A central premix system with a flammable mixture in the blower or compressor shall consist of the following components:
- Gas-mixing machine in the form of an automatic gas-air proportioning device combined with a downstream blower or compressor.
- Flammable mixture piping. not less than Schedule 40 NPS.
- Automatic firecheck(s).
- Safety blowout(s) or backfire preventers for systems utilizing flammable mixture lines above 21/2 inches (65 mm) nominal pipe size (NPS) or the equivalent. [NFPA 54:7.12.1]