Rescue 40 (Smiley) just cleared back to back runs. First, responding to Interstate 95 northbound just prior to Chichester Ave for the accident with injuries. Upon arrival the crew secured hazards before clearing. The Rescue and Engine 40 (Powers) then responded to a 39 box on Market Street. The Rescue arrived as the first due special, and the Engine as the second due engine. It was determined to be a heater malfunction and all units cleared. As the day went on Rescue 40 (Minner), Utility 40 (Pintof), Medic 40-7, Medic 100-7, Ambulance 17-7, and multiple traffic units were dispatched to back to back accidents with injuries on Conchester Highway. The first accident was minor, involving 3 cars, with one refusal. The second was more serious, involving 5 vehicles, with 4 injuries. Units operated for about 1.5 hours.