Grease in the hood is fuel waiting for a spark. The fire code sets how often it goes.

NFPA 96 sets how often a kitchen exhaust system is inspected for grease buildup. When the inspection finds grease, the system gets cleaned.

• Monthly: Systems over solid-fuel cooking, like wood- or charcoal-burning ovens and grills.
• Quarterly: High-volume cooking, like 24-hour kitchens, charbroiling and wok cooking.
• Twice a year: Moderate-volume cooking, which covers many full-service restaurants.
• Once a year: Low-volume cooking, like churches, day camps and seasonal businesses.

Your local fire marshal enforces the code, and your insurer may set its own terms. Ask both which interval applies to each store.

A full hood cleaning covers the hood, the filters, the ducts all the way to the roof and the exhaust fan. It's done by a hood cleaning company, usually overnight. They should leave a dated label on the hood and a report with before and after photos.

Keep those reports in the store's file. Inspectors and insurers ask for them.

The baffle filters in the hood catch most of the grease before it reaches the duct. They fill up fast.

• Pull and wash the filters on a schedule, often weekly, and more often over fryers and charbroilers.
• Run them through the dish machine or soak them in hot, soapy water.
• Never run the hood without filters in place.
• Wipe the inside of the hood where grease drips.
• Empty the grease cups or troughs before they overflow.

A clean hood that doesn't pull smoke has a different problem. Common causes are a slipping or broken fan belt, a failing fan motor, or not enough make-up air coming in to replace what the hood pulls out.

Signs to watch for:

• Smoke rolls out from under the hood instead of up into it.
• The fan sounds different, or squeals at start-up.
• Kitchen doors whistle or are hard to open.
• The kitchen gets hotter and greasier than it used to.

The fan sits on the roof, so the crew can't see it. Have it checked when you see any of these.

The fire suppression system above the line is inspected on its own schedule, usually every six months, by a fire protection company. Keep that tag current too. A clean hood and a working suppression system work together.