Kitchen Exhaust System

How often should my kitchen exhaust system be cleaned?
According to NFPA-96 Standard (Standard for Ventilation Control and Fire Protection of Commercial Cooking Operations) the following schedule shall be followed:

What Components of a kitchen exhaust system should typically be cleaned?
According to NFPA-96 section 11.6.1: “Upon inspection, if found to be contaminated with deposits from grease-laden vapors, the entire exhaust system shall be cleaned by a properly trained, qualified, and certified company or person(s) acceptable to the authority having jurisdiction in accordance with Section 11.4.”   

The entire exhaust system includes the hood, filters, fan and all associated horizontal and vertical ductwork. 

What should I consider to be clean?
According to NFPA-96 section 11.6.2: “Hoods, grease removal devices, fans, ducts, and other appurtenances shall be cleaned to remove combustible contaminants prior to surfaces becoming heavily contaminated with grease or oily sludge.”

IKECA has developed a Grease Gauge to determine cleanliness of the system. You can contact IKECA for more information.  

What risks am I exposed to in not properly cleaning a kitchen exhaust system?
Grease and particulate buildup in the exhaust system is a fire hazard, and greatly impacts on the efficiency and lifetime of mechanical equipment.  According to the National Fire Protection Association, the majority of restaurant fires originate on the kitchen cooking appliances and flare into the kitchen exhaust system.  If the entire exhaust system is not cleaned, a significant risk for fire exists whenever cooking appliances are used.  

NFPA 96 - 11.4 Exhaust System Inspection Schedule