Supports up to four relief fans. Relief fans are lead or lag alternated. Group together operating relief fans which serve a pressure zone as if they were one system, running at the same speed when enabled and using the same control loop, even if they are on separate AHUs. This may require some network setup. Relief fans enable whenever their associated supply fan is proven on and disabled otherwise. A single P-only control loop for the pressure zone will maintain the setpoint (BLDGP-SP). The loop enables whenever any supply fan for any system in the pressure zone is proven on and set to zero otherwise. The building pressure is maintained using a sequencer which supports up to four relief fans. The first stage shall only utilize the pressure zone exhaust air dampers. Subsequent stages lead or lag the relief fans of the pressure zone. If the control effort required to maintain the static pressure setpoint is too large for longer than the interstage on delay (RLF-INTER-ON AI) the system stages up (open dampers or turn on a fan). If the control effort is too small (below the minimum speed) for longer than the interstage off delay (RLF-INTER-OFF) the system stages down (turn off a fan or shut all exhaust dampers). For systems where the relief fans share a common inlet plenum, the SHARED-PLENUM BI set to true, all dampers close whenever a relief fan is on with the exception of the dampers associated with any running relief fans. For systems which do not share a common inlet plenum, the SHARED-PLENUM BI set to false, exhaust dampers remain open whenever their associated supply fan is proven on unless all fans and subsequently the dampers are staged down.