(1)
A concealed space used as a plenum within a floor assembly or within a roof assembly need not conform to Sentence 3.1.5.18.(1) and Article 3.6.5.1. 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 with combustible insulation, jackets or sheathes that are used for the transmission of voice, sound or data and conform to Sentences 3.1.4.3.(2) and 3.1.5.21.(2),
(iii)
totally enclosed non-metallic raceways with an FT6 rating, when tested in accordance with Clause 3.1.5.23.(1)(a), in buildings required to be of noncombustible construction or in buildings or parts of buildings permitted to be of encapsulated mass timber construction, and
(iv)
totally enclosed non-metallic raceways with an FT4 rating, when tested in accordance with Clause 3.1.5.23.(1)(a), in buildings permitted to be of combustible construction, 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
(a)
stops the flow of air into the concealed space in the event of a fire,
(b)
is 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,
(c)
conforms to CAN/ULC-S112.2, “Standard Method Fire Test of Ceiling Firestop Flap Assemblies,” and
(d)
activates at a temperature approximately 30°C above the normal maximum temperature that occurs in the return-air plenum, whether the air duct system is operating or shut down.