Combined-cycle plants, gas and steam turbines carry 10,000-25,000 L of mineral oil for hydraulic and bearing lubrication. ISO VG 32/46 oil autoignites around 320 C; a high-pressure (15-20 bar) pipe leak creates a jet fire. NFPA 850 (Electric Generating Plants) specifies water spray and CO2 protection for oil reservoirs, pumps and bearing pedestals.
Oil System Risk Points
- Main reservoir: 15,000-25,000 L stainless tank
- AC/DC oil pump: seal failure risks jet fire
- Bearing pedestal: oil leak ignites on hot turbine casing
- Oil cooler: plate heat exchanger leaks into boiler room
- Hydraulic system: 200-300 bar phosphate ester (Skydrol) has higher flash point
Water Spray Design (NFPA 15)
- Density: 10.2 L/min/m2 (0.25 gpm/ft2)
- Area: reservoir + pump + 6 m radius
- Nozzle: medium-velocity spray, 90 deg cone
- Activation: linear heat detector (thermistor cable) at 57 C
- Water reserve: 30 min minimum; AHJ may require 2 hours
CO2 Total Flooding
- NFPA 12: CO2 surface total flooding for bearing enclosure
- Design concentration: 34 percent (mineral oil)
- Discharge time: 2 min
- Interlocks: 30 s pre-discharge alarm, door lock, HVAC shutdown
- Caveat: CO2 is an asphyxiant — mandatory evacuation
Emergency Shutdown
- Oil pump ESD: 5 s after detection
- Dump valve: main reservoir drains to underground emergency tank
- Turbine trip: burner management system (BMS) fuel cut
- HVAC shutdown: prevents smoke spread
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SprinkCalc sizes turbo generator water spray at 10.2 L/min/m2, medium-velocity nozzle count and 2-hour water reserve per NFPA 850.
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Sources & Further Reading
NFPA 850, NFPA 15, NFPA 12, FM Global DS 7-101, IEEE 979. NFPA 850 Electric Generating Plants.