I was wondering what the FSL, FFC, FIC and I blocks mean

PAH PIC Methane AR M AT Catalyst tubes Pressure compensated FIC S HV Product (CO + 3H.) Firing rate set point Firing controls Hydrocarbon feed gas (TYP) FC Shutdown (CH) FAL FSL Preheat coil (Figure 2) /11 2.7:1 Hundreds of burners Furnace BH FEC FAL 3:1 HIC Superheated steam (H,0) Typical for all burner fuel valves FO FV 2