3.6.4.3.

(1) A concealed space used as a plenum within a floor assembly or within a roof assembly need not conform to Sentence 3.1.5.15.(1) and Article 6.2.3.2. provided,

(a) all materials within the concealed space have a flame-spread rating not more than 25 and a smoke developed classification not more than 50, except for,

(i) tubing for pneumatic controls,

(ii) optical fibre cables and electrical wires and cables that exhibit a flame spread not more than 1.5 m, a smoke density not more than 0.5 at peak optical density and a smoke density not more than 0.15 at average optical density when tested in conformance with the Flame and Smoke Test in the Appendix to CAN/CSA C22.2 No. 0.3, “Test Methods for Electrical Wires and Cables” (FT6 Rating),

(iii) optical fibre cables and electrical wires and cables that are located in totally enclosed noncombustible raceways,

(iv) totally enclosed nonmetallic raceways that exhibit a horizontal flame distance of not more than 1.5 m, an average optical smoke density of not more than 0.15, and a peak optical smoke density of not more than 0.5 when tested in conformance with the Test for Flame Propagation and Smoke Density Values in Section 3.3 of the ULC/ORD-C2024, “Fire Tests for Optical Fibre Cable Raceway” (FT-6 Rating), and

(v) single conductor electrical wires and cables that exhibit a vertical char of not more than 1.5 m when tested in conformance with the Vertical Flame Test —Cables in Cabletrough in Clause 4.11.4. of CSA C22.2 No. 0.3, “Test Methods for Electrical Wires and Cables” (FT4 Rating), and

(b) the supports for the ceiling membrane are of noncombustible material having a melting point not below 760°C.

(2) If a concealed space referred to in Sentence (1) is used as a return-air plenum and incorporates a ceiling membrane that forms part of the required fire-resistance rating of the assembly, every opening through the membrane shall be protected by a fire stop flap that shall,

(a) stop the flow of air into the concealed space in the event of a fire,

(b) be supported in a manner that will maintain the integrity of the ceiling membrane for the duration of time required to provide the required fire-resistance rating, and

(c) conform to CAN4-S112.2-M, “Fire Test of Ceiling Firestop Flap Assemblies”.

(3) Asbestos paper shall not be exposed in supply and return-air systems.