Commercial kitchens (hotel, hospital, school cafeteria) see deep-fryer fires as the most common grease-fire type. Vegetable oil auto-ignites at 365 C and cannot be extinguished with water (oil-water steam explosion). NFPA 96 covers hood, duct, fan, damper and suppression; UL 300 specifies wet-chemical (K-class) agent and saponification.
Oil Auto-Ignition Physics
- Flash point: 315 C
- Auto-ignition: 365 C (soy/sunflower)
- Smoke point: 220-240 C (normal frying)
- Cooking temp: 180 C (french fries)
- Safe range: 145 C thermostat cutout
NFPA 96 Hood and Duct
- Hood overhang: 150 mm on all sides
- Capture velocity: 0.4-0.5 m/s horizontal
- Duct slope: 20 mm/m toward drain
- Access door: every 3.6 m (12 ft)
- Material: 1.5 mm (16 gauge) carbon steel or 1.2 mm stainless
- Clearance: 450 mm from combustibles
UL 300 Wet Chemical
- Agent: potassium acetate / citrate
- Saponification: oil + K+ forms soap film on surface
- Cooling: steam 100 C below oil's 365 C
- Capacity: 6 L agent - 3 fryer coverage
- Discharge: 30 s, appliance-specific nozzle
- Test: UL 300 2019 - new protocol
Interlock and Detection
- Fusible link: 260 C in hood
- Spot heat detector: modern electronic
- Gas shutoff: auto on suppression activation
- Fan: exhaust continues, makeup closes
- Alarm: customer evacuation + kitchen staff
Common Errors and Cleaning
- Grease buildup: 0.05 inch max on duct
- Cleaning frequency: NFPA 96 Table - monthly/quarterly/annual
- K-class extinguisher: 1 per 11 m2 (mandatory)
- Staff training: water on oil fire FORBIDDEN
- Records: cleaning certificate per NFPA 96 Annex
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Sources & Further Reading
NFPA 96, NFPA 17A, UL 300, OSHA 29 CFR, IMC 507. NFPA 96 Ventilation of Commercial Cooking.