Something is cooking for NFPA 96

NFPA Journal, May/Jun 2004 by Eden, Chris

At NFPA's World Safety Conference and Exposition(TM) this May, NFPA members will vote on a revision to NFPA 96, Ventilation Control and Fire Protection of Commercial Cooking Operations, that aims to simplify the code by moving toward a unified test standard.

The food service industry is big business in the United States. Just look around. Restaurants are popping up everywhere. Sports stadiums offer more choices of food, and the mall food court concept is well established. More and more people trade home-cooked meals for a quick bile out.

According to the National Restaurant Association's 2004 Industry Forecast, the United States will have 878,000 food establishments by the end of 2004, an increase of almost 80 percent from 1972. And the number of establishments is expected to hit more than 1 million within six years.

According to NFPA 96 staff liaison Jim Lake, NFPA data show that the biggest property protection issue for the restaurant industry is grease fires because of the significant expense per fire.

Every vaporized or coagulated drop of grease in a duct is tremendously flammable, and duct fires can reach temperatures of 1,600°F (871°C) to 2,000°F (1,093°C) within minutes, hot enough to melt aluminum and ignite surrounding combustibles within seconds.

"The duct system is but one component of the safety intervention associated with grease risk factor. But it's a crucial factor-it must be hermetic and designed in a fashion that it can be cleaned and doesn't leak," says Tom Johnson, owner of Johnson Diversified Products, a consulting and manufacturer's representative firm.

Johnson serves on the NSF Joint Committee for Food Equipment, as well as Underwriters Laboratories, Inc.'s User Advisory Council.

NSF provides product certification and safety audits for the food and water industries.

Types of systems

Several types of grease duct systems are currently available. For years, the rectangular site-built system, made of carbon steel, welded on site, and enclosed in a constructed, fire-rated shaft, was the only system allowed. Various building codes specify the construction, building materials are easy to come by, and the system can be customized on site.

In the early 1960s, the rectangular, site-built, ductwrapped system made its debut. Instead of being enclosed in a constructed shaft, the duct is wrapped in layers of insulation, and the seams are taped or clamped. This type of system reduces code-prescribed clearances to combustibles, in some cases to zero.

Finally, there's the factory-built, insulated, integralchased duct system that came into being when manufacturers oi insulated chimneys realized the product they used for industrial chimneys could also be used to replace welded grease ducts, duct wraps, and constructed shafts. The components of this type of system are manufactured and inspected off site, and assembled on site, without welding. The stainless steel duct is cylindrical, wrapped with insulation, and enclosed with a stainless-steel casing.

Each system design has different weaknesses and strengths

Among the weaknesses are inconsistent welds, which expand at different rates and often fracture or contort the duct system. If the torsion is too great, the duct can separate itself from supporting braces. At best, the system must be repaired; at worst, the shaft may be damaged or the duct may move too close to surrounding combustibles.

When welds are inconsistent or fractured, or when adjoining components aren't sealed and assembled according to manufacturers' specifications, the duct may also leak, depositing more grease that can produce hotter, longer-lasting fires.

"The closer we get to zero for a deposition rate, the safer the assembly," Johnson says. "The safest assemblies are totally insulated [so] there is no temperature change in the side wall. When you have a stream of air that is hotter than the duct wall, you end up with condensation and precipitation. It's basic physics. Just like stepping out of the shower in the morning and seeing condensation on the windows."

A consistent cleaning schedule for grease ducts is essential. Depending on use, ducts can be cleaned monthly, quarterly, or semi-annually, as prescribed by the NFPA 96, Ventilation Control and Fire Protection of Gmmeraal Cooking Operations.

According to 11.3 Inspection of Exhaust Systems, "The entire exhaust system shall be inspected by a properly trained, qualified, and certified company or person(s) acceptable to the authority having jurisdiction in accordance with Table 11.3."

Table 11.3, Exhaust System Inspection Schedule, dictates that systems serving solid fuel cooking operations should be cleaned monthly. Systems serving high-volume cooking operations such as 24-hour cooking, charbroiling, or wok cooking should be inspected quarterly. Those systems serving moderate-volume cooking operations should be inspected semi-annually and systems serving low-volume cooking operations, such as churches, day camps, seasonal businesses, or senior centers should be inspected annually.