An arsonist kept firefighters and sheriff’s deputies busy Thursday morning with a string of downtown dumpster fires. The incidents happened at dumpsters behind businesses in the hospital district that’s along the downtown Walton Way corridor. They included fires behind a dialysis clinic, a gas station and other businesses, mostly along Walton Way but also extending south to the 1100 block of Druid Park Avenue near Paine College. The incidents started sometime after 8 a.m. and continued until about 8:45. Firefighters at the scene said Richmond County deputies were looking for a single suspect in the string of fires.