LYNN – A Molotov cocktail explosion on a Henry Avenue sidewalk Tuesday night is one of three fires in the past week under investigation by the Fire Department arson squad.Witnesses described a 20-foot bank of flames in front of 10 Henry Ave. at about 7:50 p.m. No one was hurt and no property damage was reported.”We don’t know the intended target but if anybody has information, they should call 599-0232,” said Fire Lt. David Legere.Firefighters are also investigating a dump truck fire last Saturday at 7:47 a.m. in a fenced-in area at the rear of 1071 Western Ave.”We consider this arson,” Legere said.He said a 27-year-old Malden man will be summonsed into District Court and charged with burning personal property following another fire last Saturday shortly after 10 p.m. in the driveway of 3 O’Leary Place.Legere said Sean McDermott will be charged with setting a rental car on fire following an argument with his father and his father’s girlfriend.”Alcohol definitely was a large factor,” Legere said.