset County park, according to police. The man was attending a block party at Cooper Street Park in Manville when an “improvised fireworks device” exploded, injuring the man in his upper body, local police said on Sunday. Police did not elaborate on the type of equipment used to discharge the fireworks or say if the man was the person handling the explosives at the time. About 100 people were attending the party when the explosion happened around 8:15 p.m., police said. The park, with a playgr…