Making an Assist

Key to the mechanical design are six kitchen exhaust systems used for the concession stands on the first and second levels. Hoods are connected via grease duct to six upblast roof fans. The six individual grease duct systems handle a combined 32,150 cfm of grease-laden air. Six upblast fans exhaust this air up into the atmosphere, rather than near the roof where the grease could collect and cause fire risk, along with unsightly stains - an obvious aesthetic problem.

After considering life safety issues within the stadium, Series 4G grease duct from Metal-Fab Inc. (Wichita, KS) was specified. "We became familiar with this grease duct on other projects," says Bud Bernsdorff, specifying engineer on this project with H.T. Bernsdorff, Inc.

"We worked closely with the parties involved, ensuring that the system that was designed would work. We made sure that the installing sheet metal contractor wouldn't run into any surprises on the job," says Butch Amey, Metal-Fab's application engineer on the project. "Rather than shipping drawings back and forth, potentially losing days in the process, we received 3-D CAD drawings of the system via e-mail. We checked them, relabeled system components based on our design criteria, and e-mailed them back. After a couple of revisions and discussions, we were able to provide them with finished 'as-built' drawings."

Series 4G's unique cylindrical design, with its integral chase, provides "0" clearance to combustibles. This allowed the duct to be installed in tighter spaces than a typical duct-and-chase system. Uninsulated, single-wall grease duct, requiring 18-in. clearances to combustibles, could require up to an 8-ft-wide chase. Comparable Series 4G with an integral chase has a nominal outside diameter of 3 ft.

good scouting always helps

During grease fires, duct systems expand, causing potential deformation and fracturing, thus negating the safety of the system. That's a risk that the engineers at H.T. Bernsdorff didn't want to take with 10,000 people. "We had discussed the Series 4G grease duct with a code official, on the (Toledo, OH) Juvenile Justice System building. We were comfortable specifying the grease duct on this job too," says Bernsdorff.

With 4 in. of high-density ceramic insulation and an integral steel chase, Series 4G is well suited for fire protection. Metal-Fab also incorporates adjustable lengths when designing Series 4G systems to compensate for thermal expansion. "High temperatures associated with grease fires cause distortion and potential fracturing of site-welded duct. Rigid duct cannot compensate for thermal expansion. It just doesn't have the room to expand without damaging the duct," says Tim Toffler, Toledo office branch manager of Air Control Products Inc., the Metal-Fab representative in the Toledo area.

Metal-Fab tested Series 4G to all applicable portions of UL 103, UL 1978, ASTM E814, and ASTM E119. Utilizing independent testing laboratories, Series 4G test results are recognized by BOCA, ICBO, and SBCCI as an alternative grease duct system as provided in NFPA 96.

Factory-built Series 4G saves costs in installation, maintenance, and potential future repairs. Systems are assembled on site with minimal welding required. Series 4G's integral chase and "0" clearance capability eliminates the need for a fire-rated chase. Two-to-three-hour, fire-rated walls and floors are penetrated utilizing simple fire-stops. Series 4G offers a safer, easier, and less costly alternative.

Series 4G's design minimizes temperature loss and grease deposition within the system. Because the duct is cylindrical, Series 4G offers less airflow resistance (lower K factor), and less turbulence, thereby keeping more grease in suspension and reducing noise associated with rectangular ducting.

Grease that does condense flows easily to inspection/clean-out ports, rather than collecting in the corners and flat surfaces of traditional rectangular duct. Modern duct cleaning equipment can easily clean round duct, greatly reducing the necessity of entering a duct and manually scraping deposits from corners.

Sliding in Safely

Metal-Fab anticipated that the Fifth Third Field grease duct systems would require at least four full truckloads of material. Logistically, this would have been very difficult if all material was shipped simultaneously. Metal-Fab, in conjunction with Toffler developed a shipping schedule based on individual system requirements and staging restrictions. "We tagged and shipped each component by system number for the installing contractor. The systems shipped in the specified sequence, making it easy for installers to locate and stage the components," says Tim Farris, eastern regional sales manager for Metal-Fab.

With opening day fast approaching, all were pressed for time. Every day an average of 120 to 140 construction workers and 13 construction companies worked together to make sure the Mud Hens would have a nice, safe home when the first pitch was thrown.ES