Something is cooking for NFPA 96

NFPA Journal, May/Jun 2004 by Eden, Chris

Cylindrical, stainless-steel ducts are generally easy to clean with rotary cleaning systems that push the grease down the inside walls towards cleanouts. Welded rectangular ducts are cleaned with a pressure wash system or by scraping deposits where they pool in corners, which may create leaks.

Another problem results when duct enclosures are damaged. In areas where damage can occur, extra protection is required.

Duct system designers must also consider the surrounding combustibles, especially when penetrating fire-rated walls, floors, or ceilings. Codes and test standards specify the clearances between duct systems and combustibles, which engineers and architects usually prefer to be as small as safely possible.

"Space is a premium. If you can save just 1 square foot (0.09 square meters) of space in an overall building, you are saving dollars," says Vicky Floyd, a senior marketing manager for the duct-wrap manufacturer Thermal Ceramics.

Other factors designers must take into consideration are the possible structural effects of a grease fire. After a fire has been extinguished, inspectors must look at the system to see what failed and decide whether the system needs to be replaced. The cost of replacing a system may be significant, but it's nothing compared to the cost of fire that escapes confinement.

Code complexities

NFPA 96 is the installation standard that regulates the way grease duct systems are installed in a structure once they have met the requirements of the various product standards. Perhaps the most widely accepted grease duct product standard is UL 1978, Standard for Grease Duck. However, there are other product testing standards, and authorities having jurisdiction (AHJs) can accept all or none of them. No single product is accepted everywhere.

This makes it expensive and labor-intensive for manufacturers to go to market, since they must test to multiple standards and adhere to code requirements that vary by area of the country and sometimes conflict. It also limits engineers' and installers' choices.

"The lack of conformity or harmonization from one region to another gets confusing for the industry," says Shaun Ray, director of Engineering for Metal-Fab Inc., a manufacturer of factory-built grease duct products. "The industry has been looking for one type of test for all products, a unified standard for a safe system that simplifies the approval process."

In 2000, industry experts began developing a new UL test standard that, combined with UL 1978, would do just that: evaluate an entire grease duct system from hood to roof, regardless of fire-rated structure penetrations. The new standard would be one that code-making bodies could accept, would apply to both factory-built and duct-wrapped systems, would be easy to reference, and could be confidently enforced. After three years and three sets of revisions, UL 2221, Tests of Fire Resistive Duct Enclosure Assemblies, was published.

The next step in the simplification process occurred in 2003, when the NFPA 96 committee decided to incorporate UL 2221 into the next edition of NFPA 96.