What materials are considered acceptable for factory built commercial kitchen grease ducts as exceptions?

The correct choice identifies listed and labeled ducts as acceptable materials for factory-built commercial kitchen grease ducts. This is important because grease ducts must conform to certain safety and performance standards due to the specific demands of handling grease-laden vapors and preventing grease fires.

Listed and labeled ducts are products that have been tested and certified to meet certain criteria outlined by recognized testing laboratories. This means they have been evaluated for their effectiveness in preventing fire hazards and ensuring proper ventilation in commercial kitchen environments, where grease and heat are common concerns.

Additionally, these ducts typically provide assurance that they have been designed and manufactured with materials that can reliably withstand the corrosive properties of grease, as well as maintain structural integrity at high temperatures. Adhering to the requirements for listed and labeled ducts helps ensure compliance with the North Carolina Mechanical Code, which emphasizes safety and performance in mechanical system installations.

Other options, such as standard steel and wood, noncombustible materials only, and flexible ducts, may not meet the specific safety standards required for commercial kitchen applications, making them less appropriate choices for grease ducts.