1. Partial or complete pulverizing system failure
2. Primary fan, blower, or air preheating trip
3. Boiler MFT
4. Failure of furnace negative pressure automatic control
5. Primary and secondary air dampers of air preheater, blower/primary fan blades and outlet dampers are closed
6. Blower trips, and the corresponding side induced draft fan does not trip
5. Primary and secondary air dampers of air preheater, blower/primary fan blades and outlet dampers are closed
7. Automatic induced draft failure, sudden increase in opening
