506.0 Product-Conveying Ducts.506.1 Materials. Materials

systems shall be suitable for the intended use and shall be of metal. Exceptions: (1) Asbestos-cement, concrete, clay, or ceramic materials

shall be permitted to be used where it is shown that these

(1) Asbestos-cement, concrete, clay, or ceramic materials

shall be permitted to be used where it is shown that these materials will be equivalent to metal ducts installed in accordance with this chapter. (2) Ducts serving a Class 5 system shall be permitted to be

constructed of approved nonmetallic material where the

Ducts serving a Class 5 system shall be permitted to be

constructed of approved nonmetallic material where the corrosive characteristics of the material being conveyed make a metal system unsuitable and where the mixture being conveyed is nonflammable.

(2) Ducts used in central vacuuming systems within a dwelling

unit shall be constructed of materials in accordance with the applicable standards referenced in Chapter 17. Penetrations of fire-resistive walls or floor-ceiling or roof-ceiling assemblies shall be in accordance with the building code. Copper or ferrous pipes or conduit extending from within the separation between a garage and dwelling unit to the central vacuum unit shall be permitted to be used. The use of rectangular ducts conveying particulates shall be subject to approval of the Authority Having Jurisdiction. The design of rectangular ducts shall consider the adhesiveness and buildup of products being conveyed within the duct.

Aluminum construction shall be permitted to be used in Class 1 duct systems. The thickness of aluminum ducts shall be not less than two Brown and Sharpe gauges thicker than the gauges required for steel ducts set forth in Table 506.2(1) and Table 506.2(2).