Section 7.24 - Technical requirements(a) Brattice cloth shall be flame resistant when tested in accordance with the flame resistance test in § 7.27 .(b) Flexible ventilation tubing shall be manufactured using an MSHA-approved brattice cloth. If a supporting structure is used, it shall be metal or other noncombustible material which will not ignite, burn, support combustion or release flammable vapors when subjected to fire or heat.(c) Rigid ventilation tubing shall be flame resistant when tested in accordance with the flame resistance test in § 7.28 .